path: root/lib/public_key/doc/src/public_key.xml

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<!DOCTYPE erlref SYSTEM "erlref.dtd">

<erlref>
  <header>
    <copyright>
      <year>2008</year>
      <year>2016</year>
      <holder>Ericsson AB, All Rights Reserved</holder>
    </copyright>
    <legalnotice>
  Licensed under the Apache License, Version 2.0 (the "License");
  you may not use this file except in compliance with the License.
  You may obtain a copy of the License at
 
      http://www.apache.org/licenses/LICENSE-2.0

  Unless required by applicable law or agreed to in writing, software
  distributed under the License is distributed on an "AS IS" BASIS,
  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  See the License for the specific language governing permissions and
  limitations under the License.

  The Initial Developer of the Original Code is Ericsson AB.
    </legalnotice>

    <title>public_key</title>
    <prepared>Ingela Anderton Andin</prepared>
    <responsible></responsible>
    <docno></docno>
    <date></date>
    <rev></rev>
  </header>
  <module>public_key</module>
  <modulesummary>API module for public-key infrastructure.</modulesummary>
  <description>
    <p>Provides functions to handle public-key infrastructure,
    for details see
    <seealso marker="public_key_app">public_key(6)</seealso>.
    </p>
  </description>

  <section>
    <title>DATA TYPES</title> 
    
    <note><p>All records used in this Reference Manual 
    <!--     except #policy_tree_node{}  -->
    are generated from ASN.1 specifications
    and are documented in the User's Guide. See <seealso 
    marker="public_key_records">Public-key Records</seealso>.
    </p></note>
    
    <p>Use the following include directive to get access to the 
    records and constant macros described here and in the User's Guide:</p>
    
    <code> -include_lib("public_key/include/public_key.hrl").</code>

    <p>The following data types are used in the functions for <c>public_key</c>:</p>

    <taglist>
      <tag><c>oid()</c></tag>
      <item><p>Object identifier, a tuple of integers as generated by the <c>ASN.1</c> compiler.</p></item>

      <tag><c>boolean() =</c></tag>
      <item><p><c>true | false</c></p></item>
      
      <tag><c>string() =</c></tag>
      <item><p><c>[bytes()]</c></p></item>

      <tag><c>der_encoded() =</c></tag>
      <item><p><c>binary()</c></p></item>

      <tag><c>pki_asn1_type() =</c></tag>
      <item>
	<p><c>'Certificate'</c></p>
	<p><c>| 'RSAPrivateKey'</c></p>
	<p><c>| 'RSAPublicKey'</c></p>
	<p><c>| 'DSAPrivateKey'</c></p>
	<p><c>| 'DSAPublicKey'</c></p>
	<p><c>| 'DHParameter'</c></p>
	<p><c>| 'SubjectPublicKeyInfo'</c></p>
	<p><c>| 'PrivateKeyInfo'</c></p>
	<p><c>| 'CertificationRequest'</c></p>
	<p><c>| 'CertificateList'</c></p>
	<p><c>| 'ECPrivateKey'</c></p>
	<p><c>| 'EcpkParameters'</c></p>
      </item>

      <tag><c>pem_entry () =</c></tag>
      <item><p><c>{pki_asn1_type(), binary(), %% DER or encrypted DER</c></p>
      <p><c> not_encrypted | cipher_info()}</c></p></item>
      
      <tag><c>cipher_info() = </c></tag>
      <item><p><c>{"RC2-CBC" | "DES-CBC" | "DES-EDE3-CBC", crypto:strong_rand_bytes(8)</c></p>
      <p><c>| {#'PBEParameter{}, digest_type()} | #'PBES2-params'{}}</c></p>
      </item>
      
      <tag><c>public_key() =</c></tag>
      <item><p><c>rsa_public_key() | dsa_public_key() | ec_public_key()</c></p></item>
      
      <tag><c>private_key() =</c></tag>
      <item><p><c>rsa_private_key() | dsa_private_key() | ec_private_key()</c></p></item>

      <tag><c>rsa_public_key() =</c></tag>
      <item><p><c>#'RSAPublicKey'{}</c></p></item>

      <tag><c>rsa_private_key() =</c></tag>
      <item><p><c>#'RSAPrivateKey'{}</c></p></item>

      <tag><c>dsa_public_key() =</c></tag>
      <item><p><c>{integer(),  #'Dss-Parms'{}}</c></p></item>

      <tag><c>dsa_private_key() =</c></tag>
      <item><p><c>#'DSAPrivateKey'{}</c></p></item>

      <tag><c>ec_public_key()</c></tag>
      <item><p>= <c>{#'ECPoint'{}, #'ECParameters'{} | {namedCurve, oid()}}</c></p></item>

      <tag><c>ec_private_key() =</c></tag>
      <item><p><c>#'ECPrivateKey'{}</c></p></item>

