PKIX Working Group L. Bassham (NIST)
Internet Draft R. Housley (Spyrus)
expires January 14, 2000 W. Polk (NIST)
July 14, 2000
Internet X.509 Public Key Infrastructure
Representation of Public Keys and Digital Signatures
in Internet X.509 Public Key Infrastructure Certificates
Status of this Memo
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC 2026. Internet-Drafts are
working documents of the Internet Engineering Task Force (IETF), its
areas, and its working groups. Note that other groups may also
distribute working documents as Internet-Drafts.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt.
The list of Internet-Drafts Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.
Abstract
This is the first draft of a specification of algorithm identifiers
and encoding formats for the representation of cryptographic keys,
associated parameters and digital sigantures in Internet Public Key
Infrastructure X.509 certificates and certificate revocation lists.
This specification was created by combining Section 7, Cryptographic
Support, from RFC 2459 with the Internet-Draft "Representation of
Elliptic Curve Digital Signature Algorithm (ECDSA) Keys and
Signatures in Internet X.509 Public Key Infrastructure Certificates".
This specification is a companion to the "son of 2459";
implementations must also conform to "son of 2459". This document
does not define the cryptographic algorithms themselves; instead, it
references other appropriate standards.
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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.
Please send comments on this document to the ietf-pkix@imc.org mail
list.
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Table of Contents
1 Executive Summary ........................................... 4
2 Requirements and Assumptions ................................ 4
2.1 Communication and Topology ................................ 4
2.2 Acceptability Criteria .................................... 4
2.3 User Expectations ......................................... 5
2.4 Administrator Expectations ................................ 5
3 Algorithm Support ........................................... 5
3.1 One-Way Hash Functions .................................... 6
3.1.1 MD2 One-Way Hash Functions .............................. 6
3.1.2 MD5 One-Way Hash Functions .............................. 6
3.1.3 SHA-1 One-Way Hash Functions ............................ 6
3.2 Signature Algorithms ...................................... 7
3.2.1 RSA Signature Algorithm ................................. 7
3.2.2 DSA Signature Algorithm ................................. 8
3.2.3 Elliptic Curve Digital Signature Algorithm .............. 9
3.3 Subject Public Key Algorithms ............................. 10
3.3.1 RSA Keys ................................................ 11
3.3.2 Diffie-Hellman Key Exchange Keys ........................ 12
3.3.3 DSA Signature Keys ...................................... 13
3.3.4 KEA Public Keys ......................................... 14
3.3.5 Elliptic Curve Public Keys .............................. 22
4 ASN.1 Module ................................................ 19
5 References .................................................. 24
6 Intellectual Property Rights ................................ 25
7 Security Considerations ..................................... 26
8 Intellectual Property Rights ................................ 26
9 Author Addresses ............................................ 27
10 Full Copyright Statement ................................... 27
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1 Executive Summary
This document specifies encoding formats for digital signatures and
public keys in Internet Public Key Infrastructure (IPKI) certificates
and CRLs. This specification is an addendum to RFC 2459, "Internet
Public Key Infrastructure: X.509 Certificate and CRL Profile".
Implementations of this specification must also conform to RFC 2459.
Implementations of this specification are not required to conform to
other parts from that series.
This specification defines the contents of the signatureAlgorithm,
signatureValue, signature and subjectPublicKeyInfo fields in IPKI
certificates and CRLs when using common cryptographic algorithms.
This document identifies secure hash algorithms for use in the gen-
eration of digital signatures in IPKI certificates and CRLs. These
algorithms are used in conjunction with digital signature algorithms.
This specification describes the encoding of digital signatures gen-
erated with the following cryptographic algorithms: the Rivest-
Shamir-Adelman (RSA) algorithm, the Digital Signature Algorithm
(DSA), and the Elliptic Curve Digital Signature Algorithm (ECDSA).
This document specifies the contents of the subjectPublicKeyInfo
field and the keyUsage extension in IPKI certificates. This specifi-
cation describes encoding formats for public keys used with the fol-
lowing cryptographic algorithms: RSA, DSA, the Diffie-Hellman algo-
rithm, and ECDSA.
2 Requirements and Assumptions
The goal is to augment the X.509 certificate profile presented in the
Internet PKI X.509 Certificate and CRL Profile.
2.1 Communication and Topology
This profile, as presented in Part 1 and augmented by this specifica-
tion, supports users without high bandwidth, real-time IP connec-
tivity, or high connection availability. In addition, the profile
allows for the presence of firewall or other filtered communication.
This profile does not assume the deployment of an X.500 Directory
system. The profile does not prohibit the use of an X.500 Directory,
but other means of distributing certificates and certificate revoca-
tion lists (CRLs) are supported.
