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NAME

       public_key - API module for public-key infrastructure.

DESCRIPTION

       Provides functions to handle public-key infrastructure, for details see public_key(7).

COMMON RECORDS AND ASN.1 TYPES

   Note:
       All  records  used in this Reference Manual are generated from ASN.1 specifications and are documented in
       the User's Guide. See Public-key Records.

       Use the following include directive to get access to the records and constant macros described  here  and
       in the User's Guide:

        -include_lib("public_key/include/public_key.hrl").

DATA TYPES

       oid() = tuple()

              Object identifier, a tuple of integers as generated by the ASN.1 compiler.

       der_encoded() = binary()

       pki_asn1_type() =
           'Certificate' | 'RSAPrivateKey' | 'RSAPublicKey' |
           'DSAPrivateKey' | 'DSAPublicKey' | 'DHParameter' |
           'SubjectPublicKeyInfo' | 'PrivateKeyInfo' |
           'CertificationRequest' | 'CertificateList' | 'ECPrivateKey' |
           'EcpkParameters'

       asn1_type() = atom()

              ASN.1 type present in the Public Key applications ASN.1 specifications.

       pem_entry() =
           {pki_asn1_type(),
            der_or_encrypted_der(),
            not_encrypted | cipher_info()}

       der_or_encrypted_der() = binary()

       cipher_info() = {cipher(), cipher_info_params()}

       cipher() = string()

       salt() = binary()

       cipher_info_params() =
           salt() |
           {#'PBEParameter'{}, digest_type()} |
           #'PBES2-params'{}

              Cipher = "RC2-CBC" | "DES-CBC" | "DES-EDE3-CBC"

              Salt could be generated with crypto:strong_rand_bytes(8).

       public_key() =
           rsa_public_key() |
           dsa_public_key() |
           ec_public_key() |
           ed_public_key()

       rsa_public_key() = #'RSAPublicKey'{}

       dsa_public_key() = {integer(), #'Dss-Parms'{}}

       ec_public_key() = {#'ECPoint'{}, ecpk_parameters_api()}

       ecpk_parameters() =
           {ecParameters, #'ECParameters'{}} |
           {namedCurve, Oid :: tuple()}

       ecpk_parameters_api() =
           ecpk_parameters() |
           #'ECParameters'{} |
           {namedCurve, Name :: crypto:ec_named_curve()}

       ed_public_key() = {ed_pub, ed25519 | ed448, Key :: binary()}

          Warning:
              This format of the EdDSA curves is temporary and may change without prior notice!

       private_key() =
           rsa_private_key() |
           dsa_private_key() |
           ec_private_key() |
           ed_private_key()

       rsa_private_key() = #'RSAPrivateKey'{}

       dsa_private_key() = #'DSAPrivateKey'{}

       ec_private_key() = #'ECPrivateKey'{}

       ed_private_key() =
           {ed_pri, ed25519 | ed448, Pub :: binary(), Priv :: binary()}

          Warning:
              This format of the EdDSA curves is temporary and may change without prior notice!

       key_params() =
           #'DHParameter'{} |
           {namedCurve, oid()} |
           #'ECParameters'{} |
           {rsa, Size :: integer(), PubExp :: integer()}

       digest_type() =
           none | sha1 |
           crypto:rsa_digest_type() |
           crypto:dss_digest_type() |
           crypto:ecdsa_digest_type()

       crl_reason() =
           unspecified | keyCompromise | cACompromise |
           affiliationChanged | superseded | cessationOfOperation |
           certificateHold | privilegeWithdrawn | aACompromise

       issuer_id() = {SerialNr :: integer(), issuer_name()}

       issuer_name() = {rdnSequence, [#'AttributeTypeAndValue'{}]}

       ssh_file() =
           openssh_public_key | rfc4716_public_key | known_hosts |
           auth_keys

EXPORTS

       compute_key(OthersECDHkey, MyECDHkey) -> SharedSecret

              Types:

                 OthersECDHkey = #'ECPoint'{}
                 MyECDHkey = #'ECPrivateKey'{}
                 SharedSecret = binary()

              Computes shared secret.

       compute_key(OthersDHkey, MyDHkey, DHparms) -> SharedSecret

              Types:

                 OthersDHkey = crypto:dh_public()
                 MyDHkey = crypto:dh_private()
                 DHparms = #'DHParameter'{}
                 SharedSecret = binary()

              Computes shared secret.

       decrypt_private(CipherText, Key) -> PlainText

       decrypt_private(CipherText, Key, Options) -> PlainText

              Types:

                 CipherText = binary()
                 Key = rsa_private_key()
                 Options = crypto:pk_encrypt_decrypt_opts()
                 PlainText = binary()

              Public-key decryption using the private key. See also crypto:private_decrypt/4

       decrypt_public(CipherText, Key) -> PlainText

       decrypt_public(CipherText, Key, Options) -> PlainText

              Types:

                 CipherText = binary()
                 Key = rsa_public_key()
                 Options = crypto:pk_encrypt_decrypt_opts()
                 PlainText = binary()

              Public-key decryption using the public key. See also crypto:public_decrypt/4

       der_decode(Asn1Type, Der) -> Entity

              Types:

                 Asn1Type = asn1_type()
                 Der = binary()
                 Entity = term()

              Decodes a public-key ASN.1 DER encoded entity.

       der_encode(Asn1Type, Entity) -> Der

              Types:

                 Asn1Type = asn1_type()
                 Entity = term()
                 Der = binary()

              Encodes a public-key entity with ASN.1 DER encoding.

       dh_gex_group(MinSize, SuggestedSize, MaxSize, Groups) ->
                       {ok, {Size, Group}} | {error, term()}

              Types:

                 MinSize = SuggestedSize = MaxSize = integer() >= 1
                 Groups = undefined | [{Size, [Group]}]
                 Size = integer() >= 1
                 Group = {G, P}
                 G = P = integer() >= 1

              Selects  a  group for Diffie-Hellman key exchange with the key size in the range MinSize...MaxSize
              and as close to SuggestedSize as possible. If Groups == undefined a  default  set  will  be  used,
              otherwise the group is selected from Groups.

              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
              MinSize and MaxSize is available, {error,no_group_found} is returned.

              The  default  set  of groups is listed in lib/public_key/priv/moduli. This file may be regenerated
              like this:

                   $> 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

       encrypt_private(PlainText, Key) -> CipherText

       encrypt_private(PlainText, Key, Options) -> CipherText

              Types:

                 PlainText = binary()
                 Key = rsa_private_key()
                 Options = crypto:pk_encrypt_decrypt_opts()
                 CipherText = binary()

              Public-key encryption using the private key. See also crypto:private_encrypt/4.

       encrypt_public(PlainText, Key) -> CipherText

       encrypt_public(PlainText, Key, Options) -> CipherText

              Types:

                 PlainText = binary()
                 Key = rsa_public_key()
                 Options = crypto:pk_encrypt_decrypt_opts()
                 CipherText = binary()

              Public-key encryption using the public key. See also crypto:public_encrypt/4.

       generate_key(Params :: DHparams | ECparams | RSAparams) ->
                       DHkeys | ECkey | RSAkey

              Types:

                 DHparams = #'DHParameter'{}
                 DHkeys = {PublicDH :: binary(), PrivateDH :: binary()}
                 ECparams = ecpk_parameters_api()
                 ECkey = #'ECPrivateKey'{}
                 RSAparams = {rsa, Size, PubExp}
                 Size = PubExp = integer() >= 1
                 RSAkey = #'RSAPrivateKey'{}

              Generates a new keypair. Note that except for Diffie-Hellman the public key  is  included  in  the
              private key structure. See also crypto:generate_key/2

       pem_decode(PemBin :: binary()) -> [pem_entry()]

              Decodes PEM binary data and returns entries as ASN.1 DER encoded entities.

