
RFC 3279
Algorithms and Identifiers for the Internet X.509 Public Key Infrastructure Certificate and Certificate Revocation List (CRL) Profile. L. Bassham, W. Polk, R. Housley. April 2002.

Network Working Group W. Polk
Request for Comments: 3279 NIST
Obsoletes: 2528 R. Housley
Category: Standards Track RSA Laboratories
L. Bassham
NIST
April 2002
Algorithms and Identifiers for the
Internet X.509 Public Key Infrastructure
Certificate and Certificate Revocation List (CRL) Profile
Status of this Memo
This document specifies an Internet standards track protocol for the
Internet community, and requests discussion and suggestions for
improvements. Please refer to the current edition of the "Internet
Official Protocol Standards" (STD 1) for the standardization state
and status of this protocol. Distribution of this memo is unlimited.
Copyright Notice
Copyright (C) The Internet Society (2002). All Rights Reserved.
Abstract
This document specifies algorithm identifiers and ASN.1 encoding
formats for digital signatures and subject public keys used in the
Internet X.509 Public Key Infrastructure (PKI). Digital signatures
are used to sign certificates and certificate revocation list (CRLs).
Certificates include the public key of the named subject.
Table of Contents
1 Introduction . . . . . . . . . . . . . . . . . . . . . . 2
2 Algorithm Support . . . . . . . . . . . . . . . . . . . . 3
2.1 OneWay Hash Functions . . . . . . . . . . . . . . . . 3
2.1.1 MD2 OneWay Hash Functions . . . . . . . . . . . . . 3
2.1.2 MD5 OneWay Hash Functions . . . . . . . . . . . . . 4
2.1.3 SHA1 OneWay Hash Functions . . . . . . . . . . . . 4
2.2 Signature Algorithms . . . . . . . . . . . . . . . . . 4
2.2.1 RSA Signature Algorithm . . . . . . . . . . . . . . . 5
2.2.2 DSA Signature Algorithm . . . . . . . . . . . . . . . 6
2.2.3 Elliptic Curve Digital Signature Algorithm . . . . . 7
2.3 Subject Public Key Algorithms . . . . . . . . . . . . . 7
2.3.1 RSA Keys . . . . . . . . . . . . . . . . . . . . . . 8
2.3.2 DSA Signature Keys . . . . . . . . . . . . . . . . . 9
2.3.3 DiffieHellman Key Exchange Keys . . . . . . . . . . 10
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2.3.4 KEA Public Keys . . . . . . . . . . . . . . . . . . . 11
2.3.5 ECDSA and ECDH Public Keys . . . . . . . . . . . . . 13
3 ASN.1 Module . . . . . . . . . . . . . . . . . . . . . . 18
4 References . . . . . . . . . . . . . . . . . . . . . . . 24
5 Security Considerations . . . . . . . . . . . . . . . . . 25
6 Intellectual Property Rights . . . . . . . . . . . . . . 26
7 Author Addresses . . . . . . . . . . . . . . . . . . . . 26
8 Full Copyright Statement . . . . . . . . . . . . . . . . 27
1 Introduction
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC 2119].
This document specifies algorithm identifiers and ASN.1 [X.660]
encoding formats for digital signatures and subject public keys used
in the Internet X.509 Public Key Infrastructure (PKI). This
specification supplements [RFC 3280], "Internet X.509 Public Key
Infrastructure: Certificate and Certificate Revocation List (CRL)
Profile." Implementations of this specification MUST also conform to
RFC 3280.
This specification defines the contents of the signatureAlgorithm,
signatureValue, signature, and subjectPublicKeyInfo fields within
Internet X.509 certificates and CRLs.
This document identifies oneway hash functions for use in the
generation of digital signatures. These algorithms are used in
conjunction with digital signature algorithms.
This specification describes the encoding of digital signatures
generated with the following cryptographic algorithms:
* RivestShamirAdelman (RSA);
* Digital Signature Algorithm (DSA); and
* Elliptic Curve Digital Signature Algorithm (ECDSA).
This document specifies the contents of the subjectPublicKeyInfo
field in Internet X.509 certificates. For each algorithm, the
appropriate alternatives for the the keyUsage extension are provided.
This specification describes encoding formats for public keys used
with the following cryptographic algorithms:
* RivestShamirAdelman (RSA);
* Digital Signature Algorithm (DSA);
* DiffieHellman (DH);
* Key Encryption Algorithm (KEA);
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* Elliptic Curve Digital Signature Algorithm (ECDSA); and
* Elliptic Curve DiffieHellman (ECDH).
2 Algorithm Support
This section describes cryptographic algorithms which may be used
with the Internet X.509 certificate and CRL profile [RFC 3280]. This
section describes oneway hash functions and digital signature
algorithms which may be used to sign certificates and CRLs, and
identifies object identifiers (OIDs) for public keys contained in a
certificate.
Conforming CAs and applications MUST, at a minimum, support digital
signatures and public keys for one of the specified algorithms. When
using any of the algorithms identified in this specification,
conforming CAs and applications MUST support them as described.
2.1 Oneway Hash Functions
This section identifies oneway hash functions for use in the
Internet X.509 PKI. Oneway hash functions are also called message
digest algorithms. SHA1 is the preferred oneway hash function for
the Internet X.509 PKI. However, PEM uses MD2 for certificates [RFC
1422] [RFC 1423] and MD5 is used in other legacy applications. For
these reasons, MD2 and MD5 are included in this profile. The data
that is hashed for certificate and CRL signing is fully described in
[RFC 3280].
2.1.1 MD2 Oneway Hash Function
MD2 was developed by Ron Rivest for RSA Security. RSA Security has
recently placed the MD2 algorithm in the public domain. Previously,
RSA Data Security had granted license for use of MD2 for non
commercial Internet PrivacyEnhanced Mail (PEM). MD2 may continue to
be used with PEM certificates, but SHA1 is preferred. MD2 produces
a 128bit "hash" of the input. MD2 is fully described in [RFC 1319].
