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Versions: (draft-schaad-cose) 00 01 draft-ietf-cose-msg

Network Working Group                                          J. Schaad
Internet-Draft                                            August Cellars
Intended status: Informational                             June 10, 2015
Expires: December 12, 2015


                      CBOR Encoded Message Syntax
                        draft-schaad-cose-msg-00

Abstract

   Concise Binary Object Representation (CBOR) is data format designed
   for small code size and small message size.  There is a need for the
   ability to have the basic security services defined for this data
   format.  This document specifies how to do signatures, message
   authentication codes and encryption using this data format.  The work
   in this document is derived in part from the JSON web security
   documents using the same parameters and algorithm identifiers as they
   do.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on December 12, 2015.

Copyright Notice

   Copyright (c) 2015 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must



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   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1.  Design changes from JOSE  . . . . . . . . . . . . . . . .   3
     1.2.  Requirements Terminology  . . . . . . . . . . . . . . . .   4
     1.3.  CBOR Grammar  . . . . . . . . . . . . . . . . . . . . . .   4
   2.  The COSE_MSG structure  . . . . . . . . . . . . . . . . . . .   4
   3.  Header Parameters . . . . . . . . . . . . . . . . . . . . . .   5
     3.1.  COSE Headers  . . . . . . . . . . . . . . . . . . . . . .   6
   4.  Signing Structure . . . . . . . . . . . . . . . . . . . . . .   6
   5.  Encryption object . . . . . . . . . . . . . . . . . . . . . .   9
     5.1.  Key Management Methods  . . . . . . . . . . . . . . . . .  10
       5.1.1.  Direct Encryption . . . . . . . . . . . . . . . . . .  11
       5.1.2.  Key Wrapping  . . . . . . . . . . . . . . . . . . . .  11
       5.1.3.  Key Encryption  . . . . . . . . . . . . . . . . . . .  11
       5.1.4.  Direct Key Agreement  . . . . . . . . . . . . . . . .  12
       5.1.5.  Key Agreement with Key Wrapping . . . . . . . . . . .  12
     5.2.  Encryption Algorithm for AEAD algorithms  . . . . . . . .  13
     5.3.  Encryption algorithm for AE algorithms  . . . . . . . . .  13
   6.  MAC objects . . . . . . . . . . . . . . . . . . . . . . . . .  13
   7.  Key Structure . . . . . . . . . . . . . . . . . . . . . . . .  15
   8.  CBOR Encoder Restrictions . . . . . . . . . . . . . . . . . .  16
   9.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  17
     9.1.  CBOR Tag assignment . . . . . . . . . . . . . . . . . . .  17
     9.2.  COSE Parameter Table  . . . . . . . . . . . . . . . . . .  17
     9.3.  COSE Header Key Table . . . . . . . . . . . . . . . . . .  17
     9.4.  COSE Header Algorithm Key Table . . . . . . . . . . . . .  18
     9.5.  COSE Algorithm Registry . . . . . . . . . . . . . . . . .  19
     9.6.  COSE Key Map Registry . . . . . . . . . . . . . . . . . .  19
     9.7.  COSE Key Parameter Registry . . . . . . . . . . . . . . .  20
   10. Security Considerations . . . . . . . . . . . . . . . . . . .  20
   11. References  . . . . . . . . . . . . . . . . . . . . . . . . .  21
     11.1.  Normative References . . . . . . . . . . . . . . . . . .  21
     11.2.  Informative References . . . . . . . . . . . . . . . . .  21
   Appendix A.  AEAD and AE algorithms . . . . . . . . . . . . . . .  22
   Appendix B.  Three Levels of Recipient Information  . . . . . . .  23
   Appendix C.  Examples . . . . . . . . . . . . . . . . . . . . . .  23
     C.1.  Direct MAC  . . . . . . . . . . . . . . . . . . . . . . .  24
     C.2.  Wrapped MAC . . . . . . . . . . . . . . . . . . . . . . .  24
     C.3.  Multi-recipient MAC message . . . . . . . . . . . . . . .  24
     C.4.  Direct ECDH . . . . . . . . . . . . . . . . . . . . . . .  25
     C.5.  Single Signature  . . . . . . . . . . . . . . . . . . . .  26
     C.6.  Multiple Signers  . . . . . . . . . . . . . . . . . . . .  26
   Appendix D.  Top Level Parameter Table  . . . . . . . . . . . . .  27



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   Appendix E.  COSE Header Key Registry . . . . . . . . . . . . . .  29
   Appendix F.  COSE Header Algorithm Key Table  . . . . . . . . . .  31
   Appendix G.  COSE Algorithm Name Values . . . . . . . . . . . . .  31
   Appendix H.  COSE General Values  . . . . . . . . . . . . . . . .  33
   Appendix I.  COSE Key Map Keys  . . . . . . . . . . . . . . . . .  33
   Appendix J.  COSE Key Parameter Keys  . . . . . . . . . . . . . .  34
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .  35

1.  Introduction

   The JOSE working group produced a set of documents that defined how
   to perform encryption, signatures and message authentication (MAC)
   operations for JavaScript Object Notation (JSON) documents and then
   to encode the results using the JSON format [RFC7159].  This document
   does the same work for use with the Concise Binary Object
   Representation (CBOR) [RFC7049] document format.  While there is a
   strong attempt to keep the flavor of the original JOSE documents, two
   considerations are taking into account:

   o  CBOR has capabilities that are not present in JSON and should be
      used.  One example of this is the fact that CBOR has a method of
      encoding binary directly without first converting it into a base64
      encoded sting.

   o  The authors did not always agree with some of the decisions made
      by the JOSE working group.  Many of these decisions have been re-
      examined, and where it seems to the authors to be superior or
      simpler, replaced.

1.1.  Design changes from JOSE

   o  Define a top level message structure so that encrypted, signed and
      MAC-ed messages can easily identified and still have a consistent
      view.

   o  Signed messages separate the concept of protected and unprotected
      attributes that are for the content and the signature.

   o  Key management has been made to be more uniform.  All key
      management techniques are represented as a recipient rather than
      only have some of them be so.

   o  MAC messages are separated from signed messages.

   o  MAC messages have the ability to do key management on the MAC key.

   o  Use binary encodings for binary data rather than base64url
      encodings.



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   o  Remove the authentiction tag for encryption algorithms as a
      separate item.

   o  Remove the flattened mode of encoding.  Forcing the use of an
      array of recipients at all times forces the message size to be two
      bytes larger, but one gets a corresponding decrease in the
      implementation size that should compenstate for this.

1.2.  Requirements Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in
   [RFC2119].

   When the words appear in lower case, their natural language meaning
   is used.

1.3.  CBOR Grammar

   There currently is no standard CBOR grammar available for use by
   specifications.  In this document, we use the grammar defined in the
   CBOR data definition language (CDDL)
   [I-D.greevenbosch-appsawg-cbor-cddl].

2.  The COSE_MSG structure

   The COSE_MSG structure is a top level CBOR object which corresponds
   to the DataContent type in [RFC5652].  This structure allows for a
   top level message to be sent which could be any of the different
   security services, where the security service is identified.  The
   presence of this structure does not preclude a protocol to use one of
   the individual structures as a stand alone component.

   COSE_MSG = {msg_type=>1, COSE_Sign} /
              {msg_type=>2, COSE_encrypt} /
              {msg_type=>3, COSE_mac}

   COSE_Tagged_MSG = #6.999(COSE_MSG)   ; Replace 999 with TBD1


   The top level of each of the COSE message structures are encoded as
   arrays.
   We use an integer to distingish bettwen the different security
   message types.  By looking at the integer in the first element, one
   can determine which security message is being used and thus what the
   syntax is for the rest of the elements in the array.




