information used by the recipient to determine the key-encryption
key used by the sender.
6.2.4 PasswordRecipientInfo Type
Recipient information using a password or shared secret value is
represented in the type PasswordRecipientInfo. Each instance of
PasswordRecipientInfo will transfer the content-encryption key to one
or more recipients who possess the password or shared secret value.
The PasswordRecipientInfo Type is specified in RFC3211 [PWRI]. The
PasswordRecipientInfo structure is repeated here for completeness.
PasswordRecipientInfo ::= SEQUENCE {
version CMSVersion, -- Always set to 0
keyDerivationAlgorithm [0] KeyDerivationAlgorithmIdentifier
OPTIONAL,
keyEncryptionAlgorithm KeyEncryptionAlgorithmIdentifier,
encryptedKey EncryptedKey }
The fields of type PasswordRecipientInfo have the following meanings:
version is the syntax version number. It MUST always be 0.
keyDerivationAlgorithm identifies the key-derivation algorithm,
and any associated parameters, used to derive the key-encryption
key from the password or shared secret value. If this field is
absent, the key-encryption key is supplied from an external
source, for example a hardware crypto token such as a smart card.
keyEncryptionAlgorithm identifies the encryption algorithm, and
any associated parameters, used to encrypt the content-encryption
key with the key-encryption key.
encryptedKey is the result of encrypting the content-encryption
key with the key-encryption key.
6.2.5 OtherRecipientInfo Type
Recipient information for additional key management techniques are
represented in the type OtherRecipientInfo. The OtherRecipientInfo
type allows key management techniques beyond key transport, key
agreement, previously distributed symmetric key-encryption keys, and
password-based key management to be specified in future documents.
An object identifier uniquely identifies such key management
techniques.
OtherRecipientInfo ::= SEQUENCE {
oriType OBJECT IDENTIFIER,
oriValue ANY DEFINED BY oriType }
The fields of type OtherRecipientInfo have the following meanings:
oriType identifies the key management technique.
oriValue contains the protocol data elements needed by a recipient
using the identified key management technique.
6.3 Content-encryption Process
The content-encryption key for the desired content-encryption
algorithm is randomly generated. The data to be protected is padded
as described below, then the padded data is encrypted using the
content-encryption key. The encryption operation maps an arbitrary
string of octets (the data) to another string of octets (the
ciphertext) under control of a content-encryption key. The encrypted
data is included in the envelopedData encryptedContentInfo
encryptedContent OCTET STRING.
Some content-encryption algorithms assume the input length is a
multiple of k octets, where k is greater than one. For such
algorithms, the input shall be padded at the trailing end with
k-(lth mod k) octets all having value k-(lth mod k), where lth is
the length of the input. In other words, the input is padded at
the trailing end with one of the following strings:
01 -- if lth mod k = k-1
02 02 -- if lth mod k = k-2
.
.
.
k k ... k k -- if lth mod k = 0
The padding can be removed unambiguously since all input is padded,
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
well defined if and only if k is less than 256.
6.4 Key-encryption Process
The input to the key-encryption process -- the value supplied to the
recipient's key-encryption algorithm -- is just the "value" of the
content-encryption key.
Any of the aforementioned key management techniques can be used for
each recipient of the same encrypted content.
7. Digested-data Content Type
The digested-data content type consists of content of any type and a
message digest of the content.
Typically, the digested-data content type is used to provide content
integrity, and the result generally becomes an input to the
enveloped-data content type.
The following steps construct digested-data:
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 following object identifier identifies the digested-data content
type:
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 CMSVersion,
digestAlgorithm DigestAlgorithmIdentifier,
encapContentInfo EncapsulatedContentInfo,
digest Digest }
Digest ::= OCTET STRING
The fields of type DigestedData have the following meanings:
version is the syntax version number. If the encapsulated content
type is id-data, then the value of version MUST be 0; however, if
the encapsulated content type is other than id-data, then the
value of version MUST be 2.
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 5.4 in the
case when there are no signed attributes.
encapContentInfo is the content that is digested, as defined in
section 5.2.
digest is the result of the message-digesting process.
The ordering of the digestAlgorithm field, the encapContentInfo
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 MUST 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 derived from a password.
The following object identifier identifies the encrypted-data content
type:
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 CMSVersion,
encryptedContentInfo EncryptedContentInfo,
unprotectedAttrs [1] IMPLICIT UnprotectedAttributes OPTIONAL }
The fields of type EncryptedData have the following meanings:
version is the syntax version number. If unprotectedAttrs is
present, then version MUST be 2. If unprotectedAttrs is absent,
then version MUST be 0.
encryptedContentInfo is the encrypted content information, as
defined in Section 6.1.
unprotectedAttrs is a collection of attributes that are not
encrypted. The field is optional. Useful attribute types are
defined in Section 11.
9. Authenticated-data Content Type
The authenticated-data content type consists of content of any type,
a message authentication code (MAC), and encrypted authentication
keys for one or more recipients. The combination of the MAC and one
encrypted authentication key for a recipient is necessary for that
recipient to verify the integrity of the content. Any type of
content can be integrity protected for an arbitrary number of
recipients.