      <tag><c>public_crypt_options() =</c></tag>
      <item><p><c>[{rsa_pad, rsa_padding()}]</c></p></item>

      <tag><c>rsa_padding() =</c></tag>
      <item>
	<p><c>'rsa_pkcs1_padding'</c></p>
	<p><c>| 'rsa_pkcs1_oaep_padding'</c></p>
	<p><c>| 'rsa_no_padding'</c></p>
      </item>

      <tag><c>digest_type() = </c></tag>
      <item><p>Union of <c>rsa_digest_type()</c>, <c>dss_digest_type()</c>, 
      and <c>ecdsa_digest_type()</c>.</p></item>

      <tag><c>rsa_digest_type() = </c></tag>
      <item><p><c>'md5' | 'sha' | 'sha224' | 'sha256' | 'sha384' | 'sha512'</c></p></item>

      <tag><c>dss_digest_type() = </c></tag>
      <item><p><c>'sha'</c></p></item>

      <tag><c>ecdsa_digest_type() = </c></tag>
      <item><p><c>'sha'| 'sha224' | 'sha256' | 'sha384' | 'sha512'</c></p></item>
      
      <tag><c>crl_reason() = </c></tag>
      <item>
	<p><c>unspecified</c></p>
	<p><c>| keyCompromise</c></p>
	<p><c>| cACompromise</c></p>
	<p><c>| affiliationChanged</c></p>
	<p><c>| superseded</c></p>
	<p><c>| cessationOfOperation</c></p>
	<p><c>| certificateHold</c></p>
	<p><c>| privilegeWithdrawn</c></p>
	<p><c>| aACompromise</c></p>
      </item>

      <tag><c>issuer_name() =</c></tag>
      <item><p><c>{rdnSequence,[#'AttributeTypeAndValue'{}]}</c></p>  
      </item>
      
      <tag><c>ssh_file() =</c></tag>
      <item>
	<p><c>openssh_public_key</c></p>
	<p><c>| rfc4716_public_key</c></p>
	<p><c>| known_hosts</c></p>
	<p><c>| auth_keys</c></p>
      </item>
    </taglist>
    
    
<!--     <p><code>policy_tree() = [Root, Children]</code></p> -->
    
<!--     <p><code>Root = #policy_tree_node{}</code></p>    -->

<!--     <p><code>Children = [] | policy_tree()</code></p> -->
	
<!--     <p>The <c>policy_tree_node</c> record has the following fields:</p> -->
    
<!--     <taglist> -->
      
<!--       <tag>valid_policy</tag> -->
<!--       <item>A single policy OID representing a -->
<!--          valid policy for the path of length x.</item> -->
      
<!--       <tag>qualifier_set</tag> -->
<!--       <item>A set of policy qualifiers associated -->
<!--          with the valid policy in certificate x.</item> -->
      
<!--       <tag>critically_indicator</tag> -->
<!--       <item>Indicates whether the -->
<!--          certificate policy extension in certificate x was marked as -->
<!--          critical.</item> -->
      
<!--       <tag>expected_policy_set</tag> -->
<!--       <item>Contains one or more policy OIDs -->
<!--          that would satisfy this policy in the certificate x+1.</item>         -->
<!--     </taglist> -->
  </section> 

<funcs>    

  <func>
    <name>compute_key(OthersKey, MyKey)-></name>
    <name>compute_key(OthersKey, MyKey, Params)-></name>
    <fsummary>Computes shared secret.</fsummary>
    <type>
      <v>OthersKey = #'ECPoint'{} | binary(), MyKey = #'ECPrivateKey'{} | binary()</v>
      <v>Params =  #'DHParameter'{}</v>
    </type>
  <desc>
    <p>Computes shared secret.</p>
  </desc>
  </func>

  <func>
    <name>decrypt_private(CipherText, Key) -> binary()</name>
    <name>decrypt_private(CipherText, Key, Options) -> binary()</name>
    <fsummary>Public-key decryption.</fsummary>
    <type>
      <v>CipherText = binary()</v>
      <v>Key = rsa_private_key()</v>
      <v>Options = public_crypt_options()</v>
  </type> 
  <desc> 
    <p>Public-key decryption using the private key. See also <seealso
	marker="crypto:crypto#private_decrypt/4">crypto:private_decrypt/4</seealso></p> 
  </desc> 
  </func>

  <func>
    <name>decrypt_public(CipherText, Key) - > binary()</name>
    <name>decrypt_public(CipherText, Key, Options) - > binary()</name>
    <fsummary>Public-key decryption.</fsummary>
    <type>
      <v>CipherText = binary()</v>
      <v>Key = rsa_public_key()</v>
      <v>Options = public_crypt_options()</v>
  </type> 
  <desc> 
    <p>Public-key decryption using the public key. See also <seealso
	marker="crypto:crypto#public_decrypt/4">crypto:public_decrypt/4</seealso></p> 
  </desc> 
  </func> 

