draft-ietf-smime-cms-01.txt   draft-ietf-smime-cms-02.txt 
S/MIME Working Group R. Housley S/MIME Working Group R. Housley
Internet Draft SPYRUS Internet Draft SPYRUS
expires in six months November 1997 expires in six months December 1997
Cryptographic Message Syntax Cryptographic Message Syntax
<draft-ietf-smime-cms-01.txt> <draft-ietf-smime-cms-02.txt>
Status of this Memo Status of this Memo
This document is an Internet-Draft. Internet-Drafts are working This document is an Internet-Draft. Internet-Drafts are working
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and its working groups. Note that other groups may also distribute and its working groups. Note that other groups may also distribute
working documents as Internet-Drafts. working documents as Internet-Drafts.
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and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
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ftp.isi.edu (US West Coast). ftp.isi.edu (US West Coast).
Abstract Abstract
This document describes the Cryptographic Message Syntax. This This document describes the Cryptographic Message Syntax. This
syntax is used to digitally sign or encrypt arbitrary messages. syntax is used to digitally sign, digest, or encrypt arbitrary
messages.
The Cryptographic Message Syntax is derived from PKCS #7 version 1.5. The Cryptographic Message Syntax is derived from PKCS #7 version 1.5.
Wherever possible, backward compatibility is preserved; however, Wherever possible, backward compatibility is preserved; however,
changes were necessary to accomodate attribute certificate transfer changes were necessary to accommodate attribute certificate transfer
and key agreement techniques for key management. and key agreement techniques for key management.
This drfat obosletes the previously released <draft-housley-smime-
cms-00.txt>.
This draft is being discussed on the ''ietf-smime'' mailing list. To This draft is being discussed on the ''ietf-smime'' mailing list. To
subscribe, send a message to: subscribe, send a message to:
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with the single ''subscribe'' word in the body of the message. Also, with the single ''subscribe'' word in the body of the message. Also,
there is a Web site for the mailing list at: there is a Web site for the mailing list at:
<http://www.imc.org/ietf-smime/>. <http://www.imc.org/ietf-smime/>.
1 Introduction 1 Introduction
This document describes the Cryptographic Message Syntax. This This document describes the Cryptographic Message Syntax. This
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The fields of ContentInfo have the following meanings: The fields of ContentInfo have the following meanings:
contentType indicates the type of content. It is an object contentType indicates the type of content. It is an object
identifier, which means it is a unique string of integers assigned identifier, which means it is a unique string of integers assigned
by the authority that defines the content type. by the authority that defines the content type.
content is the content. The field is optional, although it is content is the content. The field is optional, although it is
generally present. In the rare cases where it is absent, the generally present. In the rare cases where it is absent, the
intended value must be supplied by other means. intended value must be supplied by other means.
The methods below assume that the type of content can be determined The type of content can be determined uniquely by contentType, so the
uniquely by contentType, so the type defined along with the object type defined along with the object identifier should not be a CHOICE
identifier should not be a CHOICE type. type.
When a ContentInfo value is encapsulated within signed-data, a
message-digest algorithm is applied to the contents octets of the DER
encoding of the content field. When a ContentInfo value is
encapsulated within enveloped-data, a content-encryption algorithm is
applied to the contents octets of a definite-length BER encoding of
the content field.
The optional omission of the content field makes it possible to The optional omission of the content field makes it possible to
construct "external signatures." In the case of external signatures, construct "external signatures." In the case of external signatures,
the content being signed would be absent from the encapsulated the content being signed would be absent from the encapsulated
ContentInfo value included in the signed-data content type. ContentInfo value included in the signed-data content type. If the
ContentInfo value is absent, the signatureValue is calculated as
though the ContentInfo value were present. The presumed ContentInfo
must have the content type set to id-data and the content omitted.
4 Data Content Type 4 Data Content Type
The data content type is identified by the following object The data content type is identified by the following object
identifier: identifier:
id-data OBJECT IDENTIFIER ::= { iso(1) member-body(2) id-data OBJECT IDENTIFIER ::= { iso(1) member-body(2)
us(840) rsadsi(113549) pkcs(1) pkcs7(7) 1 } us(840) rsadsi(113549) pkcs(1) pkcs7(7) 1 }
The data content type is just an octet string. It shall have ASN.1 The data content type is just an octet string. It shall have ASN.1
type Data: type Data:
Data ::= OCTET STRING Data ::= OCTET STRING
The data content type is intended to refer to arbitrary octet The data content type is intended to refer to arbitrary octet
strings, such as ASCII text files; the interpretation is left to the strings, such as ASCII text files; the interpretation is left to the
application. Such strings need not have any internal structure application. Such strings need not have any internal structure
(although they may; they could even be DER encoded). (although they may; they could even be DER encoded).
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SignerInfo ::= SEQUENCE { SignerInfo ::= SEQUENCE {
version Version, version Version,
issuerAndSerialNumber IssuerAndSerialNumber, issuerAndSerialNumber IssuerAndSerialNumber,
digestAlgorithm DigestAlgorithmIdentifier, digestAlgorithm DigestAlgorithmIdentifier,
authenticatedAttributes [0] IMPLICIT Attributes OPTIONAL, authenticatedAttributes [0] IMPLICIT Attributes OPTIONAL,
signatureAlgorithm SignatureAlgorithmIdentifier, signatureAlgorithm SignatureAlgorithmIdentifier,
signature SignatureValue, signature SignatureValue,
unauthenticatedAttributes [1] IMPLICIT Attributes OPTIONAL } unauthenticatedAttributes [1] IMPLICIT Attributes OPTIONAL }
Attributes ::= SET OF Attribute
SignatureValue ::= OCTET STRING SignatureValue ::= OCTET STRING
The fields of type SignerInfo have the following meanings: The fields of type SignerInfo have the following meanings:
version is the syntax version number. It shall always be 1. version is the syntax version number. It shall always be 1.
