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Versions: (draft-nottingham-http-encryption-encoding) 00 01 02 draft-ietf-httpbis-encryption-encoding

Network Working Group                                         M. Thomson
Internet-Draft                                                   Mozilla
Intended status: Standards Track                        October 19, 2015
Expires: April 21, 2016


                  Encrypted Content-Encoding for HTTP
                    draft-thomson-http-encryption-02

Abstract

   This memo introduces a content-coding for HTTP that allows message
   payloads to be encrypted.

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
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   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 April 21, 2016.

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
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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.






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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Notational Conventions  . . . . . . . . . . . . . . . . .   3
   2.  The "aesgcm128" HTTP Content Encoding . . . . . . . . . . . .   3
   3.  The Encryption HTTP Header Field  . . . . . . . . . . . . . .   5
     3.1.  Encryption Header Field Parameters  . . . . . . . . . . .   6
     3.2.  Content Encryption Key Derivation . . . . . . . . . . . .   6
     3.3.  Nonce Derivation  . . . . . . . . . . . . . . . . . . . .   7
   4.  Encryption-Key Header Field . . . . . . . . . . . . . . . . .   7
     4.1.  Explicit Key  . . . . . . . . . . . . . . . . . . . . . .   8
     4.2.  Diffie-Hellman  . . . . . . . . . . . . . . . . . . . . .   8
   5.  Examples  . . . . . . . . . . . . . . . . . . . . . . . . . .   9
     5.1.  Successful GET Response . . . . . . . . . . . . . . . . .   9
     5.2.  Encryption and Compression  . . . . . . . . . . . . . . .   9
     5.3.  Encryption with More Than One Key . . . . . . . . . . . .   9
     5.4.  Encryption with Explicit Key  . . . . . . . . . . . . . .  10
     5.5.  Diffie-Hellman Encryption . . . . . . . . . . . . . . . .  10
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .  11
     6.1.  Key and Nonce Reuse . . . . . . . . . . . . . . . . . . .  11
     6.2.  Content Integrity . . . . . . . . . . . . . . . . . . . .  12
     6.3.  Leaking Information in Headers  . . . . . . . . . . . . .  12
     6.4.  Poisoning Storage . . . . . . . . . . . . . . . . . . . .  13
     6.5.  Sizing and Timing Attacks . . . . . . . . . . . . . . . .  13
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  13
     7.1.  The "aesgcm128" HTTP Content Encoding . . . . . . . . . .  13
     7.2.  Encryption Header Fields  . . . . . . . . . . . . . . . .  13
     7.3.  The HTTP Encryption Parameter Registry  . . . . . . . . .  14
       7.3.1.  keyid . . . . . . . . . . . . . . . . . . . . . . . .  14
       7.3.2.  salt  . . . . . . . . . . . . . . . . . . . . . . . .  14
       7.3.3.  rs  . . . . . . . . . . . . . . . . . . . . . . . . .  15
     7.4.  The HTTP Encryption-Key Parameter Registry  . . . . . . .  15
       7.4.1.  keyid . . . . . . . . . . . . . . . . . . . . . . . .  15
       7.4.2.  aesgcm128 . . . . . . . . . . . . . . . . . . . . . .  15
       7.4.3.  dh  . . . . . . . . . . . . . . . . . . . . . . . . .  16
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  16
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .  16
     8.2.  Informative References  . . . . . . . . . . . . . . . . .  17
   Appendix A.  JWE Mapping  . . . . . . . . . . . . . . . . . . . .  18
   Appendix B.  Acknowledgements . . . . . . . . . . . . . . . . . .  19
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .  19

1.  Introduction

   It is sometimes desirable to encrypt the contents of a HTTP message
   (request or response) so that when the payload is stored (e.g., with
   a HTTP PUT), only someone with the appropriate key can read it.




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   For example, it might be necessary to store a file on a server
   without exposing its contents to that server.  Furthermore, that same
   file could be replicated to other servers (to make it more resistant
   to server or network failure), downloaded by clients (to make it
   available offline), etc.  without exposing its contents.

   These uses are not met by the use of TLS [RFC5246], since it only
   encrypts the channel between the client and server.

