S/MIME Working Group R. Housley
Internet Draft SPYRUS
expires in six months May 1998
Cryptographic Message Syntax
<draft-ietf-smime-cms-05.txt>
Status of this Memo
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Abstract
This document describes the Cryptographic Message Syntax. This
syntax is used to digitally sign, digest, authenticate, or encrypt
arbitrary messages.
The Cryptographic Message Syntax is derived from PKCS #7 version 1.5
[RFC 2315]. Wherever possible, backward compatibility is preserved;
however, changes were necessary to accommodate attribute certificate
transfer and key agreement techniques for key management.
This draft is being discussed on the "ietf-smime" mailing list. To
join the list, send a message to <ietf-smime-request@imc.org> with
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Acknowledgements
This document is the result of contributions from many professionals.
I appreciate the hard work of all members of the IETF S/MIME Working
Group. I extend a special thanks to Rich Ankney, Tim Dean, Steve
Dusse, Paul Hoffman, Scott Hollenbeck, Burt Kaliski, John Pawling,
Blake Ramsdell, Jim Schaad, and Dave Solo for their efforts and
support.
1 Introduction
This document describes the Cryptographic Message Syntax. This
syntax is used to digitally sign or encrypt arbitrary messages.
The Cryptographic Message Syntax describes an encapsulation syntax
for data protection. It supports digital signatures and encryption.
The syntax allows multiple encapsulation, so one encapsulation
envelope can be nested inside another. Likewise, one party can
digitally sign some previously encapsulated data. It also allows
arbitrary attributes, such as signing time, to be signed along with
the message content, and provides for other attributes such as
countersignatures to be associated with a signature.
The Cryptographic Message Syntax can support a variety of
architectures for certificate-based key management, such as the one
defined by the PKIX working group.
The Cryptographic Message Syntax values are generated using ASN.1,
using BER-encoding. Values are typically represented as octet
strings. While many systems are capable of transmitting arbitrary
octet strings reliably, it is well known that many electronic-mail
systems are not. This document does not address mechanisms for
encoding octet strings for reliable transmission in such
environments.
2 General Overview
The Cryptographic Message Syntax is general enough to support many
different content types. This document defines six content types:
data, signed-data, enveloped-data, digested-data, encrypted-data, and
authenticated-data. Also, additional content types can be defined
outside this document.
An implementation that conforms to this specification must implement
the data, signed-data, and enveloped-data content types. The other
content types may be implemented if desired.
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As a general design philosophy, content types permit single pass
processing using indefinite-length Basic Encoding Rules (BER)
encoding. Single-pass operation is especially helpful if content is
large, stored on tapes, or is "piped" from another process. Single-
pass operation has one significant drawback: it is difficult to
perform encode operations using the Distinguished Encoding Rules
(DER) encoding in a single pass since the lengths of the various
components may not be known in advance. However, signed attributes
within the signed-data content type and authenticated attributes
within the authenticated-data content type require DER encoding.
Signed attributes and authenticated attributes must be transmitted in
DER form to ensure that recipients can validate a content that
contains an unrecognized attribute.
3 General Syntax
The Cryptographic Message Syntax associates a protection content type
with a protection content. The syntax shall have ASN.1 type
ContentInfo:
ContentInfo ::= SEQUENCE {
contentType ContentType,
content [0] EXPLICIT ANY DEFINED BY contentType }
ContentType ::= OBJECT IDENTIFIER
The fields of ContentInfo have the following meanings:
contentType indicates the type of protection content. It is an
object identifier; it is a unique string of integers assigned by
an authority that defines the content type.
content is the protection content. The type of protection content
can be determined uniquely by contentType. Protection content
types for signed-data, enveloped-data, digested-data, encrypted-
data, and authenticated-data are defined in this document. If
additional protection content types are defined in other
documents, the ASN.1 type defined along with the object identifier
should not be a CHOICE type.
4 Data Content Type
The following object identifier identifies the data content type:
id-data OBJECT IDENTIFIER ::= { iso(1) member-body(2)
us(840) rsadsi(113549) pkcs(1) pkcs7(7) 1 }
The data content type is intended to refer to arbitrary octet
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strings, such as ASCII text files; the interpretation is left to the
application. Such strings need not have any internal structure
(although they could have their own ASN.1 definition or other
structure).
The data content type is generally used in conjunction with the
signed-data, enveloped-data, digested-data, encrypted-data, and
authenticated-data protection content types. The data content type
is encapsulated in one of these protection content types.
5 Signed-data Content Type
The signed-data content type consists of a content of any type and
zero or more signature values. Any number of signers in parallel can
sign any type of content.
The typical application of the signed-data content type represents
one signer's digital signature on content of the data content type.
Another typical application disseminates certificates and certificate
revocation lists (CRLs).
The process by which signed-data is constructed involves the
following steps:
1. For each signer, a message digest, or hash value, is computed
on the content with a signer-specific message-digest algorithm.
If two signers employ the same message digest algorithm, then the
message digest need be computed for only one of them. If the
signer is signing any information other than the content, the
message digest of the content and the other information are
digested with the signer's message digest algorithm (see Section
5.4), and the result becomes the "message digest."
2. For each signer, the message digest is digitally signed using
the signer's private key.
3. For each signer, the signature value and other signer-specific
information are collected into a SignerInfo value, as defined in
Section 5.3. Certificates and CRLs for each signer, and those not
corresponding to any signer, are collected in this step.