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   Implementations SHOULD be prepared to find an integer in the location
   which does not correspond to the values 1 to 3.  If this is found
   then the client MUST stop attempting to parse the structure and fail.
   Clients need to recognize that the set of values could be extended at
   a later date, but should not provide a security service based on
   guesses of what is there.

3.  Header Parameters

   The structure of COSE has been designed to have two buckets of
   information that are not considered to be part of the message
   structure itself, but are used for holding information about
   algorithms, keys, or evaluation hints for the processing of the
   layer.  These two buckets are available for use in all of the
   structures in this document except for keys.  While these buckets can
   be present, they may not all be usable in all instances.  For
   example, while the protected bucket is present for recipient
   structures, most of the algorithms that are-used for recipients do
   not provide the necessary functionality to provide the needed
   protection and thus the element is not used.

   Both buckets are implemented as CBOR maps.  The maps can be keyed by
   negative integers, unsigned integers and strings.  The negative and
   unsigned integers are used for compactness of encoding.  The value
   portion is dependent on the key definition.  Both maps use the same
   set of key/value pairs.  The integer key range has been divided into
   several sections with a standard range, a private range, and a range
   that is dependent on the algorithm selected.  The tables of keys
   defined can be found in Appendix E.

   Two buckets are provided for each layer:

   protected  contains attributes about the layer which are to be
      cryptographically protected.  This bucket MUST NOT be used if it
      is not going to be included in a cryptographic computation.

   unprotected  contains attributes about the layer which are not
      cryptographically protected.

   Both of the buckets are optional and are omitted if there are no
   items contained in the map.  The CDDL fragment which describes the
   two buckets is:









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   keys = int / tstr
   header_map = {+ keys => any }

   Headers = (
       ? protected => bstr,
       ? unprotected => header_map
   )


3.1.  COSE Headers

   TODO: Do we need to repeat definitions for all or just for some and
   refer to the JOSE documents?

   TODO: Should we move table Appendix E to here or leave it as an
   appendix.  Some what redundant if we document things in text.

4.  Signing Structure

   The signature structure allows for one or more signatures to be
   applied to a message payload.  There are provisions for attributes
   about the content and attributes about the signature to be carried
   along with the signature itself.  These attributes may be
   authenticated by the signature, or just present.  Examples of
   attributes about the content would be the type of content, when the
   content was created, and who created the content.  Examples of
   attributes about the signature would be the algorithm and key used to
   create the signature, when the signature was created, and counter-
   signatures.

   When more than one signature is present, the successful validation of
   one signature associated with a given signer is usually treated as a
   successful signature by that signer.  However, there are some
   application environments where other rules are needed.  An
   application that employs a rule other than one valid signature for
   each signer must specify those rules.  Also, where simple matching of
   the signer identifier is not sufficient to determine whether the
   signatures were generated by the same signer, the application
   specification must describe how to determine which signatures were
   generated by the same signer.  Support of different communities of
   recipients is the primary reason that signers choose to include more
   than one signature.  For example, the COSE_Sign structure might
   include signatures generated with the RSA signature algorithm and
   with the Elliptic Curve Digital Signature Algorithm (ECDSA) signature
   algorithm.  This allows recipients to verify the signature associated
   with one algorithm or the other.  (Source of text is [RFC5652].)
   More detailed information on multiple signature evaluation can be
   found in [RFC5752].



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   The CDDL grammar structure for a signature message is:

   COSE_Sign = (
       Headers,
       ? payload => bstr,
       signatures=> [+{COSE_signature}]
   )


   The keys in the COSE_Sign map are keyed by the values in Appendix D.
   While other keys can be present in the map, it is not generally a
   recommended practice.  The other keys can be either of integer or
   string type, use of other types is strongly discouraged.  See the
   note in {{CBOR-Canonical} about options for allowing or disallowing
   other keys.

   The fields is the structure have the following semantics:

   protected  contains attributes about the payload which are to be
      protected by the signature.  An example of such an attribute would
      be the content type ('cty') attribute.  The content is a CBOR map
      of attributes which is encoded to a byte stream.  This field MUST
      NOT contain attributes about the signature, even if those
      attributes are common across multiple signatures.  This fields in
      this map are typically keyed by Appendix E.  Other keys can be
      used either as int or tstr values.  Other types MUST NOT be
      present in the map as key values.

   unprotected  contains attributes about the payload which are not
      protected by the signature.  An example of such an attribute would
      be the content type ('cty') attribute.  This field MUST NOT
      contain attributes about a signature, even if the attributes are
      common across multiple signatures.  This fields int his map are
      typically keyed by Appendix E.  Other keys can be used either as
      int or tstr values.  Other types MUST NOT be present in the map as
      key values.

   payload  contains the serialized content to be signed.
      If the payload is not present in the message, the application is
      required to supply the payload separately.
      The payload is wrapped in a bstr to ensure that it is transported
      without changes, if the payload is transported separately it is
      the responsibility of the application to ensure that it will be
      transported without changes.

   signatures  is an array of signature items.  Each of these items uses
      the COSE_signature structure for its representation.




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   The keys in the COSE_signature map are keyed by the values in
   Appendix D.  While other keys can be present in the map, it is not
   generally a recommended practice.  The other keys can be either of
   integer or string type, use of other types is strongly discouraged.
   See the note in {{CBOR-Canonical} about options for allowing or
   disallowing other keys.

   The CDDL grammar structure for a signature is:

   COSE_signature =  (
       ? protected => bstr,
       ? unprotected => header_map,
       signature => bstr
   )


   The fields in the structure have the following semantics:

   protected  contains additional information to be authenticated by the
      signature.  The field holds data about the signature operation.
      The field MUST NOT hold attributes about the payload being signed.
      The content is a CBOR map of attributes which is encoded to a byte
      stream.  At least one of protected and unprotected MUST be
      present.

   unprotected  contains attributes about the signature which are not
      protected by the signature.  This field MUST NOT contain
      attributes about the payload being signed.  At least one of
      protected and unprotected MUST be present.

   signature  contains the computed signature value.

   The COSE structure used to create the byte stream to be signed uses
   the following CDDL grammar structure:

   Sig_structure = [
       body_protected => bstr,
       sign_protected => bstr,
       payload => bstr
   ]


   How to compute a signature:

   1.  Create a Sig_structure object and populate it with the
       appropriate fields.  For body_protected and sign_protected, if
       the fields are not present in their corresponding maps, an bstr
       of length zero is be used.



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   2.  Create the value to be hashed by encoding the Sig_structure to a
       byte string.

   3.  Comput the hash value from the byte string.

   4.  Sign the hash

   5.  Place the signature value into the appropriate signature field.

5.  Encryption object

   In this section we describe the structure and methods to be used when
   doing an encryption in COSE.  In COSE, we use the same techniques and
   structures for encrypting both the plain text and the keys used to
   protect the text.  This is different from the approach used by both
   [RFC5652] and [RFC7516] where different structures are used for the
   plain text and for the different key management techniques.

   One of the byproducts of using the same technique for encrypting and
   encoding both the content and the keys using the various key
   management techniques, is a requirement that all of the key
   management techniques use an Authenticated Encryption (AE) algorithm.
   (For the purpose of this document we use a slightly loose definition
   of AE algorithms.)  When encrypting the plain text, it is normal to
   use an Authenticated Encryption with Additional Data (AEAD)
   algorithm.  For key management, either AE or AEAD algorithms can be
   used.  See Appendix A for more details about the different types of
   algorithms.