  <func>
    <name>der_decode(Asn1type, Der) -> term()</name>
    <fsummary>Decodes a public-key ASN.1 DER encoded entity.</fsummary>
    <type>
      <v>Asn1Type = atom()</v>
      <d>ASN.1 type present in the Public Key applications
      ASN.1 specifications.</d>
      <v>Der = der_encoded()</v>
    </type> 
    <desc> 
      <p>Decodes a public-key ASN.1 DER encoded entity.</p>
    </desc> 
  </func>
    
  <func>
    <name>der_encode(Asn1Type, Entity) -> der_encoded()</name>
    <fsummary>Encodes a public-key entity with ASN.1 DER encoding.</fsummary>
    <type>
      <v>Asn1Type = atom()</v>
      <d>ASN.1 type present in the Public Key applications
	 ASN.1 specifications.</d>
      <v>Entity = term()</v>
      <d>Erlang representation of <c>Asn1Type</c></d>
  </type> 
  <desc> 
    <p>Encodes a public-key entity with ASN.1 DER encoding.</p>
  </desc> 
  </func>

  <func>
    <name>dh_gex_group(MinSize, SuggestedSize, MaxSize, Groups) -> {ok, {Size,Group}} | {error,Error}</name>
    <fsummary>Selects a group for Diffie-Hellman key exchange</fsummary>
    <type>
      <v>MinSize = positive_integer()</v>
      <v>SuggestedSize = positive_integer()</v>
      <v>MaxSize = positive_integer()</v>
      <v>Groups = undefined | [{Size,[{G,P}]}]</v>
      <v>Size = positive_integer()</v>
      <v>Group = {G,P}</v>
      <v>G = positive_integer()</v>
      <v>P = positive_integer()</v>
    </type>
    <desc>
      <p>Selects a group for Diffie-Hellman key exchange with the key size in the range <c>MinSize...MaxSize</c>
      and as close to <c>SuggestedSize</c> as possible. If <c>Groups == undefined</c> a default set will be
      used, otherwise the group is selected from <c>Groups</c>.</p>
      <p>First a size, as close as possible to SuggestedSize, is selected. Then one group with that key size
      is randomly selected from the specified set of groups. If no size within the limits of <c>MinSize</c>
      and <c>MaxSize</c> is available, <c>{error,no_group_found}</c> is returned.</p>
      <p>The default set of groups is listed in <c>lib/public_key/priv/moduli</c>. This file may be regenerated like this:</p>
      <pre>
	$> cd $ERL_TOP/lib/public_key/priv/
	$> generate
         ---- wait until all background jobs has finished. It may take several days !
	$> cat moduli-* > moduli
	$> cd ..; make 
      </pre>
    </desc>
  </func>

    <func>
    <name>encrypt_private(PlainText, Key) -> binary()</name>
    <fsummary>Public-key encryption using the private key.</fsummary>
    <type>
      <v>PlainText = binary()</v>
      <v>Key = rsa_private_key()</v> 
  </type> 
  <desc> 
    <p>Public-key encryption using the private key.
     See also <seealso
	marker="crypto:crypto#private_encrypt/4">crypto:private_encrypt/4</seealso>.</p> 
  </desc> 
  </func>   

  <func>
    <name>encrypt_public(PlainText, Key) -> binary()</name>
    <fsummary>Public-key encryption using the public key.</fsummary>
    <type>
      <v>PlainText = binary()</v>
      <v>Key = rsa_public_key()</v> 
  </type> 
  <desc> 
    <p>Public-key encryption using the public key. See also <seealso
	marker="crypto:crypto#public_encrypt/4">crypto:public_encrypt/4</seealso>.</p> 
  </desc> 
  </func>   
  
  <func>
    <name>generate_key(Params) -> {Public::binary(), Private::binary()}  | #'ECPrivateKey'{} </name>
    <fsummary>Generates a new keypair.</fsummary>
    <type>
      <v>Params = #'DHParameter'{} |  {namedCurve, oid()} |  #'ECParameters'{}</v>
    </type>
  <desc>
    <p>Generates a new keypair.</p>
  </desc>
  </func>

  <func>
    <name>pem_decode(PemBin) -> [pem_entry()]</name>
    <fsummary>Decodes PEM binary data and returns
    entries as ASN.1 DER encoded entities.</fsummary>
    <type>
      <v>PemBin = binary()</v>
      <d>Example {ok, PemBin} = file:read_file("cert.pem").</d>
    </type> 
  <desc> 
    <p>Decodes PEM binary data and returns
    entries as ASN.1 DER encoded entities.</p>
  </desc> 
  </func> 
    