2.2 Acceptability Criteria
The goal of the Internet Public Key Infrastructure (PKI) is to meet
the needs of deterministic, automated identification, authentication,
access control, and authorization functions. Support for these
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services determines the attributes contained in the certificate as
well as the ancillary control information in the certificate such as
policy data and certification path constraints.
The goal of this document is to profile ECDSA certificates, specify-
ing the contents and semantics of attributes which were not fully
specified by Part 1. If not specifically addressed by this document,
the contents and semantics of the fields and extensions must be as
described in Part 1.
2.3 User Expectations
Users of the Internet PKI are people and processes who use client
software and are the subjects named in certificates. These uses
include readers and writers of electronic mail, the clients for WWW
browsers, WWW servers, and the key manager for IPSEC within a router.
This profile recognizes the limitations of the platforms these users
employ and the sophistication/attentiveness of the users themselves.
This manifests itself in minimal user configuration responsibility
(e.g., root keys, rules), explicit platform usage constraints within
the certificate, certification path constraints which shield the user
from many malicious actions, and applications which sensibly automate
validation functions.
2.4 Administrator Expectations
As with users, the Internet PKI profile is structured to support the
individuals who generally operate Certification Authorities (CAs).
Providing administrators with unbounded choices increases the chances
that a subtle CA administrator mistake will result in broad comprom-
ise or unnecessarily limit interoperability. This profile defines
the object identifiers and data formats that must be supported to
interpret ECDSA public keys.
3 Algorithm Support
This section describes cryptographic algorithms which may be used
with this profile. The section describes one-way hash functions and
digital signature algorithms which may be used to sign certificates
and CRLs, and identifies OIDs for public keys contained in a certifi-
cate.
Conforming CAs and applications are not required to support the algo-
rithms or algorithm identifiers described in this section. However,
conforming CAs and applications that use the algorithms identified
here MUST support them as specified.
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3.1 One-way Hash Functions
This section identifies one-way hash functions for use in the Inter-
net PKI. One-way hash functions are also called message digest algo-
rithms. SHA-1 is the preferred one-way hash function for the Internet
PKI. However, PEM uses MD2 for certificates [RFC 1422] [RFC 1423]
and MD5 is used in other legacy applications. For this reason, MD2
and MD5 are included in this profile.
3.1.1 MD2 One-way Hash Function
MD2 was developed by Ron Rivest for RSA Data Security. RSA Data Secu-
rity has not placed the MD2 algorithm in the public domain. Rather,
RSA Data Security has granted license to use MD2 for non-commercial
Internet Privacy-Enhanced Mail. For this reason, MD2 may continue to
be used with PEM certificates, but SHA-1 is preferred. MD2 produces
a 128-bit "hash" of the input. MD2 is fully described in RFC 1319
[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.
3.1.2 MD5 One-way Hash Function
MD5 was developed by Ron Rivest for RSA Data Security. RSA Data Secu-
rity 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
[RFC 1321].
Den Boer and Bosselaers [DB94] have found pseudo-collisions 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.
3.1.3 SHA-1 One-way Hash Function
SHA-1 was developed by the U.S. Government. SHA-1 produces a 160-bit
"hash" of the input. SHA-1 is fully described in FIPS 180-1 [FIPS
180-1].
SHA-1 is the one-way hash function of choice for use with the RSA,
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DSA, and ECDSA signature algorithms (see sec. 3.2).
3.2 Signature Algorithms
Certificates and CRLs described by this standard 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 in a Certificate or CertificateList. This
algorithm identifier is an OID and has optionally associated parame-
ters. This section identifies algorithm identifiers and parameters
that shall be used in the signatureAlgorithm field in a Certificate
or CertificateList.
RSA and DSA are the most popular signature algorithms used in the
Internet. Signature algorithms are always used in conjunction with a
one-way hash function.
The signature algorithm and one-way hash function used to sign a cer-
tificate or CRL is indicated by use of an algorithm identifier. An
algorithm identifier is an OID, and may include associated parame-
ters. This section identifies OIDS for RSA and DSA. The contents of
the parameters component for each algorithm vary; details are pro-
vided for each algorithm.
The data to be signed (e.g., the one-way 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 sig-
nature field.
3.2.1 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 SHA-1 one-way hash func-
tions.