   I don't follow/understand this text{:aeds}

   The CDDL grammar structure for encryption is:

   COSE_encrypt = (
      Headers,
      ? iv => bstr,
      ? aad => bstr,
      ? ciphertext => bstr,
      ? recipients => [+COSE_encrypt_a]
   )

   COSE_encrypt_a = {COSE_encrypt}


   Description of the fields:

   protected  contains the information about the plain text or
      encryption process that is to be integrity protected.  The field



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      is encoded in CBOR as a 'bstr'.  The contents of the protected
      field is a CBOR map of the protected data names and values.  The
      map is CBOR encoded before placing it into the bstr.  Only values
      associated with the current cipher text are to be placed in this
      location even if the value would apply to multiple recipient
      structures.

   unprotected  contains information about the plain text that is not
      integrity protected.  Only values associated with the current
      cipher text are to be placed in this location even if the value
      would apply to multiple recipient structures.

   iv contains the initialization vector (IV), or it's equivalent, if
      one is needed by the encryption algorithm.

   aad  contains additional authenticated data (aad) supplied by the
      application.  This field contains information about the plain text
      data that is authenticated, but not encrypted.

   cipherText  contains the encrypted plain text.  If the cipherText is
      to be transported independently of the control information about
      the encryption process (i.e. detached content) then the field is
      omitted.

   recipients  contains the recipient information.  The field can have
      one of two data types:

   o  An array of COSE_encrypt elements, one for each recipient.

5.1.  Key Management Methods

   There are a number of different key management methods that can be
   used in the COSE encryption system.  In this section we will discuss
   each of the key management methods and what fields need to be
   specified to deal with each of them.

   The names of the key management methods used here are the same as are
   defined in [RFC7517].  Other specifications use different terms for
   the key management methods or do not support some of the key
   management methods.

   At the moment we do not have any key management methods that allow
   for the use of protected headers.  This may be changed in the future
   if, for example, the AES-GCM Key wrap method defined in [RFC7518]
   were extended to allow for authenticated data.  In that event the use
   of the 'protected' field, which is current forbidden below, would be
   permitted.




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5.1.1.  Direct Encryption

   In direct encryption mode, a shared secret between the sender and the
   recipient is used as the CEK.  When direct encryption mode is used,
   it MUST be the only mode used on the message.  It is a massive
   security leak to have both direct encryption and a different key
   management mode on the same message.

   For JOSE, direct encryption key management is the only key management
   method allowed for doing MAC-ed messages.  In COSE, all of the key
   management methods can be used for MAC-ed messages.

   The COSE_encrypt structure for the recipient is organized as follows:

   o  The 'protected', 'iv', 'aad', 'ciphertext' and 'recipients' fields
      MUST be absent.

   o  At a minimum, the 'unprotected' field SHOULD contain the 'alg'
      parameter as well as a parameter identifying the shared secret.

5.1.2.  Key Wrapping

   In key wrapping mode, the CEK is randomly generated and that key is
   then encrypted by a shared secret between the sender and the
   recipient.  All of the currently defined key wrapping algorithms for
   JOSE (and thus for COSE) are AE algorithms.  Key wrapping mode is
   considered to be superior to direct encryption if the system has any
   capability for doing random key generation.  This is because the
   shared key is used to wrap random data rather than data has some
   degree of organization and may in fact be repeating the same content.

   The COSE_encrypt structure for the recipient is organized as follows:

   o  The 'protected', 'aad', and 'recipients' fields MUST be absent.

   o  The plain text to be encrypted is the key from next layer down
      (usually the content layer).

   o  At a minimum, the 'unprotected' field SHOULD contain the 'alg'
      parameter as well as a parameter identifying the shared secret.

   o  Use of the 'iv' field will depend on the key wrap algorithm.

5.1.3.  Key Encryption

   Key Encryption mode is also called key transport mode in some
   standards.  Key Encryption mode differs from Key Wrap mode in that it
   uses an asymmetric encryption algorithm rather than a symmetric



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   encryption algorithm to protect the key.  The only current Key
   Encryption mode algorithm supported is RSAES-OAEP.

   The COSE_encrypt structure for the recipient is organized as follows:

   o  The 'protected', 'aad', and 'iv' fields MUST be absent.

   o  The plain text to be encrypted is the key from next layer down
      (usually the content layer).

   o  At a minimum, the 'unprotected' field SHOULD contain the 'alg'
      parameter as well as a parameter identifying the asymmetric key.

5.1.4.  Direct Key Agreement

   Direct Key Agreement derives the CEK from the shared secret computed
   by the key agreement operation.

   When direct key agreement mode is used, it SHOULD be the only mode
   used on the message.  This method creates the CEK directly and that
   makes it difficult to mix with additional recipients.

   The COSE_encrypt structure for the recipient is organized as follows:

   o  The 'protected', 'aad', and 'iv' fields MUST be absent.

   o  At a minimum, the 'unprotected' field SHOULD contain the 'alg'
      parameter as well as a parameter identifying the asymmetric key.

   o  The 'unprotected' field MUST contain the 'epk' parameter.

5.1.5.  Key Agreement with Key Wrapping

   Key Agreement with Key Wrapping uses a randomly generated CEK.  The
   CEK is then encrypted using a Key Wrapping algorithm and a key
   derived from the shared secret computed by the key agreement
   algorithm.

   The COSE_encrypt structure for the recipient is organized as follows:

   o  The 'protected', 'aad', and 'iv' fields MUST be absent.

   o  The plain text to be encrypted is the key from next layer down
      (usually the content layer).

   o  At a minimum, the 'unprotected' field SHOULD contain the 'alg'
      parameter, a parameter identifying the recipient asymmetric key,
      and a parameter with the sender's asymmetric public key.



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5.2.  Encryption Algorithm for AEAD algorithms

   The encryption algorithm for AEAD algorithms is fairly simple.
   In order to get a consistent encoding of the data to be
   authenticated, the Enc_structure is used to have canonical form of
   the AAD.

   Enc_structure = [
      protected => bstr,
      aad => bstr
   ]


   1.  If there is protected data, CBOR encode the map to a byte string
       and place in the protected field of the Enc_structure and the
       COSE_Encrypt structure.

   2.  Copy the 'aad' field from the COSE_Encrypt structure to the
       Enc_Structure.

   3.  Encode the Enc_structure using a CBOR Canonical encoding
       Section 8 to get the AAD value.

   4.  Encrypt the plain text and place it in the 'ciphertext' field.
       The AAD value is passed in as part of the encryption process.

   5.  For recipient of the message, recursively perform the encryption
       algorithm for that recipient using the encryption key as the
       plain text.

5.3.  Encryption algorithm for AE algorithms

   1.  Verify that the 'protected' field is absent.

   2.  Verify that the 'aad' field is absent.

   3.  Encrypt the plain text and place in the 'ciphertext' field.

6.  MAC objects

   In this section we describe the structure and methods to be used when
   doing MAC authentication in COSE.  JOSE used a variant of the
   signature structure for doing MAC operations and it is restricted to
   using a single pre-shared secret to do the authentication.  This
   document allows for the use of all of the same methods of key
   management as are allowed for encryption.





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   When using MAC operations, there are two modes in which it can be
   used.  The first is just a check that the content has not been
   changed since the MAC was computed.  Any of the key management
   methods can be used for this purpose.  The second mode is to both
   check that the content has not been changed since the MAC was
   computed, and to use key management to verify who sent it.  The key
   management modes that support this are ones that either use a pre-
   shared secret, or do static-static key agreement.  In both of these
   cases the entity MAC-ing the message can be validated by a key
   binding.  (The binding of identity assumes that there are only two
   parties involved and you did not send the message yourself.)