issuerAndSerialNumber specifies the signer's certificate (and issuerAndSerialNumber specifies the signer's certificate (and
thereby the signer's public key) by issuer distinguished name and thereby the signer's public key) by issuer distinguished name and
issuer-specific serial number. issuer-specific serial number.
digestAlgorithm identifies the message digest algorithm, and any digestAlgorithm identifies the message digest algorithm, and any
associated parameters, used by the signer. The message digest is associated parameters, used by the signer. The message digest is
computed over the the content and authenticated attributes, if computed over the content and authenticated attributes, if
present. The message digest algorithm should be among those listed present. The message digest algorithm should be among those listed
in the digestAlgorithms field of the superior SignerInfo value. in the digestAlgorithms field of the superior SignerInfo value.
The message digesting process is described in Section 5.3. The message digesting process is described in Section 5.3.
authenticatedAttributes is a collection of attributes that are authenticatedAttributes is a collection of attributes that are
signed. The field is optional, but it must be present if the signed. The field is optional, but it must be present if the
content type of the ContentInfo value being signed is not data. If content type of the ContentInfo value being signed is not data. If
the field is present, it must contain, at a minimum, two the field is present, it must contain, at a minimum, two
attributes: attributes:
A PKCS #9 content-type attribute having as its value the A content-type attribute having as its value the content type
content type of the ContentInfo value being signed. of the ContentInfo value being signed. Section 8.1 defines the
content-type attribute.
A PKCS #9 message-digest attribute, having as its value the A message-digest attribute, having as its value the message
message digest of the content. digest of the content. Section 8.2 defines the message-digest
attribute.
Other attribute types that might be useful here, such as Other attribute types that might be useful here, such as
signing time, are also defined in PKCS #9. signing time, are defined in Section 8.
signatureAlgorithm identifies the signature algorithm, and any signatureAlgorithm identifies the signature algorithm, and any
associated parameters, used by the signer to generate the digital associated parameters, used by the signer to generate the digital
signature. signature.
signature is the result of digital signature generation, using the signature is the result of digital signature generation, using the
message digest and the signer's private key. message digest and the signer's private key.
unauthenticatedAttributes is a collection of attributes that are unauthenticatedAttributes is a collection of attributes that are
not signed. The field is optional. Attribute types that might be not signed. The field is optional. Attribute types that might be
useful here, such as countersignatures, are defined in PKCS #9. useful here, such as countersignatures, are defined in Section 10.
5.3 Message Digest Calculation Process 5.3 Message Digest Calculation Process
The message digest calculation process computes a message digest on The message digest calculation process computes a message digest on
either the content being signed or the content together with the either the content being signed or the content together with the
signer's authenticated attributes. In either case, the initial input signer's authenticated attributes. In either case, the initial input
to the message digest calculation process is the "value" of the to the message digest calculation process is the "value" of the
content being signed. Specifically, the initial input is the content content being signed. Specifically, the initial input is the content
octets of the DER encoding of the content field of the ContentInfo octets of the DER encoding of the content field of the ContentInfo
value to which the signing process is applied. Only the contents value to which the signing process is applied. Only the contents
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The input to the signature generation process includes the result of The input to the signature generation process includes the result of
the message digest calculation process and the signer's private key. the message digest calculation process and the signer's private key.
The details of the signature generation depend on the signature The details of the signature generation depend on the signature
algorithm employed. The object identifier, along with any algorithm employed. The object identifier, along with any
parameters, that specifies the signature algorithm employed by the parameters, that specifies the signature algorithm employed by the
signer is carried in the signatureAlgorithm field. The signature signer is carried in the signatureAlgorithm field. The signature
value generated by the signer is encoded as an OCTET STRING and value generated by the signer is encoded as an OCTET STRING and
carried in the signature field. carried in the signature field.
5.5 Message Signature Validation Process
The input to the signature validation process includes the result of
the message digest calculation process and the signer's public key.
The details of the signature generation depend on the signature
algorithm employed.
The recipient may not rely on any message digest values computed by
the originator. If the signedData signerInfo includes
authenticatedAttributes, then the ASN.1 DER encoded content of the
signedData object must be digested as described in section 5.3. For
the signature to be valid, the message digest value calculated by the
recipient must be the same as the value of the messageDigest
attribute included in the authenticatedAttributes of the signedData
signerInfo.
6 Enveloped-data Content Type 6 Enveloped-data Content Type
The enveloped-data content type consists of an encrypted content of The enveloped-data content type consists of an encrypted content of
any type and encrypted content-encryption keys for one or more any type and encrypted content-encryption keys for one or more
recipients. The combination of the encrypted content and one recipients. The combination of the encrypted content and one
encrypted content-encryption key for a recipient is a "digital encrypted content-encryption key for a recipient is a "digital
envelope" for that recipient. Any type of content can be enveloped envelope" for that recipient. Any type of content can be enveloped
for any number of recipients. for any number of recipients.
The typical application of the enveloped-data content type will The typical application of the enveloped-data content type will
represent one or more recipients' digital envelopes on content of the represent one or more recipients' digital envelopes on content of the
data or signed-data content types. data or signed-data content types.
Enveloped-data is constructed by the following steps: Enveloped-data is constructed by the following steps:
1. A content-encryption key for a particular content-encryption 1. A content-encryption key for a particular content-encryption
algorithm is generated at random. algorithm is generated at random.
2. The content-encryption key is encrypted for each recipient. 2. The content-encryption key is encrypted for each recipient.