              Example {ok, PemBin} = file:read_file("cert.pem"). PemEntries = public_key:pem_decode(PemBin).

       pem_encode(PemEntries :: [pem_entry()]) -> binary()

              Creates a PEM binary.

       pem_entry_decode(PemEntry) -> term()

       pem_entry_decode(PemEntry, Password) -> term()

              Types:

                 PemEntry = pem_entry()
                 Password = string()

              Decodes  a  PEM entry. pem_decode/1 returns a list of PEM entries. Notice that if the PEM entry is
              of type 'SubjectPublickeyInfo', it is further decoded to an rsa_public_key() or dsa_public_key().

       pem_entry_encode(Asn1Type, Entity) -> pem_entry()

       pem_entry_encode(Asn1Type, Entity, InfoPwd) -> pem_entry()

              Types:

                 Asn1Type = pki_asn1_type()
                 Entity = term()
                 InfoPwd = {CipherInfo, Password}
                 CipherInfo = cipher_info()
                 Password = string()

              Creates a PEM entry that can be feed to pem_encode/1.

              If Asn1Type is 'SubjectPublicKeyInfo', Entity must be either an rsa_public_key(), dsa_public_key()
              or an ec_public_key() and this function creates the appropriate 'SubjectPublicKeyInfo' entry.

       pkix_decode_cert(Cert, Type) ->
                           #'Certificate'{} | #'OTPCertificate'{}

              Types:

                 Cert = der_encoded()
                 Type = plain | otp

              Decodes an ASN.1 DER-encoded PKIX certificate. Option otp uses the customized ASN.1  specification
              OTP-PKIX.asn1 for decoding and also recursively decode most of the standard parts.

       pkix_encode(Asn1Type, Entity, Type) -> Der

              Types:

                 Asn1Type = asn1_type()
                 Entity = term()
                 Type = otp | plain
                 Der = der_encoded()

              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 otp format, whereas
              for the plain format this function directly calls der_encode/2.

       pkix_is_issuer(Cert, IssuerCert) -> boolean()

              Types:

                 Cert =
                     der_encoded() | #'OTPCertificate'{} | #'CertificateList'{}
                 IssuerCert = der_encoded() | #'OTPCertificate'{}

              Checks if IssuerCert issued Cert.

       pkix_is_fixed_dh_cert(Cert) -> boolean()

              Types:

                 Cert = der_encoded() | #'OTPCertificate'{}

              Checks if a certificate is a fixed Diffie-Hellman certificate.

       pkix_is_self_signed(Cert) -> boolean()

              Types:

                 Cert = der_encoded() | #'OTPCertificate'{}

              Checks if a certificate is self-signed.

       pkix_issuer_id(Cert, IssuedBy) ->
                         {ok, issuer_id()} | {error, Reason}

              Types:

                 Cert = der_encoded() | #'OTPCertificate'{}
                 IssuedBy = self | other
                 Reason = term()

              Returns the issuer id.

       pkix_normalize_name(Issuer) -> Normalized

              Types:

                 Issuer = Normalized = issuer_name()

              Normalizes an issuer name so that it can be easily compared to another issuer name.

       pkix_path_validation(TrustedCert, CertChain, Options) ->  {ok,  {PublicKeyInfo,  PolicyTree}}  |  {error,
       {bad_cert, Reason}}

              Types:

                 TrustedCert = #'OTPCertificate'{} | der_encoded() | atom()
                   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
                   verify_fun. Examples are unknown_ca and selfsigned_peer.
                 CertChain = [der_encoded()]
                   A list of DER-encoded certificates in trust order ending with the peer certificate.
                 Options = proplists:proplist()
                 PublicKeyInfo  =  {?'rsaEncryption'  |  ?'id-dsa', rsa_public_key() | integer(), 'NULL' | 'Dss-
                 Parms'{}}
                 PolicyTree = term()
                   At the moment this is always an empty list as policies are not currently supported.
                 Reason  =  cert_expired  |  invalid_issuer   |   invalid_signature   |   name_not_permitted   |
                 missing_basic_constraint | invalid_key_usage | {revoked, crl_reason()} | atom()

              Performs a basic path validation according to RFC 5280. However, CRL validation is done separately
              by pkix_crls_validate/3  and is to be called from the supplied verify_fun.

              Available options:

                {verify_fun, {fun(), InitialUserState::term()}:
                  The fun must be defined as:

                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()}.

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

                {max_path_length, integer()}:
                   The max_path_length is the maximum number of non-self-issued intermediate  certificates  that
                  can  follow  the  peer certificate in a valid certification path. So, if max_path_length 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.