   COSE_mac = (
      Headers,
      ? payload => bstr,
      tag => bstr,
      ? recipients => [+COSE_encrypt_a]
   )


   Field descriptions:

   protected  contains attributes about the payload which are to be
      protected by the MAC.  An example of such an attribute would be
      the content type ('cty') attribute.  The content is a CBOR map of
      attributes which is encoded to a byte stream.  This field MUST NOT
      contain attributes about the recipient, even if those attributes
      are common across multiple recipients.  At least one of protected
      and unprotected MUST be present.

   unprotected  contains attributes about the payload which are not
      protected by the MAC.  An example of such an attribute would be
      the content type ('cty') attribute.  This field MUST NOT contain
      attributes about a recipient, even if the attributes are common
      across multiple recipients.  At least one of protected and
      unprotected MUST be present.

   payload  contains the serialized content to be MAC-ed.
      If the payload is not present in the message, the application is
      required to supply the payload separately.
      The payload is wrapped in a bstr to ensure that it is transported
      without changes, if the payload is transported separately it is
      the responsibility of the application to ensure that it will be
      transported without changes.

   tag  contains the MAC value.





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   recipients  contains the recipient information.  See the description
      under COSE_Encryption for more info.

   MAC_structure = [
      protected => bstr,
      payload => bstr
   ]


   How to compute a MAC:

   1.  Create a MAC_structure and copy the protected and payload
       elements from the COSE_mac structure.

   2.  Encode the MAC_structure using a canonical CBOR encoder.  The
       resulting bytes is the value to compute the MAC on.

   3.  Compute the MAC and place the result in the 'tag' field of the
       COSE_mac structure.

   4.  Encrypt and encode the MAC key for each recipient of the message.

7.  Key Structure

   There are only a few changes between JOSE and COSE for how keys are
   formatted.  As with JOSE, COSE uses a map to contain the elements of
   a key.  Those values, which in JOSE, are base64url encoded because
   they are binary values, are encoded as bstr values in COSE.

   For COSE we use the same set of fields that were defined in
   [RFC7517].

   COSE_Key = {
       kty => tstr / int,
       ? key_ops => [+tstr / int ],
       ? alg => tstr / int,
       ? kid => bstr,
       * keys => values
   }

   COSE_KeySet = [+COSE_Key]


   The element "kty" is a required element in a COSE_Key map.
   All other elements are optional and not all of the elements listed in
   [RFC7517] or [RFC7518] have been listed here even though they can all
   appear in a COSE_Key map.




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   The "key_ops" element is prefered over the "use" element as the
   information provided that way is more finely detailed about the
   operations allowed.  It is strongly suggested that this element be
   present for all keys.

   The same fields defined in [RFC7517] are used here with the following
   changes in rules:

   o  Any item which is base64 encoded in JWK, is bstr encoded for COSE.

   o  Any item which is integer encoded in JWK, is int encoded for COSE.

   o

      Any item which is string (but not base64) encoded in JWK, is tstr
      encoded for COSE.

      Exceptions to this are the following fields:

      kid  is always bstr encoded rather than tstr encoded.  This change
         in encoded is due to the fact that frequently, values such as a
         hash of the public key is used for a kid value.  Since the
         field is defined as not having a specific structure, making it
         binary rather than textual makes sense.

8.  CBOR Encoder Restrictions

   There as been an attempt to resrict the number of places where the
   document needs to impose restrictions on how the CBOR Encoder needs
   to work.  We have managed to narrow it down to the following
   restrictions:

   o  The restriction applies to the encoding the Sig_structure, the
      Enc_structure, and the MAC_structure.

   o  The rules for Canonical CBOR (Section 3.9 of RFC 7049) MUST be
      used in these locations.  The main rule that needs to be enforced
      is that all lengths in these structures MUST be encoded such that
      they are encoded using definite lengths and the minimum length
      encoding is used.

   o  All parsers used SHOULD fail on both parsing and generation if the
      same key is used twice in a map.

   While it is permitted to have key values other than those specified
   in this document in the outer maps (COSE_Sign, COSE_Signature,
   COSE_encrypt, COSE_recipient and COSE_mac), doing so is not
   encouraged.  Applications should make a determination if it will be



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   permitted for that application.  In general, any needed new fields
   can be accomadated by the introduction of new header fields to be
   carried in the protected or unprotected fields.  Applications that
   need to have new fields in these maps should consider getting new
   message types assigned for these usages.  Without this change, old
   applications will not see and process the new fields.

9.  IANA Considerations

9.1.  CBOR Tag assignment

   It is requested that IANA assign a new tag from the "Concise Binary
   Object Represetion (CBOR) Tags" registry.  It is requested that the
   tag be assigned in the 0 to 23 value range.

   Tag Value: TBD1

   Data Item: CBOR map

   Semantics: COSE security message.

9.2.  COSE Parameter Table

9.3.  COSE Header Key Table

   It is requested that IANA create a new registry entitled "COSE Header
   Key".

   The columns of the registry are:

   name  The name is present to make it easier to refer to and discuss
      the registration entry.  The value is not used in the protocol.
      Names are to be unique in the table.

   key  This is the value used for the key.  The key can be either an
      integer or a string.  Registration in the table is based on the
      value of the key requested.  Integer values between 0 and 255 and
      strings of length 1 are designated as Standards Track Document
      required.  Integer values from 256 to 65535 and strings of length
      2 are designated as Specification Required.  Integer values of
      greater than 65535 and strings of length greater than 2 are
      designated as first come first server.  Integer values in the
      range -1 to -65536 are delegated to the "COSE Header Algorithm
      Key" registry.  Integer values beyond -65536 are marked as private
      use.

   value  This contains the CBOR type for the value portion of the key.




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   value registry  This contains a pointer to the registry used to
      contain values where the set is limited.

   description  This contains a brief description of the header field.

   specification  This contains a pointer to the specification defining
      the header field (where public).

   The initial contents of the registry can be found in Appendix E.  The
   specification column for all rows in that table should be this
   document.

   NOTE: Need to review the range assignments.  It does not necessarily
   make sense as specification required uses 1 byte positive integers
   and 2 byte strings.

9.4.  COSE Header Algorithm Key Table

   It is requested that IANA create a new registry entitled "COSE Header
   Algorithm Keys".

   The columns of the registry are:

   name  The name is present to make it easier to refer to and discuss
      the registration entry.  The value is not used in the protocol.

   algorithm  The algorithm(s) that this registry entry is used for.
      This value is taken from the "COSE Algorithm Value" registry.
      Multiple algorithms can be specified in this entry.  For the
      table, the algorithm, key pair MUST be unique.

   key  This is the value used for the key.  The key is an integer in
      the range of -1 to -65536.

   value  This contains the CBOR type for the value portion of the key.

   value registry  This contains a pointer to the registry used to
      contain values where the set is limited.

   description  This contains a brief description of the header field.

   specification  This contains a pointer to the specification defining
      the header field (where public).

   The initial contents of the registry can be found in Appendix F.  The
   specification column for all rows in that table should be this
   document.




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9.5.  COSE Algorithm Registry

   It is requested that IANA create a new registry entitled "COSE
   Algorithm Registry".

   The columns of the registry are:

   key  The value to be used to identify this algorithm.  Algorithm keys
      MUST be unique.  The key can be a positive integer, a negative
      integer or a string.  Integer values between 0 and 255 and strings
      of length 1 are designated as Standards Track Document required.
      Integer values from 256 to 65535 and strings of length 2 are
      designated as Specification Required.  Integer values of greater
      than 65535 and strings of length greater than 2 are designated as
      first come first server.  Integer values in the range -1 to -65536
      are delegated to the "COSE Header Algorithm Key" registry.
      Integer values beyond -65536 are marked as private use.

   description  A short description of the algorithm.

   specification  A document where the algorithm is defined (if publicly
      available).

   The initial contents of the registry can be found in Appendix G.  The
   specification column for all rows in that table should be this
   document.

9.6.  COSE Key Map Registry

   It is requested that IANA create a new registry entitied "COSE Key
   Map Registry".