The details of this encryption depend on the key management The details of this encryption depend on the key management
algorithm used, but three genral techniques are supported: algorithm used, but three general techniques are supported:
key transport: the content-encryption key is encrypted in the key transport: the content-encryption key is encrypted in the
recipient's public key; recipient's public key;
key agreement: the recipient's public key and the sender's key agreement: the recipient's public key and the sender's
private key are used to generate a pairwise symmetric key, then private key are used to generate a pairwise symmetric key, then
the content-encryption key is encrypted in the pairwise the content-encryption key is encrypted in the pairwise
symmetric key; and symmetric key; and
mail list keys: the content-encryption key is encrypted in a mail list keys: the content-encryption key is encrypted in a
previously distributed symmetric key. previously distributed symmetric key.
3. For each recipient, the encrypted content-encryption key and 3. For the originator and each recipient, the encrypted content-
other recipient-specific information are collected into a encryption key and other recipient-specific information are
RecipientInfo value, defined in Section 6.2. collected into a RecipientInfo value, defined in Section 6.2.
4. The content is encrypted with the content-encryption key. 4. The content is encrypted with the content-encryption key.
Content encryption may require that the content be padded to a Content encryption may require that the content be padded to a
multiple of some block size; see Section 6.3. multiple of some block size; see Section 6.3.
5. The RecipientInfo values for all the recipients are collected 5. The RecipientInfo values for all the recipients are collected
together with the encrypted content into a EnvelopedData value as together with the encrypted content into a EnvelopedData value as
defined in Section 6.1. defined in Section 6.1.
A recipient opens the envelope by decrypting the one of the encrypted A recipient opens the envelope by decrypting one of the encrypted
content-encryption keys and decrypting the encrypted content with the content-encryption keys and decrypting the encrypted content with the
recovered content-encryption key. recovered content-encryption key.
This section is divided into four parts. The first part describes the This section is divided into four parts. The first part describes the
top-level type EnvelopedData, the second part describes the per- top-level type EnvelopedData, the second part describes the per-
recipient information type RecipientInfo, and the third and fourth recipient information type RecipientInfo, and the third and fourth
parts describe the content-encryption and key-encryption processes. parts describe the content-encryption and key-encryption processes.
6.1 EnvelopedData Type 6.1 EnvelopedData Type
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contentEncryptionAlgorithm identifies the content-encryption contentEncryptionAlgorithm identifies the content-encryption
algorithm, and any associated parameters, used to encrypt the algorithm, and any associated parameters, used to encrypt the
content. The content-encryption process is described in Section content. The content-encryption process is described in Section
6.3. The same algorithm is used for all recipients. 6.3. The same algorithm is used for all recipients.
encryptedContent is the result of encrypting the content. The encryptedContent is the result of encrypting the content. The
field is optional, and if the field is not present, its intended field is optional, and if the field is not present, its intended
value must be supplied by other means. value must be supplied by other means.
The recipientInfos field comes before the encryptedContentInfo field The recipientInfos field comes before the encryptedContentInfo field
so that an EnvelopedData value may be preoceesed in a single pass. so that an EnvelopedData value may be processed in a single pass.
6.2 RecipientInfo Type 6.2 RecipientInfo Type
Per-recipient information is represented in the type RecipientInfo: Per-recipient information is represented in the type RecipientInfo:
RecipientInfo ::= SEQUENCE { RecipientInfo ::= SEQUENCE {
version Version, version Version,
rid RecipientIdentifier, rid RecipientIdentifier,
originatorCert [0] EXPLICIT EntityIdentifier OPTIONAL,
keyEncryptionAlgorithm KeyEncryptionAlgorithmIdentifier, keyEncryptionAlgorithm KeyEncryptionAlgorithmIdentifier,
encryptedKey EncryptedKey } encryptedKey EncryptedKey }
RecipientIdentifier ::= CHOICE { RecipientIdentifier ::= CHOICE {
issuerAndSerialNumber IssuerAndSerialNumber, issuerAndSerialNumber IssuerAndSerialNumber,
rKeyId [0] IMPLICIT RecipientKeyIdentifier, rKeyId [0] IMPLICIT RecipientKeyIdentifier,
mlKeyId [1] IMPLICIT MailListKeyIdentifier } mlKeyId [1] IMPLICIT MailListKeyIdentifier }
RecipientKeyIdentifier ::= SEQUENCE { RecipientKeyIdentifier ::= SEQUENCE {
subjectKeyIdentifier OCTET STRING, subjectKeyIdentifier SubjectKeyIdentifier,
date GeneralizedTime OPTIONAL, date GeneralizedTime OPTIONAL,
other OtherKeyAttribute OPTIONAL } other OtherKeyAttribute OPTIONAL }
MailListKeyIdentifier ::= SEQUENCE { MailListKeyIdentifier ::= SEQUENCE {
kekIdentifier OCTET STRING, kekIdentifier OCTET STRING,
date GeneralizedTime OPTIONAL, date GeneralizedTime OPTIONAL,
other OtherKeyAttribute OPTIONAL } other OtherKeyAttribute OPTIONAL }
OtherKeyAttribute ::= SEQUENCE { EntityIdentifier ::= CHOICE {
keyAttrId OBJECT IDENTIFIER, issuerAndSerialNumber IssuerAndSerialNumber,
keyAttr ANY DEFINED BY keyAttrId OPTIONAL } subjectKeyIdentifier SubjectKeyIdentifier }
SubjectKeyIdentifier ::= OCTET STRING
EncryptedKey ::= OCTET STRING EncryptedKey ::= OCTET STRING
The fields of type RecipientInfo have the following meanings: The fields of type RecipientInfo have the following meanings:
version is the syntax version number. If the RecipientIdentifier version is the syntax version number. If the OriginatorCert is
is the CHOICE issuerAndSerialNumber, then the version shall be 0. absent and the RecipientIdentifier is the CHOICE
If the RecipientIdentifier is either the CHOICE rKeyId or mlKeyId, issuerAndSerialNumber, then the version shall be 0. If the
then the version shall be 2. OriginatorCert is present or the RecipientIdentifier is either the
CHOICE rKeyId or mlKeyId, then the version shall be 2.