At the Selected Areas in Cryptography '95 conference in May 1995,
Rogier and Chauvaud presented an attack on MD2 that can nearly find
collisions [RC95]. Collisions occur when one can find two different
messages that generate the same message digest. A checksum operation
in MD2 is the only remaining obstacle to the success of the attack.
For this reason, the use of MD2 for new applications is discouraged.
It is still reasonable to use MD2 to verify existing signatures, as
the ability to find collisions in MD2 does not enable an attacker to
find new messages having a previously computed hash value.
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2.1.2 MD5 Oneway Hash Function
MD5 was developed by Ron Rivest for RSA Security. RSA Security has
placed the MD5 algorithm in the public domain. MD5 produces a 128
bit "hash" of the input. MD5 is fully described in [RFC 1321].
Den Boer and Bosselaers [DB94] have found pseudocollisions for MD5,
but there are no other known cryptanalytic results. The use of MD5
for new applications is discouraged. It is still reasonable to use
MD5 to verify existing signatures.
2.1.3 SHA1 Oneway Hash Function
SHA1 was developed by the U.S. Government. SHA1 produces a 160bit
"hash" of the input. SHA1 is fully described in [FIPS 1801]. RFC
3174 [RFC 3174] also describes SHA1, and it provides an
implementation of the algorithm.
2.2 Signature Algorithms
Certificates and CRLs conforming to [RFC 3280] may be signed with any
public key signature algorithm. The certificate or CRL indicates the
algorithm through an algorithm identifier which appears in the
signatureAlgorithm field within the Certificate or CertificateList.
This algorithm identifier is an OID and has optionally associated
parameters. This section identifies algorithm identifiers and
parameters that MUST be used in the signatureAlgorithm field in a
Certificate or CertificateList.
Signature algorithms are always used in conjunction with a oneway
hash function.
This section identifies OIDS for RSA, DSA, and ECDSA. The contents
of the parameters component for each algorithm vary; details are
provided for each algorithm.
The data to be signed (e.g., the oneway hash function output value)
is formatted for the signature algorithm to be used. Then, a private
key operation (e.g., RSA encryption) is performed to generate the
signature value. This signature value is then ASN.1 encoded as a BIT
STRING and included in the Certificate or CertificateList in the
signature field.
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2.2.1 RSA Signature Algorithm
The RSA algorithm is named for its inventors: Rivest, Shamir, and
Adleman. This profile includes three signature algorithms based on
the RSA asymmetric encryption algorithm. The signature algorithms
combine RSA with either the MD2, MD5, or the SHA1 oneway hash
functions.
The signature algorithm with SHA1 and the RSA encryption algorithm
is implemented using the padding and encoding conventions described
in PKCS #1 [RFC 2313]. The message digest is computed using the
SHA1 hash algorithm.
The RSA signature algorithm, as specified in PKCS #1 [RFC 2313]
includes a data encoding step. In this step, the message digest and
the OID for the oneway hash function used to compute the digest are
combined. When performing the data encoding step, the md2, md5, and
idsha1 OIDs MUST be used to specify the MD2, MD5, and SHA1 oneway
hash functions, respectively:
md2 OBJECT IDENTIFIER ::= {
iso(1) memberbody(2) US(840) rsadsi(113549)
digestAlgorithm(2) 2 }
md5 OBJECT IDENTIFIER ::= {
iso(1) memberbody(2) US(840) rsadsi(113549)
digestAlgorithm(2) 5 }
idsha1 OBJECT IDENTIFIER ::= {
iso(1) identifiedorganization(3) oiw(14) secsig(3)
algorithms(2) 26 }
The signature algorithm with MD2 and the RSA encryption algorithm is
defined in PKCS #1 [RFC 2313]. As defined in PKCS #1 [RFC 2313], the
ASN.1 OID used to identify this signature algorithm is:
md2WithRSAEncryption OBJECT IDENTIFIER ::= {
iso(1) memberbody(2) us(840) rsadsi(113549) pkcs(1)
pkcs1(1) 2 }
The signature algorithm with MD5 and the RSA encryption algorithm is
defined in PKCS #1 [RFC 2313]. As defined in PKCS #1 [RFC 2313], the
ASN.1 OID used to identify this signature algorithm is:
md5WithRSAEncryption OBJECT IDENTIFIER ::= {
iso(1) memberbody(2) us(840) rsadsi(113549) pkcs(1)
pkcs1(1) 4 }
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The ASN.1 object identifier used to identify this signature algorithm
is:
sha1WithRSAEncryption OBJECT IDENTIFIER ::= {
iso(1) memberbody(2) us(840) rsadsi(113549) pkcs(1)
pkcs1(1) 5 }
When any of these three OIDs appears within the ASN.1 type
AlgorithmIdentifier, the parameters component of that type SHALL be
the ASN.1 type NULL.
The RSA signature generation process and the encoding of the result
is described in detail in PKCS #1 [RFC 2313].
2.2.2 DSA Signature Algorithm
The Digital Signature Algorithm (DSA) is defined in the Digital
Signature Standard (DSS). DSA was developed by the U.S. Government,
and DSA is used in conjunction with the SHA1 oneway hash function.
DSA is fully described in [FIPS 186]. The ASN.1 OID used to identify
this signature algorithm is:
iddsawithsha1 OBJECT IDENTIFIER ::= {
iso(1) memberbody(2) us(840) x957 (10040)
x9cm(4) 3 }
When the iddsawithsha1 algorithm identifier appears as the
algorithm field in an AlgorithmIdentifier, the encoding SHALL omit
the parameters field. That is, the AlgorithmIdentifier SHALL be a
SEQUENCE of one component: the OBJECT IDENTIFIER iddsawithsha1.
The DSA parameters in the subjectPublicKeyInfo field of the
certificate of the issuer SHALL apply to the verification of the
signature.