The signature algorithm with MD2 and the RSA encryption algorithm is
defined in PKCS #1 [RFC 2313]. As defined in RFC 2313, the ASN.1 OID
used to identify this signature algorithm is:
md2WithRSAEncryption OBJECT IDENTIFIER ::= {
iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1)
pkcs-1(1) 2 }
The signature algorithm with MD5 and the RSA encryption algorithm is
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defined in PKCS #1 [RFC 2313]. As defined in RFC 2313, the ASN.1 OID
used to identify this signature algorithm is:
md5WithRSAEncryption OBJECT IDENTIFIER ::= {
iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1)
pkcs-1(1) 4 }
The signature algorithm with SHA-1 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 SHA-1
hash algorithm. The ASN.1 object identifier used to identify this
signature algorithm is:
sha-1WithRSAEncryption OBJECT IDENTIFIER ::= {
iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1)
pkcs-1(1) 5 }
When any of these three OIDs appears within the ASN.1 type Algorith-
mIdentifier, 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 RFC 2313.
3.2.2 DSA Signature Algorithm
The Digital Signature Algorithm (DSA) is defined in the Digital Sig-
nature Standard (DSS). DSA was developed by the U.S. Government, and
DSA is used in conjunction with the SHA-1 one-way hash function. DSA
is fully described in FIPS 186 [FIPS 186]. The ASN.1 OIDs used to
identify this signature algorithm are:
id-dsa-with-sha1 ID ::= {
iso(1) member-body(2) us(840) x9-57 (10040)
x9cm(4) 3 }
Where the id-dsa-with-sha1 algorithm identifier appears as the algo-
rithm 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 id-dsa-with-sha1.
The DSA parameters in the subjectPublicKeyInfo field of the certifi-
cate 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 fol-
lowing ASN.1 structure:
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Dss-Sig-Value ::= SEQUENCE {
r INTEGER,
s INTEGER }
3.2.3 Elliptic Curve Digital Signature Algorithm
The Elliptic Curve Digital Signature Algorithm (ECDSA) is defined in
the ANSI X9.62 standard [X9.62]. The ASN.1 object identifiers used
to identify the ECDSA algorithm are defined in the following arc:
ansi-X9-62 OBJECT IDENTIFIER ::=
{ iso(1) member-body(2) us(840) 10045 }
When used to sign certificates, CRLs, or PKI messages, the ECDSA
shall be used with the SHA-1 hash algorithm. The ASN.1 object iden-
tifier used to identify the ECDSA algorithm with SHA-1 shall be:
id-ecSigType OBJECT IDENTIFIER ::= { ansi-X9-62 signatures(4) }
ecdsa-with-SHA1 OBJECT IDENTIFIER ::= { id-ecSigType 1 }
When the ecdsa-with-SHA1 algorithm identifier is used in the SIGNED
parameterized TYPE (e.g., in the signature on a certificate or CRL)
it shall have NULL parameters. The ECDSA parameters in the certifi-
cate 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 shall be ASN.1 encoded using the fol-
lowing ASN.1 structure:
Ecdsa-Sig-Value ::= SEQUENCE {
r INTEGER,
s INTEGER }
3.3 Subject Public Key Algorithms
Certificates described by this profile 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, and Diffie-Hellman algorithms. Conforming CAs shall use the
identified OIDs when issuing certificates containing public keys for
these algorithms. Conforming applications supporting any of these
algorithms shall, at a minimum, recognize the OID identified in this
section.
3.3.1 RSA Keys
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The OID rsaEncryption identifies RSA public keys.
pkcs-1 OBJECT IDENTIFIER ::= { iso(1) member-body(2) us(840)
rsadsi(113549) pkcs(1) 1 }
rsaEncryption OBJECT IDENTIFIER ::= { pkcs-1 1}
The rsaEncryption OID is intended to be used in the algorithm field
of a value of type AlgorithmIdentifier. The parameters field shall
have ASN.1 type NULL for this algorithm identifier.
The RSA public key shall be encoded using the ASN.1 type RSAPub-
licKey:
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 sec. 4.2.1.3). 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; keyEnci-
pherment; and dataEncipherment. If the keyUsage extension is present
in a CA certificate which conveys an RSA public key, any combination
of the following values may be present: digitalSignature; nonRepudi-
ation; keyEncipherment; dataEncipherment; keyCertSign; and cRLSign.
However, this specification RECOMMENDS that if keyCertSign or cRLSign
is present, both keyEncipherment and dataEncipherment should not be
present.
3.3.2 Diffie-Hellman Key Exchange Key
The Diffie-Hellman OID supported by this profile is defined by ANSI
X9.42 [X9.42].
dhpublicnumber OBJECT IDENTIFIER ::= { iso(1) member-body(2)
us(840) ansi-x942(10046) number-type(2) 1 }
The dhpublicnumber OID is intended to be used in the algorithm field
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of a value of type AlgorithmIdentifier. The parameters field of that
type, which has the algorithm-specific syntax ANY DEFINED BY algo-
rithm, have the ASN.1 type GroupParameters for this algorithm.