4. The message digest algorithms for all the signers and the
SignerInfo values for all the signers are collected together with
the content into a SignedData value, as defined in Section 5.1.
A recipient independently computes the message digest. This message
digest and the signer's public key are used to validate the signature
value. The signer's public key is referenced by an issuer
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distinguished name and an issuer-specific serial number that uniquely
identify the certificate containing the public key. The signer's
certificate may be included in the SignedData certificates field.
This section is divided into five parts. The first part describes
the top-level type SignedData, the second part describes the per-
signer information type SignerInfo, and the third, fourth, and fifth
parts describe the message digest calculation, signature generation,
and signature validation processes, respectively.
5.1 SignedData Type
The following object identifier identifies the signed-data content
type:
id-signedData OBJECT IDENTIFIER ::= { iso(1) member-body(2)
us(840) rsadsi(113549) pkcs(1) pkcs7(7) 2 }
The signed-data content type shall have ASN.1 type SignedData:
SignedData ::= SEQUENCE {
version Version,
digestAlgorithms DigestAlgorithmIdentifiers,
encapContentInfo EncapsulatedContentInfo,
certificates [0] IMPLICIT CertificateSet OPTIONAL,
crls [1] IMPLICIT CertificateRevocationLists OPTIONAL,
signerInfos SignerInfos }
DigestAlgorithmIdentifiers ::= SET OF DigestAlgorithmIdentifier
SignerInfos ::= SET OF SignerInfo
The fields of type SignedData have the following meanings:
version is the syntax version number. If no attribute
certificates are present in the certificates field and the
encapsulated content type is id-data, then the value of version
shall be 1; however, if attribute certificates are present or the
encapsulated content type is other than id-data, then the value of
version shall be 3.
digestAlgorithms is a collection of message digest algorithm
identifiers. There may be any number of elements in the
collection, including zero. Each element identifies the message
digest algorithm, along with any associated parameters, used by
one or more signer. The collection is intended to list the
message digest algorithms employed by all of the signers, in any
order, to facilitate one-pass signature verification. The message
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digesting process is described in Section 5.4.
encapContentInfo is the signed content, consisting of a content
type identifier and the content itself. Details of the
EncapsulatedContentInfo type are discussed in section 5.2.
certificates is a collection of certificates. It is intended that
the set of certificates be sufficient to contain chains from a
recognized "root" or "top-level certification authority" to all of
the signers in the signerInfos field. There may be more
certificates than necessary, and there may be certificates
sufficient to contain chains from two or more independent top-
level certification authorities. There may also be fewer
certificates than necessary, if it is expected that recipients
have an alternate means of obtaining necessary certificates (e.g.,
from a previous set of certificates). If no attribute
certificates are present in the collection, then the value of
version shall be 1; however, if attribute certificates are
present, then the value of version shall be 3.
crls is a collection of certificate revocation lists (CRLs). It
is intended that the set contain information sufficient to
determine whether or not the certificates in the certificates
field are valid, but such correspondence is not necessary. There
may be more CRLs than necessary, and there may also be fewer CRLs
than necessary.
signerInfos is a collection of per-signer information. There may
be any number of elements in the collection, including zero. The
details of the SignerInfo type are discussed in section 5.3.
The optional omission of the eContent within the
EncapsulatedContentInfo field makes it possible to construct
"external signatures." In the case of external signatures, the
content being signed is absent from the EncapsulatedContentInfo value
included in the signed-data content type. If the eContent value
within EncapsulatedContentInfo is absent, then the signatureValue is
calculated and the eContentType is assigned as though the eContent
value was present.
In the degenerate case where there are no signers, the
EncapsulatedContentInfo value being "signed" is irrelevant. In this
case, the content type within the EncapsulatedContentInfo value being
"signed" should be id-data (as defined in section 4), and the content
field of the EncapsulatedContentInfo value should be omitted.
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5.2 EncapsulatedContentInfo Type
Per-signer information is represented in the type SignerInfo:
EncapsulatedContentInfo ::= SEQUENCE {
eContentType ContentType,
eContent [0] EXPLICIT OCTET STRING OPTIONAL }
ContentType ::= OBJECT IDENTIFIER
The fields of type EncapsulatedContentInfo have the following
meanings:
eContentType is an object identifier uniquely specifies the
content type.
eContent in the content itself, carried as an octet string. The
eContent need not be DER encoded.
5.3 SignerInfo Type
Per-signer information is represented in the type SignerInfo:
SignerInfo ::= SEQUENCE {
version Version,
issuerAndSerialNumber IssuerAndSerialNumber,
digestAlgorithm DigestAlgorithmIdentifier,
signedAttrs [0] IMPLICIT SignedAttributes OPTIONAL,
signatureAlgorithm SignatureAlgorithmIdentifier,
signature SignatureValue,
unsignedAttrs [1] IMPLICIT UnsignedAttributes OPTIONAL }
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
The fields of type SignerInfo have the following meanings:
version is the syntax version number; it shall be 1.
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issuerAndSerialNumber specifies the signer's certificate (and
thereby the signer's public key) by issuer distinguished name and
issuer-specific serial number.
digestAlgorithm identifies the message digest algorithm, and any
associated parameters, used by the signer. The message digest is
computed over the encapsulated content and signed attributes, if
present. The message digest algorithm should be among those
listed in the digestAlgorithms field of the associated SignerData.
The message digesting process is described in Section 5.4.
signedAttributes is a collection of attributes that are signed.