When signing, the DSA algorithm generates two values. These values
are commonly referred to as r and s. To easily transfer these two
values as one signature, they SHALL be ASN.1 encoded using the
following ASN.1 structure:
DssSigValue ::= SEQUENCE {
r INTEGER,
s INTEGER }
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2.2.3 ECDSA Signature Algorithm
The Elliptic Curve Digital Signature Algorithm (ECDSA) is defined in
[X9.62]. The ASN.1 object identifiers used to identify ECDSA are
defined in the following arc:
ansiX962 OBJECT IDENTIFIER ::= {
iso(1) memberbody(2) us(840) 10045 }
idecSigType OBJECT IDENTIFIER ::= {
ansiX962 signatures(4) }
ECDSA is used in conjunction with the SHA1 oneway hash function.
The ASN.1 object identifier used to identify ECDSA with SHA1 is:
ecdsawithSHA1 OBJECT IDENTIFIER ::= {
idecSigType 1 }
When the ecdsawithSHA1 algorithm identifier appears as the
algorithm field in an AlgorithmIdentifier, the encoding MUST omit the
parameters field. That is, the AlgorithmIdentifier SHALL be a
SEQUENCE of one component: the OBJECT IDENTIFIER ecdsawithSHA1.
The elliptic curve parameters in the subjectPublicKeyInfo field of
the certificate of the issuer SHALL apply to the verification of the
signature.
When signing, the ECDSA algorithm generates two values. These values
are commonly referred to as r and s. To easily transfer these two
values as one signature, they MUST be ASN.1 encoded using the
following ASN.1 structure:
EcdsaSigValue ::= SEQUENCE {
r INTEGER,
s INTEGER }
2.3 Subject Public Key Algorithms
Certificates conforming to [RFC 3280] may convey a public key for any
public key algorithm. The certificate indicates the algorithm
through an algorithm identifier. This algorithm identifier is an OID
and optionally associated parameters.
This section identifies preferred OIDs and parameters for the RSA,
DSA, DiffieHellman, KEA, ECDSA, and ECDH algorithms. Conforming CAs
MUST use the identified OIDs when issuing certificates containing
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public keys for these algorithms. Conforming applications supporting
any of these algorithms MUST, at a minimum, recognize the OID
identified in this section.
2.3.1 RSA Keys
The OID rsaEncryption identifies RSA public keys.
pkcs1 OBJECT IDENTIFIER ::= { iso(1) memberbody(2) us(840)
rsadsi(113549) pkcs(1) 1 }
rsaEncryption OBJECT IDENTIFIER ::= { pkcs1 1}
The rsaEncryption OID is intended to be used in the algorithm field
of a value of type AlgorithmIdentifier. The parameters field MUST
have ASN.1 type NULL for this algorithm identifier.
The RSA public key MUST be encoded using the ASN.1 type RSAPublicKey:
RSAPublicKey ::= SEQUENCE {
modulus INTEGER,  n
publicExponent INTEGER }  e
where modulus is the modulus n, and publicExponent is the public
exponent e. The DER encoded RSAPublicKey is the value of the BIT
STRING subjectPublicKey.
This OID is used in public key certificates for both RSA signature
keys and RSA encryption keys. The intended application for the key
MAY be indicated in the key usage field (see [RFC 3280]). The use of
a single key for both signature and encryption purposes is not
recommended, but is not forbidden.
If the keyUsage extension is present in an end entity certificate
which conveys an RSA public key, any combination of the following
values MAY be present:
digitalSignature;
nonRepudiation;
keyEncipherment; and
dataEncipherment.
If the keyUsage extension is present in a CA or CRL issuer
certificate which conveys an RSA public key, any combination of the
following values MAY be present:
digitalSignature;
nonRepudiation;
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keyEncipherment;
dataEncipherment;
keyCertSign; and
cRLSign.
However, this specification RECOMMENDS that if keyCertSign or cRLSign
is present, both keyEncipherment and dataEncipherment SHOULD NOT be
present.
2.3.2 DSA Signature Keys
The Digital Signature Algorithm (DSA) is defined in the Digital
Signature Standard (DSS) [FIPS 186]. The DSA OID supported by this
profile is:
iddsa OBJECT IDENTIFIER ::= {
iso(1) memberbody(2) us(840) x957(10040) x9cm(4) 1 }
The iddsa algorithm syntax includes optional domain parameters.
These parameters are commonly referred to as p, q, and g. When
omitted, the parameters component MUST be omitted entirely. That is,
the AlgorithmIdentifier MUST be a SEQUENCE of one component: the
OBJECT IDENTIFIER iddsa.
If the DSA domain parameters are present in the subjectPublicKeyInfo
AlgorithmIdentifier, the parameters are included using the following
ASN.1 structure:
DssParms ::= SEQUENCE {
p INTEGER,
q INTEGER,
g INTEGER }
The AlgorithmIdentifier within subjectPublicKeyInfo is the only place
within a certificate where the parameters may be used. If the DSA
algorithm parameters are omitted from the subjectPublicKeyInfo
AlgorithmIdentifier and the CA signed the subject certificate using
DSA, then the certificate issuer's DSA parameters apply to the
subject's DSA key. If the DSA domain parameters are omitted from the
SubjectPublicKeyInfo AlgorithmIdentifier and the CA signed the
subject certificate using a signature algorithm other than DSA, then
the subject's DSA domain parameters are distributed by other means.
If the subjectPublicKeyInfo AlgorithmIdentifier field omits the
parameters component, the CA signed the subject with a signature
algorithm other than DSA, and the subject's DSA parameters are not
available through other means, then clients MUST reject the
certificate.
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The DSA public key MUST be ASN.1 DER encoded as an INTEGER; this
encoding shall be used as the contents (i.e., the value) of the
subjectPublicKey component (a BIT STRING) of the SubjectPublicKeyInfo
data element.
DSAPublicKey ::= INTEGER  public key, Y
If the keyUsage extension is present in an end entity certificate
which conveys a DSA public key, any combination of the following
values MAY be present:
digitalSignature;
nonRepudiation;
If the keyUsage extension is present in a CA or CRL issuer
certificate which conveys a DSA public key, any combination of the
following values MAY be present:
digitalSignature;
nonRepudiation;
keyCertSign; and
cRLSign.