rid specifies the recipient's certificate or key that was used by rid specifies the recipient's certificate or key that was used by
the sender to protect the content-encryption key. the sender to protect the content-encryption key.
originatorCert optionally specifies the originator's certificate
to be used by this recipient. This field should be included when
the originator has more than one certificate containing a public
key associated with the key management algorithm used for this
recipient.
keyEncryptionAlgorithm identifies the key-encryption algorithm, keyEncryptionAlgorithm identifies the key-encryption algorithm,
and any associated parameters, used to encrypt the content- and any associated parameters, used to encrypt the content-
encryption key for the recipient. The key-encryption process is encryption key for the recipient. The key-encryption process is
described in Section 6.4. described in Section 6.4.
encryptedKey is the result of encrypting the content-encryption encryptedKey is the result of encrypting the content-encryption
key for the recipient. key for the recipient.
The RecipientIdentifier is a CHOICE with three alternatives. The The RecipientIdentifier is a CHOICE with three alternatives. The
first two alternatives, issuerAndSerialNumber and rKeyId, specifies first two alternatives, issuerAndSerialNumber and rKeyId, specifies
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including input values that are already a multiple of the block size, including input values that are already a multiple of the block size,
and no padding string is a suffix of another. This padding method is and no padding string is a suffix of another. This padding method is
well-defined if and only if k is less than 256. well-defined if and only if k is less than 256.
6.4 Key-encryption Process 6.4 Key-encryption Process
The input to the key-encryption process -- the value supplied to the The input to the key-encryption process -- the value supplied to the
recipient's key-encryption algorithm --is just the "value" of the recipient's key-encryption algorithm --is just the "value" of the
content-encryption key. content-encryption key.
7 Useful Types 7 Digested-data Content Type
The digested-data content type consists of content of any type and a
message digest of the content.
The typical application of the digested-data content type will be to
provide content integrity, and that the result generally becomes the
input to the enveloped-data content type.
Digested-data is constructed by the following steps:
1. A message digest is computed on the content with a message-
digest algorithm.
2. The message-digest algorithm and the message digest are
collected together with the content into a DigestedData value.
A recipient verifies the message digest by comparing the message
digest to an independently computed message digest.
The digested-data content type is identified by the following object
identifier:
id-digestedData OBJECT IDENTIFIER ::= { iso(1) member-body(2)
us(840) rsadsi(113549) pkcs(1) pkcs7(7) 5 }
The digested-data content type shall have ASN.1 type DigestedData:
DigestedData ::= SEQUENCE {
version Version,
digestAlgorithm DigestAlgorithmIdentifier,
contentInfo ContentInfo,
digest Digest }
Digest ::= OCTET STRING
The fields of type DigestedData have the following meanings:
version is the syntax version number. It shall be 0.
digestAlgorithm identifies the message digest algorithm, and any
associated parameters, under which the content is digested. The
message-digesting process is the same as in Section 5.3 in the
case when there are no authenticated attributes.
contentInfo is the content that is digested. It may have any of
the defined content types.
digest is the result of the message-digesting process.
The ordering of the digestAlgorithm field, the contentInfo field, and
the digest field makes it possible to process a DigestedData value in
a single pass.
8 Encrypted-data Content Type
The encrypted-data content type consists of encrypted content of any
type. Unlike the enveloped-data content type, the encrypted-data
content type has neither recipients nor encrypted content-encryption
keys. Keys are assumed to be managed by other means.
The typical application of the encrypted-data content type will be to
encrypt the content of the data content type for local storage,
perhaps where the encryption key is a password.
The encrypted-data content type is identified by the following object
identifier:
id-encryptedData OBJECT IDENTIFIER ::= { iso(1) member-body(2)
us(840) rsadsi(113549) pkcs(1) pkcs7(7) 6 }
The encrypted-data content type shall have ASN.1 type EncryptedData:
EncryptedData ::= SEQUENCE {
version Version,
encryptedContentInfo EncryptedContentInfo }
The fields of type EncryptedData have the following meanings:
version is the syntax version number. It shall be 0.
encryptedContentInfo is the encrypted content information, as
defined in Section 6.1.
9 Useful Types
This section defines types that are used other places in the This section defines types that are used other places in the
document. The types are not listed in any particular order. document. The types are not listed in any particular order.
7.1 CertificateRevocationLists 9.1 CertificateRevocationLists
The CertificateRevocationLists type gives a set of certificate The CertificateRevocationLists type gives a set of certificate
revocation lists (CRLs). It is intended that the set contain revocation lists (CRLs). It is intended that the set contain
information sufficient to determine whether the certificates with information sufficient to determine whether the certificates with
which the set is associated are revoked or not. However, there may which the set is associated are revoked or not. However, there may
be more CRLs than necessary, or there may be fewer than necessary. be more CRLs than necessary, or there may be fewer than necessary.
The definition of CertificateRevocationList is imported from X.509. The definition of CertificateList is imported from X.509.
CertificateRevocationLists ::= SET OF CertificateRevocationList CertificateRevocationLists ::= SET OF CertificateList
7.2 ContentEncryptionAlgorithmIdentifier 9.2 ContentEncryptionAlgorithmIdentifier
The ContentEncryptionAlgorithmIdentifier type identifies a content- The ContentEncryptionAlgorithmIdentifier type identifies a content-
encryption algorithm such as DES. A content-encryption algorithm encryption algorithm such as DES. A content-encryption algorithm
supports encryption and decryption operations. The encryption supports encryption and decryption operations. The encryption
operation maps an octet string (the message) to another octet string operation maps an octet string (the message) to another octet string
(the ciphertext) under control of a content-encryption key. The (the ciphertext) under control of a content-encryption key. The
decryption operation is the inverse of the encryption operation. decryption operation is the inverse of the encryption operation.