The process by which authenticated-data is constructed involves the
following steps:
1. A message-authentication key for a particular message-
authentication algorithm is generated at random.
2. The message-authentication key is encrypted for each
recipient. The details of this encryption depend on the key
management algorithm used.
3. For each recipient, the encrypted message-authentication key
and other recipient-specific information are collected into a
RecipientInfo value, defined in Section 6.2.
4. Using the message-authentication key, the originator computes
a MAC value on the content. If the originator is authenticating
any information in addition to the content (see Section 9.2), a
message digest is calculated on the content, the message digest of
the content and the other information are authenticated using the
message-authentication key, and the result becomes the "MAC
value."
9.1 AuthenticatedData Type
The following object identifier identifies the authenticated-data
content type:
id-ct-authData OBJECT IDENTIFIER ::= { iso(1) member-body(2)
us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16)
ct(1) 2 }
The authenticated-data content type shall have ASN.1 type
AuthenticatedData:
AuthenticatedData ::= SEQUENCE {
version CMSVersion,
originatorInfo [0] IMPLICIT OriginatorInfo OPTIONAL,
recipientInfos RecipientInfos,
macAlgorithm MessageAuthenticationCodeAlgorithm,
digestAlgorithm [1] DigestAlgorithmIdentifier OPTIONAL,
encapContentInfo EncapsulatedContentInfo,
authAttrs [2] IMPLICIT AuthAttributes OPTIONAL,
mac MessageAuthenticationCode,
unauthAttrs [3] IMPLICIT UnauthAttributes OPTIONAL }
AuthAttributes ::= SET SIZE (1..MAX) OF Attribute
UnauthAttributes ::= SET SIZE (1..MAX) OF Attribute
MessageAuthenticationCode ::= OCTET STRING
The fields of type AuthenticatedData have the following meanings:
version is the syntax version number. The version MUST be
assigned as follows:
IF ((originatorInfo is present) AND
(any version 2 attribute certificates are present))
THEN version is 1
ELSE version is 0
originatorInfo optionally provides information about the
originator. It is present only if required by the key management
algorithm. It MAY contain certificates, attribute certificates,
and CRLs, as defined in Section 6.1.
recipientInfos is a collection of per-recipient information, as
defined in Section 6.1. There MUST be at least one element in the
collection.
macAlgorithm is a message authentication code (MAC) algorithm
identifier. It identifies the MAC algorithm, along with any
associated parameters, used by the originator. Placement of the
macAlgorithm field facilitates one-pass processing by the
recipient.
digestAlgorithm identifies the message digest algorithm, and any
associated parameters, used to compute a message digest on the
encapsulated content if authenticated attributes are present. The
message digesting process is described in Section 9.2. Placement
of the digestAlgorithm field facilitates one-pass processing by
the recipient. If the digestAlgorithm field is present, then the
authAttrs field MUST also be present.
encapContentInfo is the content that is authenticated, as defined
in section 5.2.
authAttrs is a collection of authenticated attributes. The
authAttrs structure is optional, but it MUST be present if the
content type of the EncapsulatedContentInfo value being
authenticated is not id-data. If the authAttrs field is present,
then the digestAlgorithm field MUST also be present. The
AuthAttributes structure MUST be DER encoded, even if the rest of
the structure is BER encoded. Useful attribute types are defined
in Section 11. If the authAttrs field is present, it MUST
contain, at a minimum, the following two attributes:
A content-type attribute having as its value the content type
of the EncapsulatedContentInfo value being authenticated.
Section 11.1 defines the content-type attribute.
A message-digest attribute, having as its value the message
digest of the content. Section 11.2 defines the message-digest
attribute.
mac is the message authentication code.
unauthAttrs is a collection of attributes that are not
authenticated. The field is optional. To date, no attributes
have been defined for use as unauthenticated attributes, but other
useful attribute types are defined in Section 11.
9.2 MAC Generation
The MAC calculation process computes a message authentication code
(MAC) on either the content being authenticated or a message digest
of content being authenticated together with the originator's
authenticated attributes.
If authAttrs field is absent, the input to the MAC calculation
process is the value of the encapContentInfo eContent OCTET STRING.
Only the octets comprising the value of the eContent OCTET STRING are
input to the MAC algorithm; the tag and the length octets are
omitted. This has the advantage that the length of the content being
authenticated need not be known in advance of the MAC generation
process.
If authAttrs field is present, the content-type attribute (as
described in Section 11.1) and the message-digest attribute (as
described in section 11.2) MUST be included, and the input to the MAC
calculation process is the DER encoding of authAttrs. A separate
encoding of the authAttrs field is performed for message digest
calculation. The IMPLICIT [2] tag in the authAttrs field is not used
for the DER encoding, rather an EXPLICIT SET OF tag is used. That
is, the DER encoding of the SET OF tag, rather than of the IMPLICIT
[2] tag, is to be included in the message digest calculation along
with the length and content octets of the authAttrs value.
The message digest calculation process computes a message digest on
the content being authenticated. The initial input to the message
digest calculation process is the "value" of the encapsulated content
being authenticated. Specifically, the input is the encapContentInfo
eContent OCTET STRING to which the authentication process is applied.
