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<?xml version="1.0" encoding="latin1" ?>
<!DOCTYPE chapter SYSTEM "chapter.dtd">
<chapter>
<header>
<copyright>
<year>2003</year><year>2009</year>
<holder>Ericsson AB. All Rights Reserved.</holder>
</copyright>
<legalnotice>
The contents of this file are subject to the Erlang Public License,
Version 1.1, (the "License"); you may not use this file except in
compliance with the License. You should have received a copy of the
Erlang Public License along with this software. If not, it can be
retrieved online at http://www.erlang.org/.
Software distributed under the License is distributed on an "AS IS"
basis, WITHOUT WARRANTY OF ANY KIND, either express or implied. See
the License for the specific language governing rights and limitations
under the License.
</legalnotice>
<title>PKIX Certificates</title>
<prepared>UAB/F/P Peter Högfeldt</prepared>
<docno></docno>
<date>2003-06-09</date>
<rev>A</rev>
<file>pkix_certs.xml</file>
</header>
<section>
<title>Introduction to Certificates</title>
<p>Certificates were originally defined by ITU (CCITT) and the latest
definitions are described in <cite id="X.509"></cite>, but those definitions
are (as always) not working.
</p>
<p>Working certificate definitions for the Internet Community are found
in the the PKIX RFCs <cite id="rfc3279"></cite>and <cite id="rfc3280"></cite>.
The parsing of certificates in the Erlang/OTP SSL application is
based on those RFCS.
</p>
<p>Certificates are defined in terms of ASN.1 (<cite id="X.680"></cite>).
For an introduction to ASN.1 see <url href="http://asn1.elibel.tm.fr/">ASN.1 Information Site</url>.
</p>
</section>
<section>
<title>PKIX Certificates</title>
<p>Here we base the PKIX certificate definitions in RFCs <cite id="rfc3279"></cite>and <cite id="rfc3280"></cite>. We however present the
definitions according to <c>SSL-PKIX.asn1</c> module,
which is an amelioration of the <c>PKIX1Explicit88.asn1</c>,
<c>PKIX1Implicit88.asn1</c>, and <c>PKIX1Algorithms88.asn1</c>
modules. You find all these modules in the <c>pkix</c> subdirectory
of SSL.
</p>
<p>The Erlang terms that are returned by the functions
<c>ssl:peercert/1/2</c>, <c>ssl_pkix:decode_cert/1/2</c>, and
<c>ssl_pkix:decode_cert_file/1/2</c> when the option <c>ssl</c>
is used in those functions, correspond the ASN.1 structures
described in the sequel.
</p>
<section>
<title>Certificate and TBSCertificate</title>
<code type="none">
Certificate ::= SEQUENCE {
tbsCertificate TBSCertificate,
signatureAlgorithm SignatureAlgorithm,
signature BIT STRING }
TBSCertificate ::= SEQUENCE {
version [0] Version DEFAULT v1,
serialNumber CertificateSerialNumber,
signature SignatureAlgorithm,
issuer Name,
validity Validity,
subject Name,
subjectPublicKeyInfo SubjectPublicKeyInfo,
issuerUniqueID [1] IMPLICIT UniqueIdentifier OPTIONAL,
-- If present, version MUST be v2 or v3
subjectUniqueID [2] IMPLICIT UniqueIdentifier OPTIONAL,
-- If present, version MUST be v2 or v3
extensions [3] Extensions OPTIONAL
-- If present, version MUST be v3 -- }
Version ::= INTEGER { v1(0), v2(1), v3(2) }
CertificateSerialNumber ::= INTEGER
Validity ::= SEQUENCE {
notBefore Time,
notAfter Time }
Time ::= CHOICE {
utcTime UTCTime,
generalTime GeneralizedTime }
</code>
<p>The meaning of the fields <c>version</c>, <c>serialNumber</c>,
and <c>validity</c> are quite obvious given the type definitions
above, so we do not go further into their details.
</p>
<p>The <c>signatureAlgorithm</c> field of <c>Certificate</c> and
the <c>signature</c> field of <c>TBSCertificate</c> contain
the name and parameters of the algorithm used for signing the
certificate. The values of these two fields must be equal.
</p>
<p>The <c>signature</c> field of <c>Certificate</c> contains the
value of the signature that the issuer computed by using the
prescribed algorithm.
</p>
<p>The <c><![CDATA[issuer<c> and <c>subject]]></c> fields can contain many
different types av data, and is therefore considered in a
separate section. The same holds for the <c>extensions</c>
field.