   This document specifies a content-coding (Section 3.1.2 of [RFC7231])
   for HTTP to serve these and other use cases.

   This content-coding is not a direct adaptation of message-based
   encryption formats - such as those that are described by [RFC4880],
   [RFC5652], [RFC7516], and [XMLENC] - which are not suited to stream
   processing, which is necessary for HTTP.  The format described here
   cleaves more closely to the lower level constructs described in
   [RFC5116].

   To the extent that message-based encryption formats use the same
   primitives, the format can be considered as sequence of encrypted
   messages with a particular profile.  For instance, Appendix A
   explains how the format is congruent with a sequence of JSON Web
   Encryption [RFC7516] values with a fixed header.

   This mechanism is likely only a small part of a larger design that
   uses content encryption.  How clients and servers acquire and
   identify keys will depend on the use case.  Though a complete key
   management system is not described, this document defines an
   Encryption-Key header field that can be used to convey keying
   material.

1.1.  Notational Conventions

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

2.  The "aesgcm128" HTTP Content Encoding

   The "aesgcm128" HTTP content-coding indicates that a payload has been
   encrypted using Advanced Encryption Standard (AES) in Galois/Counter
   Mode (GCM) as identified as AEAD_AES_128_GCM in [RFC5116],
   Section 5.1.  The AEAD_AES_128_GCM algorithm uses a 128 bit content
   encryption key.

   When this content-coding is in use, the Encryption header field
   (Section 3) describes how encryption has been applied.  The



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   Encryption-Key header field (Section 4) can be included to describe
   how the content encryption key is derived or retrieved.

   The "aesgcm128" content-coding uses a single fixed set of encryption
   primitives.  Cipher suite agility is achieved by defining a new
   content-coding scheme.  This ensures that only the HTTP Accept-
   Encoding header field is necessary to negotiate the use of
   encryption.

   The "aesgcm128" content-coding uses a fixed record size.  The
   resulting encoding is a series of fixed-size records, with a final
   record that is one or more octets shorter than a fixed sized record.

          +------+         input of between rs-256
          | data |            and rs-1 octets
          +------+      (one fewer for the last record)
              |
              v
   +-----+-----------+
   | pad |   data    |     add padding to form plaintext
   +-----+-----------+
            |
            v
   +--------------------+
   |    ciphertext      |  encrypt with AEAD_AES_128_GCM
   +--------------------+     expands by 16 octets

   The record size determines the length of each portion of plaintext
   that is enciphered, with the exception of the final record, which is
   necessarily smaller.  The record size defaults to 4096 octets, but
   can be changed using the "rs" parameter on the Encryption header
   field.

   AEAD_AES_128_GCM expands ciphertext to be 16 octets longer than its
   input plaintext.  Therefore, the length of each enciphered record
   other than the last is equal to the value of the "rs" parameter plus
   16 octets.  A receiver MUST fail to decrypt if the final record
   ciphertext is 16 octets or less in size.  Valid records always
   contain at least one byte of padding and a 16 octet authentication
   tag.

   Each record contains between 1 and 256 octets of padding, inserted
   into a record before the enciphered content.  Padding consists of a
   length byte, followed that number of zero-valued octets.  A receiver
   MUST fail to decrypt if any padding octet other than the first is
   non-zero, or a record has more padding than the record size can
   accommodate.




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   The nonce for each record is a 96-bit value constructed from the
   record sequence number and the input keying material.  Nonce
   derivation is covered in Section 3.3.

   The additional data passed to each invocation of AEAD_AES_128_GCM is
   a zero-length octet sequence.

   A sequence of full-sized records can be truncated to produce a
   shorter sequence of records with valid authentication tags.  To
   prevent an attacker from truncating a stream, an encoder MUST append
   a record that contains only padding and is smaller than the full
   record size if the final record ends on a record boundary.  A
   receiver MUST treat the stream as failed due to truncation if the
   final record is the full record size.

   A consequence of this record structure is that range requests
   [RFC7233] and random access to encrypted payload bodies are possible
   at the granularity of the record size.  However, without data from
   adjacent ranges, partial records cannot be used.  Thus, it is best if
   records start and end on multiples of the record size, plus the 16
   octet authentication tag size.