DomainParameters ::= SEQUENCE {
p INTEGER, -- odd prime, p=jq +1
g INTEGER, -- generator, g
q INTEGER, -- factor of p-1
j INTEGER OPTIONAL, -- subgroup factor
validationParms ValidationParms OPTIONAL }
ValidationParms ::= SEQUENCE {
seed BIT STRING,
pgenCounter INTEGER }
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 p-1;
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 system parameter generation process; and
pgenCounter optionally specifies the integer value output as part
of the of the system parameter prime generation process.
If either of the parameter generation components (pgencounter or
seed) is provided, the other shall be present as well.
The Diffie-Hellman public key shall 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. At most one of encipherOnly and
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decipherOnly shall be asserted in keyUsage extension.
3.3.3 DSA Signature Keys
The Digital Signature Algorithm (DSA) is defined in the Digital Sig-
nature Standard (DSS). The DSA OID supported by this profile is
id-dsa ID ::= { iso(1) member-body(2) us(840) x9-57(10040)
x9cm(4) 1 }
The id-dsa algorithm syntax includes optional parameters. These
parameters are commonly referred to as p, q, and g. When omitted,
the parameters component shall be omitted entirely. That is, the
AlgorithmIdentifier shall be a SEQUENCE of one component - the OBJECT
IDENTIFIER id-dsa.
If the DSA algorithm parameters are present in the subjectPublicKey-
Info AlgorithmIdentifier, the parameters are included using the fol-
lowing ASN.1 structure:
Dss-Parms ::= SEQUENCE {
p INTEGER,
q INTEGER,
g INTEGER }
If the DSA algorithm parameters are absent from the subjectPublicKey-
Info 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 algorithm parameters are absent from
the subjectPublicKeyInfo AlgorithmIdentifier and the CA signed the
subject certificate using a signature algorithm other than DSA, then
the subject's DSA parameters are distributed by other means. If the
subjectPublicKeyInfo AlgorithmIdentifier field omits the parameters
component and the CA signed the subject with a signature algorithm
other than DSA, then clients shall reject the certificate.
When signing, 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 are ASN.1 encoded using the following ASN.1
structure:
Dss-Sig-Value ::= SEQUENCE {
r INTEGER,
s INTEGER }
The encoded signature is conveyed as the value of the BIT STRING sig-
nature in a Certificate or CertificateList.
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The DSA public key shall be ASN.1 DER encoded as an INTEGER; this
encoding shall be used as the contents (i.e., the value) of the sub-
jectPublicKey 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; and nonRepudiation.
If the keyUsage extension is present in a CA certificate which con-
veys a DSA public key, any combination of the following values may be
present: digitalSignature; nonRepudiation; keyCertSign; and cRLSign.
3.3.4 KEA Public Keys
The certificate identifies the KEA algorithm, conveys optional param-
eters, and specifies the KEA public key in the subjectPublicKeyInfo
field. The subjectPublicKeyInfo field is a SEQUENCE of an algorithm
identifier and the subjectPublicKey field.
The certificate indicates the algorithm through an algorithm identif-
ier. This algorithm identifier consists of an object identifier
(OID) and optional associated parameters. Section 3.1.1 identifies
the preferred OID and parameters for the KEA algorithm. Conforming
CAs shall use the identified OID when issuing certificates containing
public keys for the KEA algorithm. Conforming applications supporting
the KEA algorithm shall, at a minimum, recognize the OID identified
in section 3.1.1.
The certificate conveys the KEA public key through the subjectPub-
licKey field. This subjectPublicKey field is a BIT STRING. Section
3.1.2 specifies the method for encoding a KEA public key as a BIT
STRING. Conforming CAs shall encode the KEA public key as described
in Section 3.1.2 when issuing certificates containing public keys for
the KEA algorithm. Conforming applications supporting the KEA algo-
rithm shall decode the subjectPublicKey as described in section 3.1.2
when the algorithm identifier is the one presented in 3.1.1.
The Key Exchange Algorithm (KEA) is a classified algorithm for
exchanging keys. A KEA "pairwise key" may be generated between two
users if their KEA public keys were generated with the same KEA
parameters. The KEA parameters are not included in a certificate;
instead a "domain identifier" is supplied in the parameters field.