Context determines which operation is intended. Context determines which operation is intended.
The definition of AlgorithmIdentifier is imported from X.509. The definition of AlgorithmIdentifier is imported from X.509.
ContentEncryptionAlgorithmIdentifier ::= AlgorithmIdentifier ContentEncryptionAlgorithmIdentifier ::= AlgorithmIdentifier
7.3 DigestAlgorithmIdentifier 9.3 DigestAlgorithmIdentifier
The DigestAlgorithmIdentifier type identifies a message-digest The DigestAlgorithmIdentifier type identifies a message-digest
algorithm. Examples include SHA-1, MD2, and MD5. A message-digest algorithm. Examples include SHA-1, MD2, and MD5. A message-digest
algorithm maps an octet string (the message) to another octet string algorithm maps an octet string (the message) to another octet string
(the message digest). (the message digest).
The definition of AlgorithmIdentifier is imported from X.509. The definition of AlgorithmIdentifier is imported from X.509.
DigestAlgorithmIdentifier ::= AlgorithmIdentifier DigestAlgorithmIdentifier ::= AlgorithmIdentifier
7.4 SignatureAlgorithmIdentifier 9.4 SignatureAlgorithmIdentifier
The SignatureAlgorithmIdentifier type identifies a signture The SignatureAlgorithmIdentifier type identifies a signature
algorithm. Examples include DSS and RSA. A signature algorithm algorithm. Examples include DSS and RSA. A signature algorithm
supports signature generation and verification operations. The supports signature generation and verification operations. The
signature generation operation uses the message digest and the signature generation operation uses the message digest and the
signer's private key to generate a signutre value. The signature signer's private key to generate a signature value. The signature
verification operation uses the message digest and the signer's verification operation uses the message digest and the signer's
public key to determine whether or not a signutre value is valid. public key to determine whether or not a signature value is valid.
Context determines which operation is intended. Context determines which operation is intended.
The definition of AlgorithmIdentifier is imported from X.509. The definition of AlgorithmIdentifier is imported from X.509.
SignatureAlgorithmIdentifier ::= AlgorithmIdentifier SignatureAlgorithmIdentifier ::= AlgorithmIdentifier
7.5 CertificateChoices 9.5 CertificateChoices
The CertificateChoices type gives either a PKCS #6 extended The CertificateChoices type gives either a PKCS #6 extended
certificate, an X.509 certificate, or an X.509 attrinute certificate. certificate, an X.509 certificate, or an X.509 attribute certificate.
The PKCS #6 extended certificate is obsolete. It is included for The PKCS #6 extended certificate is obsolete. It is included for
backwards compatibility, and its use should be avoided. backwards compatibility, and its use should be avoided.
The definitions of Certificate and AttributeCertificate are imported The definitions of Certificate and AttributeCertificate are imported
from X.509. from X.509.
CertificateChoices ::= CHOICE { CertificateChoices ::= CHOICE {
certificate Certificate, -- See X.509 certificate Certificate, -- See X.509
extendedCertificate [0] IMPLICIT ExtendedCertificate, -- Obsolete extendedCertificate [0] IMPLICIT ExtendedCertificate, -- Obsolete
attrCert [1] IMPLICIT AttributeCertificate } -- See X.509 and X9.57 attrCert [1] IMPLICIT AttributeCertificate } -- See X.509 and X9.57
7.6 CertificateSet 9.6 CertificateSet
The CertificateSet type provides a set of certificates. It is The CertificateSet type provides a set of certificates. It is
intended that the set be sufficient to contain chains from a intended that the set be sufficient to contain chains from a
recognized "root" or "top-level certification authority" to all of recognized "root" or "top-level certification authority" to all of
the sender certificates with which the set is associated. However, the sender certificates with which the set is associated. However,
there may be more certificates than necessary, or there may be fewer there may be more certificates than necessary, or there may be fewer
than necessary. than necessary.
The precise meaning of a "chain" is outside the scope of this The precise meaning of a "chain" is outside the scope of this
document. Some applications may impose upper limits on the length of document. Some applications may impose upper limits on the length of
a chain; others may enforce certain relationships between the a chain; others may enforce certain relationships between the
subjects and issuers of certificates within a chain. subjects and issuers of certificates within a chain.
CertificateSet ::= SET OF CertificateChoices CertificateSet ::= SET OF CertificateChoices
7.7 IssuerAndSerialNumber 9.7 IssuerAndSerialNumber
The IssuerAndSerialNumber type identifies a certificate, and thereby The IssuerAndSerialNumber type identifies a certificate, and thereby
an entity and a public key, by the distinguished name of the an entity and a public key, by the distinguished name of the
certificate issuer and an issuer-specific certificate serial number. certificate issuer and an issuer-specific certificate serial number.
The definition of Name is imported from X.501, and the definition of The definition of Name is imported from X.501, and the definition of
SerialNumber is imported from X.509. SerialNumber is imported from X.509.
IssuerAndSerialNumber ::= SEQUENCE { IssuerAndSerialNumber ::= SEQUENCE {
issuer Name, issuer Name,
serialNumber SerialNumber } serialNumber SerialNumber }
7.8 KeyEncryptionAlgorithmIdentifier SerialNumber ::= INTEGER
9.8 KeyEncryptionAlgorithmIdentifier
The KeyEncryptionAlgorithmIdentifier type identifies a key-encryption The KeyEncryptionAlgorithmIdentifier type identifies a key-encryption
algorithm used to encrypt a content-encryption key. The encryption algorithm used to encrypt a content-encryption key. The encryption
operation maps an octet string (the key) to another octet string (the operation maps an octet string (the key) to another octet string (the
encrypted key) under control of a key-encryption key. The decryption encrypted key) under control of a key-encryption key. The decryption
operation is the inverse of the encryption operation. Context operation is the inverse of the encryption operation. Context
determines which operation is intended. determines which operation is intended.