              Possible reasons for a bad certificate:

                cert_expired:
                  Certificate is no longer valid as its expiration date has passed.

                invalid_issuer:
                  Certificate issuer name does not match the name of the issuer certificate in the chain.

                invalid_signature:
                  Certificate was not signed by its issuer certificate in the chain.

                name_not_permitted:
                  Invalid Subject Alternative Name extension.

                missing_basic_constraint:
                  Certificate, required to  have  the  basic  constraints  extension,  does  not  have  a  basic
                  constraints extension.

                invalid_key_usage:
                  Certificate key is used in an invalid way according to the key-usage extension.

                {revoked, crl_reason()}:
                  Certificate has been revoked.

                atom():
                  Application-specific error reason that is to be checked by the verify_fun.

       pkix_crl_issuer(CRL :: CRL | #'CertificateList'{}) -> Issuer

              Types:

                 CRL = der_encoded()
                 Issuer = issuer_name()

              Returns the issuer of the CRL.

       pkix_crls_validate(OTPcertificate, DPandCRLs, Options) ->
                             CRLstatus

              Types:

                 OTPcertificate = #'OTPCertificate'{}
                 DPandCRLs = [DPandCRL]
                 DPandCRL = {DP, {DerCRL, CRL}}
                 DP = #'DistributionPoint'{}
                 DerCRL = der_encoded()
                 CRL = #'CertificateList'{}
                 Options = [{atom(), term()}]
                 CRLstatus = valid | {bad_cert, BadCertReason}
                 BadCertReason =
                     revocation_status_undetermined |
                     {revocation_status_undetermined, Reason :: term()} |
                     {revoked, crl_reason()}

              Performs   CRL   validation.   It   is   intended   to   be   called   from   the  verify  fun  of
              pkix_path_validation/3 .

              Available options:

                {update_crl, fun()}:
                  The fun has the following type specification:

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

                  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:

                 fun(_DP, CRL) -> CRL end

                {issuer_fun, fun()}:
                  The fun has the following type specification:

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

                  The fun returns the root certificate and certificate chain that has signed the CRL.

                 fun(DP, CRL, Issuer, UserState) -> {ok, RootCert, CertChain}

                {undetermined_details, boolean()}:
                  Defaults  to  false.  When  revocation  status cannot be determined, and this option is set to
                  true, details of why no CRLs where accepted are included in the return value.

       pkix_crl_verify(CRL, Cert) -> boolean()

              Types:

                 CRL = der_encoded() | #'CertificateList'{}
                 Cert = der_encoded() | #'OTPCertificate'{}

              Verify that Cert is the CRL signer.

       pkix_dist_point(Cert) -> DistPoint

              Types:

                 Cert = der_encoded() | #'OTPCertificate'{}
                 DistPoint = #'DistributionPoint'{}

              Creates a distribution point for CRLs issued by the same issuer as Cert. Can be used as  input  to
              pkix_crls_validate/3

       pkix_dist_points(Cert) -> DistPoints

              Types:

                 Cert = der_encoded() | #'OTPCertificate'{}
                 DistPoints = [#'DistributionPoint'{}]

              Extracts distribution points from the certificates extensions.

       pkix_match_dist_point(CRL, DistPoint) -> boolean()

              Types:

                 CRL = der_encoded() | #'CertificateList'{}
                 DistPoint = #'DistributionPoint'{}

              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.

       pkix_sign(Cert, Key) -> Der

              Types:

                 Cert = #'OTPTBSCertificate'{}
                 Key = private_key()
                 Der = der_encoded()

              Signs an 'OTPTBSCertificate'. Returns the corresponding DER-encoded certificate.

       pkix_sign_types(AlgorithmId) -> {DigestType, SignatureType}

              Types:

                 AlgorithmId = oid()
                 DigestType = crypto:rsa_digest_type()
                 SignatureType = rsa | dsa | ecdsa

              Translates signature algorithm OID to Erlang digest and signature types.