   The columns of the registry are:

   name  This is a descriptive name that enables easier reference to the
      item.  It is not used in the encoding.

   key  The value to be used to identify this algorithm.  Algorithm keys
      MUST be unique.  The key can be a positive integer, a negative
      integer or a string.  Integer values between 0 and 255 and strings
      of length 1 are designated as Standards Track Document required.
      Integer values from 256 to 65535 and strings of length 2 are
      designated as Specification Required.  Integer values of greater
      than 65535 and strings of length greater than 2 are designated as
      first come first server.  Integer values in the range -1 to -65536
      are used for key parameters specific to a single algoirthm
      delegated to the "COSE Key Parameter Key" registry.  Integer
      values beyond -65536 are marked as private use.



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   CBOR Type  This field contains the CBOR type for the field

   registry  This field denotes the registry that values come from, if
      one exists.

   description  This field contains a brief description for the field

   specification  This contains a pointer to the public specification
      for the field if one exists

   This registry will be initially populated bythe values in Appendix I.
   The specification column for all of these entries will be this
   document.

9.7.  COSE Key Parameter Registry

   It is requested that IANA create a new registry "COSE Key
   Parameters".

   The columns of the table are:

   key type  This field contains a descriptive string of a key type.
      This should be a value that is in the COSE General Values table
      and is placed in the 'kty' field of a COSE Key structure.

   name  This is a descriptive name that enables easier reference to the
      item.  It is not used in the encoding.

   key  The key is to be unqiue for every value of key type.  The range
      of values is from -256 to -1.  Keys are expected to be re-used for
      different keys.

   CBOR type  This field contains the CBOR type for the field

   description  This field contains a brief description for the field

   specification  This contains a pointer to the public specification
      for the field if one exists

   This registry will be initially populated bythe values in Appendix J.
   The specification column for all of these entries will be this
   document.

10.  Security Considerations

   There are security considerations:

   1.  Protect private keys



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   2.  MAC messages with more than one recipient means one cannot figure
       out who sent the message

   3.  Use of direct key with other recipient structures hands the key
       to other recipients.

   4.  Use of direcct ECDH direct encryption is easy for people to leak
       information on if there are other recipients in the message.

   5.  Considerations about protected vs unprotected header fields.

11.  References

11.1.  Normative References

   [I-D.greevenbosch-appsawg-cbor-cddl]
              Vigano, C., Birkholz, H., and R. Sun, "CBOR data
              definition language: a notational convention to express
              CBOR data structures.", draft-greevenbosch-appsawg-cbor-
              cddl-05 (work in progress), March 2015.

   [RFC7049]  Bormann, C. and P. Hoffman, "Concise Binary Object
              Representation (CBOR)", RFC 7049, October 2013.

   [RFC7518]  Jones, M., "JSON Web Algorithms (JWA)", RFC 7518, May
              2015.

11.2.  Informative References

   [AES-GCM]  Dworkin, M., "NIST Special Publication 800-38D:
              Recommendation for Block Cipher Modes of Operation:
              Galois/Counter Mode (GCM) and GMAC.", June 2015.

   [I-D.mcgrew-aead-aes-cbc-hmac-sha2]
              McGrew, D., Foley, J., and K. Paterson, "Authenticated
              Encryption with AES-CBC and HMAC-SHA", draft-mcgrew-aead-
              aes-cbc-hmac-sha2-05 (work in progress), July 2014.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC3394]  Schaad, J. and R. Housley, "Advanced Encryption Standard
              (AES) Key Wrap Algorithm", RFC 3394, September 2002.

   [RFC3447]  Jonsson, J. and B. Kaliski, "Public-Key Cryptography
              Standards (PKCS) #1: RSA Cryptography Specifications
              Version 2.1", RFC 3447, February 2003.




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   [RFC3610]  Whiting, D., Housley, R., and N. Ferguson, "Counter with
              CBC-MAC (CCM)", RFC 3610, September 2003.

   [RFC5652]  Housley, R., "Cryptographic Message Syntax (CMS)", STD 70,
              RFC 5652, September 2009.

   [RFC5752]  Turner, S. and J. Schaad, "Multiple Signatures in
              Cryptographic Message Syntax (CMS)", RFC 5752, January
              2010.

   [RFC5990]  Randall, J., Kaliski, B., Brainard, J., and S. Turner,
              "Use of the RSA-KEM Key Transport Algorithm in the
              Cryptographic Message Syntax (CMS)", RFC 5990, September
              2010.

   [RFC7159]  Bray, T., "The JavaScript Object Notation (JSON) Data
              Interchange Format", RFC 7159, March 2014.

   [RFC7515]  Jones, M., Bradley, J., and N. Sakimura, "JSON Web
              Signature (JWS)", RFC 7515, May 2015.

   [RFC7516]  Jones, M. and J. Hildebrand, "JSON Web Encryption (JWE)",
              RFC 7516, May 2015.

   [RFC7517]  Jones, M., "JSON Web Key (JWK)", RFC 7517, May 2015.

Appendix A.  AEAD and AE algorithms

   The set of encryption algorithms that can be used with this
   specification is restricted to authenticated encryption (AE) and
   authenticated encryption with additional data (AEAD) algorithms.
   This means that there is a strong check that the data decrypted by
   the recipient is the same as what was encrypted by the sender.
   Encryption modes such as counter have no check on this at all.  The
   CBC encryption mode had a weak check that the data is correct, given
   a random key and random data, the CBC padding check will pass one out
   of 256 times.  There have been several times that a normal encryption
   mode has been combined with an integrity check to provide a content
   encryption mode that does provide the necessary authentication.  AES-
   GCM [AES-GCM], AES-CCM [RFC3610], AES-CBC-HMAC
   [I-D.mcgrew-aead-aes-cbc-hmac-sha2] are examples of these composite
   modes.

   2PKCS v1.5 RSA key transport does not qualify as an AE algorithm.
   There are only three bytes in the encoding that can be checked as
   having decrypted correctly, the rest of the content can only be
   probabilistically checked as having decrypted correctly.  For this
   reason, PKCS v1.5 RSA key transport MUST NOT be used with this



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   specification.  RSA-OAEP was designed to have the necessary checks
   that that content correctly decrypted and does qualify as an AE
   algorithm.

   When dealing with authenticated encryption algorithms, there is
   always some type of value that needs to be checked to see if the
   authentication level has passed.  This authentication value may be:

   o  A separately generated tag computed by both the encrypter and
      decrypter and then compared by the decryptor.  This tag value may
      be either placed at the end of the cipher text (the decision we
      made) or kept separately (the decision made by the JOSE working
      group).  This is the approach followed by AES-GCM [AES-GCM] and
      AES-CCM [RFC3610].

   o  A fixed value which is part of the encoded plain text.  This is
      the approach followed by the AES key wrap algorithm [RFC3394].

   o  A computed value is included as part of the encoded plain text.
      The computed value is then checked by the decryptor using the same
      computation path.  This is the approach followed by RSAES-OAEP
      [RFC3447].

Appendix B.  Three Levels of Recipient Information

   All of the currently defined Key Management methods only use two
   levels of the COSE_Encrypt structure.  The first level is the message
   content and the second level is the content key encryption.  However,
   if one uses a key management technique such as RSA-KEM (see
   Appendix A of RSA-KEM [RFC5990], then it make sense to have three
   levels of the COSE_Encrypt structure.

   These levels would be:

   o  Level 0: The content encryption level.  This level contains the
      payload of the message.

   o  Level 1: The encryption of the CEK by a KEK.

   o  Level 2: The encryption of a long random secret using an RSA key
      and a key derivation function to convert that secret into the KEK.

Appendix C.  Examples

   The examples can be found at https://github.com/cose-wg/Examples.  I
   am currently still in the process of getting the examples up there
   along with some control information for people to be albe to check
   and reproduce the examples.