Only the octets comprising the value of the encapContentInfo eContent
OCTET STRING are input to the message digest algorithm, not the tag
or the length octets. This has the advantage that the length of the
content being authenticated need not be known in advance. Although
the encapContentInfo eContent OCTET STRING tag and length octets are
not included in the message digest calculation, they are still
protected by other means. The length octets are protected by the
nature of the message digest algorithm since it is computationally
infeasible to find any two distinct contents of any length that have
the same message digest.
The input to the MAC calculation process includes the MAC input data,
defined above, and an authentication key conveyed in a recipientInfo
structure. The details of MAC calculation depend on the MAC
algorithm employed (e.g., HMAC). The object identifier, along with
any parameters, that specifies the MAC algorithm employed by the
originator is carried in the macAlgorithm field. The MAC value
generated by the originator is encoded as an OCTET STRING and carried
in the mac field.
9.3 MAC Verification
The input to the MAC verification process includes the input data
(determined based on the presence or absence of the authAttrs field,
as defined in 9.2), and the authentication key conveyed in
recipientInfo. The details of the MAC verification process depend on
the MAC algorithm employed.
The recipient MUST NOT rely on any MAC values or message digest
values computed by the originator. The content is authenticated as
described in section 9.2. If the originator includes authenticated
attributes, then the content of the authAttrs is authenticated as
described in section 9.2. For authentication to succeed, the MAC
value calculated by the recipient MUST be the same as the value of
the mac field. Similarly, for authentication to succeed when the
authAttrs field is present, the content message digest value
calculated by the recipient MUST be the same as the message digest
value included in the authAttrs message-digest attribute.
If the AuthenticatedData includes authAttrs, then the content-type
attribute value MUST match the AuthenticatedData encapContentInfo
eContentType value.
10. Useful Types
This section is divided into two parts. The first part defines
algorithm identifiers, and the second part defines other useful
types.
10.1 Algorithm Identifier Types
All of the algorithm identifiers have the same type:
AlgorithmIdentifier. The definition of AlgorithmIdentifier is taken
from X.509 [X.509-88].
There are many alternatives for each algorithm type.
10.1.1 DigestAlgorithmIdentifier
The DigestAlgorithmIdentifier type identifies a message-digest
algorithm. Examples include SHA-1, MD2, and MD5. A message-digest
algorithm maps an octet string (the content) to another octet string
(the message digest).
DigestAlgorithmIdentifier ::= AlgorithmIdentifier
10.1.2 SignatureAlgorithmIdentifier
The SignatureAlgorithmIdentifier type identifies a signature
algorithm. Examples include RSA, DSA, and ECDSA. A signature
algorithm supports signature generation and verification operations.
The signature generation operation uses the message digest and the
signer's private key to generate a signature value. The signature
verification operation uses the message digest and the signer's
public key to determine whether or not a signature value is valid.
Context determines which operation is intended.
SignatureAlgorithmIdentifier ::= AlgorithmIdentifier
10.1.3 KeyEncryptionAlgorithmIdentifier
The KeyEncryptionAlgorithmIdentifier type identifies a key-encryption
algorithm used to encrypt a content-encryption key. The encryption
operation maps an octet string (the key) to another octet string (the
encrypted key) under control of a key-encryption key. The decryption
operation is the inverse of the encryption operation. Context
determines which operation is intended.
The details of encryption and decryption depend on the key management
algorithm used. Key transport, key agreement, previously distributed
symmetric key-encrypting keys, and symmetric key-encrypting keys
derived from passwords are supported.
KeyEncryptionAlgorithmIdentifier ::= AlgorithmIdentifier
10.1.4 ContentEncryptionAlgorithmIdentifier
The ContentEncryptionAlgorithmIdentifier type identifies a content-
encryption algorithm. Examples include Triple-DES and RC2. A
content-encryption algorithm supports encryption and decryption
operations. The encryption operation maps an octet string (the
plaintext) to another octet string (the ciphertext) under control of
a content-encryption key. The decryption operation is the inverse of
the encryption operation. Context determines which operation is
intended.
ContentEncryptionAlgorithmIdentifier ::= AlgorithmIdentifier
10.1.5 MessageAuthenticationCodeAlgorithm
The MessageAuthenticationCodeAlgorithm type identifies a message
authentication code (MAC) algorithm. Examples include DES-MAC and
HMAC-SHA-1. A MAC algorithm supports generation and verification
operations. The MAC generation and verification operations use the
same symmetric key. Context determines which operation is intended.
MessageAuthenticationCodeAlgorithm ::= AlgorithmIdentifier
10.1.6 KeyDerivationAlgorithmIdentifier
The KeyDerivationAlgorithmIdentifier type is specified in RFC3211
[PWRI]. The KeyDerivationAlgorithmIdentifier definition is repeated
here for completeness.
Key derivation algorithms convert a password or shared secret value
into a key-encryption key.
KeyDerivationAlgorithmIdentifier ::= AlgorithmIdentifier
10.2 Other Useful Types
This section defines types that are used other places in the
document. The types are not listed in any particular order.
10.2.1 CertificateRevocationLists
The CertificateRevocationLists type gives a set of certificate
revocation lists (CRLs). It is intended that the set contain
information sufficient to determine whether the certificates and
attribute certificates with which the set is associated are revoked.
