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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).

DATA 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").

       The following data types are used in the functions for public_key:

         oid():
           Object identifier, a tuple of integers as generated by the ASN.1 compiler.

         boolean() =:
           true | false

         string() =:
           [bytes()]

         der_encoded() =:
           binary()

         pki_asn1_type() =:
           'Certificate'

           | 'RSAPrivateKey'

           | 'RSAPublicKey'

           | 'DSAPrivateKey'

           | 'DSAPublicKey'

           | 'DHParameter'

           | 'SubjectPublicKeyInfo'

           | 'PrivateKeyInfo'

           | 'CertificationRequest'

           | 'CertificateList'

           | 'ECPrivateKey'

           | 'EcpkParameters'

         pem_entry () =:
           {pki_asn1_type(), binary(), %% DER or encrypted DER

            not_encrypted | cipher_info()}

         cipher_info() = :
           {"RC2-CBC" | "DES-CBC" | "DES-EDE3-CBC", crypto:strong_rand_bytes(8)

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

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

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

         rsa_public_key() =:
           #'RSAPublicKey'{}

         rsa_private_key() =:
           #'RSAPrivateKey'{}

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

         dsa_private_key() =:
           #'DSAPrivateKey'{}

         ec_public_key():
           = {#'ECPoint'{}, #'ECParameters'{} | {namedCurve, oid()}}

         ec_private_key() =:
           #'ECPrivateKey'{}

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

         public_crypt_options() =:
           [{rsa_pad, rsa_padding()}]

         rsa_padding() =:
           'rsa_pkcs1_padding'

           | 'rsa_pkcs1_oaep_padding'

           | 'rsa_no_padding'

         public_sign_options() =:
           [{rsa_pad, rsa_sign_padding()} | {rsa_pss_saltlen, integer()}]

         rsa_sign_padding() =:
           'rsa_pkcs1_padding'

           | 'rsa_pkcs1_pss_padding'

         digest_type() = :
           Union of rsa_digest_type(), dss_digest_type(), and ecdsa_digest_type().

         rsa_digest_type() = :
           'md5' | 'ripemd160' | 'sha' | 'sha224' | 'sha256' | 'sha384' | 'sha512'

         dss_digest_type() = :
           'sha' | 'sha224' | 'sha256' | 'sha384' | 'sha512'

           Note that the actual  supported  dss_digest_type  depends  on  the  underlying  crypto
           library.  In  OpenSSL version >= 1.0.1 the listed digest are supported, while in 1.0.0
           only sha, sha224 and sha256 are supported. In version 0.9.8 only sha is supported.

         ecdsa_digest_type() = :
           'sha' | 'sha224' | 'sha256' | 'sha384' | 'sha512'

         crl_reason() = :
           unspecified

           | keyCompromise

           | cACompromise

           | affiliationChanged

           | superseded

           | cessationOfOperation

           | certificateHold

           | privilegeWithdrawn

           | aACompromise

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

         ssh_file() =:
           openssh_public_key

           | rfc4716_public_key

           | known_hosts

           | auth_keys

EXPORTS

       compute_key(OthersKey, MyKey)->
       compute_key(OthersKey, MyKey, Params)->

              Types:

                 OthersKey = #'ECPoint'{} | binary(), MyKey = #'ECPrivateKey'{} | binary()
                 Params = #'DHParameter'{}

              Computes shared secret.

       decrypt_private(CipherText, Key) -> binary()
       decrypt_private(CipherText, Key, Options) -> binary()

              Types:

                 CipherText = binary()
                 Key = rsa_private_key()
                 Options = public_crypt_options()

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

       decrypt_public(CipherText, Key) - > binary()
       decrypt_public(CipherText, Key, Options) - > binary()

              Types:

                 CipherText = binary()
                 Key = rsa_public_key()
                 Options = public_crypt_options()

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

       der_decode(Asn1type, Der) -> term()

              Types:

                 Asn1Type = atom()
                   ASN.1 type present in the Public Key applications ASN.1 specifications.
                 Der = der_encoded()

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

       der_encode(Asn1Type, Entity) -> der_encoded()

              Types:

                 Asn1Type = atom()
                   ASN.1 type present in the Public Key applications ASN.1 specifications.
                 Entity = term()
                   Erlang representation of Asn1Type