   <func>
    <name>pem_encode(PemEntries) -> binary()</name>
    <fsummary>Creates a PEM binary.</fsummary>
    <type>
      <v> PemEntries = [pem_entry()] </v> 
  </type> 
  <desc> 
    <p>Creates a PEM binary.</p> 
  </desc> 
  </func>

   <func>
    <name>pem_entry_decode(PemEntry) -> term()</name>
    <name>pem_entry_decode(PemEntry, Password) -> term()</name>
    <fsummary>Decodes a PEM entry.</fsummary>
    <type>
      <v>PemEntry = pem_entry()</v> 
      <v>Password = string()</v> 
  </type> 
  <desc> 
    <p>Decodes a PEM entry. <c>pem_decode/1</c> returns a list of PEM
    entries. Notice that if the PEM entry is of type
    'SubjectPublickeyInfo', it is further decoded to an
    <c>rsa_public_key()</c> or <c>dsa_public_key()</c>.</p>
  </desc> 
  </func>

   <func>
    <name>pem_entry_encode(Asn1Type, Entity) -> pem_entry()</name>
    <name>pem_entry_encode(Asn1Type, Entity, {CipherInfo, Password}) -> pem_entry()</name>
    <fsummary>Creates a PEM entry that can be fed to <c>pem_encode/1</c>.</fsummary>
    <type>
      <v>Asn1Type = pki_asn1_type()</v>
      <v>Entity = term()</v>
      <d>Erlang representation of
      <c>Asn1Type</c>.  If <c>Asn1Type</c> is 'SubjectPublicKeyInfo',
      <c>Entity</c> must be either an <c>rsa_public_key()</c>, 
      <c>dsa_public_key()</c> or an <c>ec_public_key()</c>
      and this function creates the appropriate
      'SubjectPublicKeyInfo' entry.
      </d>
      <v>CipherInfo = cipher_info()</v>
      <v>Password = string()</v> 
    </type> 
  <desc> 
    <p>Creates a PEM entry that can be feed to <c>pem_encode/1</c>.</p>
  </desc> 
  </func>
  
  <func>
    <name>pkix_decode_cert(Cert, otp|plain) ->  #'Certificate'{} | #'OTPCertificate'{}</name>
    <fsummary>Decodes an ASN.1 DER-encoded PKIX x509 certificate.</fsummary>
    <type>
      <v>Cert = der_encoded()</v> 
  </type> 
  <desc> 
    <p>Decodes an ASN.1 DER-encoded PKIX certificate. Option <c>otp</c>
    uses the customized ASN.1 specification OTP-PKIX.asn1 for
    decoding and also recursively decode most of the standard
    parts.</p>
  </desc> 
  </func>

  <func>
    <name>pkix_encode(Asn1Type, Entity, otp | plain) -> der_encoded()</name>
    <fsummary>DER encodes a PKIX x509 certificate or part of such a
    certificate.</fsummary>
    <type>
      <v>Asn1Type = atom()</v>
      <d>The ASN.1 type can be 'Certificate', 'OTPCertificate' or a subtype of either.</d>
      <v>Entity = #'Certificate'{} | #'OTPCertificate'{} | a valid subtype</v>
  </type> 
  <desc> 
    <p>DER encodes a PKIX x509 certificate or part of such a
    certificate. This function must be used for encoding certificates or parts of certificates
    that are decoded/created in the <c>otp</c> format, whereas for the plain format this
    function directly calls <c>der_encode/2</c>.</p> 
  </desc> 
  </func>

 <func>
    <name>pkix_is_issuer(Cert, IssuerCert) -> boolean()</name>
    <fsummary>Checks if <c>IssuerCert</c> issued <c>Cert</c>.</fsummary>
    <type>
      <v>Cert = der_encoded() | #'OTPCertificate'{} | #'CertificateList'{}</v>
      <v>IssuerCert = der_encoded() | #'OTPCertificate'{}</v>
  </type> 
  <desc> 
    <p>Checks if <c>IssuerCert</c> issued <c>Cert</c>.</p> 
  </desc> 
  </func>
  
  <func>
    <name>pkix_is_fixed_dh_cert(Cert) -> boolean()</name>
    <fsummary>Checks if a certificate is a fixed Diffie-Hellman certificate.</fsummary>
    <type>
        <v>Cert = der_encoded() | #'OTPCertificate'{}</v>
  </type> 
  <desc> 
    <p>Checks if a certificate is a fixed Diffie-Hellman certificate.</p> 
  </desc> 
  </func>  
  
  <func>
    <name>pkix_is_self_signed(Cert) -> boolean()</name>
    <fsummary>Checks if a certificate is self-signed.</fsummary>
    <type>
       <v>Cert = der_encoded() | #'OTPCertificate'{}</v>
  </type> 
  <desc> 
    <p>Checks if a certificate is self-signed.</p> 
  </desc> 
  </func>