The field is optional, but it must be present if the content type
of the EncapsulatedContentInfo value being signed is not id-data.
Each SignedAttribute in the SET must be DER encoded. Useful
attribute types, such as signing time, are defined in Section 11.
If the 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 signed. 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.
signatureAlgorithm identifies the signature algorithm, and any
associated parameters, used by the signer to generate the digital
signature.
signature is the result of digital signature generation, using the
message digest and the signer's private key.
unsignedAttributes is a collection of attributes that are not
signed. The field is optional. Useful attribute types, such as
countersignatures, are defined in Section 11.
The fields of type SignedAttribute and UnsignedAttribute have the
following meanings:
attrType indicates the type of attribute. It is an object
identifier.
attrValues is a set of values that comprise the attribute. The
type of each value in the set can be determined uniquely by
attrType.
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5.4 Message Digest Calculation Process
The message digest calculation process computes a message digest on
either the content being signed or the content together with the
signed attributes. In either case, the initial input to the message
digest calculation process is the "value" of the encapsulated content
being signed. Specifically, the initial input is the
encapContentInfo eContent OCTET STRING to which the signing process
is applied. Only the octets comprising the value of the eContent
OCTET STRING are input to the message digest algorithm, not the tag
or the length octets.
The result of the message digest calculation process depends on
whether the signedAttributes field is present. When the field is
absent, the result is just the message digest of the content as
described above. When the field is present, however, the result is
the message digest of the complete DER encoding of the
SignedAttributes value contained in the signedAttributes field.
Since the SignedAttributes value, when present, must contain the
content type and the content message digest attributes, those values
are indirectly included in the result. A separate encoding of the
signedAttributes field is performed for message digest calculation.
The IMPLICIT [0] tag in the signedAttributes 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 [0]
tag, is to be included in the message digest calculation along with
the length and content octets of the SignedAttributes value.
When the signedAttributes field is absent, then only the octets
comprising the value of the signedData encapContentInfo eContent
OCTET STRING (e.g., the contents of a file) are input to the message
digest calculation. This has the advantage that the length of the
content being signed need not be known in advance of the signature
generation process.
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 messages of any
length that have the same message digest.
5.5 Message Signature Generation Process
The input to the signature generation process includes the result of
the message digest calculation process and the signer's private key.
The details of the signature generation depend on the signature
algorithm employed. The object identifier, along with any
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parameters, that specifies the signature algorithm employed by the
signer is carried in the signatureAlgorithm field. The signature
value generated by the signer is encoded as an OCTET STRING and
carried in the signature field.
5.6 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 validation 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
signedAttributes, then the content message digest must be calculated
as described in section 5.4. 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
signedAttributes of the signedData signerInfo.
6 Enveloped-data Content Type
The enveloped-data content type consists of an encrypted content of
any type and encrypted content-encryption keys for one or more
recipients. The combination of the encrypted content and one
encrypted content-encryption key for a recipient is a "digital
envelope" for that recipient. Any type of content can be enveloped
for an arbitrary number of recipients.
The typical application of the enveloped-data content type will
represent one or more recipients' digital envelopes on content of the
data or signed-data content types.
Enveloped-data is constructed by the following steps:
1. A content-encryption key for a particular content-encryption
algorithm is generated at random.
2. The content-encryption key is encrypted for each recipient.
The details of this encryption depend on the key management
algorithm used, but three general techniques are supported:
key transport: the content-encryption key is encrypted in the
recipient's public key;
key agreement: the recipient's public key and the sender's
private key are used to generate a pairwise symmetric key, then
the content-encryption key is encrypted in the pairwise
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symmetric key; and
mail list keys: the content-encryption key is encrypted in a
previously distributed symmetric key.
3. For each recipient, the encrypted content-encryption key and
other recipient-specific information are collected into a
RecipientInfo value, defined in Section 6.2.
4. The content is encrypted with the content-encryption key.
Content encryption may require that the content be padded to a
multiple of some block size; see Section 6.3.
5. The RecipientInfo values for all the recipients are collected
together with the encrypted content to form an EnvelopedData value
as defined in Section 6.1.
A recipient opens the digital envelope by decrypting one of the
encrypted content-encryption keys and then decrypting the encrypted
content with the recovered content-encryption key.
This section is divided into four parts. The first part describes
the top-level type EnvelopedData, the second part describes the per-
recipient information type RecipientInfo, and the third and fourth
parts describe the content-encryption and key-encryption processes.
6.1 EnvelopedData Type
The following object identifier identifies the enveloped-data content
type:
id-envelopedData OBJECT IDENTIFIER ::= { iso(1) member-body(2)
us(840) rsadsi(113549) pkcs(1) pkcs7(7) 3 }
The enveloped-data content type shall have ASN.1 type EnvelopedData:
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 }
RecipientInfos ::= SET OF RecipientInfo
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EncryptedContentInfo ::= SEQUENCE {
contentType ContentType,
contentEncryptionAlgorithm ContentEncryptionAlgorithmIdentifier,
encryptedContent [0] IMPLICIT EncryptedContent OPTIONAL }
EncryptedContent ::= OCTET STRING
The fields of type EnvelopedData have the following meanings:
version is the syntax version number. If originatorInfo is
present, then version shall be 2. If any of the RecipientInfo
structures included have a version other than 0, then the version
shall be 2. If originatorInfo is absent and all of the
RecipientInfo structures are version 0, then version shall be 0.
originatorInfo optionally provides information about the
originator. It is present only if required by the key management
algorithm. It may contain certificates and CRLs:
certs is a collection of certificates. certs may contain
originator certificates associated with several different key
management algorithms. The certificates contained in certs are
intended to be sufficient to make chains from a recognized
"root" or "top-level certification authority" to all
recipients. However, certs may contain more certificates than
necessary, and there may be certificates sufficient to make
chains from two or more independent top-level certification
authorities. Alternatively, certs may contain fewer
certificates than necessary, if it is expected that recipients
have an alternate means of obtaining necessary certificates
(e.g., from a previous set of certificates).
crls is a collection of CRLs. It is intended that the set
contain information sufficient to determine whether or not the
certificates in the certs field are valid, but such
correspondence is not necessary. There may be more CRLs than
necessary, and there may also be fewer CRLs than necessary.
recipientInfos is a collection of per-recipient information.