3.  The Encryption HTTP Header Field

   The "Encryption" HTTP header field describes the encrypted content
   encoding(s) that have been applied to a payload body, and therefore
   how those content encoding(s) can be removed.

   The "Encryption" header field uses the extended ABNF syntax defined
   in Section 1.2 of [RFC7230] and the "parameter" rule from [RFC7231]

     Encryption-val = #encryption_params
     encryption_params = [ parameter *( ";" parameter ) ]

   If the payload is encrypted more than once (as reflected by having
   multiple content-codings that imply encryption), each application of
   the content encoding is reflected in the Encryption header field, in
   the order in which they were applied.

   The Encryption header MAY be omitted if the sender does not intend
   for the immediate recipient to be able to decrypt the payload body.
   Alternatively, the Encryption header field MAY be omitted if the
   sender intends for the recipient to acquire the header field by other
   means.

   Servers processing PUT requests MUST persist the value of the
   Encryption header field, unless they remove the content-coding by
   decrypting the payload.



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3.1.  Encryption Header Field Parameters

   The following parameters are used in determining the content
   encryption key that is used for encryption:

   keyid:  The "keyid" parameter contains a string that identifies the
      keying material that is used.  The "keyid" parameter SHOULD be
      included, unless key identification is guaranteed by other means.
      The "keyid" parameter MUST be used if keying material included in
      an Encryption-Key header field is needed to derive the content
      encryption key.

   salt:  The "salt" parameter contains a base64 URL-encoded octets that
      is used as salt in deriving a unique content encryption key (see
      Section 3.2).  The "salt" parameter MUST be present, and MUST be
      exactly 16 octets long when decoded.  The "salt" parameter MUST
      NOT be reused for two different payload bodies that have the same
      input keying material; generating a random salt for every
      application of the content encoding ensures that content
      encryption key reuse is highly unlikely.

   rs:  The "rs" parameter contains a positive decimal integer that
      describes the record size in octets.  This value MUST be greater
      than 1.  If the "rs" parameter is absent, the record size defaults
      to 4096 octets.

3.2.  Content Encryption Key Derivation

   In order to allow the reuse of keying material for multiple different
   HTTP messages, a content encryption key is derived for each message.
   The content encryption key is derived from the decoded value of the
   "salt" parameter using the HMAC-based key derivation function (HKDF)
   described in [RFC5869] using the SHA-256 hash algorithm [FIPS180-2].

   The decoded value of the "salt" parameter is the salt input to HKDF
   function.  The keying material identified by the "keyid" parameter is
   the input keying material (IKM) to HKDF.  Input keying material can
   either be prearranged, or can be described using the Encryption-Key
   header field (Section 4).  The first step of HKDF is therefore:

      PRK = HMAC-SHA-256(salt, IKM)

   AEAD_AES_128_GCM requires a 16 octet (128 bit) content encryption
   key, so the length (L) parameter to HKDF is 16.  The info parameter
   is set to the ASCII-encoded string "Content-Encoding: aesgcm128".
   The second step of HKDF can therefore be simplified to the first 16
   octets of a single HMAC:




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      CEK = HMAC-SHA-256(PRK, "Content-Encoding: aesgcm128" || 0x01)

3.3.  Nonce Derivation

   The nonce input to AEAD_AES_128_GCM is constructed for each record.
   The nonce for each record is a 12 octet (96 bit) value is produced
   from the record sequence number and a value derived from the input
   keying material.

   The input keying material and salt values are input to HKDF with
   different info and length parameters.  The info parameter for the
   nonce is the ASCII-encoded string "Content-Encoding: nonce" and the
   length (L) parameter is 12 octets.

   The result is combined with the record sequence number - using
   exclusive or - to produce the nonce.  The record sequence number
   (SEQ) is a 96-bit unsigned integer in network byte order that starts
   at zero.