  <func>
    <name>pkix_issuer_id(Cert, IssuedBy) -> {ok, IssuerID} | {error, Reason}</name>
    <fsummary>Returns the issuer id.</fsummary>
    <type>
        <v>Cert = der_encoded() | #'OTPCertificate'{}</v>
	<v>IssuedBy = self | other</v>
	<v>IssuerID = {integer(), issuer_name()}</v>
	<d>The issuer id consists of the serial number and the issuers name.</d>
	<v>Reason = term()</v>
    </type> 
    <desc> 
    <p>Returns the issuer id.</p> 
    </desc> 
  </func>
  
 
  <func>
    <name>pkix_normalize_name(Issuer) -> Normalized</name>
    <fsummary>Normalizes an issuer name so that it can be easily
    compared to another issuer name.</fsummary>
    <type>
      <v>Issuer = issuer_name()</v>
      <v>Normalized = issuer_name()</v>
  </type> 
  <desc> 
    <p>Normalizes an issuer name so that it can be easily
    compared to another issuer name.</p> 
  </desc> 
  </func>
   
  <func>
    <name>pkix_path_validation(TrustedCert, CertChain, Options) -> {ok, {PublicKeyInfo, PolicyTree}} | {error, {bad_cert, Reason}} </name>
    <fsummary>Performs a basic path validation according to RFC 5280.</fsummary>
     <type>
       <v>TrustedCert =  #'OTPCertificate'{} | der_encoded() | atom()</v>
       <d>Normally a trusted certificate, but it can also be a path-validation
       error that can be discovered while
       constructing the input to this function and that is to be run through the <c>verify_fun</c>.
       Examples are <c>unknown_ca</c> and <c>selfsigned_peer.</c>
       </d>
       <v>CertChain = [der_encoded()]</v>
       <d>A list of DER-encoded certificates in trust order ending with the peer certificate.</d>
       <v>Options = proplists:proplist()</v>
       <v>PublicKeyInfo = {?'rsaEncryption' | ?'id-dsa',
       rsa_public_key() | integer(), 'NULL' | 'Dss-Parms'{}}</v>
       <v>PolicyTree = term()</v>
       <d>At the moment this is always an empty list as policies are not currently supported.</d>
       <v>Reason = cert_expired | invalid_issuer | invalid_signature | name_not_permitted |
       missing_basic_constraint | invalid_key_usage | {revoked, crl_reason()} | atom()
       </v>
     </type>
     <desc>
       <p>
	 Performs a basic path validation according to
	 <url href="http://www.ietf.org/rfc/rfc5280.txt">RFC 5280.</url>
	 However, CRL validation is done separately by <seealso
	 marker="#pkix_crls_validate-3">pkix_crls_validate/3 </seealso> and is to be called
	 from the supplied <c>verify_fun</c>.
       </p>

       <p>Available options:</p>

       <taglist>
	<tag>{verify_fun, fun()}</tag>
	<item>
	  <p>The fun must be defined as:</p>

	  <code>
fun(OtpCert :: #'OTPCertificate'{},
    Event :: {bad_cert, Reason :: atom() | {revoked, atom()}} |
             {extension, #'Extension'{}},
    InitialUserState :: term()) ->
	{valid, UserState :: term()} |
	{valid_peer, UserState :: term()} |
	{fail, Reason :: term()} |
	{unknown, UserState :: term()}.
	  </code>

	<p>If the verify callback fun returns <c>{fail, Reason}</c>, the
	verification process is immediately stopped. If the verify
	callback fun returns <c>{valid, UserState}</c>, the verification
	process is continued. This can be used to accept specific path
	validation errors, such as <c>selfsigned_peer</c>, as well as
	verifying application-specific extensions. If called with an
	extension unknown to the user application, the return value
	<c>{unknown, UserState}</c> is to be used.</p>

	</item>
	<tag>{max_path_length, integer()}</tag>
	<item>
	  The <c>max_path_length</c> is the maximum number of non-self-issued
	  intermediate certificates that can follow the peer certificate
	  in a valid certification path. So, if <c>max_path_length</c> is 0, the PEER must
	  be signed by the trusted ROOT-CA directly, if it is 1, the path can
	  be PEER, CA, ROOT-CA, if it is 2, the path can
	  be PEER, CA, CA, ROOT-CA, and so on.
	</item>
      </taglist>

      <p>Possible reasons for a bad certificate: </p>
      <taglist>
	<tag>cert_expired</tag>
	<item><p>Certificate is no longer valid as its expiration date has passed.</p></item>

	<tag>invalid_issuer</tag>
	<item><p>Certificate issuer name does not match the name of the issuer certificate in the chain.</p></item>

	<tag>invalid_signature</tag>
	<item><p>Certificate was not signed by its issuer certificate in the chain.</p></item>

	<tag>name_not_permitted</tag>
	<item><p>Invalid Subject Alternative Name extension.</p></item>