However, there may be more CRLs than necessary or there MAY be fewer
CRLs than necessary.
The CertificateList may contain a CRL, an Authority Revocation List
(ARL), a Delta CRL, or an Attribute Certificate Revocation List. All
of these lists share a common syntax.
CRLs are specified in X.509 [X.509-97], and they are profiled for use
in the Internet in RFC3280 [PROFILE].
The definition of CertificateList is taken from X.509.
CertificateRevocationLists ::= SET OF CertificateList
10.2.2 CertificateChoices
The CertificateChoices type gives either a PKCS #6 extended
certificate [PKCS#6], an X.509 certificate, a version 1 X.509
attribute certificate (ACv1) [X.509-97], or a version 2 X.509
attribute certificate (ACv2) [X.509-00]. The PKCS #6 extended
certificate is obsolete. The PKCS #6 certificate is included for
backward compatibility, and PKCS #6 certificates SHOULD NOT be used.
The ACv1 is also obsolete. ACv1 is included for backward
compatibility, and ACv1 SHOULD NOT be used. The Internet profile of
X.509 certificates is specified in the "Internet X.509 Public Key
Infrastructure: Certificate and CRL Profile" [PROFILE]. The Internet
profile of ACv2 is specified in the "An Internet Attribute
Certificate Profile for Authorization" [ACPROFILE].
The definition of Certificate is taken from X.509.
The definitions of AttributeCertificate are taken from X.509-1997 and
X.509-2000. The definition from X.509-1997 is assigned to
AttributeCertificateV1 (see section 12.2), and the definition from
X.509-2000 is assigned to AttributeCertificateV2.
CertificateChoices ::= CHOICE {
certificate Certificate,
extendedCertificate [0] IMPLICIT ExtendedCertificate, -- Obsolete
v1AttrCert [1] IMPLICIT AttributeCertificateV1, -- Obsolete
v2AttrCert [2] IMPLICIT AttributeCertificateV2 }
10.2.3 CertificateSet
The CertificateSet type provides a set of certificates. It is
intended that the set be sufficient to contain chains from a
recognized "root" or "top-level certification authority" to all of
the sender certificates with which the set is associated. However,
there may be more certificates than necessary, or there MAY be fewer
than necessary.
The precise meaning of a "chain" is outside the scope of this
document. Some applications may impose upper limits on the length of
a chain; others may enforce certain relationships between the
subjects and issuers of certificates within a chain.
CertificateSet ::= SET OF CertificateChoices
10.2.4 IssuerAndSerialNumber
The IssuerAndSerialNumber type identifies a certificate, and thereby
an entity and a public key, by the distinguished name of the
certificate issuer and an issuer-specific certificate serial number.
The definition of Name is taken from X.501 [X.501-88], and the
definition of CertificateSerialNumber is taken from X.509 [X.509-97].
IssuerAndSerialNumber ::= SEQUENCE {
issuer Name,
serialNumber CertificateSerialNumber }
CertificateSerialNumber ::= INTEGER
10.2.5 CMSVersion
The CMSVersion type gives a syntax version number, for compatibility
with future revisions of this specification.
CMSVersion ::= INTEGER { v0(0), v1(1), v2(2), v3(3), v4(4) }
10.2.6 UserKeyingMaterial
The UserKeyingMaterial type gives a syntax for user keying material
(UKM). Some key agreement algorithms require UKMs to ensure that a
different key is generated each time the same two parties generate a
pairwise key. The sender provides a UKM for use with a specific key
agreement algorithm.
UserKeyingMaterial ::= OCTET STRING
10.2.7 OtherKeyAttribute
The OtherKeyAttribute type gives a syntax for the inclusion of other
key attributes that permit the recipient to select the key used by
the sender. The attribute object identifier must be registered along
with the syntax of the attribute itself. Use of this structure
should be avoided since it might impede interoperability.
OtherKeyAttribute ::= SEQUENCE {
keyAttrId OBJECT IDENTIFIER,
keyAttr ANY DEFINED BY keyAttrId OPTIONAL }
11. Useful Attributes
This section defines attributes that may be used with signed-data,
enveloped-data, encrypted-data, or authenticated-data. The syntax of
Attribute is compatible with X.501 [X.501-88] and RFC3280 [PROFILE].
Some of the attributes defined in this section were originally
defined in PKCS #9 [PKCS#9]; others were originally defined in a
previous version of this specification [OLDCMS]. The attributes are
not listed in any particular order.
Additional attributes are defined in many places, notably the S/MIME
Version 3 Message Specification [MSG] and the Enhanced Security
Services for S/MIME [ESS], which also include recommendations on the
placement of these attributes.
11.1 Content Type
The content-type attribute type specifies the content type of the
ContentInfo within signed-data or authenticated-data. The content-
type attribute type MUST be present whenever signed attributes are
present in signed-data or authenticated attributes present in
authenticated-data. The content-type attribute value MUST match the
encapContentInfo eContentType value in the signed-data or
authenticated-data.
The content-type attribute MUST be a signed attribute or an
authenticated attribute; it MUST NOT be an unsigned attribute,
unauthenticated attribute, or unprotected attribute.