   Thus, the final nonce for each record is a 12 octet value:

      NONCE = HMAC-SHA-256(PRK, "Content-Encoding: nonce" || 0x01) ^ SEQ

4.  Encryption-Key Header Field

   An Encryption-Key header field can be used to describe the input
   keying material used in the Encryption header field.

   The Encryption-Key header field uses the extended ABNF syntax defined
   in Section 1.2 of [RFC7230] and the "parameter" rule from [RFC7231].

     Encryption-Key-val = #encryption_key_params
     encryption_key_params = [ parameter *( ";" parameter ) ]

   keyid:  The "keyid" parameter corresponds to the "keyid" parameter in
      the Encryption header field.

   aesgcm128:  The "aesgcm128" parameter contains the URL-safe base64
      [RFC4648] octets of the input keying material.

   dh:  The "dh" parameter contains an ephemeral Diffie-Hellman share.
      This form of the header field can be used to encrypt content for a
      specific recipient.

   The input keying material used by the content-encoding key derivation
   (see Section 3.2) can be determined based on the information in the
   Encryption-Key header field.  The method for key derivation depends
   on the parameters that are present in the header field.



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   The value or values provided in the Encryption-Key header field is
   valid only for the current HTTP message unless additional information
   indicates a greater scope.

   Note that different methods for determining input keying material
   will produce different amounts of data.  The HKDF process ensures
   that the final content encryption key is the necessary size.

   Alternative methods for determining input keying material MAY be
   defined by specifications that use this content-encoding.

4.1.  Explicit Key

   The "aesgcm128" parameter is decoded and used as the input keying
   material for the "aesgcm128" content encoding.  The "aesgcm128"
   parameter MUST decode to at least 16 octets in order to be used as
   input keying material for "aesgcm128" content encoding.

   Other key determination parameters can be ignored if the "aesgcm128"
   parameter is present.

4.2.  Diffie-Hellman

   The "dh" parameter is included to describe a Diffie-Hellman share,
   either modp (or finite field) Diffie-Hellman [DH] or elliptic curve
   Diffie-Hellman (ECDH) [RFC4492].

   This share is combined with other information at the recipient to
   determine the HKDF input keying material.  In order for the exchange
   to be successful, the following information MUST be established out
   of band:

   o  Which Diffie-Hellman form is used.

   o  The modp group or elliptic curve that will be used.

   o  The format of the ephemeral public share that is included in the
      "dh" parameter.  For instance, using ECDH both parties need to
      agree whether this is an uncompressed or compressed point.

   In addition to identifying which content-encoding this input keying
   material is used for, the "keyid" parameter is used to identify this
   additional information at the receiver.

   The intended recipient recovers their private key and are then able
   to generate a shared secret using the appropriate Diffie-Hellman
   process.




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   Specifications that rely on an Diffie-Hellman exchange for
   determining input keying material MUST either specify the parameters
   for Diffie-Hellman (group parameters, or curves and point format)
   that are used, or describe how those parameters are negotiated
   between sender and receiver.

5.  Examples

5.1.  Successful GET Response

   HTTP/1.1 200 OK
   Content-Type: application/octet-stream
   Content-Encoding: aesgcm128
   Connection: close
   Encryption: keyid="http://example.org/bob/keys/123";
               salt="XZwpw6o37R-6qoZjw6KwAw"

   [encrypted payload]

   Here, a successful HTTP GET response has been encrypted using input
   keying material that is identified by a URI.

   Note that the media type has been changed to "application/octet-
   stream" to avoid exposing information about the content.

5.2.  Encryption and Compression

   HTTP/1.1 200 OK
   Content-Type: text/html
   Content-Encoding: aesgcm128, gzip
   Transfer-Encoding: chunked
   Encryption: keyid="mailto:me@example.com";
               salt="m2hJ_NttRtFyUiMRPwfpHA"

   [encrypted payload]

5.3.  Encryption with More Than One Key














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   PUT /thing HTTP/1.1
   Host: storage.example.com
   Content-Type: application/http
   Content-Encoding: aesgcm128, aesgcm128
   Content-Length: 1234
   Encryption: keyid="mailto:me@example.com";
               salt="NfzOeuV5USPRA-n_9s1Lag",
               keyid="http://example.org/bob/keys/123";
               salt="bDMSGoc2uobK_IhavSHsHA"; rs=1200

   [encrypted payload]

   Here, a PUT request has been encrypted twice with different input
   keying material; decrypting twice is necessary to read the content.
   The outer layer of encryption uses a 1200 octet record size.