There must be at least one element in the collection.
encryptedContentInfo is the encrypted content information.
The fields of type EncryptedContentInfo have the following meanings:
contentType indicates the type of content.
contentEncryptionAlgorithm identifies the content-encryption
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algorithm, and any associated parameters, used to encrypt the
content. The content-encryption process is described in Section
6.3. The same algorithm is used for all recipients.
encryptedContent is the result of encrypting the content. The
field is optional, and if the field is not present, its intended
value must be supplied by other means.
The recipientInfos field comes before the encryptedContentInfo field
so that an EnvelopedData value may be processed in a single pass.
6.2 RecipientInfo Type
Per-recipient information is represented in the type RecipientInfo.
RecipientInfo has a different format for the three key management
techniques that are supported: key transport, key agreement, and
previously distributed mail list keys. In all cases, the content-
encryption key is transferred to one or more recipient in encrypted
form.
RecipientInfo ::= CHOICE {
ktri KeyTransRecipientInfo,
kari KeyAgreeRecipientInfo,
mlri MailListRecipientInfo }
EncryptedKey ::= OCTET STRING
6.2.1 KeyTransRecipientInfo Type
Per-recipient information using key transport is represented in the
type KeyTransRecipientInfo. Each instance of KeyTransRecipientInfo
transfers the content-encryption key to one recipient.
KeyTransRecipientInfo ::= SEQUENCE {
version Version, -- always set to 0 or 2
rid EntityIdentifier,
keyEncryptionAlgorithm KeyEncryptionAlgorithmIdentifier,
encryptedKey EncryptedKey }
EntityIdentifier ::= CHOICE {
issuerAndSerialNumber IssuerAndSerialNumber,
subjectKeyIdentifier [0] SubjectKeyIdentifier }
The fields of type KeyTransRecipientInfo have the following meanings:
version is the syntax version number. If the RecipientIdentifier
is the CHOICE issuerAndSerialNumber, then the version shall be 0.
If the RecipientIdentifier is rKeyId, then the version shall be 2.
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rid specifies the recipient's certificate or key that was used by
the sender to protect the content-encryption key.
keyEncryptionAlgorithm identifies the key-encryption algorithm,
and any associated parameters, used to encrypt the content-
encryption key for the recipient. The key-encryption process is
described in Section 6.4.
encryptedKey is the result of encrypting the content-encryption
key for the recipient.
The EntityIdentifier is a CHOICE with two alternatives specifying the
recipient's certificate, and thereby the recipient's public key. The
recipient's certificate must contain a key transport public key. The
content-encryption key is encrypted with the recipient's public key.
The issuerAndSerialNumber alternative identifies the recipient's
certificate by the issuer's distinguished name and the certificate
serial number; the subjectKeyIdentifier identifies the recipient's
certificate by the X.509 subjectKeyIdentifier extension value.
6.2.2 KeyAgreeRecipientInfo Type
Recipient information using key agreement is represented in the type
KeyAgreeRecipientInfo. Each instance of KeyAgreeRecipientInfo will
transfer the content-encryption key to one or more recipient.
KeyAgreeRecipientInfo := SEQUENCE {
version Version, -- always set to 3
originatorCert [0] EXPLICIT EntityIdentifier,
ukm [1] EXPLICIT UserKeyingMaterial OPTIONAL,
keyEncryptionAlgorithm KeyEncryptionAlgorithmIdentifier,
recipientEncryptedKeys RecipientEncryptedKeys }
RecipientEncryptedKeys ::= SEQUEENCE OF RecipientEncryptedKey
RecipientEncryptedKey := SEQUENCE {
rid RecipientIdentifier,
encryptedKey EncryptedKey }
RecipientIdentifier ::= CHOICE {
issuerAndSerialNumber IssuerAndSerialNumber,
rKeyId [0] IMPLICIT RecipientKeyIdentifier }
RecipientKeyIdentifier ::= SEQUENCE {
subjectKeyIdentifier SubjectKeyIdentifier,
date GeneralizedTime OPTIONAL,
other OtherKeyAttribute OPTIONAL }
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SubjectKeyIdentifier ::= OCTET STRING
The fields of type KeyAgreeRecipientInfo have the following meanings:
version is the syntax version number. It shall always be 3.
originatorCert is a CHOICE with two alternatives specifying the
sender's certificate, and thereby the sender's public key. The
sender's certificate must contain a key agreement public key, and
the sender uses the corresponding private key and the recipient's
public key to generate a pairwise key. The content-encryption key
is encrypted in the pairwise key. The issuerAndSerialNumber
alternative identifies the sender's certificate by the issuer's
distinguished name and the certificate serial number; the
subjectKeyIdentifier alternative identifies the sender's
certificate by the X.509 subjectKeyIdentifier extension value.