              The AlgorithmId is the signature OID from a certificate or a certificate revocation list.

       pkix_test_data(Options) -> Config
       pkix_test_data([chain_opts()]) -> [conf_opt()]

              Types:

                 Options = #{chain_type() := chain_opts()}
                   Options for ROOT, Intermediate and Peer certs
                 chain_type() = server_chain | client_chain
                 chain_opts()  =  #{root  :=  [cert_opt()] | root_cert(), peer := [cert_opt()], intermediates =>
                 [[cert_opt()]]}
                    A valid chain must have at least a ROOT and a peer cert. The root cert can be  given  either
                   as a cert pre-generated by  pkix_test_root_cert/2 , or as root cert generation options.
                 root_cert() = #{cert := der_encoded(), key := Key}
                    A root certificate generated by  pkix_test_root_cert/2 .
                 cert_opt() = {Key, Value}
                   For available options see  cert_opt() below.
                 Config = #{server_config := [conf_opt()], client_config := [conf_opt()]}
                 conf_opt() = {cert, der_encoded()} | {key, PrivateKey} |{cacerts, [der_encoded()]}
                    This is a subset of the type  ssl:tls_option(). PrivateKey is what generate_key/1 returns.

              Creates  certificate  configuration(s)  consisting  of  certificate  and  its  private key plus CA
              certificate bundle, for a client and  a  server,  intended  to  facilitate  automated  testing  of
              applications  using  X509-certificates,  often through SSL/TLS. The test data can be used when you
              have control over both the client and the server in a test scenario.

              When this function is called with a map containing client  and  server  chain  specifications;  it
              generates  both  a client and a server certificate chain where the cacerts returned for the server
              contains the root cert the server should trust and the intermediate certificates the server should
              present to connecting clients. The root cert the server should trust is the one used  as  root  of
              the  client certificate chain. Vice versa applies to the cacerts returned for the client. The root
              cert(s) can either be pre-generated with  pkix_test_root_cert/2 , or if options are specified;  it
              is (they are) generated.

              When this function is called with a list of certificate options; it generates a configuration with
              just  one  node  certificate  where cacerts contains the root cert and the intermediate certs that
              should be presented to a peer. In this case the same root cert must be used for all peers. This is
              useful in for example an Erlang distributed cluster where any node,  towards  another  node,  acts
              either  as  a  server  or as a client depending on who connects to whom. The generated certificate
              contains a subject altname, which is not needed in a client certificate, but makes the certificate
              useful for both roles.

              The cert_opt() type consists of the following options:

                  {digest, digest_type()}: Hash algorithm to be used for signing the certificate  together  with
                  the key option. Defaults to sha that is sha1.

                  {key,  key_params() | private_key()}: Parameters to be used to call public_key:generate_key/1,
                  to generate a key, or an existing key. Defaults to generating an ECDSA key.  Note  this  could
                  fail if Erlang/OTP is compiled with a very old cryptolib.

                  {validity,  {From::erlang:timestamp(),  To::erlang:timestamp()}}  : The validity period of the
                  certificate.

                  {extensions, [#'Extension'{}]}: Extensions to include in the certificate.

                  Default extensions included in CA certificates if not otherwise specified are:

                [#'Extension'{extnID = ?'id-ce-keyUsage',
                              extnValue = [keyCertSign, cRLSign],
                              critical = false},
                #'Extension'{extnID = ?'id-ce-basicConstraints',
                             extnValue = #'BasicConstraints'{cA = true},
                             critical = true}]

                  Default extensions included in the server peer cert if not otherwise specified are:

                [#'Extension'{extnID = ?'id-ce-keyUsage',
                              extnValue = [digitalSignature, keyAgreement],
                              critical = false},
                #'Extension'{extnID = ?'id-ce-subjectAltName',
                             extnValue = [{dNSName, Hostname}],
                             critical = false}]

                  Hostname is the result of calling net_adm:localhost() in the Erlang node where this funcion is
                  called.

          Note:
              Note that the generated certificates and keys does not provide a formally correct PKIX-trust-chain
              and they cannot be used to achieve real security. This function is provided for  testing  purposes
              only.

       pkix_test_root_cert(Name, Options) -> RootCert

              Types:

                 Name = string()
                   The root certificate name.
                 Options = [cert_opt()]
                    For available options see cert_opt() under pkix_test_data/1.
                 RootCert = #{cert := der_encoded(), key := Key}
                    A root certificate and key. The Key is generated by generate_key/1.