The <c>issuerUniqueID</c> and the <c>subjectUniqueID</c> fields
are not considered further.</p>
</section>
<section>
<title>TBSCertificate issuer and subject</title>
<p></p>
<code type="none"><![CDATA[
Name ::= CHOICE { -- only one possibility for now --
rdnSequence RDNSequence }
RDNSequence ::= SEQUENCE OF RelativeDistinguishedName
DistinguishedName ::= RDNSequence
RelativeDistinguishedName ::=
SET SIZE (1 .. MAX) OF AttributeTypeAndValue
AttributeTypeAndValue ::= SEQUENCE {
type ATTRIBUTE-TYPE-AND-VALUE-CLASS.&id
\011\011({SupportedAttributeTypeAndValues}),
value ATTRIBUTE-TYPE-AND-VALUE-CLASS.&Type
\011\011({SupportedAttributeTypeAndValues}{@type}) }
SupportedAttributeTypeAndValues ATTRIBUTE-TYPE-AND-VALUE-CLASS ::=
\011{ name | surname | givenName | initials | generationQualifier |
\011 commonName | localityName | stateOrProvinceName | organizationName |
\011 organizationalUnitName | title | dnQualifier | countryName |
\011 serialNumber | pseudonym | domainComponent | emailAddress } ]]></code>
</section>
<section>
<title>TBSCertificate extensions</title>
<p>The <c>extensions</c> field of a <c>TBScertificate</c> is a
sequence of type <c>Extension</c>, defined as follows,</p>
<code type="none">
Extension ::= SEQUENCE {
extnID OBJECT IDENTIFIER,
critical BOOLEAN DEFAULT FALSE,
extnValue ANY } </code>
<p>Each extension has a unique object identifier. An extension
with a <c>critical</c> value set to <c>TRUE</c><em>must</em>
be recognised by the reader of a certificate, or else the
certificate must be rejected.
</p>
<p>Extensions are divided into two groups: standard extensions
and internet certificate extensions. All extensions listed in
the table that follows are standard extensions, except for
<c>authorityInfoAccess</c> and <c>subjectInfoAccess</c>, which
are internet extensions.
</p>
<p>Depending on the object identifier the <c>extnValue</c> is
parsed into an appropriate welldefined structure.
</p>
<p>The following table shows the purpose of each extension, but
does not specify the structure. To see the structure consult
the <c>PKIX1Implicit88.asn1</c> module.
</p>
<table>
<row>
<cell align="left" valign="middle">authorityKeyIdentifier</cell>
<cell align="left" valign="middle">Used by to identify a certificate signed that has multiple signing keys. </cell>
</row>
<row>
<cell align="left" valign="middle">subjectKeyIdentifier</cell>
<cell align="left" valign="middle">Used to identify certificates that contain a public key. Must appear i CA certificates.</cell>
</row>
<row>
<cell align="left" valign="middle">keyUsage </cell>
<cell align="left" valign="middle">Defines the purpose of the certificate. Can be one or several of<c>digitalSignature</c>, <c>nonRepudiation</c>,<c>keyEncipherment</c>, <c>dataEncipherment</c>,<c>keyAgreement</c>, <c>keyCertSign</c>, <c>cRLSign</c>,<c>encipherOnly</c>, <c>decipherOnly</c>.</cell>
</row>
<row>
<cell align="left" valign="middle">privateKeyUsagePeriod </cell>
<cell align="left" valign="middle">Allows certificate issuer to provide a private key usage period to be short than the certificate usage period.</cell>
</row>
<row>
<cell align="left" valign="middle">certificatePolicies</cell>
<cell align="left" valign="middle">Contains one or more policy information terms indicating the policies under which the certificate has been issued.</cell>
</row>
<row>
<cell align="left" valign="middle">policyMappings</cell>
<cell align="left" valign="middle">Used i CA certificates. </cell>
</row>
<row>
<cell align="left" valign="middle">subjectAltName</cell>
<cell align="left" valign="middle">Allows additional identities to be bound the the subject. </cell>
</row>
<row>
<cell align="left" valign="middle">issuerAltName</cell>
<cell align="left" valign="middle">Allows additional identities to be bound the the issuer.</cell>
</row>
<row>
<cell align="left" valign="middle">subjectDirectoryAttributes</cell>
<cell align="left" valign="middle">Conveys identity attributes of the subject.</cell>
</row>
<row>
<cell align="left" valign="middle">basicConstraints</cell>
<cell align="left" valign="middle">Tells if the certificate holder is a CA or not.</cell>
</row>
<row>
<cell align="left" valign="middle">nameConstraints</cell>
<cell align="left" valign="middle">Used in CA certificates.</cell>
</row>
<row>
<cell align="left" valign="middle">policyConstraints</cell>
<cell align="left" valign="middle">Used in CA certificates.</cell>
</row>
<row>
<cell align="left" valign="middle">extKeyUsage</cell>
<cell align="left" valign="middle">Indicates for which purposed the public key may be used. </cell>
</row>
<row>
<cell align="left" valign="middle">cRLDistributionPoints</cell>
<cell align="left" valign="middle">Indicates how CRL (Certificate Revokation List) information is obtained.</cell>
</row>
<row>
<cell align="left" valign="middle">inhibitAnyPolicy</cell>
<cell align="left" valign="middle">Used i CA certificates.</cell>
</row>
<row>
<cell align="left" valign="middle">freshestCRL</cell>
<cell align="left" valign="middle">For CRLs.</cell>
</row>
<row>
<cell align="left" valign="middle">authorityInfoAccess</cell>
<cell align="left" valign="middle">How to access CA information of the issuer of the certificate.</cell>
</row>
<row>
<cell align="left" valign="middle">subjectInfoAccess</cell>
<cell align="left" valign="middle">How to access CA information of the subject of the certificate.</cell>
</row>
<tcaption>PKIX Extensions</tcaption>
</table>
</section>
</section>
</chapter>
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