The details of encryption and decryption depend on the key management The details of encryption and decryption depend on the key management
algorithm used. Key transport, key agreement, and previously algorithm used. Key transport, key agreement, and previously
distributed symmetric key-encrypting keys are supported. distributed symmetric key-encrypting keys are supported.
The definition of AlgorithmIdentifier is imported from X.509. The definition of AlgorithmIdentifier is imported from X.509.
KeyEncryptionAlgorithmIdentifier ::= AlgorithmIdentifier KeyEncryptionAlgorithmIdentifier ::= AlgorithmIdentifier
7.9 Version 9.9 Version
The Version type gives a syntax version number, for compatibility The Version type gives a syntax version number, for compatibility
with future revisions of this document. with future revisions of this document.
Version ::= INTEGER Version ::= INTEGER
7.10 UserKeyingMaterial 9.10 UserKeyingMaterial
The UserKeyingMaterial type gives a syntax user keying material The UserKeyingMaterial type gives a syntax user keying material
(UKM). Some key management algorithms require UKMs. The sender (UKM). Some key management algorithms require UKMs. The sender
provides a UKM for the specific key management algorithm. provides a UKM for the specific key management algorithm.
The definition of AlgorithmIdentifier is imported from X.509. The definition of AlgorithmIdentifier is imported from X.509.
UserKeyingMaterial ::= SEQUENCE { UserKeyingMaterial ::= SEQUENCE {
algorithm AlgorithmIdentifier, algorithm AlgorithmIdentifier,
ukm OCTET STRING } ukm OCTET STRING }
7.11 UserKeyingMaterials 9.11 UserKeyingMaterials
The UserKeyingMaterial type provides a set of user keying materials The UserKeyingMaterial type provides a set of user keying materials
(UKMs). This allows the sender to provide a UKM for each key (UKMs). This allows the sender to provide a UKM for each key
management algorithm that requires one. management algorithm that requires one.
UserKeyingMaterials ::= SET OF UserKeyingMaterial UserKeyingMaterials ::= SET OF UserKeyingMaterial
7.12 OtherKeyAttribute 9.12 OtherKeyAttribute
The OtherKeyAttribute type gives a syntax for the inclusion of other The OtherKeyAttribute type gives a syntax for the inclusion of other
key attributes that permit the recipient to select the key used by key attributes that permit the recipient to select the key used by
the sender. The attribute object identifier must be registered along the sender. The attribute object identifier must be registered along
with the syntax of the attribute itself. Use of this structure with the syntax of the attribute itself. Use of this structure should
should be avoided since it may impede interoperability. be avoided since it may impede interoperability.
OtherKeyAttribute ::= SEQUENCE { OtherKeyAttribute ::= SEQUENCE {
keyAttrId OBJECT IDENTIFIER, keyAttrId OBJECT IDENTIFIER,
keyAttr ANY DEFINED BY keyAttrId OPTIONAL } keyAttr ANY DEFINED BY keyAttrId OPTIONAL }
10 Useful Attributes
This section defines attributes that may used with signed-data. All
of these attributes ware originally defined in PKCS #9, and they are
included here for easy reference. The attributes are not listed in
any particular order.
10.1 Content Type
The content-type attribute type specifies the content type of the
ContentInfo value being signed in signed-data. The content-type
attribute type is required if there are any authenticated attributes
present.
The content-type attribute is identified by the following object
identifier:
id-contentType OBJECT IDENTIFIER ::= { iso(1) member-body(2)
us(840) rsadsi(113549) pkcs(1) pkcs9(9) 3 }
Content-type attribute values have ASN.1 type ContentType:
ContentType ::= OBJECT IDENTIFIER
A content-type attribute must have a single attribute value.
10.2 Message Digest
The message-digest attribute type specifies the message digest of the
contents octets of the DER encoding of the content field of the
ContentInfo value being signed in signed-data, where the message
digest is computed using the signer's message digest algorithm. The
message-digest attribute type is required if there are any
authenticated attributes present.
The message-digest attribute is identified by the following object
identifier:
id-messageDigest OBJECT IDENTIFIER ::= { iso(1) member-body(2)
us(840) rsadsi(113549) pkcs(1) pkcs9(9) 4 }
Message-digest attribute values have ASN.1 type MessageDigest:
MessageDigest ::= OCTET STRING
A message-digest attribute must have a single attribute value.
10.3 Signing Time
The signing-time attribute type specifies the time at which the
signer (purportedly) performed the signing process. The signing-time
attribute type is intended for use in signed-data.
The signing-time attribute is identified by the following object
identifier:
id-signingTime OBJECT IDENTIFIER ::= { iso(1) member-body(2)
us(840) rsadsi(113549) pkcs(1) pkcs9(9) 5 }
Signing-time attribute values have ASN.1 type SigningTime:
SigningTime ::= Time
Time ::= CHOICE {
utcTime UTCTime,
generalizedTime GeneralizedTime }
Note: The definition of Time matches the one specified in the 1997
version of X.509.
Dates through the year 2049 must be encoded as UTCTime, and dates in
the year 2050 or later must be encoded as GeneralizedTime.
A signing-time attribute must have a single attribute value.
No requirement is imposed concerning the correctness of the signing
time, and acceptance of a purported signing time is a matter of a
recipient's discretion. It is expected, however, that some signers,
such as time-stamp servers, will be trusted implicitly.