2.3.3 DiffieHellman Key Exchange Keys
The DiffieHellman OID supported by this profile is defined in
[X9.42].
dhpublicnumber OBJECT IDENTIFIER ::= { iso(1) memberbody(2)
us(840) ansix942(10046) numbertype(2) 1 }
The dhpublicnumber OID is intended to be used in the algorithm field
of a value of type AlgorithmIdentifier. The parameters field of that
type, which has the algorithmspecific syntax ANY DEFINED BY
algorithm, have the ASN.1 type DomainParameters for this algorithm.
DomainParameters ::= SEQUENCE {
p INTEGER,  odd prime, p=jq +1
g INTEGER,  generator, g
q INTEGER,  factor of p1
j INTEGER OPTIONAL,  subgroup factor
validationParms ValidationParms OPTIONAL }
ValidationParms ::= SEQUENCE {
seed BIT STRING,
pgenCounter INTEGER }
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The fields of type DomainParameters have the following meanings:
p identifies the prime p defining the Galois field;
g specifies the generator of the multiplicative subgroup of order
g;
q specifies the prime factor of p1;
j optionally specifies the value that satisfies the equation
p=jq+1 to support the optional verification of group parameters;
seed optionally specifies the bit string parameter used as the
seed for the domain parameter generation process; and
pgenCounter optionally specifies the integer value output as part
of the of the domain parameter prime generation process.
If either of the domain parameter generation components (pgenCounter
or seed) is provided, the other MUST be present as well.
The DiffieHellman public key MUST be ASN.1 encoded as an INTEGER;
this encoding shall be used as the contents (i.e., the value) of the
subjectPublicKey component (a BIT STRING) of the SubjectPublicKeyInfo
data element.
DHPublicKey ::= INTEGER  public key, y = g^x mod p
If the keyUsage extension is present in a certificate which conveys a
DH public key, the following values may be present:
keyAgreement;
encipherOnly; and
decipherOnly.
If present, the keyUsage extension MUST assert keyAgreement and MAY
assert either encipherOnly and decipherOnly. The keyUsage extension
MUST NOT assert both encipherOnly and decipherOnly.
2.3.4 KEA Public Keys
This section identifies the preferred OID and parameters for the
inclusion of a KEA public key in a certificate. The Key Exchange
Algorithm (KEA) is a key agreement algorithm. Two parties may
generate a "pairwise key" if and only if they share the same KEA
parameters. The KEA parameters are not included in a certificate;
instead a domain identifier is supplied in the parameters field.
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When the SubjectPublicKeyInfo field contains a KEA key, the algorithm
identifier and parameters SHALL be as defined in [SDN.701r]:
idkeyExchangeAlgorithm OBJECT IDENTIFIER ::=
{ 2 16 840 1 101 2 1 1 22 }
KEAParmsId ::= OCTET STRING
CAs MUST populate the parameters field of the AlgorithmIdentifier
within the SubjectPublicKeyInfo field of each certificate containing
a KEA public key with an 80bit parameter identifier (OCTET STRING),
also known as the domain identifier. The domain identifier is
computed in three steps:
(1) the KEA domain parameters (p, q, and g) are DER encoded using
the DssParms structure;
(2) a 160bit SHA1 hash is generated from the parameters; and
(3) the 160bit hash is reduced to 80bits by performing an
"exclusive or" of the 80 high order bits with the 80 low order
bits.
The resulting value is encoded such that the most significant byte of
the 80bit value is the first octet in the octet string. The Dss
Parms is provided above in Section 2.3.2.
A KEA public key, y, is conveyed in the subjectPublicKey BIT STRING
such that the most significant bit (MSB) of y becomes the MSB of the
BIT STRING value field and the least significant bit (LSB) of y
becomes the LSB of the BIT STRING value field. This results in the
following encoding:
BIT STRING tag;
BIT STRING length;
0 (indicating that there are zero unused bits in the final octet
of y); and
BIT STRING value field including y.
The key usage extension may optionally appear in a KEA certificate.
If a KEA certificate includes the keyUsage extension, only the
following values may be asserted:
keyAgreement;
encipherOnly; and
decipherOnly.
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If present, the keyUsage extension MUST assert keyAgreement and MAY
assert either encipherOnly and decipherOnly. The keyUsage extension
MUST NOT assert both encipherOnly and decipherOnly.
2.3.5 ECDSA and ECDH Keys
This section identifies the preferred OID and parameter encoding for
the inclusion of an ECDSA or ECDH public key in a certificate. The
Elliptic Curve Digital Signature Algorithm (ECDSA) is defined in
[X9.62]. ECDSA is the elliptic curve mathematical analog of the
Digital Signature Algorithm [FIPS 186]. The Elliptic Curve Diffie
Hellman (ECDH) algorithm is a key agreement algorithm defined in
[X9.63].
ECDH is the elliptic curve mathematical analog of the DiffieHellman
key agreement algorithm as specified in [X9.42]. The ECDSA and ECDH
specifications use the same OIDs and parameter encodings. The ASN.1
object identifiers used to identify these public keys are defined in
the following arc:
ansiX962 OBJECT IDENTIFIER ::=
{ iso(1) memberbody(2) us(840) 10045 }
When certificates contain an ECDSA or ECDH public key, the
idecPublicKey algorithm identifier MUST be used. The idecPublicKey
algorithm identifier is defined as follows:
idpublickeytype OBJECT IDENTIFIER ::= { ansiX9.62 2 }
idecPublicKey OBJECT IDENTIFIER ::= { idpublicKeyType 1 }
This OID is used in public key certificates for both ECDSA signature
keys and ECDH encryption keys. The intended application for the key
may be indicated in the key usage field (see [RFC 3280]). The use of
a single key for both signature and encryption purposes is not
recommended, but is not forbidden.
ECDSA and ECDH require use of certain parameters with the public key.