	<tag>missing_basic_constraint</tag>
	<item><p>Certificate, required to have the basic constraints extension, does not have
	a basic constraints extension.</p></item>

	<tag>invalid_key_usage</tag>
	<item><p>Certificate key is used in an invalid way according to the key-usage extension.</p></item>

	<tag>{revoked, crl_reason()}</tag>
	<item><p>Certificate has been revoked.</p></item>

	<tag>atom()</tag>
	<item><p>Application-specific error reason that is to be checked by the <c>verify_fun</c>.</p></item>
      </taglist>

    </desc>
   </func>

    <func>  
      <name>pkix_crl_issuer(CRL) -> issuer_name()</name>
      <fsummary>Returns the issuer of the <c>CRL</c>.</fsummary>
      <type>
	<v>CRL = der_encoded() | #'CertificateList'{} </v> 
      </type> 
      <desc> 
	<p>Returns the issuer of the <c>CRL</c>.</p>
      </desc> 
    </func> 
   
   <func>
     <name>pkix_crls_validate(OTPCertificate, DPAndCRLs, Options) -> CRLStatus()</name>
     <fsummary>Performs CRL validation.</fsummary>
     <type>
       <v>OTPCertificate =  #'OTPCertificate'{}</v>
       <v>DPAndCRLs  = [{DP::#'DistributionPoint'{}, {DerCRL::der_encoded(), CRL::#'CertificateList'{}}}] </v>
       <v>Options = proplists:proplist()</v>
       <v>CRLStatus() =  valid | {bad_cert, revocation_status_undetermined} |
       {bad_cert, {revoked, crl_reason()}}</v>
     </type>
     <desc>
      <p>Performs CRL validation. It is intended to be called from
      the verify fun of  <seealso marker="#pkix_path_validation-3"> pkix_path_validation/3
       </seealso>.</p>

       <p>Available options:</p>

      <taglist>
	
	<tag>{update_crl, fun()}</tag>
	<item>
	  <p>The fun has the following type specification:</p>

	  <code> fun(#'DistributionPoint'{}, #'CertificateList'{}) ->
        #'CertificateList'{}</code>

	  <p>The fun uses the information in the distribution point to access
	  the latest possible version of the CRL. If this fun is not specified,
	  Public Key uses the default implementation:
	  </p>
	  <code> fun(_DP, CRL) -> CRL end</code>
	</item>

	<tag>{issuer_fun, fun()}</tag>
	<item>
	  <p>The fun has the following type specification:</p>

	  <code>
fun(#'DistributionPoint'{}, #'CertificateList'{},
    {rdnSequence,[#'AttributeTypeAndValue'{}]}, term()) ->
	{ok, #'OTPCertificate'{}, [der_encoded]}</code>

	  <p>The fun returns the root certificate and certificate chain
	  that has signed the CRL. 
	  </p>
	  <code> fun(DP, CRL, Issuer, UserState) -> {ok, RootCert, CertChain}</code>
	</item>	
      </taglist>
    </desc>
   </func>
   
   <func>  
     <name>pkix_crl_verify(CRL, Cert) -> boolean()</name>
     <fsummary> Verify that  <c>Cert</c>  is the <c> CRL</c>  signer. </fsummary>
     <type>
       <v>CRL = der_encoded() | #'CertificateList'{} </v> 
       <v>Cert = der_encoded() | #'OTPCertificate'{} </v> 
     </type> 
     <desc> 
       <p>Verify that <c>Cert</c> is the <c>CRL</c> signer.</p>
     </desc> 
   </func>

   <func>  
     <name>pkix_dist_point(Cert) -> DistPoint</name>
     <fsummary>Creates a distribution point for CRLs issued by the same issuer as <c>Cert</c>.</fsummary>
     <type>
       <v> Cert  = der_encoded() | #'OTPCertificate'{} </v> 
       <v> DistPoint =  #'DistributionPoint'{}</v> 
     </type> 
     <desc> 
       <p>Creates a distribution point for CRLs issued by the same issuer as <c>Cert</c>.
       Can be used as input to <seealso
       marker="#pkix_crls_validate-3">pkix_crls_validate/3 </seealso>
       </p>
     </desc> 
   </func>
   
   <func>  
     <name>pkix_dist_points(Cert) -> DistPoints</name>
     <fsummary> Extracts distribution points from the certificates extensions.</fsummary>
     <type>
       <v> Cert  = der_encoded() | #'OTPCertificate'{} </v> 
       <v> DistPoints =  [#'DistributionPoint'{}]</v> 
     </type> 
     <desc> 
       <p> Extracts distribution points from the certificates extensions.</p>
     </desc> 
 </func>
   
  <func>
    <name>pkix_match_dist_point(CRL, DistPoint) -> boolean()</name>
    <fsummary>Checks whether the given distribution point matches the
    Issuing Distribution Point of the CRL.</fsummary>