5.4.  Encryption with Explicit Key

   HTTP/1.1 200 OK
   Content-Length: 32
   Content-Encoding: aesgcm128
   Encryption: keyid="a1"; salt="ibZx1RNz537h1XNkRcPpjA"
   Encryption-Key: keyid="a1"; aesgcm128="9Z57YCb3dK95dSsdFJbkag"

   zK3kpG__Z8whjIkG6RYgPz11oUkTKcxPy9WP-VPMfuc

   This example shows the string "I am the walrus" encrypted using an
   directly provided value for the input keying material.  The content
   body contains a single record only and is shown here encoded in URL-
   safe base64 for presentation reasons only.

5.5.  Diffie-Hellman Encryption

   HTTP/1.1 200 OK
   Content-Length: 32
   Content-Encoding: aesgcm128
   Encryption: keyid="dhkey"; salt="5hpuYfxDzG6nSs9-EQuaBg"
   Encryption-Key: keyid="dhkey";
                   dh="BLsyIPbDn6bquEOwHaju2gj8kUVoflzTtPs_6fGoock_
                       dwxi1BcgFtObPVnic4alcEucx8I6G8HmEZCJnAl36Zg"

   BmuHqRzdD4W1mibxglrPiRHZRSY49Dzdm6jHrWXzZrE

   This example shows the same string, "I am the walrus", encrypted
   using ECDH over the P-256 curve [FIPS186].  The content body is shown
   here encoded in URL-safe base64 for presentation reasons only.





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   The receiver (in this case, the HTTP client) uses a key pair that is
   identified by the string "dhkey" and the sender (the server) uses a
   key pair for which the public share is included in the "dh" parameter
   above.  The keys shown below use uncompressed points [X.692] encoded
   using URL-safe base64.  Line wrapping is added for presentation
   purposes only.

      Receiver:
         private key: iCjNf8v4ox_g1rJuSs_gbNmYuUYx76ZRruQs_CHRzDg
         public key: BPM1w41cSD4BMeBTY0Fz9ryLM-LeM22Dvt0gaLRukf05
                     rMhzFAvxVW_mipg5O0hkWad9ZWW0uMRO2Nrd32v8odQ
      Sender:
         private key: W0cxgeHDZkR3uMQYAbVgF5swKQUAR7DgoTaaQVlA-Fg
         public key: <the value of the "dh" parameter>

6.  Security Considerations

   This mechanism assumes the presence of a key management framework
   that is used to manage the distribution of keys between valid senders
   and receivers.  Defining key management is part of composing this
   mechanism into a larger application, protocol, or framework.

   Implementation of cryptography - and key management in particular -
   can be difficult.  For instance, implementations need to account for
   the potential for exposing keying material on side channels, such as
   might be exposed by the time it takes to perform a given operation.
   The requirements for a good implementation of cryptographic
   algorithms can change over time.

6.1.  Key and Nonce Reuse

   Encrypting different plaintext with the same content encryption key
   and nonce in AES-GCM is not safe [RFC5116].  The scheme defined here
   uses a fixed progression of nonce values.  Thus, a new content
   encryption key is needed for every application of the content
   encoding.  Since input keying material can be reused, a unique "salt"
   parameter is needed to ensure a content encryption key is not reused.

   If a content encryption key is reused - that is, if input keying
   material and salt are reused - this could expose the plaintext and
   the authentication key, nullifying the protection offered by
   encryption.  Thus, if the same input keying material is reused, then
   the salt parameter MUST be unique each time.  This ensures that the
   content encryption key is not reused.  An implementation SHOULD
   generate a random salt parameter for every message; a counter could
   achieve the same result.





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6.2.  Content Integrity

   This mechanism only provides content origin authentication.  The
   authentication tag only ensures that an entity with access to the
   content encryption key produced the encrypted data.