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

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

              Types:

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

              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) -> binary()

              Types:

                 PlainText = binary()
                 Key = rsa_private_key()

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

       encrypt_public(PlainText, Key) -> binary()

              Types:

                 PlainText = binary()
                 Key = rsa_public_key()

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

       generate_key(Params)   ->  {Public::binary(),  Private::binary()}  |  #'ECPrivateKey'{}  |
       #'RSAPrivateKey'{}

              Types:

                 Params = key_params()

              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) -> [pem_entry()]

              Types:

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

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

       pem_encode(PemEntries) -> binary()

              Types:

                  PemEntries = [pem_entry()]

              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, {CipherInfo, Password}) -> pem_entry()

              Types:

                 Asn1Type = pki_asn1_type()
                 Entity = term()
                   Erlang  representation  of  Asn1Type.  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.
                 CipherInfo = cipher_info()
                 Password = string()

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

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

              Types:

                 Cert = der_encoded()

              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, otp | plain) -> der_encoded()

              Types:

                 Asn1Type = atom()
                   The ASN.1 type can be 'Certificate', 'OTPCertificate' or a subtype of either.
                 Entity = #'Certificate'{} | #'OTPCertificate'{} | a valid subtype

              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, IssuerID} | {error, Reason}

              Types:

                 Cert = der_encoded() | #'OTPCertificate'{}
                 IssuedBy = self | other
                 IssuerID = {integer(), issuer_name()}
                   The issuer id consists of the serial number and the issuers name.
                 Reason = term()

              Returns the issuer id.

       pkix_normalize_name(Issuer) -> Normalized

              Types:

                 Issuer = issuer_name()
                 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()}:
                  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) -> issuer_name()

              Types:

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

              Returns the issuer of the CRL.

       pkix_crls_validate(OTPCertificate, DPAndCRLs, Options) -> CRLStatus()

              Types:

                 OTPCertificate = #'OTPCertificate'{}
                 DPAndCRLs      =      [{DP::#'DistributionPoint'{},      {DerCRL::der_encoded(),
                 CRL::#'CertificateList'{}}}]
                 Options = proplists:proplist()
                 CRLStatus() = valid | {bad_cert,  revocation_status_undetermined}  |  {bad_cert,
                 {revocation_status_undetermined,   {bad_crls,  Details::term()}}}  |  {bad_cert,
                 {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  can  not  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(#'OTPTBSCertificate'{}, Key) -> der_encoded()

              Types:

                 Key = rsa_private_key() | dsa_private_key()

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

       pkix_sign_types(AlgorithmId) -> {DigestType, SignatureType}

              Types:

                 AlgorithmId = oid()
                   Signature OID from a certificate or a certificate revocation list.
                 DigestType = rsa_digest_type() | dss_digest_type()
                 SignatureType = rsa | dsa | ecdsa

              Translates signature algorithm OID to Erlang digest and signature types.

       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:ssl_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 can not 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 = rsa_public_key() | dsa_public_key() | ec_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 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
              Manual 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 that term 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.

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

              Types:

                 Msg = binary() | {digest,binary()}
                   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.
                 DigestType = rsa_digest_type() | dss_digest_type() | ecdsa_digest_type()
                 Key = rsa_private_key() | dsa_private_key() | ec_private_key()
                 Options = public_sign_options()

              Creates a digital signature.

       ssh_decode(SshBin, Type) -> [{public_key(), Attributes::list()}]

              Types:

                 SshBin = binary()
                   Example {ok, SshBin} = file:read_file("known_hosts").
                 Type = public_key | ssh_file()
                   If Type is public_key the binary can be either an RFC4716  public  key  or  an
                   OpenSSH public key.

              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.

                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.

       ssh_encode([{Key, Attributes}], Type) -> binary()

              Types:

                 Key = public_key()
                 Attributes = list()
                 Type = ssh_file()

              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 .

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

              Types:

                 Key = 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()}
                   The  Msg  is  either the binary "plain text" data or it is the hashed value of
                   "plain text", that is, the digest.
                 DigestType = rsa_digest_type() | dss_digest_type() | ecdsa_digest_type()
                 Signature = binary()
                 Key = rsa_public_key() | dsa_public_key() | ec_public_key()
                 Options = public_sign_options()

              Verifies a digital signature.

       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.