When the subjectPublicKeyInfo field contains a KEA key, the algorithm
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identifier and parameters shall be as defined in [sdn.701r]:
id-keyExchangeAlgorithm OBJECT IDENTIFIER ::=
{ 2 16 840 1 101 2 1 1 22 }
KEA-Parms-Id ::= OCTET STRING
CAs shall populate the parameters field of the AlgorithmIdentifier
within the subjectPublicKeyInfo field of each certificate containing
a KEA public key with an 80-bit parameter identifier (OCTET STRING),
also known as the domain identifier. The domain identifier will be
computed in three steps: (1) the KEA parameters are DER encoded using
the Dss-Parms structure; (2) a 160-bit SHA-1 hash is generated from
the parameters; and (3) the 160-bit hash is reduced to 80-bits 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 80-bit value is the first octet in the octet
string.
The Dss-Parms is provided in [RFC 2459] and reproduced below for com-
pleteness.
Dss-Parms ::= SEQUENCE {
p INTEGER,
q INTEGER,
g INTEGER }
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), 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 fol-
lowing values may be asserted:
keyAgreement;
encipherOnly; and
decipherOnly.
The encipherOnly and decipherOnly values may only be asserted if the
keyAgreement value is also asserted. At most one of encipherOnly and
decipherOnly shall be asserted in keyUsage extension.
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3.3.5 Elliptic Curve Keys
This section describes object identifiers and data formats which may
be used with PKIX certificate profile to describe X.509 certificates
containing an ECDSA public key or signed with ECDSA. Conforming CAs
are required to use the object identifiers and data formats when
issuing ECDSA certificates. Conforming applications shall recognize
the object identifiers and process the data formats when processing
such certificates.
The Elliptic Curve Digital Signature Algorithm (ECDSA) is defined in
the ANSI X9.62 standard [X9.62]. The ASN.1 object identifiers used
to identify the ECDSA algorithm are defined in the following arc:
ansi-X9-62 OBJECT IDENTIFIER ::=
{ iso(1) member-body(2) us(840) 10045 }
When certificates contain an ECDSA public key, the id-ecPublicKey
algorithm identifier shall be used. The id-ecPublicKey algorithm
identifier is defined as follows:
id-public-key-type OBJECT IDENTIFIER ::= { ansi-X9.62 2 }
id-ecPublicKey OBJECT IDENTIFIER ::= { id-publicKeyType 1 }
ECDSA requires 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 }
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 named-
Curve choice, which is an an object identifier. When the parameters
are explicitly included, they shall be encoded in the ASN.1 structure
ECParameters:
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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
4.3.1] The value of ECPoint shall be the octet string representation
of an elliptic curve point following the conversion routine in
[X9.62, Section 4.4.3.b]
The components of type ECParameters have the following meanings:
* version specifies the version number of the elliptic curve parame-
ters. It shall have the value 1 for this version of the specifica-
tion. The notation above creates an INTEGER named ecpVer1 and gives
it a value of one. It is used to constrain version to a single value.
* fieldID identifies the finite field over which the elliptic curve
is defined. Finite fields are represented by values of the parameter-
ized 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 shall be represented as a value of type FieldEle-
ment, an OCTET STRING. seed is an optional parameter used to derive
the coefficients of a randomly generated elliptic curve.
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* base specifies the base point P on the elliptic curve. The base
point shall be 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. Note: This optional parameter
is not used in ECDSA, except in parameter validation. Parameter vali-
dation is not required by this specification. It is included for
compatibility with Elliptic Curve Key Agreement public key parame-
ters, and to support parameter validation.
The AlgorithmIdentifier within subjectPublicKeyInfo is the only place
within a certificate where the parameters may be used. If the ECDSA
algorithm parameters are absent from the subjectPublicKeyInfo Algor-
ithmIdentifier 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 ECDSA algorithm parameters are absent from the
subjectPublicKeyInfo AlgorithmIdentifier and the CA signed the certi-
ficate using a signature algorithm other than ECDSA, then clients
shall not validate the certificate.
FieldID ::= SEQUENCE { -- Finite field
fieldType OBJECT IDENTIFIER,
parameters ANY DEFINED BY fieldType
}
FieldID is a SEQUENCE of two components, fieldType and parameters.
In an instance of FieldID, "fieldType" will contain an object iden-
tifier value that uniquely identifies the type contained in "parame-
ters". The effect of referencing "fieldType" in both components of
the fieldID sequence is to tightly bind the object identifier and its
type.
