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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.