ukm is optional. With some key agreement algorithms, the sender
provides a User Keying Material (UKM) to ensure that a different
key is generated each time the same two parties generate a
pairwise key.
keyEncryptionAlgorithm identifies the key-encryption algorithm,
and any associated parameters, used to encrypt the content-
encryption key in the key-encryption key. The key-encryption
process is described in Section 6.4.
recipientEncryptedKeys includes a recipient identifier and the
encrypted key for one or more recipients. The RecipientIdentifier
is a CHOICE with two alternatives specifying the recipient's
certificate, and thereby the recipient's public key, that was used
by the sender to generate a pairwise key. The recipient's
certificate must contain a key agreement public key. The
content-encryption key is encrypted in the pairwise key. The
issuerAndSerialNumber alternative identifies the recipient's
certificate by the issuer's distinguished name and the certificate
serial number; the RecipientKeyIdentifier is described below. The
encryptedKey is the result of encrypting the content-encryption
key in the pairwise key generated using the key agreement
algorithm.
The fields of type RecipientKeyIdentifier have the following
meanings:
subjectKeyIdentifier identifies the recipient's certificate by the
X.509 subjectKeyIdentifier extension value.
date is optional. When present, the date specifies which of the
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recipient's previously distributed UKMs was used by the sender.
other is optional. When present, this field contains additional
information used by the recipient to locate the public keying
material used by the sender.
6.2.3 MailListRecipientInfo Type
Recipient information using previously distributed symmetric keys is
represented in the type MailListRecipientInfo. Each instance of
MailListRecipientInfo will transfer the content-encryption key to one
or more recipients who have the previously distributed key-encryption
key.
MailListRecipientInfo := SEQUENCE {
version Version, -- always set to 4
mlid MailListKeyIdentifier,
keyEncryptionAlgorithm KeyEncryptionAlgorithmIdentifier,
encryptedKey EncryptedKey }
MailListKeyIdentifier ::= SEQUENCE {
kekIdentifier OCTET STRING,
date GeneralizedTime OPTIONAL,
other OtherKeyAttribute OPTIONAL }
The fields of type MailListRecipientInfo have the following meanings:
version is the syntax version number. It shall always be 4.
mlKeyId specifies a symmetric key encryption key that was
previously distributed to the sender and one or more recipients.
keyEncryptionAlgorithm identifies the key-encryption algorithm,
and any associated parameters, used to encrypt the content-
encryption key in the key-encryption key. The key-encryption
process is described in Section 6.4.
encryptedKey is the result of encrypting the content-encryption
key in the key-encryption key.
The fields of type MailListKeyIdentifier have the following meanings:
kekIdentifier identifies the key-encryption key that was
previously distributed to the sender and one or more recipients.
date is optional. When present, the date specifies a single key-
encryption key from a set that was previously distributed.
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other is optional. When present, this field contains additional
information used by the recipient to determine the key-encryption
key used by the sender.
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.
The input to the content-encryption process is the "value" of the
content being enveloped. Only the value octets of the envelopedData
encryptedContentInfo encryptedContent OCTET STRING are encrypted; the
OCTET STRING tag and length octets are not encrypted.
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-(l mod k) octets all having value k-(l mod k), where l 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 l mod k = k-1
02 02 -- if l mod k = k-2
.
.
.
k k ... k k -- if l 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.
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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 Version,
digestAlgorithm DigestAlgorithmIdentifier,
encapContentInfo EncapsulatedContentInfo,
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 5.4 in the
case when there are no signed attributes.
encapContentInfo is the content that is digested, as defined in
section 5.2.
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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 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 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 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 validate 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:
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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), the
MAC value of the content and the other information are generated
using the same message authentication code algorithm and 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 Version,
originatorInfo [0] IMPLICIT OriginatorInfo OPTIONAL,
recipientInfos RecipientInfos,
macAlgorithm MessageAuthenticationCodeAlgorithm,
encapContentInfo EncapsulatedContentInfo,
authenticatedAttributes [1] IMPLICIT AuthAttributes OPTIONAL,
mac MessageAuthenticationCode,
unauthenticatedAttributes [2] 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:
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version is the syntax version number. It shall be 0.
originatorInfo optionally provides information about the
originator. It is present only if required by the key management
algorithm. It may contain certificates, CRLs, and user keying
material (UKMs), 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 algorithm
identifier. It identifies the message authentication code
algorithm, along with any associated parameters, used by the
originator. Placement of the macAlgorithm field facilitates one-
pass processing by the recipient.
encapContentInfo is the content that is authenticated, as defined
in section 5.2.
authenticatedAttributes is a collection of attributes that are
authenticated. The field is optional, but it must be present if
the content type of the EncapsulatedContentInfo value being
authenticated is not id-data. Each AuthenticatedAttribute in the
SET must be DER encoded. Useful attribute types are defined in
Section 11. If the 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 signed. Section
11.1 defines the content-type attribute.
A mac-value attribute, having as its value the message
authentication code of the content. Section 11.5 defines the
mac-value attribute.
mac is the message authentication code.
unauthenticatedAttributes is a collection of attributes that are
not authenticated. The field is optional. Useful attribute types
are defined in Section 11.
9.2 MAC Generation
The MAC calculation process computes a message authentication code on
either the message content or the content together with the
originator's authenticated attributes.