              Generates  a root certificate that can be used in multiple calls to pkix_test_data/1 when you want
              the same root certificate for several generated certificates.

       pkix_verify(Cert, Key) -> boolean()

              Types:

                 Cert = der_encoded()
                 Key = public_key()

              Verifies PKIX x.509 certificate signature.

       pkix_verify_hostname(Cert, ReferenceIDs) -> boolean()
       pkix_verify_hostname(Cert, ReferenceIDs, Opts) -> boolean()

              Types:

                 Cert = der_encoded() | #'OTPCertificate'{}
                 ReferenceIDs = [ RefID ]
                 RefID     =     {dns_id,string()}     |     {srv_id,string()}     |     {uri_id,string()}     |
                 {ip,inet:ip_address()|string()} | {OtherRefID,term()}}
                 OtherRefID = atom()
                 Opts = [ PvhOpt() ]
                 PvhOpt = [MatchOpt | FailCallBackOpt | FqdnExtractOpt]
                 MatchOpt = {match_fun, fun(RefId | FQDN::string(), PresentedID) -> boolean() | default}
                 PresentedID      =      {dNSName,string()}      |     {uniformResourceIdentifier,string()     |
                 {iPAddress,list(byte())} | {OtherPresId,term()}}
                 OtherPresID = atom()
                 FailCallBackOpt = {fail_callback, fun(#'OTPCertificate'{}) -> boolean()}
                 FqdnExtractOpt = {fqdn_fun, fun(RefID) -> FQDN::string() | default | undefined}

              This function checks that the Presented Identifier  (e.g hostname) in a  peer  certificate  is  in
              agreement  with  at least one of the Reference Identifier  that the client expects to be connected
              to. The function is intended to be added as an extra client check of  the  peer  certificate  when
              performing public_key:pkix_path_validation/3

              See  RFC  6125  for  detailed  information  about hostname verification. The User's Guide and code
              examples describes this function more detailed.

              The {OtherRefId,term()} is defined by the user and is passed to the match_fun, if defined. If  the
              term in OtherRefId is a binary, it will be converted to a string.

              The  ip  Reference ID takes an inet:ip_address() or an ip address in string format (E.g "10.0.1.1"
              or "1234::5678:9012") as second element.

              The options are:

                match_fun:
                   The fun/2 in this option replaces the default host name matching rules. The fun should return
                  a boolean to tell if the Reference ID and Presented ID matches or not. The fun can also return
                  a third value, the atom default, if the default matching rules  shall  apply.  This  makes  it
                  possible to augment the tests with a special case:

                fun(....) -> true;   % My special case
                   (_, _) -> default % all others falls back to the inherit tests
                end

                See  pkix_verify_hostname_match_fun/1  for a function that takes a protocol name as argument and
                returns a fun/2 suitable for this option and Re-defining the match operation in the User's Guide
                for an example.

                fail_callback:
                  If a matching fails, there could be circumstances when  the  certificate  should  be  accepted
                  anyway. Think for example of a web browser where you choose to accept an outdated certificate.
                  This  option  enables  implementation  of  such  a  function.  This  fun/1  is  called when no
                  ReferenceID matches. The return value of the fun (a boolean()) decides the  outcome.  If  true
                  the  the  certificate is accepted otherwise it is rejected. See "Pinning" a Certificate in the
                  User's Guide.

                fqdn_fun:
                  This option augments the host name extraction from URIs and other Reference IDs. It could  for
                  example  be  a  very  special  URI  that  is not standardised. The fun takes a Reference ID as
                  argument and returns one of:

                  * the hostname

                  * the atom default: the default host name extract function will be used

                  * the atom undefined: a host name could not  be  extracted.  The  pkix_verify_hostname/3  will
                    return false.

                For an example, see Hostname extraction in the User's Guide.

       pkix_verify_hostname_match_fun(Protcol)  ->  fun(RefId  |  FQDN::string(),  PresentedID)  ->  boolean() |
       default

              Types:

                 Protocol = https
                   The algorithm for wich the fun should implement the special matching rules
                 RefId
                   See pkix_verify_hostname/3.
                 FQDN
                   See pkix_verify_hostname/3.
                 PresentedID
                   See pkix_verify_hostname/3.