10.4 Countersignature
The countersignature attribute type specifies one or more signatures
on the contents octets of the DER encoding of the signatureValue
field of a SignerInfo value in signed-data. Thus, the
countersignature attribute type countersigns (signs in serial)
another signature. The countersignature attribute must be an
unauthenticated attribute; it cannot be an authenticated attribute.
The signing-time attribute is identified by the following object
identifier:
id-countersignature OBJECT IDENTIFIER ::= { iso(1) member-body(2)
us(840) rsadsi(113549) pkcs(1) pkcs9(9) 6 }
Countersignature attribute values have ASN.1 type Countersignature:
Countersignature ::= SignerInfo
Countersignature values have the same meaning as SignerInfo values
for ordinary signatures, except that:
1. The authenticatedAttributes field must contain a message-
digest attribute if it contains any other attributes, but need not
contain a content-type attribute, as there is no content type for
countersignatures.
2. The input to the message-digesting process is the contents
octets of the DER encoding of the signatureValue field of the
SignerInfo value with which the attribute is associated.
A countersignature attribute can have multiple attribute values.
The fact that a countersignature is computed on a signature value
means that the countersigning process need not know the original
content input to the signing process. This has advantages both in
efficiency and in confidentiality. A countersignature, since it has
type SignerInfo, can itself contain a countersignature attribute.
Thus it is possible to construct arbitrarily long series of
countersignatures.
11 Supported Algorithms
To be supplied. However, this section will list the must implement
algorithms and other algorithms that may be implemented. Here are my
current thoughts...
MUST implement: DSS, SHA-1, Diffie-Hellman (X9.42), and Triple-DES
CBC (with three keys).
MAY implement: RSA (signature and key management), MD5, KEA, RC2, DES
CBC, and SKIPJACK.
Appendix A: ASN.1 Module Appendix A: ASN.1 Module
To be supplied. CryptographicMessageSyntax
{ iso(1) member-body(2) us(840) rsadsi(113549)
pkcs(1) pkcs-9(9) smime(16) modules(0) cms(1) }
DEFINITIONS IMPLICIT TAGS ::=
BEGIN
IMPORTS
-- Directory Information Framework (X.501)
Attribute, Name
FROM InformationFramework { joint-iso-itu-t ds(5) modules(1)
informationFramework(1) 3 }
-- Directory Authentication Framework (X.509)
AlgorithmIdentifier, AttributeCertificate, Certificate,
CertificateList, CertificateSerialNumber
FROM AuthenticationFramework { joint-iso-itu-t ds(5) module(1)
authenticationFramework(7) 3 } ;
-- Cryptographic Message Syntax
ContentInfo ::= SEQUENCE {
contentType ContentType,
content [0] EXPLICIT ANY DEFINED BY contentType OPTIONAL }
ContentType ::= OBJECT IDENTIFIER
Data ::= OCTET STRING
SignedData ::= SEQUENCE {
version Version,
digestAlgorithms DigestAlgorithmIdentifiers,
contentInfo ContentInfo,
certificates [0] IMPLICIT CertificateSet OPTIONAL,
crls [1] IMPLICIT CertificateRevocationLists OPTIONAL,
signerInfos SignerInfos }
DigestAlgorithmIdentifiers ::= SET OF DigestAlgorithmIdentifier
SignerInfos ::= SET OF SignerInfo
SignerInfo ::= SEQUENCE {
version Version,
issuerAndSerialNumber IssuerAndSerialNumber,
digestAlgorithm DigestAlgorithmIdentifier,
authenticatedAttributes [0] IMPLICIT Attributes OPTIONAL,
signatureAlgorithm SignatureAlgorithmIdentifier,
signature SignatureValue,
unauthenticatedAttributes [1] IMPLICIT Attributes OPTIONAL }
Attributes ::= SET OF Attribute
SignatureValue ::= OCTET STRING
EnvelopedData ::= SEQUENCE {
version Version,
originatorInfo [0] IMPLICIT OriginatorInfo OPTIONAL,
recipientInfos RecipientInfos,
encryptedContentInfo EncryptedContentInfo }
OriginatorInfo ::= SEQUENCE {
certs [0] IMPLICIT CertificateSet OPTIONAL,
crls [1] IMPLICIT CertificateRevocationLists OPTIONAL,
ukms [2] IMPLICIT UserKeyingMaterials OPTIONAL }
RecipientInfos ::= SET OF RecipientInfo
EncryptedContentInfo ::= SEQUENCE {
contentType ContentType,
contentEncryptionAlgorithm ContentEncryptionAlgorithmIdentifier,
encryptedContent [0] IMPLICIT EncryptedContent OPTIONAL }
EncryptedContent ::= OCTET STRING
RecipientInfo ::= SEQUENCE {
version Version,
rid RecipientIdentifier,
originatorCert [0] EXPLICIT EntityIdentifier OPTIONAL,
keyEncryptionAlgorithm KeyEncryptionAlgorithmIdentifier,
encryptedKey EncryptedKey }
RecipientIdentifier ::= CHOICE {
issuerAndSerialNumber IssuerAndSerialNumber,
rKeyId [0] IMPLICIT RecipientKeyIdentifier,
mlKeyId [1] IMPLICIT MailListKeyIdentifier }
RecipientKeyIdentifier ::= SEQUENCE {
subjectKeyIdentifier SubjectKeyIdentifier,
date GeneralizedTime OPTIONAL,
other OtherKeyAttribute OPTIONAL }
MailListKeyIdentifier ::= SEQUENCE {
kekIdentifier OCTET STRING,
date GeneralizedTime OPTIONAL,
other OtherKeyAttribute OPTIONAL }