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If there are no authenticated attributes, the MAC input data is the
content octets of the DER encoding of the content field of the
ContentInfo value to which the MAC process is applied. Only the
contents octets of the DER encoding of that field are input to the
MAC algorithm, not the identifier octets or the length octets.
If authenticated attributes are present, they must include the
content-type attribute (as described in Section 11.1) and mac-value
attribute (as described in section 11.5). The MAC input data is the
complete DER encoding of the Attributes value contained in the
authenticatedAttributes field. Since the Attributes value, when the
field is present, must contain as attributes the content type and the
mac value of the content, those values are indirectly included in the
result. A separate encoding of the authenticatedAttributes field is
performed for MAC calculation. The IMPLICIT [0] tag in the
authenticatedAttributes 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 [0] tag, is to be
included in the MAC calculation along with the length and contents
octets of the AuthAttributes value.
If the content has content type id-data and the
authenticatedAttributes field is absent, then just the value of the
data (e.g., the contents of a file) is input to the MAC calculation.
This has the advantage that the length of the content need not be
known in advance of the MAC calculation process. Although the tag
and length octets are not included in the MAC calculation, they are
still protected by other means. The length octets are protected by
the nature of the MAC algorithm since it is computationally
infeasible to find any two distinct messages of any length that have
the same MAC.
The fact that the MAC is computed on part of a DER encoding does not
mean that DER is the required method of representing that part for
data transfer. Indeed, it is expected that some implementations will
store objects in forms other than their DER encodings, but such
practices do not affect MAC computation.
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., DES-MAC and 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.
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9.3 MAC Validation
The input to the MAC validation process includes the input data
(determined based on the presence or absence of authenticated
attributes, as defined in 9.2), and the authentication key conveyed
in recipientInfo. The details of the MAC validation process depend
on the MAC algorithm employed.
The recipient may not rely on any MAC values computed by the
originator. If the originator includes authenticated attributes,
then the content of the authenticatedAttributes must be autenticated
as described in section 9.2. For the MAC to be valid, the message
MAC value calculated by the recipient must be the same as the value
of the macValue attribute included in the authenticatedAttributes.
Likewise, the attribute MAC value calculated by the recipient must be
the same as the value of the mac field included in the
authenticatedData.
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
imported from X.509.
There are many alternatives for each type of algorithm listed. For
each of these five types, Section 12 lists the algorithms that must
be included in a CMS implementation.
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 message) to another octet string
(the message digest).
DigestAlgorithmIdentifier ::= AlgorithmIdentifier
10.1.2 SignatureAlgorithmIdentifier
The SignatureAlgorithmIdentifier type identifies a signature
algorithm. Examples include DSS and RSA. A signature algorithm
supports signature generation and verification operations. The
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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, and previously
distributed symmetric key-encrypting keys are supported.
KeyEncryptionAlgorithmIdentifier ::= AlgorithmIdentifier
10.1.4 ContentEncryptionAlgorithmIdentifier
The ContentEncryptionAlgorithmIdentifier type identifies a content-
encryption algorithm. Examples include DES, Triple-DES, and RC2. A
content-encryption algorithm supports encryption and decryption
operations. The encryption operation maps an octet string (the
message) 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. 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
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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 with
which the set is associated are revoked or not. However, there may
be more CRLs than necessary or there may be fewer CRLs than
necessary.
The definition of CertificateList is imported 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, or an X.509 attribute
certificate. The PKCS #6 extended certificate is obsolete. It is
included for backward compatibility, and its use should be avoided.
The definitions of Certificate and AttributeCertificate are imported
from X.509.
CertificateChoices ::= CHOICE {
certificate Certificate, -- See X.509
extendedCertificate [0] IMPLICIT ExtendedCertificate, -- Obsolete
attrCert [1] IMPLICIT AttributeCertificate } -- See X.509 and X9.57
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
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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 imported from X.501, and the definition of
CertificateSerialNumber is imported from X.509.
IssuerAndSerialNumber ::= SEQUENCE {
issuer Name,
serialNumber CertificateSerialNumber }
CertificateSerialNumber ::= INTEGER
10.2.5 Version
The Version type gives a syntax version number, for compatibility
with future revisions of this document.
Version ::= INTEGER { v0(0), v1(1), v2(2), v3(3), v4(4) }
10.2.6 UserKeyingMaterial
The UserKeyingMaterial type gives a syntax 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 may impede interoperability.
OtherKeyAttribute ::= SEQUENCE {
keyAttrId OBJECT IDENTIFIER,
keyAttr ANY DEFINED BY keyAttrId OPTIONAL }
11 Useful Attributes
This section defines attributes that may used with signed-data or
authenticated-data. Some of these attributes were originally defined
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in PKCS #9 [PKCS #9], others are defined and specified here. The
attributes are not listed in any particular order.
11.1 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 must be a signed attribute or an
authenticated attribute; it cannot be an unsigned attribute or
unauthenticated 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
A content-type attribute must have a single attribute value.
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), where the message digest is computed using the
signer's message digest algorithm.
Within signed-data, the message-digest signed attribute type is
required if there are any attributes present.
The message-digest attribute must be a signed attribute; it cannot be
an unsigned attribute, an authenticated attribute, or unauthenticated
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:
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MessageDigest ::= OCTET STRING
A message-digest attribute must have a single attribute value.
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 may be a signed attribute; it cannot be an
unsigned attribute, an authenticated attribute, or an unauthenticated
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.
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.
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.