   Any entity with the content encryption key can therefore produce
   content that will be accepted as valid.  This includes all recipients
   of the same HTTP message.

   Furthermore, any entity that is able to modify both the Encryption
   header field and the HTTP message body can replace the contents.
   Without the content encryption key or the input keying material,
   modifications to or replacement of parts of a payload body are not
   possible.

6.3.  Leaking Information in Headers

   Because only the payload body is encrypted, information exposed in
   header fields is visible to anyone who can read the HTTP message.
   This could expose side-channel information.

   For example, the Content-Type header field can leak information about
   the payload body.

   There are a number of strategies available to mitigate this threat,
   depending upon the application's threat model and the users'
   tolerance for leaked information:

   1.  Determine that it is not an issue.  For example, if it is
       expected that all content stored will be "application/json", or
       another very common media type, exposing the Content-Type header
       field could be an acceptable risk.

   2.  If it is considered sensitive information and it is possible to
       determine it through other means (e.g., out of band, using hints
       in other representations, etc.), omit the relevant headers, and/
       or normalize them.  In the case of Content-Type, this could be
       accomplished by always sending Content-Type: application/octet-
       stream (the most generic media type), or no Content-Type at all.

   3.  If it is considered sensitive information and it is not possible
       to convey it elsewhere, encapsulate the HTTP message using the
       application/http media type (Section 8.3.2 of [RFC7230]),
       encrypting that as the payload of the "outer" message.






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6.4.  Poisoning Storage

   This mechanism only offers encryption of content; it does not perform
   authentication or authorization, which still needs to be performed
   (e.g., by HTTP authentication [RFC7235]).

   This is especially relevant when a HTTP PUT request is accepted by a
   server; if the request is unauthenticated, it becomes possible for a
   third party to deny service and/or poison the store.

6.5.  Sizing and Timing Attacks

   Applications using this mechanism need to be aware that the size of
   encrypted messages, as well as their timing, HTTP methods, URIs and
   so on, may leak sensitive information.

   This risk can be mitigated through the use of the padding that this
   mechanism provides.  Alternatively, splitting up content into
   segments and storing the separately might reduce exposure.  HTTP/2
   [RFC7540] combined with TLS [RFC5246] might be used to hide the size
   of individual messages.

7.  IANA Considerations

7.1.  The "aesgcm128" HTTP Content Encoding

   This memo registers the "encrypted" HTTP content-coding in the HTTP
   Content Codings Registry, as detailed in Section 2.

   o  Name: aesgcm128

   o  Description: AES-GCM encryption with a 128-bit content encryption
      key

   o  Reference: this specification

7.2.  Encryption Header Fields

   This memo registers the "Encryption" HTTP header field in the
   Permanent Message Header Registry, as detailed in Section 3.

   o  Field name: Encryption

   o  Protocol: HTTP

   o  Status: Standard

   o  Reference: this specification



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   o  Notes:

   This memo registers the "Encryption-Key" HTTP header field in the
   Permanent Message Header Registry, as detailed in Section 4.

   o  Field name: Encryption-Key

   o  Protocol: HTTP

   o  Status: Standard

   o  Reference: this specification

   o  Notes:

7.3.  The HTTP Encryption Parameter Registry

   This memo establishes a registry for parameters used by the
   "Encryption" header field under the "Hypertext Transfer Protocol
   (HTTP) Parameters" grouping.  The "Hypertext Transfer Protocol (HTTP)
   Encryption Parameters" operates under an "Specification Required"
   policy [RFC5226].

   Entries in this registry are expected to include the following
   information:

   o  Parameter Name: The name of the parameter.

   o  Purpose: A brief description of the purpose of the parameter.

   o  Reference: A reference to a specification that defines the
      semantics of the parameter.

