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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.