The object identifier id-fieldType represents the root of a tree con-
taining the object identifiers of each field type. It has the follow-
ing value:
id-fieldType OBJECT IDENTIFIER ::= { ansi-X9-62 fieldType(1) }
The object identifiers prime-field and characteristic-two-field name
the two kinds of fields defined in this Standard. They have the fol-
lowing values:
prime-field OBJECT IDENTIFIER ::= { id-fieldType 1 }
Prime-p ::= INTEGER -- Field size p (p in bits)
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characteristic-two-field OBJECT IDENTIFIER ::= { id-fieldType 2 }
Characteristic-two ::= SEQUENCE {
m INTEGER, -- Field size 2^m
basis OBJECT IDENTIFIER,
parameters ANY DEFINED BY basis
}
The object identifier id-characteristic-two-basis represents the root
of a tree containing the object identifiers for each type of basis
for the characteristic-two finite fields. It has the following value:
id-characteristic-two-basis OBJECT IDENTIFIER ::= {
characteristic-two-field basisType(1) }
The object identifiers gnBasis, tpBasis and ppBasis name the three
kinds of basis for characteristic-two finite fields defined by
[X9.62]. They have the following values:
gnBasis OBJECT IDENTIFIER ::= { id-characteristic-two-basis 1 }
-- for gnBasis, the value of the paramters field is NULL
tpBasis OBJECT IDENTIFIER ::= { id-characteristic-two-basis 2 }
-- type of parameters field for tpBasis is Trinomial
Trinomial ::= INTEGER
ppBasis OBJECT IDENTIFIER ::= { id-characteristic-two-basis 3 }
-- type of parameters field for ppBasis is Pentanomial
Pentanomial ::= SEQUENCE {
k1 INTEGER,
k2 INTEGER,
k3 INTEGER
}
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, etc.; the least significant bit of the OCTET
STRING becomes the least significant bit of the BIT STRING.
The key usage extension may optionally appear in certificates which
convey an ECDSA public key. If a certificate containing an ECDSA
public key includes the keyUsage extension, only the following values
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may be asserted:
digitalSignature;
nonRepudiation;
keyCertSign; and
cRLSign.
The keyCertSign and cRLSign values may only be asserted if the
basicConstraints extension is present and cA is TRUE.
4 ASN.1 Module
PKIX1Algorithms88 { tbd }
DEFINITIONS EXPLICIT TAGS ::= BEGIN
-- EXPORTS All;
-- IMPORTS NONE;
----
---- DSA Keys and Signatures
----
----
-- OID for DSA public key
id-dsa OBJECT IDENTIFIER ::= {
iso(1) member-body(2) us(840) x9-57(10040) x9algorithm(4) 1 }
-- encoding for DSA public key
Dss-Parms ::= SEQUENCE {
p INTEGER,
q INTEGER,
g INTEGER }
-- OID for DSA signature generated with SHA-1 hash
id-dsa-with-sha1 OBJECT IDENTIFIER ::= {
iso(1) member-body(2) us(840) x9-57 (10040) x9algorithm(4) 3 }
-- encoding for DSA signature generated with SHA-1 hash
Dss-Sig-Value ::= SEQUENCE {
r INTEGER,
s INTEGER }
----
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---- RSA Keys and Signatures
----
----
-- arc for RSA public key and RSA signature OIDs
pkcs-1 OBJECT IDENTIFIER ::= {
iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1) 1 }
-- OID for RSA public keys
rsaEncryption OBJECT IDENTIFIER ::= { pkcs-1 1 }
-- OID for RSA signature generated with MD2 hash
md2WithRSAEncryption OBJECT IDENTIFIER ::= { pkcs-1 2 }
-- OID for RSA signature generated with MD5 hash
md5WithRSAEncryption OBJECT IDENTIFIER ::= { pkcs-1 4 }
sha1WithRSAEncryption OBJECT IDENTIFIER ::= { pkcs-1 5 }
----
---- Diffie-Hellman Keys
----
----
dhpublicnumber OBJECT IDENTIFIER ::= {
iso(1) member-body(2) us(840) ansi-x942(10046) number-type(2) 1 }
DomainParameters ::= SEQUENCE {
p INTEGER, -- odd prime, p=jq +1
g INTEGER, -- generator, g
q INTEGER, -- factor of p-1
j INTEGER OPTIONAL, -- subgroup factor, j>= 2
validationParms ValidationParms OPTIONAL }
ValidationParms ::= SEQUENCE {
seed BIT STRING,
pgenCounter INTEGER }
----
---- KEA Keys
----
----
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id-keyExchangeAlgorithm OBJECT IDENTIFIER ::=
{ 2 16 840 1 101 2 1 1 22 }
KEA-Parms-Id ::= OCTET STRING
----
---- ECDSA Keys, Signatures, and Curves
----
----
ansi-X9-62 OBJECT IDENTIFIER ::= {
iso(1) member-body(2) us(840) 10045 }