              The return value of calling this function is intended to  be  used  in  the  match_fun  option  in
              pkix_verify_hostname/3.

              The  returned  fun  augments  the verify hostname matching according to the specific rules for the
              protocol in the argument.

       sign(Msg, DigestType, Key) -> Signature

       sign(Msg, DigestType, Key, Options) -> Signature

              Types:

                 Msg = binary() | {digest, binary()}
                 DigestType = digest_type()
                 Key = private_key()
                 Options = crypto:pk_sign_verify_opts()
                 Signature = binary()

              Creates a digital signature.

              The Msg is either the binary "plain text" data to be signed or it is the hashed  value  of  "plain
              text", that is, the digest.

       ssh_decode(SshBin, Type) -> Decoded

              Types:

                 SshBin = binary()
                 Type = ssh2_pubkey | OtherType | InternalType
                 OtherType = public_key | ssh_file()
                 InternalType = new_openssh
                 Decoded = Decoded_ssh2_pubkey | Decoded_OtherType
                 Decoded_ssh2_pubkey = public_key()
                 Decoded_OtherType = [{public_key(), Attributes}]
                 Attributes = [{atom(), term()}]

              Decodes an SSH file-binary. In the case of known_hosts or auth_keys, 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.

              If the Type is  ssh2_pubkey,  the  result  will  be  Decoded_ssh2_pubkey.  Otherwise  it  will  be
              Decoded_OtherType.

                RFC4716 attributes - see RFC 4716.:
                  {headers, [{string(), utf8_string()}]}

                auth_key attributes - see manual page for sshd.:
                  {comment, string()}{options, [string()]}{bits, integer()} - In SSH version 1 files.

                known_host attributes - see manual page for sshd.:
                  {hostnames, [string()]}{comment, string()}{bits, integer()} - In SSH version 1 files.

              Example: {ok, SshBin} = file:read_file("known_hosts").

              If Type is public_key the binary can be either an RFC4716 public key or an OpenSSH public key.

       ssh_encode(InData, Type) -> binary()

              Types:

                 Type = ssh2_pubkey | OtherType
                 OtherType = public_key | ssh_file()
                 InData = InData_ssh2_pubkey | OtherInData
                 InData_ssh2_pubkey = public_key()
                 OtherInData = [{Key, Attributes}]
                 Key = public_key()
                 Attributes = [{atom(), term()}]

              Encodes  a  list of SSH file entries (public keys and attributes) to a binary. Possible attributes
              depend on the file type, see  ssh_decode/2 .

              If the Type is ssh2_pubkey,  the  InData  shall  be  InData_ssh2_pubkey.  Otherwise  it  shall  be
              OtherInData.

       ssh_hostkey_fingerprint(HostKey) -> string()
       ssh_hostkey_fingerprint(DigestType, HostKey) -> string()
       ssh_hostkey_fingerprint([DigestType], HostKey) -> [string()]

              Types:

                 HostKey = public_key()
                 DigestType = digest_type()

              Calculates a ssh fingerprint from a public host key as openssh does.

              The algorithm in ssh_hostkey_fingerprint/1 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.

              Examples:

               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"

               6> public_key:ssh_hostkey_fingerprint([sha,sha256],Key).
               ["SHA1:bSLY/C4QXLDL/Iwmhyg0PGW9UbY",
                "SHA256:aZGXhabfbf4oxglxltItWeHU7ub3Dc31NcNw2cMJePQ"]

       verify(Msg, DigestType, Signature, Key) -> boolean()

       verify(Msg, DigestType, Signature, Key, Options) -> boolean()

              Types:

                 Msg = binary() | {digest, binary()}
                 DigestType = digest_type()
                 Signature = binary()
                 Key = public_key()
                 Options = crypto:pk_sign_verify_opts()

              Verifies a digital signature.

              The Msg is either the binary "plain text" data or it is the hashed value of "plain text", that is,
              the digest.

       short_name_hash(Name) -> string()

              Types:

                 Name = issuer_name()

              Generates a short hash of an issuer name. The hash  is  returned  as  a  string  containing  eight
              hexadecimal digits.

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

Ericsson AB                                     public_key 1.7.1                                public_key(3erl)