The following object identifier identifies the content-type
attribute:
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
Even though the syntax is defined as a SET OF AttributeValue, a
content-type attribute MUST have a single attribute value; zero or
multiple instances of AttributeValue are not permitted.
The SignedAttributes and AuthAttributes syntaxes are each defined as
a SET OF Attributes. The SignedAttributes in a signerInfo MUST NOT
include multiple instances of the content-type attribute. Similarly,
the AuthAttributes in an AuthenticatedData MUST NOT include multiple
instances of the content-type attribute.
11.2 Message Digest
The message-digest attribute type specifies the message digest of the
encapContentInfo eContent OCTET STRING being signed in signed-data
(see section 5.4) or authenticated in authenticated-data (see section
9.2). For signed-data, the message digest is computed using the
signer's message digest algorithm. For authenticated-data, the
message digest is computed using the originator's message digest
algorithm.
Within signed-data, the message-digest signed attribute type MUST be
present when there are any signed attributes present. Within
authenticated-data, the message-digest authenticated attribute type
MUST be present when there are any authenticated attributes present.
The message-digest attribute MUST be a signed attribute or an
authenticated attribute; it MUST NOT be an unsigned attribute,
unauthenticated attribute, or unprotected attribute.
The following object identifier identifies the message-digest
attribute:
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, even
though the syntax is defined as a SET OF AttributeValue. There MUST
NOT be zero or multiple instances of AttributeValue present.
The SignedAttributes syntax and AuthAttributes syntax are each
defined as a SET OF Attributes. The SignedAttributes in a signerInfo
MUST include only one instance of the message-digest attribute.
Similarly, the AuthAttributes in an AuthenticatedData MUST include
only one instance of the message-digest attribute.
11.3 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 MUST be a signed attribute or an
authenticated attribute; it MUST NOT be an unsigned attribute,
unauthenticated attribute, or unprotected attribute.
The following object identifier identifies the signing-time
attribute:
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 [X.509-97].
Dates between 1 January 1950 and 31 December 2049 (inclusive) MUST be
encoded as UTCTime. Any dates with year values before 1950 or after
2049 MUST be encoded as GeneralizedTime.
UTCTime values MUST be expressed in Greenwich Mean Time (Zulu) and
MUST include seconds (i.e., times are YYMMDDHHMMSSZ), even where the
number of seconds is zero. Midnight (GMT) MUST be represented as
"YYMMDD000000Z". Century information is implicit, and the century
MUST be determined as follows:
Where YY is greater than or equal to 50, the year MUST be
interpreted as 19YY; and
Where YY is less than 50, the year MUST be interpreted as 20YY.
GeneralizedTime values MUST be expressed in Greenwich Mean Time
(Zulu) and MUST include seconds (i.e., times are YYYYMMDDHHMMSSZ),
even where the number of seconds is zero. GeneralizedTime values
MUST NOT include fractional seconds.
A signing-time attribute MUST have a single attribute value, even
though the syntax is defined as a SET OF AttributeValue. There MUST
NOT be zero or multiple instances of AttributeValue present.
The SignedAttributes syntax and the AuthAttributes syntax are each
defined as a SET OF Attributes. The SignedAttributes in a signerInfo
MUST NOT include multiple instances of the signing-time attribute.
Similarly, the AuthAttributes in an AuthenticatedData MUST NOT
include multiple instances of the signing-time attribute.
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.
11.4 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 unsigned attribute; it MUST
NOT be a signed attribute, an authenticated attribute, an
unauthenticated attribute, or an unprotected attribute.
The following object identifier identifies the countersignature
attribute:
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 signedAttributes field MUST NOT contain a content-type
attribute; there is no content type for countersignatures.
2. The signedAttributes field MUST contain a message-digest
attribute if it contains any other attributes.
3. 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
syntax is defined as a SET OF AttributeValue, and there MUST be one
or more instances of AttributeValue present.
The UnsignedAttributes syntax is defined as a SET OF Attributes. The
UnsignedAttributes in a signerInfo may include multiple instances of
the countersignature attribute.
A countersignature, since it has type SignerInfo, can itself contain
a countersignature attribute. Thus, it is possible to construct an
arbitrarily long series of countersignatures.
12. ASN.1 Modules
Section 12.1 contains the ASN.1 module for the CMS, and section 12.2
contains the ASN.1 module for the Version 1 Attribute Certificate.
12.1 CMS ASN.1 Module
CryptographicMessageSyntax
{ iso(1) member-body(2) us(840) rsadsi(113549)
pkcs(1) pkcs-9(9) smime(16) modules(0) cms-2001(14) }
DEFINITIONS IMPLICIT TAGS ::=
BEGIN
-- EXPORTS All
-- The types and values defined in this module are exported for use
-- in the other ASN.1 modules. Other applications may use them for
-- their own purposes.