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C.1.  Direct MAC

   This example has some features that are in questions but not yet
   incorporated in the document.

   To make it easier to read, this uses CBOR's diagnostic notation
   rather than a binary dump.

   This example is uses HMAC with SHA-256 as the digest algorithm.  The
   key manangment is uses two static ECDH keys along with HKDF to
   directly derive the key used in the HMAC operation.

{1: 3, 2: h'A10104', 4: h'546869732069732074686520636F6E74656E742E',
 10: h'82C136D2C8CB27356635FAFE6F2E1AB2BC23FA706A33357DB017EE51710EEDE5',
 9: [
  {3: {1: "ECDH-SS", 5: "meriadoc.brandybuck@buckland.example",
       "spk": {"kid": "peregrin.took@tuckborough.example"},
       "apu": h'4D8553E7E74F3C6A3A9DD3EF286A8195CBF8A23D19558CCFEC7D34
       B824F42D92BD06BD2C7F0271F0214E141FB779AE2856ABF585A58368B017E7F2A
       9E5CE4DB5'}}]}


C.2.  Wrapped MAC

   This example has some features that are in questions but not yet
   incorporated in the document.

   To make it easier to read, this uses CBOR's diagnostic notation
   rather than a binary dump.

   This exmple uses AES-128-MAC trucated to 64-bits as the digest
   algorithm.  It uses AES-256 Key wrap for the key manangment algorithm
   wrapping the 128-bit key used for the digest algorthm.

   {1: 3, 2: h'A1016E4145532D3132382D4D41432D3634',
    4: h'546869732069732074686520636F6E74656E742E',
    10: h'A61AE6CFB7CABCC9', 9: [
     {3: {1: -5, 5: "018c0ae5-4d9b-471b-bfd6-eef314bc7037"},
      4: h'711AB0DC2FC4585DCE27EFFA6781C8093EBA906F227B6EB0'}]}


C.3.  Multi-recipient MAC message

   This example has some features that are in questions but not yet
   incorporated in the document.

   To make it easier to read, this uses CBOR's diagnostic notation
   rather than a binary dump.



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   This example uses HMAC with SHA-256 for the digest algorithm.  There
   are three different key manangment techniques applied:

   o  An ephemeral static ECDH key agrement operation using AES-128 key
      wrap on the digest key.

   o  Key transport using RSA-OAEP with SHA-256 for the hash and the mfg
      function operations.

   o  AES 256-bit Key wrap using a pre-shared secret.

{1: 3, 2: h'A10104', 4: h'546869732069732074686520636F6E74656E742E',
 10: h'051FA3288A39AC726B4FAE79A4B93FB17D8DC3F6E666247EE7AD40CE1665FCDE',
 9: [
   {3: {1: "ECDH-ES+A128KW",
        5: h'62696C626F2E62616767696E7340686F626269746F6E2E6578616D706C65',
        4: {1: 1, -1: 5, -2: h'43B12669ACAC3FD27898FFBA0BCD2E6C366D53BC4DB
            71F909A759304ACFB5E18CDC7BA0B13FF8C7636271A6924B1AC63C02688075
            B55EF2D613574E7DC242F79C3',
            -3: h'812DD694F4EF32B11014D74010A954689C6B6E8785B333D1AB44F22B
            9D1091AE8FC8AE40B687E5CFBE7EE6F8B47918A07BB04E9F5B1A51A334A16B
            C09777434113'}},
    4: h'1B120C848C7F2F8943E402CBDBDB58EFB281753AF4169C70D0126C0D164362771
         60821790EF4FE3F'},
   {3: {1: -2, 5: h'62696C626F2E62616767696E7340686F626269746F6E2E6578616D
        706C65'},
    4: h'46C4F88069B650909A891E84013614CD58A3668F88FA18F3852940A20B3509859
         1D3AACF91C125A2595CDA7BEE75A490579F0E2F20FD6BC956623BFDE3029C318
        F82C426DAC3463B261C981AB18B72FE9409412E5C7F2D8F2B5ABAF780DF6A282D
        B033B3A863FA957408B81741878F466DCC437006CA21407181A016CA608CA8208
        BD3C5A1DDC828531E30B89A67EC6BB97B0C3C3C92036C0CB84AA0F0CE8C3E4A21
        5D173BFA668F116CA9F1177505AFB7629A9B0B5E096E81D37900E06F561A32B6B
        C993FC6D0CB5D4BB81B74E6FFB0958DAC7227C2EB8856303D989F93B4A0518307
        06A4C44E8314EC846022EAB727E16ADA628F12EE7978855550249CCB58'},
   {3: {1: -5, 5: "018c0ae5-4d9b-471b-bfd6-eef314bc7037"},
        4: h'0B2C7CFCE04E98276342D6476A7723C090DFDD15F9A518E7736549E99837
        0695E6D6A83B4AE507BB'}]}


C.4.  Direct ECDH

   This example has some features that are in questions but not yet
   incorporated in the document.

   To make it easier to read, this uses CBOR's diagnostic notation
   rather than a binary dump.

   Encoded in CBOR - 216 bytes, content is 14 bytes long



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  {1: 2, 2: h'A10101', 7: h'C9CF4DF2FE6C632BF7886413',
   4: h'45FCE2814311024D3A479E7D3EED063850F3F0B94EE043BAFDFA14636E632CF6
        75AF2DAE',
    9: [{3: {1: "ECDH-ES", 5: "meriadoc.brandybuck@buckland.example",
         4: {1: 1, -1: 4, -2: h'98F50A4FF6C05861C8860D13A638EA56C3F5AD75
             90BBFBF054E1C7B4D91D6280',
            -3: h'F01400B089867804B8E9FC96C3932161F1934F4223069170D924B7
             E03BF822BB'}}}]}


C.5.  Single Signature

   This example has some features that are in questions but not yet
   cooperated in the document.

   To make it easier to read, this uses CBOR's diagnostic notation
   rather than a binary dump.

   {1: 1, 4: h'546869732069732074686520636F6E74656E742E',
    5: [{2: h'A20165505333383405781E62696C626F2E62616767696E7340686F626
            269746F6E2E6578616D706C65',
         6: h'4D645B5FF17BCDAD7EB29ABA0EBBFFA747E72767714F26EDBC5B4C1D2
           1CBE799B71388CCC73BDB25C4443D0EA2226B774A5B4815ABA82233B33DA
           4C3958D08285384A854A8F7F8FA9635A1A63BAB2A5D8CF45939A7FA2D95C
           C827EF94EF85276611B957B402BD1756D952597751C7AF5D26023012D3DC
           BFD785F9C0BE57F60719EFB0D2F9280A8D2B18D142F76942D007B4E24087
           DA4BE8F793B646D7B03A86C12731A8EDB36A95DFE6C281B58388380354A2
           94CC21DBC1C1EEE2DB35293AD406F50283874475B9A7E22920BD79B3D055
           214EE1C9D941F125548B9F23A87DCC26CBBEFD0919CF6F89E192A78130AC
           018D1921EF5B4D0A47659E9CBC1CE58ED26'}]}


C.6.  Multiple Signers

   This example has some features that are in questions but not yet
   cooperated in the document.

   To make it easier to read, this uses CBOR's diagnostic notation
   rather than a binary dump.