EntityIdentifier ::= CHOICE {
issuerAndSerialNumber IssuerAndSerialNumber,
subjectKeyIdentifier SubjectKeyIdentifier }
SubjectKeyIdentifier ::= OCTET STRING
EncryptedKey ::= OCTET STRING
DigestedData ::= SEQUENCE {
version Version,
digestAlgorithm DigestAlgorithmIdentifier,
contentInfo ContentInfo,
digest Digest }
Digest ::= OCTET STRING
EncryptedData ::= SEQUENCE {
version Version,
encryptedContentInfo EncryptedContentInfo }
CertificateRevocationLists ::= SET OF CertificateList
ContentEncryptionAlgorithmIdentifier ::= AlgorithmIdentifier
DigestAlgorithmIdentifier ::= AlgorithmIdentifier
SignatureAlgorithmIdentifier ::= AlgorithmIdentifier
CertificateChoices ::= CHOICE {
certificate Certificate, -- See X.509
extendedCertificate [0] IMPLICIT ExtendedCertificate, -- Obsolete
attrCert [1] IMPLICIT AttributeCertificate } -- See X.509 and X9.57
CertificateSet ::= SET OF CertificateChoices
IssuerAndSerialNumber ::= SEQUENCE {
issuer Name,
serialNumber SerialNumber }
SerialNumber ::= INTEGER
KeyEncryptionAlgorithmIdentifier ::= AlgorithmIdentifier
Version ::= INTEGER
UserKeyingMaterial ::= SEQUENCE {
algorithm AlgorithmIdentifier,
ukm OCTET STRING }
UserKeyingMaterials ::= SET OF UserKeyingMaterial
OtherKeyAttribute ::= SEQUENCE {
keyAttrId OBJECT IDENTIFIER,
keyAttr ANY DEFINED BY keyAttrId OPTIONAL }
-- Attributes
MessageDigest ::= OCTET STRING
SigningTime ::= Time
Time ::= CHOICE {
utcTime UTCTime,
generalTime GeneralizedTime }
Countersignature ::= SignerInfo
-- Object Identifiers
id-data OBJECT IDENTIFIER ::= { iso(1) member-body(2)
us(840) rsadsi(113549) pkcs(1) pkcs7(7) 1 }
id-signedData OBJECT IDENTIFIER ::= { iso(1) member-body(2)
us(840) rsadsi(113549) pkcs(1) pkcs7(7) 2 }
id-envelopedData OBJECT IDENTIFIER ::= { iso(1) member-body(2)
us(840) rsadsi(113549) pkcs(1) pkcs7(7) 3 }
id-digestedData OBJECT IDENTIFIER ::= { iso(1) member-body(2)
us(840) rsadsi(113549) pkcs(1) pkcs7(7) 5 }
id-encryptedData OBJECT IDENTIFIER ::= { iso(1) member-body(2)
us(840) rsadsi(113549) pkcs(1) pkcs7(7) 6 }
id-contentType OBJECT IDENTIFIER ::= { iso(1) member-body(2)
us(840) rsadsi(113549) pkcs(1) pkcs9(9) 3 }
id-messageDigest OBJECT IDENTIFIER ::= { iso(1) member-body(2)
us(840) rsadsi(113549) pkcs(1) pkcs9(9) 4 }
id-signingTime OBJECT IDENTIFIER ::= { iso(1) member-body(2)
us(840) rsadsi(113549) pkcs(1) pkcs9(9) 5 }
id-countersignature OBJECT IDENTIFIER ::= { iso(1) member-body(2)
us(840) rsadsi(113549) pkcs(1) pkcs9(9) 6 }
-- Obsolete Extended Certificate syntax from PKCS#6
ExtendedCertificateOrCertificate ::= CHOICE {
certificate Certificate,
extendedCertificate [0] IMPLICIT ExtendedCertificate }
ExtendedCertificate ::= SEQUENCE {
extendedCertificateInfo ExtendedCertificateInfo,
signatureAlgorithm SignatureAlgorithmIdentifier,
signature Signature }
ExtendedCertificateInfo ::= SEQUENCE {
version Version,
certificate Certificate,
attributes Attributes }
Signature ::= BIT STRING
END -- of CryptographicMessageSyntax
References References
To be supplied. PKCS #6 RSA Laboratories. PKCS #6: Extended-Certificate Syntax
Standard. Version 1.5, November 1993.
PKCS #7 RSA Laboratories. PKCS #7: Cryptographic Message Syntax
Standard. Version 1.5, November 1993.
PKCS #9 RSA Laboratories. PKCS #9: Selected Attribute Types.
Version 1.1, November 1993.
X.208 CCITT. Recommendation X.208: Specification of Abstract
Syntax Notation One (ASN.1). 1988.
X.209 CCITT. Recommendation X.209: Specification of Basic Encoding
Rules for Abstract Syntax Notation One (ASN.1). 1988.
X.501 CCITT. Recommendation X.501: The Directory - Models. 1988.
X.509 CCITT. Recommendation X.509: The Directory - Authentication
Framework. 1988.
Security Considerations Security Considerations
The Cryptographic Message Syntax provides a method for digitally The Cryptographic Message Syntax provides a method for digitally
signing data and encrypting data. signing data, digesting data, and encrypting data.
Implementations must protect the signer's private key. Compromise of Implementations must protect the signer's private key. Compromise of
the signer's private key permits masquerade. the signer's private key permits masquerade.
Implementations must protect the key management private key and the Implementations must protect the key management private key and the
content-encryption key. Compromise of the key management private key content-encryption key. Compromise of the key management private key
may result in the disclosure of all messages protected with that key. may result in the disclosure of all messages protected with that key.
Similarly, compromise of the content-encryption key may result in Similarly, compromise of the content-encryption key may result in
disclosure of the encrypted content. disclosure of the encrypted content.
 End of changes. 

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