The parameters may be inherited from the issuer, implicitly included
through reference to a "named curve," or explicitly included in the
certificate.
EcpkParameters ::= CHOICE {
ecParameters ECParameters,
namedCurve OBJECT IDENTIFIER,
implicitlyCA NULL }
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When the parameters are inherited, the parameters field SHALL contain
implictlyCA, which is the ASN.1 value NULL. When parameters are
specified by reference, the parameters field SHALL contain the
namedCurve choice, which is an object identifier. When the
parameters are explicitly included, they SHALL be encoded in the
ASN.1 structure ECParameters:
ECParameters ::= SEQUENCE {
version ECPVer,  version is always 1
fieldID FieldID,  identifies the finite field over
 which the curve is defined
curve Curve,  coefficients a and b of the
 elliptic curve
base ECPoint,  specifies the base point P
 on the elliptic curve
order INTEGER,  the order n of the base point
cofactor INTEGER OPTIONAL  The integer h = #E(Fq)/n
}
ECPVer ::= INTEGER {ecpVer1(1)}
Curve ::= SEQUENCE {
a FieldElement,
b FieldElement,
seed BIT STRING OPTIONAL }
FieldElement ::= OCTET STRING
ECPoint ::= OCTET STRING
The value of FieldElement SHALL be the octet string representation of
a field element following the conversion routine in [X9.62], Section
4.3.3. The value of ECPoint SHALL be the octet string representation
of an elliptic curve point following the conversion routine in
[X9.62], Section 4.3.6. Note that this octet string may represent an
elliptic curve point in compressed or uncompressed form.
Implementations that support elliptic curve according to this
specification MUST support the uncompressed form and MAY support the
compressed form.
The components of type ECParameters have the following meanings:
version specifies the version number of the elliptic curve
parameters. It MUST have the value 1 (ecpVer1).
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fieldID identifies the finite field over which the elliptic curve
is defined. Finite fields are represented by values of the
parameterized type FieldID, constrained to the values of the
objects defined in the information object set FieldTypes.
Additional detail regarding fieldID is provided below.
curve specifies the coefficients a and b of the elliptic curve E.
Each coefficient is represented as a value of type FieldElement,
an OCTET STRING. seed is an optional parameter used to derive the
coefficients of a randomly generated elliptic curve.
base specifies the base point P on the elliptic curve. The base
point is represented as a value of type ECPoint, an OCTET STRING.
order specifies the order n of the base point.
cofactor is the integer h = #E(Fq)/n. This parameter is specified
as OPTIONAL. However, the cofactor MUST be included in ECDH
public key parameters. The cofactor is not required to support
ECDSA, except in parameter validation. The cofactor MAY be
included to support parameter validation for ECDSA keys.
Parameter validation is not required by this specification.
The AlgorithmIdentifier within SubjectPublicKeyInfo is the only place
within a certificate where the parameters may be used. If the
elliptic curve parameters are specified as implicitlyCA in the
SubjectPublicKeyInfo AlgorithmIdentifier and the CA signed the
subject certificate using ECDSA, then the certificate issuer's ECDSA
parameters apply to the subject's ECDSA key. If the elliptic curve
parameters are specified as implicitlyCA in the SubjectPublicKeyInfo
AlgorithmIdentifier and the CA signed the certificate using a
signature algorithm other than ECDSA, then clients MUST not make use
of the elliptic curve public key.
FieldID ::= SEQUENCE {
fieldType OBJECT IDENTIFIER,
parameters ANY DEFINED BY fieldType }
FieldID is a SEQUENCE of two components, fieldType and parameters.
The fieldType contains an object identifier value that uniquely
identifies the type contained in the parameters.
The object identifier idfieldType specifies an arc containing the
object identifiers of each field type. It has the following value:
idfieldType OBJECT IDENTIFIER ::= { ansiX962 fieldType(1) }
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The object identifiers primefield and characteristictwofield name
the two kinds of fields defined in this Standard. They have the
following values:
primefield OBJECT IDENTIFIER ::= { idfieldType 1 }
Primep ::= INTEGER  Field size p (p in bits)
characteristictwofield OBJECT IDENTIFIER ::= { idfieldType 2 }
Characteristictwo ::= SEQUENCE {
m INTEGER,  Field size 2^m
basis OBJECT IDENTIFIER,
parameters ANY DEFINED BY basis }
The object identifier idcharacteristictwobasis specifies an arc
containing the object identifiers for each type of basis for the
characteristictwo finite fields. It has the following value:
idcharacteristictwobasis OBJECT IDENTIFIER ::= {
characteristictwofield basisType(1) }
The object identifiers gnBasis, tpBasis and ppBasis name the three
kinds of basis for characteristictwo finite fields defined by
[X9.62]. They have the following values:
gnBasis OBJECT IDENTIFIER ::= { idcharacteristictwobasis 1 }
 for gnBasis, the value of the parameters field is NULL
tpBasis OBJECT IDENTIFIER ::= { idcharacteristictwobasis 2 }
 type of parameters field for tpBasis is Trinomial
Trinomial ::= INTEGER
ppBasis OBJECT IDENTIFIER ::= { idcharacteristictwobasis 3 }
 type of parameters field for ppBasis is Pentanomial
Pentanomial ::= SEQUENCE {
k1 INTEGER,
k2 INTEGER,
k3 INTEGER }
Polk, et al. Standards Track [Page 16]
RFC 3279 Algorithms and Identifiers April 2002
The elliptic curve public key (an ECPoint which is an OCTET STRING)
is mapped to a subjectPublicKey (a BIT STRING) as follows: the most
significant bit of the OCTET STRING becomes the most significant bit
of the BIT STRING, and the least significant bit of the OCTET STRING
becomes the least significant bit of the BIT STRING. Note that this
octet string may represent an elliptic curve point in compressed or
uncompressed form. Implementations that support elliptic curve
according to this specification MUST support the uncompressed form
and MAY support the compressed form.