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The countersignature attribute must be an unsigned attribute; it
cannot be a signed attribute, an authenticated attribute, or an
unauthenticated 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 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.
11.5 Message Authentication Code (MAC) Value
The MAC-value attribute type specifies the MAC of the
encapContentInfo eContent OCTET STRING being authenticated in
authenticated-data (see section 9), where the MAC value is computed
using the originator's MAC algorithm and the data-authentication key.
Within authenticated-data, the MAC-value attribute type is required
if there are any authenticated attributes present.
The MAC-value attribute must be a authenticated attribute; it cannot
be an signed attribute, an unsigned attribute, or unauthenticated
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attribute.
The following object identifier identifies the MAC-value attribute:
id-macValue OBJECT IDENTIFIER ::= { iso(1) member-body(2)
us(840) rsadsi(113549) pkcs(1) pkcs9(9) smime(16) aa(2) 8 }
MAC-value attribute values have ASN.1 type MACValue:
MACValue ::= OCTET STRING
A MAC-value attribute must have a single attribute value.
12 Supported Algorithms
This section lists the algorithms that must be implemented.
Additional algorithms that may be implemented are also included.
12.1 Digest Algorithms
CMS implementations must include SHA-1. CMS implementations may
include MD5.
12.1.1 SHA-1
[*** Add pointer to algorithm specification. Provide OID. ***]
12.1.2 MD5
[*** Add pointer to algorithm specification. Provide OID. ***]
12.2 Signature Algorithms
CMS implementations must include DSA. CMS implementations may
include RSA.
12.2.1 DSA
[*** Add pointer to algorithm specification. Provide OID. Provide
ASN.1 for parameters and signature value. ***]
12.2.2 RSA
[*** Add pointer to algorithm specification. Provide OID. Provide
ASN.1 for parameters and signature value. ***]
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12.3 Key Encryption Algorithms
CMS implementations must include X9.42 Static Diffie-Hellman. CMS
implementations may include RSA and Triple-DES.
12.3.1 X9.42 Static Diffie-Hellman
[*** Add pointer to algorithm specification. Provide OID. Provide
ASN.1 for parameters. ***]
12.3.2 RSA
[*** Add pointer to algorithm specification. Provide OID. Provide
ASN.1 for parameters. ***]
12.3.3 Triple-DES Key Wrap
[*** Add pointer to algorithm specification. Provide OID. ***]
12.4 Content Encryption Algorithms
CMS implementations must include Triple-DES in CBC mode. CMS
implementations may include DES in CBC mode and RC2 in CBC mode.
12.4.1 Triple-DES CBC
[*** Add pointer to algorithm specification. Provide OID. ***]
12.4.2 DES CBC
[*** Add pointer to algorithm specification. Provide OID. ***]
12.4.3 RC2 CBC
[*** Add pointer to algorithm specification. Provide OID. ***]
12.5 Message Authentication Code Algorithms
No MAC algorithms are mandatory. CMS implementations may include DES
MAC and HMAC.
12.5.1 DES MAC
[*** Add pointer to algorithm specification. Provide OID. ***]
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12.5.2 HMAC
[*** Add pointer to algorithm specification. Provide OID. ***]
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Appendix A: ASN.1 Module
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
-- 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
-- Directory Information Framework (X.501)
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
SignedData ::= SEQUENCE {
version Version,
digestAlgorithms DigestAlgorithmIdentifiers,
encapContentInfo EncapsulatedContentInfo,
certificates [0] IMPLICIT CertificateSet OPTIONAL,
crls [1] IMPLICIT CertificateRevocationLists OPTIONAL,
signerInfos SignerInfos }
DigestAlgorithmIdentifiers ::= SET OF DigestAlgorithmIdentifier
SignerInfos ::= SET OF SignerInfo
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EncapsulatedContentInfo ::= SEQUENCE {
eContentType ContentType,
eContent [0] EXPLICIT OCTET STRING OPTIONAL }
ContentType ::= OBJECT IDENTIFIER
SignerInfo ::= SEQUENCE {
version Version,
issuerAndSerialNumber IssuerAndSerialNumber,
digestAlgorithm DigestAlgorithmIdentifier,
signedAttrs [0] IMPLICIT SignedAttributes OPTIONAL,
signatureAlgorithm SignatureAlgorithmIdentifier,
signature SignatureValue,
unsignedAttrs [1] IMPLICIT UnsignedAttributes OPTIONAL }
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 Version,
originatorInfo [0] IMPLICIT OriginatorInfo OPTIONAL,
recipientInfos RecipientInfos,
encryptedContentInfo EncryptedContentInfo }
OriginatorInfo ::= SEQUENCE {
certs [0] IMPLICIT CertificateSet OPTIONAL,
crls [1] IMPLICIT CertificateRevocationLists OPTIONAL }
RecipientInfos ::= SET OF RecipientInfo
EncryptedContentInfo ::= SEQUENCE {
contentType ContentType,
contentEncryptionAlgorithm ContentEncryptionAlgorithmIdentifier,
encryptedContent [0] IMPLICIT EncryptedContent OPTIONAL }
EncryptedContent ::= OCTET STRING