    <type>
      <v>CRL = der_encoded() | #'CertificateList'{} </v>
      <v>DistPoint = #'DistributionPoint'{}</v>
    </type>
    <desc>
      <p>Checks whether the given distribution point matches the
      Issuing Distribution Point of the CRL, as described in RFC 5280.
      If the CRL doesn't have an Issuing Distribution Point extension,
      the distribution point always matches.</p>
    </desc>
  </func>

  <func>
    <name>pkix_sign(#'OTPTBSCertificate'{}, Key) -> der_encoded()</name>
    <fsummary>Signs certificate.</fsummary>
    <type>
      <v>Key = rsa_private_key() | dsa_private_key()</v> 
    </type> 
    <desc> 
      <p>Signs an 'OTPTBSCertificate'. Returns the corresponding
      DER-encoded certificate.</p> 
    </desc> 
  </func> 

  <func>
    <name>pkix_sign_types(AlgorithmId) -> {DigestType, SignatureType}</name>
    <fsummary>Translates signature algorithm OID to Erlang digest and signature algorithm types.</fsummary>
    <type>
      <v>AlgorithmId = oid()</v>
      <d>Signature OID from a certificate or a certificate revocation list.</d>
      <v>DigestType = rsa_digest_type() | dss_digest_type()</v>
      <v>SignatureType = rsa | dsa | ecdsa</v>
    </type>
    <desc>
      <p>Translates signature algorithm OID to Erlang digest and signature types.
      </p>
    </desc>
  </func>

  <func>  
    <name>pkix_verify(Cert, Key) -> boolean()</name>
    <fsummary>Verifies PKIX x.509 certificate signature.</fsummary>
    <type>
      <v>Cert = der_encoded()</v>
      <v>Key = rsa_public_key() | dsa_public_key() | ec_public_key()</v> 
    </type> 
  <desc> 
    <p>Verifies PKIX x.509 certificate signature.</p>
  </desc> 
  </func> 

  <func>
    <name>pkix_verify_hostname(Cert, ReferenceIDs) -> boolean()</name>
    <name>pkix_verify_hostname(Cert, ReferenceIDs, Opts) -> boolean()</name>
    <fsummary>Verifies that a PKIX x.509 certificate <i>presented identifier</i> (e.g hostname) is
    an expected one.</fsummary>
    <type>
      <v>Cert = der_encoded() | #'OTPCertificate'{} </v>
      <v>ReferenceIDs = [ RefID ]</v>
      <v>RefID = {IdType,string()}</v>
      <v>IdType = dns_id | srv_id | uri_id</v>
      <v>Opts = [ PvhOpt() ]</v>
      <v>PvhOpt = [MatchOpt | FailCallBackOpt | FqdnExtractOpt]</v>
      <v>MatchOpt = {fun(RefId | FQDN::string(), PresentedID) -> boolean() | default}</v>
      <v>PresentedID = {dNSName,string()} | {uniformResourceIdentifier,string()}</v>
      <v>FailCallBackOpt = {fail_callback, fun(#'OTPCertificate'{}) -> boolean()}</v>
      <v>FqdnExtractOpt = {fqdn_fun, fun(RefID) -> FQDN::string() | default | undefined}</v>
    </type>
    <desc>
      <p>This function checks that the <i>Presented Identifier</i> (e.g hostname) in a peer certificate
      conforms with the Expected Identifier that the client wants to connect to.
      This functions is intended to be added as an extra client check to the peer certificate when performing
      <seealso marker="public_key:public_key#pkix_path_validation-3">public_key:pkix_path_validation/3</seealso>
      </p>
      <p>See <url href="https://tools.ietf.org/html/rfc6125">RFC 6125</url>
      for detailed information about hostname verification.
      The <seealso marker="using_public_key#verify_hostname">User's Manual</seealso>
      and
      <seealso marker="using_public_key#verify_hostname_examples">code examples</seealso>
      describes this function more detailed.
      </p>
    </desc>
  </func>

  <func>
    <name>sign(Msg, DigestType, Key) -> binary()</name>
    <fsummary>Creates a digital signature.</fsummary>
    <type>
       <v>Msg = binary() | {digest,binary()}</v>
       <d>The <c>Msg</c> is either the binary "plain text" data to be
       signed or it is the hashed value of "plain text", that is, the
       digest.</d>
       <v>DigestType = rsa_digest_type() | dss_digest_type() | ecdsa_digest_type()</v>
       <v>Key = rsa_private_key() | dsa_private_key() | ec_private_key()</v>
  </type>
  <desc>
    <p>Creates a digital signature.</p> 
  </desc> 
  </func>   