   Encoded in CBOR - 491 bytes, content is 14 bytes long










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  {1: 1, 4: h'546869732069732074686520636F6E74656E742E',
   5: [{2: h'A10129', 3: {5: "bilbo.baggins@hobbiton.example"},
        6: h'1FD44A2BA1A8A0A664024E7E2AFD1D1D1159460E3C03B9BE8C8F60639CE
          614F59AF33108B65BBDEF3C330FB97E335DA11EEA9B6CBD7E7908FB8B5F61D
          FEB76EC6ED6A62BD9F3D338E373E1903CE2D5D3BD20086BBCA82A6F424E9F4
          1591BD6261835A74F0C0425E88666D530B72ADC1E33C10DC1D0361922B6ADC
          685B76E5CEA79FACA7C4CB66B1379B3F852A5ACE79A5812C6EE1CD3CC7CC88
          F2C9D30FF89D3BD0DE2D0C9355E9712B1BA8AB2F2B065BE0A0D93BFFA27DA0
          2221865A2B16093D92F71F9864D92C87057AE591334DB4CF881ECBEC2AC727
          77D9C88871C10733D65566B35FBFA6BAB54078C1C73AE8758196221FB2814E
          C283A95D191FB80D616'},
       {3: {1: -9, 5: "bilbo.baggins@hobbiton.example"},
        6: h'32247A4FD1CA2B69EEEB48CE65D07F2089D79271BB94847F8628DADB7AF
             FC1A34C24D10DB3C5E0D00BD9CB3BFB9666BAD6E9752564D35C5CCE375B
             A44E2FF33336008D8E07484041DBEFB179EBFFA5455E05D6B24E22DAECF
             0D76AD041A13A9DD7E3DAED7F6B09F1831092FFC5CB8BFE7DBF5E047858
             02A4CB741395F81E76A3A8AD61'}]}


Appendix D.  Top Level Parameter Table

   This table contains the list of all key values that can ocur in the
   COSE_Sign, COSE_signature, COSE_Encrypt, and COSE_MAC structures.




























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   +-------------+--------+--------------------------------------------+
   | name        | number | comments                                   |
   +-------------+--------+--------------------------------------------+
   | msg_type    | 1      | Occurs only in top level messages          |
   |             |        |                                            |
   | protected   | 2      | Occurs in all structures                   |
   |             |        |                                            |
   | unprotected | 3      | Occurs in all structures                   |
   |             |        |                                            |
   | payload     | 4      | Contains the content of the structure      |
   |             |        |                                            |
   | signatures  | 5      | For COSE_Sign - array of signatures        |
   |             |        |                                            |
   | signature   | 6      | For COSE_signature only                    |
   |             |        |                                            |
   | iv          | 7      | For COSE_encrypt only                      |
   |             |        |                                            |
   | aad         | 8      | For COSE_encrypt only                      |
   |             |        |                                            |
   | ciphertext  | 4      | TODO: Should we re-use the same as payload |
   |             |        | or not?                                    |
   |             |        |                                            |
   | recipients  | 9      | For COSE_encrypt and COSE_mac              |
   |             |        |                                            |
   | tag         | 10     | For COSE_mac only                          |
   +-------------+--------+--------------------------------------------+

   ; message_keys
   msg_type=1
   protected=2
   unprotected=3
   payload=4
   signatures=5
   signature=6
   iv=7
   aad=8
   ciphertext=4
   recipients=9
   tag=10


   M00TODO: 1.  There is no equivalent to this table in JOSE so we need
   to get a name for the table and registration rules.  2.  Initial
   registration rules: Number may be a positive or a negative value.
   Values in the range of -24 to 24 are Standards action required.
   Values in the range of -256 to -25 and 25 to 255 are specification
   required with expert review.  Values from 256 to 512 are designated
   for private use.  All other values are reserved.



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Appendix E.  COSE Header Key Registry

   This table contains a list of all of the parameters for use in
   signature and encryption message types defined by the JOSE document
   set.  In the table is the data value type to be used for CBOR as well
   as the integer value that can be used as a replacement for the name
   in order to further decrease the size of the sent item.












































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   +----------+-----+-------------+-----------+------------------------+
   | name     | key | value       | registry  | description            |
   +----------+-----+-------------+-----------+------------------------+
   | alg      | 1   | int / tstr  | COSE      | Integers are taken     |
   |          |     |             | Algorithm | from table Appendix G  |
   |          |     |             | Registry  |                        |
   |          |     |             |           |                        |
   | crit     | 2   | [+          | COSE      | integer values are     |
   |          |     | (tstr/int)] | Header    | from this table.       |
   |          |     |             | Key       |                        |
   |          |     |             | Registry  |                        |
   |          |     |             |           |                        |
   | cty      | 3   | tstr / int  |           | Value is either a      |
   |          |     |             |           | mime-content type or   |
   |          |     |             |           | an integer from the    |
   |          |     |             |           | mime-content type      |
   |          |     |             |           | table                  |
   |          |     |             |           |                        |
   | epk      | 4   | COSE_Key    |           | contains a COSE key    |
   |          |     |             |           | not a JWK key          |
   |          |     |             |           |                        |
   | jku      | *   | tstr        |           | URL to COSE key object |
   |          |     |             |           |                        |
   | jwk      | *   | COSE_Key    |           | contains a COSE key    |
   |          |     |             |           | not a JWK key          |
   |          |     |             |           |                        |
   | kid      | *   | bstr        |           | key identifier         |
   |          |     |             |           |                        |
   | x5c      | *   | bstr*       |           | X.509 Certificate      |
   |          |     |             |           | Chain                  |
   |          |     |             |           |                        |
   | x5t      | *   | bstr        |           | SHA-1 thumbprint of    |
   |          |     |             |           | key                    |
   |          |     |             |           |                        |
   | x5t#S256 | *   | bstr        |           | SHA-256 thumbprint of  |
   |          |     |             |           | key                    |
   |          |     |             |           |                        |
   | x5u      | *   | tstr        |           | URL for X.509          |
   |          |     |             |           | certificate            |
   |          |     |             |           |                        |
   | zip      | *   | int / tstr  |           | Integers are taken     |
   |          |     |             |           | from the table         |
   |          |     |             |           | Appendix G             |
   +----------+-----+-------------+-----------+------------------------+







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Appendix F.  COSE Header Algorithm Key Table

   +------+-----------------------------+-----+----------+-------------+
   | name | algorithm                   | key | CBOR     | description |
   |      |                             |     | type     |             |
   +------+-----------------------------+-----+----------+-------------+
   | apu  | ECDH                        | -1  | bstr     |             |
   |      |                             |     |          |             |
   | apv  | ECDH                        | -2  | bstr     |             |
   |      |                             |     |          |             |
   | iv   | A128GCMKW, A192GCMKW,       | -1  | bstr     |             |
   |      | A256GCMKW                   |     |          |             |
   |      |                             |     |          |             |
   | iv   | A128GCM, A192GCM, A256GCM   | -1  | bstr     |             |
   |      |                             |     |          |             |
   | p2c  | PBE                         | -1  | int      |             |
   |      |                             |     |          |             |
   | p2s  | PBE                         | -2  | bstr     |             |
   +------+-----------------------------+-----+----------+-------------+

Appendix G.  COSE Algorithm Name Values

   This table contains all of the defined algorithms for COSE.