IMPORTS
-- Imports from RFC3280 [PROFILE], Appendix A.1
AlgorithmIdentifier, Certificate, CertificateList,
CertificateSerialNumber, Name
FROM PKIX1Explicit88 { iso(1)
identified-organization(3) dod(6) internet(1)
security(5) mechanisms(5) pkix(7) mod(0)
pkix1-explicit(18) }
-- Imports from RFC3281 [ACPROFILE], Appendix B
AttributeCertificate
FROM PKIXAttributeCertificate { iso(1)
identified-organization(3) dod(6) internet(1)
security(5) mechanisms(5) pkix(7) mod(0)
attribute-cert(12) }
-- Imports from Appendix B of this document
AttributeCertificateV1
FROM AttributeCertificateVersion1 { iso(1) member-body(2)
us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16)
modules(0) v1AttrCert(15) } ;
-- Cryptographic Message Syntax
ContentInfo ::= SEQUENCE {
contentType ContentType,
content [0] EXPLICIT ANY DEFINED BY contentType }
ContentType ::= OBJECT IDENTIFIER
SignedData ::= SEQUENCE {
version CMSVersion,
digestAlgorithms DigestAlgorithmIdentifiers,
encapContentInfo EncapsulatedContentInfo,
certificates [0] IMPLICIT CertificateSet OPTIONAL,
crls [1] IMPLICIT CertificateRevocationLists OPTIONAL,
signerInfos SignerInfos }
DigestAlgorithmIdentifiers ::= SET OF DigestAlgorithmIdentifier
SignerInfos ::= SET OF SignerInfo
EncapsulatedContentInfo ::= SEQUENCE {
eContentType ContentType,
eContent [0] EXPLICIT OCTET STRING OPTIONAL }
SignerInfo ::= SEQUENCE {
version CMSVersion,
sid SignerIdentifier,
digestAlgorithm DigestAlgorithmIdentifier,
signedAttrs [0] IMPLICIT SignedAttributes OPTIONAL,
signatureAlgorithm SignatureAlgorithmIdentifier,
signature SignatureValue,
unsignedAttrs [1] IMPLICIT UnsignedAttributes OPTIONAL }
SignerIdentifier ::= CHOICE {
issuerAndSerialNumber IssuerAndSerialNumber,
subjectKeyIdentifier [0] SubjectKeyIdentifier }
SignedAttributes ::= SET SIZE (1..MAX) OF Attribute
UnsignedAttributes ::= SET SIZE (1..MAX) OF Attribute
Attribute ::= SEQUENCE {
attrType OBJECT IDENTIFIER,
attrValues SET OF AttributeValue }
AttributeValue ::= ANY
SignatureValue ::= OCTET STRING
EnvelopedData ::= SEQUENCE {
version CMSVersion,
originatorInfo [0] IMPLICIT OriginatorInfo OPTIONAL,
recipientInfos RecipientInfos,
encryptedContentInfo EncryptedContentInfo,
unprotectedAttrs [1] IMPLICIT UnprotectedAttributes OPTIONAL }
OriginatorInfo ::= SEQUENCE {
certs [0] IMPLICIT CertificateSet OPTIONAL,
crls [1] IMPLICIT CertificateRevocationLists OPTIONAL }
RecipientInfos ::= SET SIZE (1..MAX) OF RecipientInfo
EncryptedContentInfo ::= SEQUENCE {
contentType ContentType,
contentEncryptionAlgorithm ContentEncryptionAlgorithmIdentifier,
encryptedContent [0] IMPLICIT EncryptedContent OPTIONAL }
EncryptedContent ::= OCTET STRING
UnprotectedAttributes ::= SET SIZE (1..MAX) OF Attribute
RecipientInfo ::= CHOICE {
ktri KeyTransRecipientInfo,
kari [1] KeyAgreeRecipientInfo,
kekri [2] KEKRecipientInfo,
pwri [3] PasswordRecipientInfo,
ori [4] OtherRecipientInfo }
EncryptedKey ::= OCTET STRING
KeyTransRecipientInfo ::= SEQUENCE {
version CMSVersion, -- always set to 0 or 2
rid RecipientIdentifier,
keyEncryptionAlgorithm KeyEncryptionAlgorithmIdentifier,
encryptedKey EncryptedKey }
RecipientIdentifier ::= CHOICE {
issuerAndSerialNumber IssuerAndSerialNumber,
subjectKeyIdentifier [0] SubjectKeyIdentifier }
KeyAgreeRecipientInfo ::= SEQUENCE {
version CMSVersion, -- always set to 3
originator [0] EXPLICIT OriginatorIdentifierOrKey,
ukm [1] EXPLICIT UserKeyingMaterial OPTIONAL,
keyEncryptionAlgorithm KeyEncryptionAlgorithmIdentifier,
recipientEncryptedKeys RecipientEncryptedKeys }
OriginatorIdentifierOrKey ::= CHOICE {
issuerAndSerialNumber IssuerAndSerialNumber,
subjectKeyIdentifier [0] SubjectKeyIdentifier,
originatorKey [1] OriginatorPublicKey }
OriginatorPublicKey ::= SEQUENCE {
algorithm AlgorithmIdentifier,
publicKey BIT STRING }
RecipientEncryptedKeys ::= SEQUENCE OF RecipientEncryptedKey
RecipientEncryptedKey ::= SEQUENCE {
rid KeyAgreeRecipientIdentifier,
encryptedKey EncryptedKey }
KeyAgreeRecipientIdentifier ::= CHOICE {
issuerAndSerialNumber IssuerAndSerialNumber,
rKeyId [0] IMPLICIT RecipientKeyIdentifier }
RecipientKeyIdentifier ::= SEQUENCE {