If the keyUsage extension is present in a CA or CRL issuer
certificate which conveys an elliptic curve public key, any
combination of the following values MAY be present:
digitalSignature;
nonRepudiation; and
keyAgreement.
If the keyAgreement value is present, either of the following values
MAY be present:
encipherOnly; and
decipherOnly.
The keyUsage extension MUST NOT assert both encipherOnly and
decipherOnly.
If the keyUsage extension is present in a CA certificate which
conveys an elliptic curve public key, any combination of the
following values MAY be present:
digitalSignature;
nonRepudiation;
keyAgreement;
keyCertSign; and
cRLSign.
As above, if the keyUsage extension asserts keyAgreement then it MAY
assert either encipherOnly and decipherOnly. However, this
specification RECOMMENDS that if keyCertSign or cRLSign is present,
keyAgreement, encipherOnly, and decipherOnly SHOULD NOT be present.
Polk, et al. Standards Track [Page 17]
RFC 3279 Algorithms and Identifiers April 2002
3 ASN.1 Module
PKIX1Algorithms88 { iso(1) identifiedorganization(3) dod(6)
internet(1) security(5) mechanisms(5) pkix(7) idmod(0)
idmodpkix1algorithms(17) }
DEFINITIONS EXPLICIT TAGS ::= BEGIN
 EXPORTS All;
 IMPORTS NONE;

 Oneway Hash Functions

md2 OBJECT IDENTIFIER ::= {
iso(1) memberbody(2) us(840) rsadsi(113549)
digestAlgorithm(2) 2 }
md5 OBJECT IDENTIFIER ::= {
iso(1) memberbody(2) us(840) rsadsi(113549)
digestAlgorithm(2) 5 }
idsha1 OBJECT IDENTIFIER ::= {
iso(1) identifiedorganization(3) oiw(14) secsig(3)
algorithms(2) 26 }

 DSA Keys and Signatures

 OID for DSA public key
iddsa OBJECT IDENTIFIER ::= {
iso(1) memberbody(2) us(840) x957(10040) x9algorithm(4) 1 }
 encoding for DSA public key
DSAPublicKey ::= INTEGER  public key, y
DssParms ::= SEQUENCE {
p INTEGER,
q INTEGER,
g INTEGER }
Polk, et al. Standards Track [Page 18]
RFC 3279 Algorithms and Identifiers April 2002
 OID for DSA signature generated with SHA1 hash
iddsawithsha1 OBJECT IDENTIFIER ::= {
iso(1) memberbody(2) us(840) x957 (10040) x9algorithm(4) 3 }
 encoding for DSA signature generated with SHA1 hash
DssSigValue ::= SEQUENCE {
r INTEGER,
s INTEGER }

 RSA Keys and Signatures

 arc for RSA public key and RSA signature OIDs
pkcs1 OBJECT IDENTIFIER ::= {
iso(1) memberbody(2) us(840) rsadsi(113549) pkcs(1) 1 }
 OID for RSA public keys
rsaEncryption OBJECT IDENTIFIER ::= { pkcs1 1 }
 OID for RSA signature generated with MD2 hash
md2WithRSAEncryption OBJECT IDENTIFIER ::= { pkcs1 2 }
 OID for RSA signature generated with MD5 hash
md5WithRSAEncryption OBJECT IDENTIFIER ::= { pkcs1 4 }
 OID for RSA signature generated with SHA1 hash
sha1WithRSAEncryption OBJECT IDENTIFIER ::= { pkcs1 5 }
 encoding for RSA public key
RSAPublicKey ::= SEQUENCE {
modulus INTEGER,  n
publicExponent INTEGER }  e
Polk, et al. Standards Track [Page 19]
RFC 3279 Algorithms and Identifiers April 2002

 DiffieHellman Keys

dhpublicnumber OBJECT IDENTIFIER ::= {
iso(1) memberbody(2) us(840) ansix942(10046)
numbertype(2) 1 }
 encoding for DSA public key
DHPublicKey ::= INTEGER  public key, y = g^x mod p
DomainParameters ::= SEQUENCE {
p INTEGER,  odd prime, p=jq +1
g INTEGER,  generator, g
q INTEGER,  factor of p1
j INTEGER OPTIONAL,  subgroup factor, j>= 2
validationParms ValidationParms OPTIONAL }
ValidationParms ::= SEQUENCE {
seed BIT STRING,
pgenCounter INTEGER }

 KEA Keys

idkeyExchangeAlgorithm OBJECT IDENTIFIER ::=
{ 2 16 840 1 101 2 1 1 22 }
KEAParmsId ::= OCTET STRING

 Elliptic Curve Keys, Signatures, and Curves

ansiX962 OBJECT IDENTIFIER ::= {
iso(1) memberbody(2) us(840) 10045 }
FieldID ::= SEQUENCE {  Finite field
fieldType OBJECT IDENTIFIER,
parameters ANY DEFINED BY fieldType }
 Arc for ECDSA signature OIDS
idecSigType OBJECT IDENTIFIER ::= { ansiX962 signatures(4) }
Polk, et al. Standards Track [Page 20]
RFC 3279 Algorithms and Identifiers April 2002
 OID for ECDSA signatures with SHA1
ecdsawithSHA1 OBJECT IDENTIFIER ::= { idecSigType 1 }
 OID for an elliptic curve signature
 format for the value of an ECDSA signature value
ECDSASigValue ::= SEQUENCE {
r INTEGER,
s INTEGER }
 recognized field type OIDs are defined in the following arc
idfieldType OBJECT IDENTIFIER ::= { ansiX962 fieldType(1) }
 where fieldType is primefield, the parameters are of type Primep
primefield OBJECT IDENTIFIER ::= { idfieldType 1 }
Primep ::= INTEGER  Finite field F(p), where p is an odd prime