   The initial contents of this registry are:

7.3.1.  keyid

   o  Parameter Name: keyid

   o  Purpose: Identify the key that is in use.

   o  Reference: this document

7.3.2.  salt

   o  Parameter Name: salt





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   o  Purpose: Provide a source of entropy for derivation of a content
      encryption key.  This value is mandatory.

   o  Reference: this document

7.3.3.  rs

   o  Parameter Name: rs

   o  Purpose: The size of the encrypted records.

   o  Reference: this document

7.4.  The HTTP Encryption-Key Parameter Registry

   This memo establishes a registry for parameters used by the
   "Encryption-Key" header field under the "Hypertext Transfer Protocol
   (HTTP) Parameters" grouping.  The "Hypertext Transfer Protocol (HTTP)
   Encryption Parameters" operates under an "Specification Required"
   policy [RFC5226].

   Entries in this registry are expected to include the following
   information:

   o  Parameter Name: The name of the parameter.

   o  Purpose: A brief description of the purpose of the parameter.

   o  Reference: A reference to a specification that defines the
      semantics of the parameter.

   The initial contents of this registry are:

7.4.1.  keyid

   o  Parameter Name: keyid

   o  Purpose: Identify the key that is in use.

   o  Reference: this document

7.4.2.  aesgcm128

   o  Parameter Name: aesgcm128

   o  Purpose: Provide an explicit input keying material value for the
      aesgcm128 content encoding.




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   o  Reference: this document

7.4.3.  dh

   o  Parameter Name: dh

   o  Purpose: Carry a modp or elliptic curve Diffie-Hellman share used
      to derive input keying material.

   o  Reference: this document

8.  References

8.1.  Normative References

   [DH]       Diffie, W. and M. Hellman, "New Directions in
              Cryptography", IEEE Transactions on Information Theory,
              V.IT-22 n.6 , June 1977.

   [FIPS180-2]
              Department of Commerce, National., "NIST FIPS 180-2,
              Secure Hash Standard", August 2002.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/
              RFC2119, March 1997,
              <http://www.rfc-editor.org/info/rfc2119>.

   [RFC4492]  Blake-Wilson, S., Bolyard, N., Gupta, V., Hawk, C., and B.
              Moeller, "Elliptic Curve Cryptography (ECC) Cipher Suites
              for Transport Layer Security (TLS)", RFC 4492, DOI
              10.17487/RFC4492, May 2006,
              <http://www.rfc-editor.org/info/rfc4492>.

   [RFC4648]  Josefsson, S., "The Base16, Base32, and Base64 Data
              Encodings", RFC 4648, DOI 10.17487/RFC4648, October 2006,
              <http://www.rfc-editor.org/info/rfc4648>.

   [RFC5116]  McGrew, D., "An Interface and Algorithms for Authenticated
              Encryption", RFC 5116, DOI 10.17487/RFC5116, January 2008,
              <http://www.rfc-editor.org/info/rfc5116>.

   [RFC5869]  Krawczyk, H. and P. Eronen, "HMAC-based Extract-and-Expand
              Key Derivation Function (HKDF)", RFC 5869, DOI 10.17487/
              RFC5869, May 2010,
              <http://www.rfc-editor.org/info/rfc5869>.





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   [RFC7230]  Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
              Protocol (HTTP/1.1): Message Syntax and Routing", RFC
              7230, DOI 10.17487/RFC7230, June 2014,
              <http://www.rfc-editor.org/info/rfc7230>.

   [RFC7231]  Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
              Protocol (HTTP/1.1): Semantics and Content", RFC 7231, DOI
              10.17487/RFC7231, June 2014,
              <http://www.rfc-editor.org/info/rfc7231>.

8.2.  Informative References

   [FIPS186]  National Institute of Standards and Technology (NIST),
              "Digital Signature Standard (DSS)", NIST PUB 186-4 , July
              2013.

   [RFC4880]  Callas, J., Donnerhacke, L., Finney, H., Shaw, D., and R.
              Thayer, "OpenPGP Message Format", RFC 4880, DOI 10.17487/
              RFC4880, November 2007,
              <http://www.rfc-editor.org/info/rfc4880>.

   [RFC5226]  Narten, T. and H. Alvestrand, "Guidelines for Writing an
              IANA Considerations Section in RFCs", BCP 26, RFC 5226,
              DOI 10.17487/RFC5226, May 2008,
              <http://www.rfc-editor.org/info/rfc5226>.