subjectKeyIdentifier SubjectKeyIdentifier,
date GeneralizedTime OPTIONAL,
other OtherKeyAttribute OPTIONAL }
SubjectKeyIdentifier ::= OCTET STRING
KEKRecipientInfo ::= SEQUENCE {
version CMSVersion, -- always set to 4
kekid KEKIdentifier,
keyEncryptionAlgorithm KeyEncryptionAlgorithmIdentifier,
encryptedKey EncryptedKey }
KEKIdentifier ::= SEQUENCE {
keyIdentifier OCTET STRING,
date GeneralizedTime OPTIONAL,
other OtherKeyAttribute OPTIONAL }
PasswordRecipientInfo ::= SEQUENCE {
version CMSVersion, -- always set to 0
keyDerivationAlgorithm [0] KeyDerivationAlgorithmIdentifier
OPTIONAL,
keyEncryptionAlgorithm KeyEncryptionAlgorithmIdentifier,
encryptedKey EncryptedKey }
OtherRecipientInfo ::= SEQUENCE {
oriType OBJECT IDENTIFIER,
oriValue ANY DEFINED BY oriType }
DigestedData ::= SEQUENCE {
version CMSVersion,
digestAlgorithm DigestAlgorithmIdentifier,
encapContentInfo EncapsulatedContentInfo,
digest Digest }
Digest ::= OCTET STRING
EncryptedData ::= SEQUENCE {
version CMSVersion,
encryptedContentInfo EncryptedContentInfo,
unprotectedAttrs [1] IMPLICIT UnprotectedAttributes OPTIONAL }
AuthenticatedData ::= SEQUENCE {
version CMSVersion,
originatorInfo [0] IMPLICIT OriginatorInfo OPTIONAL,
recipientInfos RecipientInfos,
macAlgorithm MessageAuthenticationCodeAlgorithm,
digestAlgorithm [1] DigestAlgorithmIdentifier OPTIONAL,
encapContentInfo EncapsulatedContentInfo,
authAttrs [2] IMPLICIT AuthAttributes OPTIONAL,
mac MessageAuthenticationCode,
unauthAttrs [3] IMPLICIT UnauthAttributes OPTIONAL }
AuthAttributes ::= SET SIZE (1..MAX) OF Attribute
UnauthAttributes ::= SET SIZE (1..MAX) OF Attribute
MessageAuthenticationCode ::= OCTET STRING
DigestAlgorithmIdentifier ::= AlgorithmIdentifier
SignatureAlgorithmIdentifier ::= AlgorithmIdentifier
KeyEncryptionAlgorithmIdentifier ::= AlgorithmIdentifier
ContentEncryptionAlgorithmIdentifier ::= AlgorithmIdentifier
MessageAuthenticationCodeAlgorithm ::= AlgorithmIdentifier
KeyDerivationAlgorithmIdentifier ::= AlgorithmIdentifier
CertificateRevocationLists ::= SET OF CertificateList
CertificateChoices ::= CHOICE {
certificate Certificate,
extendedCertificate [0] IMPLICIT ExtendedCertificate, -- Obsolete
v1AttrCert [1] IMPLICIT AttributeCertificateV1, -- Obsolete
v2AttrCert [2] IMPLICIT AttributeCertificateV2 }
AttributeCertificateV2 ::= AttributeCertificate
CertificateSet ::= SET OF CertificateChoices
IssuerAndSerialNumber ::= SEQUENCE {
issuer Name,
serialNumber CertificateSerialNumber }
CMSVersion ::= INTEGER { v0(0), v1(1), v2(2), v3(3), v4(4) }
UserKeyingMaterial ::= OCTET STRING
OtherKeyAttribute ::= SEQUENCE {
keyAttrId OBJECT IDENTIFIER,
keyAttr ANY DEFINED BY keyAttrId OPTIONAL }
-- The CMS Attributes
MessageDigest ::= OCTET STRING
SigningTime ::= Time
Time ::= CHOICE {
utcTime UTCTime,
generalTime GeneralizedTime }
Countersignature ::= SignerInfo
-- Attribute Object Identifiers
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 CMSVersion,
certificate Certificate,
attributes UnauthAttributes }
Signature ::= BIT STRING
END -- of CryptographicMessageSyntax
12.2 Version 1 Attribute Certificate ASN.1 Module
AttributeCertificateVersion1
{ iso(1) member-body(2) us(840) rsadsi(113549)
pkcs(1) pkcs-9(9) smime(16) modules(0) v1AttrCert(15) }
DEFINITIONS IMPLICIT TAGS ::=
BEGIN
-- EXPORTS All
IMPORTS
-- Imports from RFC3280 [PROFILE], Appendix A.1
AlgorithmIdentifier, Attribute, CertificateSerialNumber,
Extensions, UniqueIdentifier
FROM PKIX1Explicit88 { iso(1)
identified-organization(3) dod(6) internet(1)
security(5) mechanisms(5) pkix(7) mod(0)
pkix1-explicit(18) }
-- Imports from RFC3280 [PROFILE], Appendix A.2
GeneralNames
FROM PKIX1Implicit88 { iso(1)
identified-organization(3) dod(6) internet(1)
security(5) mechanisms(5) pkix(7) mod(0)
pkix1-implicit(19) }
-- Imports from RFC3281 [ACPROFILE], Appendix B
AttCertValidityPeriod, IssuerSerial
FROM PKIXAttributeCertificate { iso(1)
identified-organization(3) dod(6) internet(1)
security(5) mechanisms(5) pkix(7) mod(0)
attribute-cert(12) } ;
-- Definition extracted from X.509-1997 [X.509-97], but
-- different type names are used to avoid collisions.