 where fieldType is characteristictwofield, the parameters are
 of type Characteristictwo
characteristictwofield OBJECT IDENTIFIER ::= { idfieldType 2 }
Characteristictwo ::= SEQUENCE {
m INTEGER,  Field size 2^m
basis OBJECT IDENTIFIER,
parameters ANY DEFINED BY basis }
 recognized basis type OIDs are defined in the following arc
idcharacteristictwobasis OBJECT IDENTIFIER ::= {
characteristictwofield basisType(3) }
 gnbasis is identified by OID gnBasis and indicates
 parameters are NULL
gnBasis OBJECT IDENTIFIER ::= { idcharacteristictwobasis 1 }
 parameters for this basis are NULL
 trinomial basis is identified by OID tpBasis and indicates
 parameters of type Pentanomial
tpBasis OBJECT IDENTIFIER ::= { idcharacteristictwobasis 2 }
Polk, et al. Standards Track [Page 21]
RFC 3279 Algorithms and Identifiers April 2002
 Trinomial basis representation of F2^m
 Integer k for reduction polynomial xm + xk + 1
Trinomial ::= INTEGER
 for pentanomial basis is identified by OID ppBasis and indicates
 parameters of type Pentanomial
ppBasis OBJECT IDENTIFIER ::= { idcharacteristictwobasis 3 }
 Pentanomial basis representation of F2^m
 reduction polynomial integers k1, k2, k3
 f(x) = x**m + x**k3 + x**k2 + x**k1 + 1
Pentanomial ::= SEQUENCE {
k1 INTEGER,
k2 INTEGER,
k3 INTEGER }
 The object identifiers gnBasis, tpBasis and ppBasis name
 three kinds of basis for characteristictwo finite fields
FieldElement ::= OCTET STRING  Finite field element
ECPoint ::= OCTET STRING  Elliptic curve point
 Elliptic Curve parameters may be specified explicitly,
 specified implicitly through a "named curve", or
 inherited from the CA
EcpkParameters ::= CHOICE {
ecParameters ECParameters,
namedCurve OBJECT IDENTIFIER,
implicitlyCA NULL }
ECParameters ::= SEQUENCE {  Elliptic curve parameters
version ECPVer,
fieldID FieldID,
curve Curve,
base ECPoint,  Base point G
order INTEGER,  Order n of the base point
cofactor INTEGER OPTIONAL }  The integer h = #E(Fq)/n
ECPVer ::= INTEGER {ecpVer1(1)}
Polk, et al. Standards Track [Page 22]
RFC 3279 Algorithms and Identifiers April 2002
Curve ::= SEQUENCE {
a FieldElement,  Elliptic curve coefficient a
b FieldElement,  Elliptic curve coefficient b
seed BIT STRING OPTIONAL }
idpublicKeyType OBJECT IDENTIFIER ::= { ansiX962 keyType(2) }
idecPublicKey OBJECT IDENTIFIER ::= { idpublicKeyType 1 }
 Named Elliptic Curves in ANSI X9.62.
ellipticCurve OBJECT IDENTIFIER ::= { ansiX962 curves(3) }
cTwoCurve OBJECT IDENTIFIER ::= {
ellipticCurve characteristicTwo(0) }
c2pnb163v1 OBJECT IDENTIFIER ::= { cTwoCurve 1 }
c2pnb163v2 OBJECT IDENTIFIER ::= { cTwoCurve 2 }
c2pnb163v3 OBJECT IDENTIFIER ::= { cTwoCurve 3 }
c2pnb176w1 OBJECT IDENTIFIER ::= { cTwoCurve 4 }
c2tnb191v1 OBJECT IDENTIFIER ::= { cTwoCurve 5 }
c2tnb191v2 OBJECT IDENTIFIER ::= { cTwoCurve 6 }
c2tnb191v3 OBJECT IDENTIFIER ::= { cTwoCurve 7 }
c2onb191v4 OBJECT IDENTIFIER ::= { cTwoCurve 8 }
c2onb191v5 OBJECT IDENTIFIER ::= { cTwoCurve 9 }
c2pnb208w1 OBJECT IDENTIFIER ::= { cTwoCurve 10 }
c2tnb239v1 OBJECT IDENTIFIER ::= { cTwoCurve 11 }
c2tnb239v2 OBJECT IDENTIFIER ::= { cTwoCurve 12 }
c2tnb239v3 OBJECT IDENTIFIER ::= { cTwoCurve 13 }
c2onb239v4 OBJECT IDENTIFIER ::= { cTwoCurve 14 }
c2onb239v5 OBJECT IDENTIFIER ::= { cTwoCurve 15 }
c2pnb272w1 OBJECT IDENTIFIER ::= { cTwoCurve 16 }
c2pnb304w1 OBJECT IDENTIFIER ::= { cTwoCurve 17 }
c2tnb359v1 OBJECT IDENTIFIER ::= { cTwoCurve 18 }
c2pnb368w1 OBJECT IDENTIFIER ::= { cTwoCurve 19 }
c2tnb431r1 OBJECT IDENTIFIER ::= { cTwoCurve 20 }
primeCurve OBJECT IDENTIFIER ::= { ellipticCurve prime(1) }
prime192v1 OBJECT IDENTIFIER ::= { primeCurve 1 }
prime192v2 OBJECT IDENTIFIER ::= { primeCurve 2 }
prime192v3 OBJECT IDENTIFIER ::= { primeCurve 3 }
prime239v1 OBJECT IDENTIFIER ::= { primeCurve 4 }
prime239v2 OBJECT IDENTIFIER ::= { primeCurve 5 }
prime239v3 OBJECT IDENTIFIER ::= { primeCurve 6 }
prime256v1 OBJECT IDENTIFIER ::= { primeCurve 7 }
END
Polk, et al. Standards Track [Page 23]
RFC 3279 Algorithms and Identifiers April 2002
4 References
[FIPS 1801] Federal Information Processing Standards Publication
(FIPS PUB) 1801, Secure Hash Standard, 17 April 1995.
[Supersedes FIPS PUB 180 dated 11 May 1993.]
[FIPS 1862] Federal Information Processing Standards Publication
(FIPS PUB) 186, Digital Signature Standard, 27 January
2000. [Supersedes FIPS PUB 1861 dated 15 December
1998.]