FieldID ::= SEQUENCE { -- Finite field
fieldType OBJECT IDENTIFIER,
parameters ANY DEFINED BY fieldType
}
-- ECDSA signatures
-- Arc for ECDSA signature OIDS
id-ecSigType OBJECT IDENTIFIER ::= { ansi-X9-62 signatures(4) }
-- OID for ECDSA signatures with SHA-1
ecdsa-with-SHA1 OBJECT IDENTIFIER ::= { id-ecSigType 1 }
-- OID for an elliptic curve signature
-- format for the value of an ECDSA signature value
ECDSA-Sig-Value ::= SEQUENCE {
r INTEGER,
s INTEGER
}
-- recognized field type OIDs are defined in the following arc
id-fieldType OBJECT IDENTIFIER ::= { ansi-X9-62 fieldType(1) }
-- where fieldType is prime-field, the parameters are of type Prime-p
prime-field OBJECT IDENTIFIER ::= { id-fieldType 1 }
Prime-p ::= INTEGER -- Finite field F(p), where p is an odd prime
-- where fieldType is characteristic-two-field, the parameters are
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-- of type Characteristic-two
characteristic-two-field OBJECT IDENTIFIER ::= { id-fieldType 2 }
Characteristic-two ::= 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
id-characteristic-two-basis OBJECT IDENTIFIER ::= {
characteristic-two-field basisType(3) }
-- gnbasis is identified by OID gnBasis and indicates
-- parameters are NULL
gnBasis OBJECT IDENTIFIER ::= { id-characteristic-two-basis 1 }
-- parameters for this basis are NULL
-- trinomial basis is identified by OID tpBasis and indicates
-- parameters of type Pentanomial
tpBasis OBJECT IDENTIFIER ::= { id-characteristic-two-basis 2 }
-- 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 ::= { id-characteristic-two-basis 3 }
Pentanomial ::= SEQUENCE {
--
-- Pentanomial basis representation of F2^m
-- reduction polynomial integers k1, k2, k3
-- f(x) = x**m + x**k3 + x**k2 + x**k1 + 1
--
k1 INTEGER,
k2 INTEGER,
k3 INTEGER
}
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-- The object identifiers gnBasis, tpBasis and ppBasis name
-- three kinds of basis for characteristic-two finite fields
FieldElement ::= OCTET STRING -- Finite field element
ECPoint ::= OCTET STRING -- Elliptic curve point
-- Elliptic Curve parameters may be specfied 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)}
Curve ::= SEQUENCE {
a FieldElement, -- Elliptic curve coefficient a
b FieldElement, -- Elliptic curve coefficient b
seed BIT STRING OPTIONAL
}
id-publicKeyType OBJECT IDENTIFIER ::= { ansi-X9-62 keyType(2) }
id-ecPublicKey OBJECT IDENTIFIER ::= { id-publicKeyType 1 }
-- Named Elliptic Curves
--
-- Standards bodies may define OIDs to represent common
-- elliptic curve parameters. Users are encouraged
-- to consult relevant standards and specifications to
-- determine which OIDs (if any) are appropriate for their
-- applications.
-- The following OIDS are defined in ANSI X9.62.
ellipticCurve OBJECT IDENTIFIER ::= { ansi-X9-62 curves(3) }
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c-TwoCurve OBJECT IDENTIFIER ::= {
ellipticCurve characteristicTwo(0) }
primeCurve OBJECT IDENTIFIER ::= { ellipticCurve prime(1) }
c2pnb163v1 OBJECT IDENTIFIER ::= { c-TwoCurve 1 }
c2pnb163v2 OBJECT IDENTIFIER ::= { c-TwoCurve 2 }
c2pnb163v3 OBJECT IDENTIFIER ::= { c-TwoCurve 3 }
c2pnb176w1 OBJECT IDENTIFIER ::= { c-TwoCurve 4 }
c2tnb191v1 OBJECT IDENTIFIER ::= { c-TwoCurve 5 }
c2tnb191v2 OBJECT IDENTIFIER ::= { c-TwoCurve 6 }
c2tnb191v3 OBJECT IDENTIFIER ::= { c-TwoCurve 7 }
c2onb191v4 OBJECT IDENTIFIER ::= { c-TwoCurve 8 }
c2onb191v5 OBJECT IDENTIFIER ::= { c-TwoCurve 9 }
c2pnb208w1 OBJECT IDENTIFIER ::= { c-TwoCurve 10 }
c2tnb239v1 OBJECT IDENTIFIER ::= { c-TwoCurve 11 }
c2tnb239v2 OBJECT IDENTIFIER ::= { c-TwoCurve 12 }
c2tnb239v3 OBJECT IDENTIFIER ::= { c-TwoCurve 13 }
c2onb239v4 OBJECT IDENTIFIER ::= { c-TwoCurve 14 }
c2onb239v5 OBJECT IDENTIFIER ::= { c-TwoCurve 15 }
c2pnb272w1 OBJECT IDENTIFIER ::= { c-TwoCurve 16 }
c2pnb304w1 OBJECT IDENTIFIER ::= { c-TwoCurve 17 }
c2tnb359v1 OBJECT IDENTIFIER ::= { c-TwoCurve 18 }
c2pnb368w1 OBJECT IDENTIFIER ::= { c-TwoCurve 19 }
c2tnb431r1 OBJECT IDENTIFIER ::= { c-TwoCurve 20 }
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
5 References
[FIPS 180-1] Federal Information Processing Standards Publication
(FIPS PUB) 180-1, Secure Hash Standard, 17 April 1995.