   +--------------------+-----+----------------------------------------+
   | name               | key | description                            |
   +--------------------+-----+----------------------------------------+
   | HS256              | 4   | HMAC w/ SHA-256                        |
   |                    |     |                                        |
   | HS384              | 5   | HMAC w/ SHA-384                        |
   |                    |     |                                        |
   | HS512              | 6   | HMAC w/ SHA-512                        |
   |                    |     |                                        |
   | RS256              | *   | RSASSA-v1.5 w/ SHA-256                 |
   |                    |     |                                        |
   | RS384              | *   | RSASSA-v1.5 w/ SHA-384                 |
   |                    |     |                                        |
   | RSA512             | *   | RSASSA-v1.5 w/ SHA-256                 |
   |                    |     |                                        |
   | ES256              | -7  | ECDSA w/ SHA-256                       |
   |                    |     |                                        |
   | ES384              | -8  | ECDSA w/ SHA-384                       |
   |                    |     |                                        |
   | ES512              | -9  | ECDSA w/ SHA-512                       |
   |                    |     |                                        |
   | PS256              | -10 | RSASSA-PSS w/ SHA-256                  |
   |                    |     |                                        |
   | PS384              | *   | RSASSA-PSS w/ SHA-384                  |



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   |                    |     |                                        |
   | PS512              | -11 | RSASSA-PSS w/ SHA-512                  |
   |                    |     |                                        |
   | RSA1_5             | *   | RSAES v1.5 Key Encryption              |
   |                    |     |                                        |
   | RSA-OAEP           | -2  | RSAES OAEP w/ SHA-256                  |
   |                    |     |                                        |
   | A128KW             | -3  | AES Key Wrap w/ 128-bit key            |
   |                    |     |                                        |
   | A192KW             | -4  | AES Key Wrap w/ 192-bit key            |
   |                    |     |                                        |
   | A256KW             | -5  | AES Key Wrap w/ 256-bit key            |
   |                    |     |                                        |
   | dir                | -6  | Direct use of CEK                      |
   |                    |     |                                        |
   | ECDH-ES            | *   | ECDH ES w/ Concat KDF as CEK           |
   |                    |     |                                        |
   | ECDH-ES+A128KW     | *   | ECDH ES w/ Concat KDF and AES Key wrap |
   |                    |     | w/ 128 bit key                         |
   |                    |     |                                        |
   | ECDH-ES+A192KW     | *   | ECDH ES w/ Concat KDF and AES Key wrap |
   |                    |     | w/ 192 bit key                         |
   |                    |     |                                        |
   | ECDH-ES+A256KW     | *   | ECDH ES w/ Concat KDF and AES Key wrap |
   |                    |     | w/ 256 bit key                         |
   |                    |     |                                        |
   | A128GCMKW          | *   | AES GCM Key Wrap w/ 128 bit key        |
   |                    |     |                                        |
   | A192GCMKW          | *   | AES GCM Key Wrap w/ 192 bit key        |
   |                    |     |                                        |
   | A256GCMKW          | *   | AES GCM Key Wrap w/ 256 bit key        |
   |                    |     |                                        |
   | PBES2-HS256+A128KW | *   | PBES2 w/ HMAC SHA-256 and AES Key wrap |
   |                    |     | w/ 128 bit key                         |
   |                    |     |                                        |
   | PBES2-HS384+A192KW | *   | PBES2 w/ HMAC SHA-384 and AES Key wrap |
   |                    |     | w/ 192 bit key                         |
   |                    |     |                                        |
   | PBES2-HS512+A256KW | *   | PBES2 w/ HMAC SHA-512 and AES Key wrap |
   |                    |     | w/ 256 bit key                         |
   |                    |     |                                        |
   | A128GCM            | 1   | AES-GCM mode w/ 128-bit key            |
   |                    |     |                                        |
   | A192GCM            | 2   | AES-GCM mode w/ 192-bit key            |
   |                    |     |                                        |
   | A256GCM            | 3   | AES-GCM mode w/ 256-bit key            |
   +--------------------+-----+----------------------------------------+




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Appendix H.  COSE General Values

                +------+--------+-------------------------+
                | name | number | description             |
                +------+--------+-------------------------+
                | EC   | 1      | Elliptic Curve key Type |
                |      |        |                         |
                | RSA  | 2      | RSA Key type            |
                |      |        |                         |
                | oct  | 3      | Octet Key type          |
                |      |        |                         |
                | P256 | 4      | EC Curve P256 (NIST)    |
                |      |        |                         |
                | P521 | 5      | EC Curve P521 (NIST)    |
                +------+--------+-------------------------+

Appendix I.  COSE Key Map Keys

   This table contains a list of all of the parameters defined for keys
   that were defined by the JOSE document set.  In the table is the data
   value type to be used for CBOR as well as the integer value that can
   be used as a replacement for the name in order to further decrease
   the size of the sent item.




























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   +----------+-----+--------+-------------+---------------------------+
   | name     | key | CBOR   | registry    | description               |
   |          |     | type   |             |                           |
   +----------+-----+--------+-------------+---------------------------+
   | kty      | 1   | tstr / | COSE        | Identification of the key |
   |          |     | int    | General     | type                      |
   |          |     |        | Values      |                           |
   |          |     |        |             |                           |
   | use      | *   | tstr   |             | deprecated - don't use    |
   |          |     |        |             |                           |
   | key_ops  | *   | [*     |             |                           |
   |          |     | tstr]  |             |                           |
   |          |     |        |             |                           |
   | alg      | 3   | tstr / | COSE        | Key usage restriction to  |
   |          |     | int    | Algorithm   | this algorithm            |
   |          |     |        | Values      |                           |
   |          |     |        |             |                           |
   | kid      | 2   | bstr   |             | Key Identification value  |
   |          |     |        |             | - match to kid in message |
   |          |     |        |             |                           |
   | x5u      | *   | tstr   |             |                           |
   |          |     |        |             |                           |
   | x5c      | *   | bstr*  |             |                           |
   |          |     |        |             |                           |
   | x5t      | *   | bstr   |             |                           |
   |          |     |        |             |                           |
   | x5t#S256 | *   | bstr   |             |                           |
   +----------+-----+--------+-------------+---------------------------+

   ;key_keys
   kty=1
   key_kid=2
   key_alg=3


Appendix J.  COSE Key Parameter Keys

   This table contains a list of all of the parameters that were defined
   by the JOSE document set for a specific key type.  In the table is
   the data value type to be used for CBOR as well as the integer value
   that can be used as a replacement for the name in order to further
   decrease the size of the sent item.  Parameters dealing with keys









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   +--------+------+-----+---------+---------------------+-------------+
   | key    | name | key | CBOR    | registry            | description |
   | type   |      |     | type    |                     |             |
   +--------+------+-----+---------+---------------------+-------------+
   | EC     | crv  | -1  | int /   | Pull from general   |             |
   |        |      |     | tstr    | value registry      |             |
   |        |      |     |         |                     |             |
   | EC     | x    | -2  | bstr    |                     |             |
   |        |      |     |         |                     |             |
   | EC     | y    | -3  | bstr    |                     |             |
   |        |      |     |         |                     |             |
   | EC     | d    | -4  | bstr    |                     |             |
   |        |      |     |         |                     |             |
   | RSA    | e    | -1  | bstr    |                     |             |
   |        |      |     |         |                     |             |
   | RSA    | n    | -2  | bstr    |                     |             |
   |        |      |     |         |                     |             |
   | RSA    | d    | -3  | bstr    |                     |             |
   |        |      |     |         |                     |             |
   | RSA    | p    | -4  | bstr    |                     |             |
   |        |      |     |         |                     |             |
   | RSA    | q    | -5  | bstr    |                     |             |
   |        |      |     |         |                     |             |
   | RSA    | dp   | -6  | bstr    |                     |             |
   |        |      |     |         |                     |             |
   | RSA    | dq   | -7  | bstr    |                     |             |
   |        |      |     |         |                     |             |
   | RSA    | qi   | -8  | bstr    |                     |             |
   |        |      |     |         |                     |             |
   | RSA    | oth  | -9  | bstr    |                     |             |
   |        |      |     |         |                     |             |
   | RSA    | r    | -10 | bstr    |                     |             |
   |        |      |     |         |                     |             |
   | RSA    | t    | -11 | bstr    |                     |             |
   |        |      |     |         |                     |             |
   | oct    | k    | -1  | bstr    |                     |             |
   +--------+------+-----+---------+---------------------+-------------+

Author's Address

   Jim Schaad
   August Cellars

   Email: ietf@augustcellars.com







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