[P1363] IEEE P1363, "Standard Specifications for PublicKey
Cryptography", 2001.
[RC95] Rogier, N. and Chauvaud, P., "The compression function
of MD2 is not collision free," Presented at Selected
Areas in Cryptography '95, May 1995.
[RFC 1034] Mockapetris, P., "Domain Names  Concepts and
Facilities", STD 13, RFC 1034, November 1987.
[RFC 1319] Kaliski, B., "The MD2 MessageDigest Algorithm", RFC
1319, April 1992.
[RFC 1321] Rivest, R., "The MD5 MessageDigest Algorithm", RFC
1321, April 1992.
[RFC 1422] Kent, S., "Privacy Enhancement for Internet Electronic
Mail: Part II: CertificateBased Key Management", RFC
1422, February 1993.
[RFC 1423] Balenson, D., "Privacy Enhancement for Internet
Electronic Mail: Part III: Algorithms, Modes, and
Identifiers", RFC 1423, February 1993.
[RFC 2119] Bradner, S., "Key Words for Use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC 2313] Kaliski, B., "PKCS #1: RSA Encryption Version 1.5",
RFC 2313, March 1998.
[RFC 2459] Housley, R., Ford, W., Polk, W. and D. Solo "Internet
X.509 Public Key Infrastructure: Certificate and CRL
Profile", RFC 2459, January, 1999.
[RFC 3174] Eastlake, D. and P. Jones, "US Secure Hash Algorithm 1
(SHA1)", RFC 3174, September 2001.
Polk, et al. Standards Track [Page 24]
RFC 3279 Algorithms and Identifiers April 2002
[RFC 3280] Housley, R., Polk, W., Ford, W. and D. Solo, "Internet
X.509 Public Key Infrastructure Certificate and
Certificate Revocation List (CRL) Profile", RFC 3280,
April 2002.
[SDN.701r] SDN.701, "Message Security Protocol 4.0", Revision A
19970206.
[X.208] CCITT Recommendation X.208: Specification of Abstract
Syntax Notation One (ASN.1), 1988.
[X.660] ITUT Recommendation X.660 Information Technology 
ASN.1 encoding rules: Specification of Basic Encoding
Rules (BER), Canonical Encoding Rules (CER) and
Distinguished Encoding Rules (DER), 1997.
[X9.42] ANSI X9.422000, "Public Key Cryptography for The
Financial Services Industry: Agreement of Symmetric
Keys Using Discrete Logarithm Cryptography", December,
1999.
[X9.62] X9.621998, "Public Key Cryptography For The Financial
Services Industry: The Elliptic Curve Digital
Signature Algorithm (ECDSA)", January 7, 1999.
[X9.63] ANSI X9.632001, "Public Key Cryptography For The
Financial Services Industry: Key Agreement and Key
Transport Using Elliptic Curve Cryptography", Work in
Progress.
5 Security Considerations
This specification does not constrain the size of public keys or
their parameters for use in the Internet PKI. However, the key size
selected impacts the strength achieved when implementing
cryptographic services. Selection of appropriate key sizes is
critical to implementing appropriate security.
This specification does not identify particular elliptic curves for
use in the Internet PKI. However, the particular curve selected
impact the strength of the digital signatures. Some curves are
cryptographically stronger than others!
In general, use of "wellknown" curves, such as the "named curves"
from ANSI X9.62, is a sound strategy. For additional information,
refer to X9.62 Appendix H.1.3, "Key Length Considerations" and
Appendix A.1, "Avoiding Cryptographically Weak Keys".
Polk, et al. Standards Track [Page 25]
RFC 3279 Algorithms and Identifiers April 2002
This specification supplements RFC 3280. The security considerations
section of that document applies to this specification as well.
6 Intellectual Property Rights
The IETF has been notified of intellectual property rights claimed in
regard to some or all of the specification contained in this
document. For more information consult the online list of claimed
rights.
The IETF takes no position regarding the validity or scope of any
intellectual property or other rights that might be claimed to
pertain to the implementation or use of the technology described in
this document or the extent to which any license under such rights
might or might not be available; neither does it represent that it
has made any effort to identify any such rights. Information on the
IETF's procedures with respect to rights in standardstrack and
standards related documentation can be found in BCP11. Copies of
claims of rights made available for publication and any assurances of
licenses to be made available, or the result of an attempt made to
obtain a general license or permission for the use of such
proprietary rights by implementors or users of this specification can
be obtained from the IETF Secretariat.
7 Author Addresses:
Tim Polk
NIST
100 Bureau Drive, Stop 8930
Gaithersburg, MD 208998930
USA
EMail: tim.polk@nist.gov
Russell Housley
RSA Laboratories
918 Spring Knoll Drive
Herndon, VA 20170
USA
EMail: rhousley@rsasecurity.com
Larry Bassham
NIST
100 Bureau Drive, Stop 8930
Gaithersburg, MD 208998930
USA
EMail: lbassham@nist.gov
Polk, et al. Standards Track [Page 26]
RFC 3279 Algorithms and Identifiers April 2002
8. Full Copyright Statement
Copyright (C) The Internet Society (2002). All Rights Reserved.
This document and translations of it may be copied and furnished to
others, and derivative works that comment on or otherwise explain it
or assist in its implementation may be prepared, copied, published
and distributed, in whole or in part, without restriction of any
kind, provided that the above copyright notice and this paragraph are
included on all such copies and derivative works. However, this
document itself may not be modified in any way, such as by removing
the copyright notice or references to the Internet Society or other
Internet organizations, except as needed for the purpose of
developing Internet standards in which case the procedures for
copyrights defined in the Internet Standards process must be
followed, or as required to translate it into languages other than
English.
The limited permissions granted above are perpetual and will not be
revoked by the Internet Society or its successors or assigns.
This document and the information contained herein is provided on an
"AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Acknowledgement
Funding for the RFC Editor function is currently provided by the
Internet Society.
Polk, et al. Standards Track [Page 27]