[Supersedes FIPS PUB 180 dated 11 May 1993.]
[FIPS 186] Federal Information Processing Standards Publication
(FIPS PUB) 186, Digital Signature Standard, 18 May 1994.
[P1363] IEEE P1363, "Standard for Public-Key Cryptography", draft
standard, 1997.
Bassham, Housley & Polk [Page 24]
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[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] P.V. Mockapetris, "Domain names - concepts and
facilities", November 1987.
[RFC 1319] Kaliski, B., "The MD2 Message-Digest Algorithm," RFC 1319,
RSA Laboratories, April 1992.
[RFC 1321] Rivest, R., "The MD5 Message-Digest Algorithm," RFC 1321,
MIT and RSA Data Security, April 1992.
[RFC 1422] Kent, S., "Privacy Enhancement for Internet Electronic
Mail: Part II: Certificate-Based Key Management," RFC
1422, BBN Communications, February 1993.
[RFC 1423] Balenson, D., "Privacy Enhancement for Internet Electronic
Mail: Part III: Algorithms, Modes, and Identifiers,"
RFC 1423, Trusted Information Systems, February 1993.
[RFC 2313] B. Kaliski, "PKCS #1: RSA Encryption Version 1.5",
March 1998.
[RFC 2459] R. Housley, W. Ford, W. Polk and D. Solo "Internet X.509
Public Key Infrastructure: Certificate and CRL Profile",
January, 1999.
[SDN.701] SDN.701, "Message Security Protocol 4.0", Revision A
1997-02-06.
[X.208] CCITT Recommendation X.208: Specification of Abstract
Syntax Notation One (ASN.1), 1988.
[X9.42] ANSI X9.42-199x, Public Key Cryptography for The Financial
Services Industry: Agreement of Symmetric Algorithm Keys
Using Diffie-Hellman (Working Draft), December 1997.
[X9.62] X9.62-1999, "Public Key Cryptography For The Financial
Services Industry: The Elliptic Curve Digital Signature
Algorithm (ECDSA)".
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 docu-
ment. For more information, consult the online list of claimed
Bassham, Housley & Polk [Page 25]
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rights.
The IETF takes no position regarding the validity or scope of any
intellectual property or other rights that might be claimed to per-
tain 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 standards-track and standards-
related documentation can be found in BCP-11. 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 Security Considerations
This specification does not constrain the key sizes or identify par-
ticular elliptic curves for use in the Internet PKI. However, both
the key size and the particular curve selected impact the the
strength of the digital signatures. Some curves are cryptographically
stronger than others!
In general, use of "well-known" curves, such as the "named curves"
from ANSI X9.62 is a sound strategy. For additional information,
refer to X9.62 Appendix D.4, "Key Length Considerations" and Appendix
F.1, "Avoiding Cryptographically Weak Keys".
This specification is a profile of RFC 2459. The security considera-
tions section of that document applies to this specification as well.
8 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 docu-
ment. 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 per-
tain 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 standards-track and standards-
related documentation can be found in BCP-11. Copies of claims of
rights made available for publication and any assurances of licenses
Bassham, Housley & Polk [Page 26]
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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.
9 Author Addresses:
Larry Bassham
NIST
100 Bureau Drive, Stop 8930
Gaithersburg, MD 20899-8930
USA
lbassham@nist.gov
Russ Housley
SPYRUS
381 Elden Street
Suite 1120
Herndon, VA 20170
housley@spyrus.com
Tim Polk
NIST
100 Bureau Drive, Stop 8930
Gaithersburg, MD 20899-8930
USA
tim.polk@nist.gov
10 Full Copyright Statement
Copyright (C) The Internet Society (date). 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. In addition, the
ASN.1 modules presented in Appendices A and B may be used in whole or
in part without inclusion of the copyright notice. 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 develop-
ing Internet standards in which case the procedures for copyrights
defined in the Internet Standards process shall be followed, or as
required to translate it into languages other than English.
The limited permissions granted above are perpetual and will not be
Bassham, Housley & Polk [Page 27]
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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.
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