AttributeCertificateV1 ::= SEQUENCE {
acInfo AttributeCertificateInfoV1,
signatureAlgorithm AlgorithmIdentifier,
signature BIT STRING }
AttributeCertificateInfoV1 ::= SEQUENCE {
version AttCertVersionV1 DEFAULT v1,
subject CHOICE {
baseCertificateID [0] IssuerSerial,
-- associated with a Public Key Certificate
subjectName [1] GeneralNames },
-- associated with a name
issuer GeneralNames,
signature AlgorithmIdentifier,
serialNumber CertificateSerialNumber,
attCertValidityPeriod AttCertValidityPeriod,
attributes SEQUENCE OF Attribute,
issuerUniqueID UniqueIdentifier OPTIONAL,
extensions Extensions OPTIONAL }
AttCertVersionV1 ::= INTEGER { v1(0) }
END -- of AttributeCertificateVersion1
13. References
[ACPROFILE] Farrell, S. and R. Housley, "An Internet Attribute
Certificate Profile for Authorization", RFC3281, April
2002.
[CMSALG] Housley, R., "Cryptographic Message Syntax (CMS)
Algorithms", RFC3269, August 2002.
[DSS] National Institute of Standards and Technology. FIPS Pub
186: Digital Signature Standard. 19 May 1994.
[ESS] Hoffman, P., "Enhanced Security Services for S/MIME", RFC
2634, June 1999.
[MSG] Ramsdell, B., "S/MIME Version 3 Message Specification",
RFC2633, June 1999.
[OLDCMS] Housley, R., "Cryptographic Message Syntax", RFC2630,
June 1999.
[OLDMSG] Dusse, S., Hoffman, P., Ramsdell, B., Lundblade, L. and
L. Repka, "S/MIME Version 2 Message Specification", RFC
2311, March 1998.
[PROFILE] Housley, R., Polk, W., Ford, W. and D. Solo, "Internet
X.509 Public Key Infrastructure: Certificate and CRL
Profile", RFC3280, April 2002.
[PKCS#6] RSA Laboratories. PKCS #6: Extended-Certificate Syntax
Standard, Version 1.5. November 1993.
[PKCS#7] Kaliski, B., "PKCS #7: Cryptographic Message Syntax,
Version 1.5.", RFC2315, March 1998.
[PKCS#9] RSA Laboratories. PKCS #9: Selected Attribute Types,
Version 1.1. November 1993.
[PWRI] Gutmann, P., "Password-based Encryption for S/MIME", RFC
3211, December 2001.
[RANDOM] Eastlake, D., Crocker, S. and J. Schiller, "Randomness
Recommendations for Security", RFC1750, December 1994.
[STDWORDS] Bradner, S., "Key Words for Use in RFCs to Indicate
Requirement Levels", BCP 14, RFC2119, March 1997.
[X.208-88] CCITT. Recommendation X.208: Specification of Abstract
Syntax Notation One (ASN.1). 1988.
[X.209-88] CCITT. Recommendation X.209: Specification of Basic
Encoding Rules for Abstract Syntax Notation One (ASN.1).
1988.
[X.501-88] CCITT. Recommendation X.501: The Directory - Models.
1988.
[X.509-88] CCITT. Recommendation X.509: The Directory -
Authentication Framework. 1988.
[X.509-97] ITU-T. Recommendation X.509: The Directory -
Authentication Framework. 1997.
[X.509-00] ITU-T. Recommendation X.509: The Directory -
Authentication Framework. 2000.
14. Security Considerations
The Cryptographic Message Syntax provides a method for digitally
signing data, digesting data, encrypting data, and authenticating
data.
Implementations must protect the signer's private key. Compromise of
the signer's private key permits masquerade.
Implementations must protect the key management private key, the
key-encryption key, and the content-encryption key. Compromise of
the key management private key or the key-encryption key may result
in the disclosure of all contents protected with that key.
Similarly, compromise of the content-encryption key may result in
disclosure of the associated encrypted content.
Implementations must protect the key management private key and the
message-authentication key. Compromise of the key management private
key permits masquerade of authenticated data. Similarly, compromise
of the message-authentication key may result in undetectable
modification of the authenticated content.
The key management technique employed to distribute message-
authentication keys must itself provide data origin authentication,
otherwise the contents are delivered with integrity from an unknown
source. Neither RSA [PKCS#1, NEWPKCS#1] nor Ephemeral-Static
Diffie-Hellman [DH-X9.42] provide the necessary data origin
authentication. Static-Static Diffie-Hellman [DH-X9.42] does provide
the necessary data origin authentication when both the originator and
recipient public keys are bound to appropriate identities in X.509
certificates.