  <func>
    <name>ssh_decode(SshBin,  Type) -> [{public_key(), Attributes::list()}]</name>
    <fsummary>Decodes an SSH file-binary.</fsummary>
    <type>
      <v>SshBin = binary()</v>
      <d>Example <c>{ok, SshBin} = file:read_file("known_hosts")</c>.</d>
      <v>Type = public_key | ssh_file()</v>
      <d>If <c>Type</c> is <c>public_key</c> the binary can be either
      an RFC4716 public key or an OpenSSH public key.</d>
    </type>
  <desc>
    <p>Decodes an SSH file-binary. In the case of <c>known_hosts</c> or
    <c>auth_keys</c>, the binary can include one or more lines of the
    file. Returns a list of public keys and their attributes, possible
    attribute values depends on the file type represented by the
    binary.
    </p>

    <taglist>
      <tag>RFC4716 attributes - see RFC 4716.</tag>
      <item><p>{headers, [{string(), utf8_string()}]}</p></item>
      <tag>auth_key attributes - see manual page for sshd.</tag>
      <item>{comment, string()}</item>
      <item>{options, [string()]}</item>
      <item><p>{bits, integer()} - In SSH version 1 files.</p></item>
      <tag>known_host attributes - see manual page for sshd.</tag>
      <item>{hostnames, [string()]}</item>
      <item>{comment, string()}</item>
      <item><p>{bits, integer()} - In SSH version 1 files.</p></item>
    </taglist>

  </desc>
  </func>

  <func>
    <name>ssh_encode([{Key, Attributes}], Type) -> binary()</name>
    <fsummary>Encodes a list of SSH file entries to a binary.</fsummary>
    <type>
      <v>Key = public_key()</v>
      <v>Attributes = list()</v>
      <v>Type = ssh_file()</v>
    </type>
  <desc>
    <p>Encodes a list of SSH file entries (public keys and attributes) to a binary. Possible
    attributes depend on the file type, see <seealso
    marker="#ssh_decode-2"> ssh_decode/2 </seealso>.</p>
  </desc>
  </func>

  <func>
    <name>ssh_hostkey_fingerprint(HostKey) -> string()</name>
    <name>ssh_hostkey_fingerprint(DigestType, HostKey) -> string()</name>
    <fsummary>Calculates a ssh fingerprint for a hostkey.</fsummary>
    <type>
      <v>Key = public_key()</v>
      <v>DigestType = digest_type()</v>
    </type>
  <desc>
    <p>Calculates a ssh fingerprint from a public host key as openssh does.</p>
    <p>The algorithm in <c>ssh_hostkey_fingerprint/1</c> is md5 to be compatible with older
    ssh-keygen commands. The string from the second variant is prepended by the algorithm name
    in uppercase as in newer ssh-keygen commands.</p>
    <p>Examples:</p>
    <code>
 2> public_key:ssh_hostkey_fingerprint(Key).    
 "f5:64:a6:c1:5a:cb:9f:0a:10:46:a2:5c:3e:2f:57:84"

 3> public_key:ssh_hostkey_fingerprint(md5,Key).
 "MD5:f5:64:a6:c1:5a:cb:9f:0a:10:46:a2:5c:3e:2f:57:84"

 4> public_key:ssh_hostkey_fingerprint(sha,Key).
 "SHA1:bSLY/C4QXLDL/Iwmhyg0PGW9UbY"

 5> public_key:ssh_hostkey_fingerprint(sha256,Key).
 "SHA256:aZGXhabfbf4oxglxltItWeHU7ub3Dc31NcNw2cMJePQ"
    </code>
  </desc>
  </func>

  <func>
    <name>verify(Msg, DigestType, Signature, Key) -> boolean()</name>
    <fsummary>Verifies a digital signature.</fsummary>
    <type>
      <v>Msg = binary() | {digest,binary()}</v>
       <d>The <c>Msg</c> is either the binary "plain text" data 
        or it is the hashed value of "plain text", that is, the digest.</d>
      <v>DigestType = rsa_digest_type() | dss_digest_type() | ecdsa_digest_type()</v>
      <v>Signature = binary()</v>
      <v>Key = rsa_public_key() | dsa_public_key() | ec_public_key()</v>
  </type>
  <desc>
    <p>Verifies a digital signature.</p>
  </desc> 
  </func>

  <func>
    <name>short_name_hash(Name) -> string()</name>
    <fsummary>Generates a short hash of an issuer name.</fsummary>
    <type>
      <v>Name = issuer_name()</v>
    </type>
    <desc>
      <p>Generates a short hash of an issuer name.  The hash is
      returned as a string containing eight hexadecimal digits.</p>

      <p>The return value of this function is the same as the result
      of the commands <c>openssl crl -hash</c> and
      <c>openssl x509 -issuer_hash</c>, when passed the issuer name of
      a CRL or a certificate, respectively.  This hash is used by the
      <c>c_rehash</c> tool to maintain a directory of symlinks to CRL
      files, in order to facilitate looking up a CRL by its issuer
      name.</p>
    </desc>
  </func>

</funcs>

</erlref>