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RecipientInfo ::= CHOICE {
ktri KeyTransRecipientInfo,
kari KeyAgreeRecipientInfo,
mlri MailListRecipientInfo }
EncryptedKey ::= OCTET STRING
KeyTransRecipientInfo ::= SEQUENCE {
version Version, -- always set to 0 or 2
rid EntityIdentifier,
keyEncryptionAlgorithm KeyEncryptionAlgorithmIdentifier,
encryptedKey EncryptedKey }
EntityIdentifier ::= CHOICE {
issuerAndSerialNumber IssuerAndSerialNumber,
subjectKeyIdentifier [0] SubjectKeyIdentifier }
KeyAgreeRecipientInfo := SEQUENCE {
version Version, -- always set to 3
originatorCert [0] EXPLICIT EntityIdentifier,
ukm [1] EXPLICIT UserKeyingMaterial OPTIONAL,
keyEncryptionAlgorithm KeyEncryptionAlgorithmIdentifier,
recipientEncryptedKeys RecipientEncryptedKeys }
RecipientEncryptedKeys ::= SEQUEENCE OF RecipientEncryptedKey
RecipientEncryptedKey := SEQUENCE {
rid RecipientIdentifier,
encryptedKey EncryptedKey }
RecipientIdentifier ::= CHOICE {
issuerAndSerialNumber IssuerAndSerialNumber,
rKeyId [0] IMPLICIT RecipientKeyIdentifier }
RecipientKeyIdentifier ::= SEQUENCE {
subjectKeyIdentifier SubjectKeyIdentifier,
date GeneralizedTime OPTIONAL,
other OtherKeyAttribute OPTIONAL }
SubjectKeyIdentifier ::= OCTET STRING
MailListRecipientInfo := SEQUENCE {
version Version, -- always set to 4
mlid MailListKeyIdentifier,
keyEncryptionAlgorithm KeyEncryptionAlgorithmIdentifier,
encryptedKey EncryptedKey }
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MailListKeyIdentifier ::= SEQUENCE {
kekIdentifier OCTET STRING,
date GeneralizedTime OPTIONAL,
other OtherKeyAttribute OPTIONAL }
DigestedData ::= SEQUENCE {
version Version,
digestAlgorithm DigestAlgorithmIdentifier,
encapContentInfo EncapsulatedContentInfo,
digest Digest }
Digest ::= OCTET STRING
EncryptedData ::= SEQUENCE {
version Version,
encryptedContentInfo EncryptedContentInfo }
AuthenticatedData ::= SEQUENCE {
version Version,
originatorInfo [0] IMPLICIT OriginatorInfo OPTIONAL,
recipientInfos RecipientInfos,
macAlgorithm MessageAuthenticationCodeAlgorithm,
encapContentInfo EncapsulatedContentInfo,
authenticatedAttributes [1] IMPLICIT AuthAttributes OPTIONAL,
mac MessageAuthenticationCode,
unauthenticatedAttributes [2] 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
CertificateRevocationLists ::= SET OF CertificateList
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CertificateChoices ::= CHOICE {
certificate Certificate, -- See X.509
extendedCertificate [0] IMPLICIT ExtendedCertificate, -- Obsolete
attrCert [1] IMPLICIT AttributeCertificate } -- See X.509 & X9.57
CertificateSet ::= SET OF CertificateChoices
IssuerAndSerialNumber ::= SEQUENCE {
issuer Name,
serialNumber CertificateSerialNumber }
KeyEncryptionAlgorithmIdentifier ::= AlgorithmIdentifier
Version ::= INTEGER { v0(0), v1(1), v2(2), v3(3), v4(4) }
UserKeyingMaterial ::= OCTET STRING
UserKeyingMaterials ::= SET SIZE (1..MAX) OF UserKeyingMaterial
OtherKeyAttribute ::= SEQUENCE {
keyAttrId OBJECT IDENTIFIER,
keyAttr ANY DEFINED BY keyAttrId OPTIONAL }
-- CMS Attributes
MessageDigest ::= OCTET STRING
SigningTime ::= Time
Time ::= CHOICE {
utcTime UTCTime,
generalTime GeneralizedTime }
Countersignature ::= SignerInfo
MACValue ::= OCTET STRING
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-- 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-ct-authData OBJECT IDENTIFIER ::= { iso(1) member-body(2)
us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16)
ct(1) 2 }
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 }
id-macValue OBJECT IDENTIFIER ::= { iso(1) member-body(2)
us(840) rsadsi(113549) pkcs(1) pkcs9(9) smime(16) aa(2) 8 }
-- Obsolete Extended Certificate syntax from PKCS#6
ExtendedCertificateOrCertificate ::= CHOICE {
certificate Certificate,
extendedCertificate [0] IMPLICIT ExtendedCertificate }
ExtendedCertificate ::= SEQUENCE {
extendedCertificateInfo ExtendedCertificateInfo,
signatureAlgorithm SignatureAlgorithmIdentifier,
signature Signature }
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ExtendedCertificateInfo ::= SEQUENCE {
version Version,
certificate Certificate,
attributes UnauthAttributes }
Signature ::= BIT STRING
END -- of CryptographicMessageSyntax
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References
RFC 2313 Kaliski, B. PKCS #1: RSA Encryption, Version 1.5.
March 1998.
RFC 2315 Kaliski, B. PKCS #7: Cryptographic Message Syntax,
Version 1.5. March 1998.
PKCS #6 RSA Laboratories. PKCS #6: Extended-Certificate 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
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 and the
content-encryption key. Compromise of the key management private key
may result in the disclosure of all messages protected with that key.
Similarly, compromise of the content-encryption key may result in
disclosure of the encrypted content.
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Author Address
Russell Housley
SPYRUS
381 Elden Street
Suite 1120
Herndon, VA 20170
USA
housley@spyrus.com
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