   [RFC5246]  Dierks, T. and E. Rescorla, "The Transport Layer Security
              (TLS) Protocol Version 1.2", RFC 5246, DOI 10.17487/
              RFC5246, August 2008,
              <http://www.rfc-editor.org/info/rfc5246>.

   [RFC5652]  Housley, R., "Cryptographic Message Syntax (CMS)", STD 70,
              RFC 5652, DOI 10.17487/RFC5652, September 2009,
              <http://www.rfc-editor.org/info/rfc5652>.

   [RFC7233]  Fielding, R., Ed., Lafon, Y., Ed., and J. Reschke, Ed.,
              "Hypertext Transfer Protocol (HTTP/1.1): Range Requests",
              RFC 7233, DOI 10.17487/RFC7233, June 2014,
              <http://www.rfc-editor.org/info/rfc7233>.

   [RFC7235]  Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
              Protocol (HTTP/1.1): Authentication", RFC 7235, DOI
              10.17487/RFC7235, June 2014,
              <http://www.rfc-editor.org/info/rfc7235>.

   [RFC7516]  Jones, M. and J. Hildebrand, "JSON Web Encryption (JWE)",
              RFC 7516, DOI 10.17487/RFC7516, May 2015,
              <http://www.rfc-editor.org/info/rfc7516>.



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   [RFC7540]  Belshe, M., Peon, R., and M. Thomson, Ed., "Hypertext
              Transfer Protocol Version 2 (HTTP/2)", RFC 7540, DOI
              10.17487/RFC7540, May 2015,
              <http://www.rfc-editor.org/info/rfc7540>.

   [X.692]    ANSI, "Public Key Cryptography For The Financial Services
              Industry: The Elliptic Curve Digital Signature Algorithm
              (ECDSA)", ANSI X9.62 , 1998.

   [XMLENC]   Eastlake, D., Reagle, J., Imamura, T., Dillaway, B., and
              E. Simon, "XML Encryption Syntax and Processing", W3C REC
              , December 2002, <http://www.w3.org/TR/xmlenc-core/>.

Appendix A.  JWE Mapping

   The "aesgcm128" content encoding can be considered as a sequence of
   JSON Web Encryption (JWE) objects [RFC7516], each corresponding to a
   single fixed size record.  The following transformations are applied
   to a JWE object that might be expressed using the JWE Compact
   Serialization:

   o  The JWE Protected Header is fixed to a value { "alg": "dir",
      "enc": "A128GCM" }, describing direct encryption using AES-GCM
      with a 128-bit content encryption key.  This header is not
      transmitted, it is instead implied by the value of the Content-
      Encoding header field.

   o  The JWE Encrypted Key is empty, as stipulated by the direct
      encryption algorithm.

   o  The JWE Initialization Vector ("iv") for each record is set to the
      exclusive or of the 96-bit record sequence number, starting at
      zero, and a value derived from the input keying material (see
      Section 3.3).  This value is also not transmitted.

   o  The final value is the concatenated JWE Ciphertext and the JWE
      Authentication Tag, both expressed without URL-safe Base 64
      encoding.  The "." separator is omitted, since the length of these
      fields is known.

   Thus, the example in Section 5.4 can be rendered using the JWE
   Compact Serialization as:

   eyAiYWxnIjogImRpciIsICJlbmMiOiAiQTEyOEdDTSIgfQ..AAAAAAAAAAAAAAAA.
   LwTC-fwdKh8de0smD2jfzA.eh1vURhu65M2lxhctbbntA

   Where the first line represents the fixed JWE Protected Header, JWE
   Encrypted Key, and JWE Initialization Vector, all of which are



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   determined algorithmically.  The second line contains the encoded
   body, split into JWE Ciphertext and JWE Authentication Tag.

Appendix B.  Acknowledgements

   Mark Nottingham was an original author of this document.

   The following people provided valuable input: Richard Barnes, David
   Benjamin, Peter Beverloo, Mike Jones, Stephen Farrell, Adam Langley,
   John Mattsson, Eric Rescorla, and Jim Schaad.

Author's Address

   Martin Thomson
   Mozilla

   Email: martin.thomson@gmail.com


































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