ssl

ssl(3erl)                   Erlang Module Definition                   ssl(3erl)



NAME
       ssl - Interface Functions for Secure Socket Layer

DESCRIPTION
       This module contains interface functions for the SSL/TLS/DTLS protocol.
       For detailed information about the supported standards see ssl(7).

DATA TYPES
       The following data types are used in the functions for SSL/TLS/DTLS:

         boolean() =:
           true | false

         option() =:
           socketoption() | ssl_option() | transport_option()

         socketoption() =:
           proplists:property()

           The default socket options are [{mode,list},{packet, 0},{header,
           0},{active, true}].


           For valid options, see the inet(3erl), gen_tcp(3erl) and
           gen_udp(3erl) manual pages in Kernel. Note that stream oriented
           options such as packet are only relevant for SSL/TLS and not DTLS


         ssl_option() =:
           {verify, verify_type()}

           | {verify_fun, {fun(), term()}}


           | {fail_if_no_peer_cert, boolean()}


           | {depth, integer()}


           | {cert, public_key:der_encoded()}


           | {certfile, path()}


           | {key, {'RSAPrivateKey'| 'DSAPrivateKey' | 'ECPrivateKey' |
           'PrivateKeyInfo', public_key:der_encoded()} | #{algorithm := rsa |
           dss | ecdsa, engine := crypto:engine_ref(), key_id :=
           crypto:key_id(), password => crypto:password()}


           | {keyfile, path()}


           | {password, string()}


           | {cacerts, [public_key:der_encoded()]}


           | {cacertfile, path()}


           | {dh, public_key:der_encoded()}


           | {dhfile, path()}


           | {ciphers, ciphers()}


           | {user_lookup_fun, {fun(), term()}}, {psk_identity, string()},
           {srp_identity, {string(), string()}}


           | {reuse_sessions, boolean()}


           | {reuse_session, fun()} {next_protocols_advertised, [binary()]}


           | {client_preferred_next_protocols, {client | server, [binary()]} |
           {client | server, [binary()], binary()}}


           | {log_alert, boolean()}


           | {server_name_indication, hostname() | disable}


           | {customize_hostname_check, list()}


           | {sni_hosts, [{hostname(), [ssl_option()]}]}


           | {sni_fun, SNIfun::fun()}


         transport_option() =:
           {cb_info, {CallbackModule::atom(), DataTag::atom(),
           ClosedTag::atom(), ErrTag:atom()}}

           Defaults to {gen_tcp, tcp, tcp_closed, tcp_error} for TLS and
           {gen_udp, udp, udp_closed, udp_error} for DTLS. Can be used to
           customize the transport layer. For TLS the callback module must
           implement a reliable transport protocol, behave as gen_tcp, and have
           functions corresponding to inet:setopts/2, inet:getopts/2,
           inet:peername/1, inet:sockname/1, and inet:port/1. The callback
           gen_tcp is treated specially and calls inet directly. For DTLS this
           feature must be considered exprimental.


           CallbackModule =:
             atom()

           DataTag =:
             atom()

             Used in socket data message.


           ClosedTag =:
             atom()

             Used in socket close message.


         verify_type() =:
           verify_none | verify_peer

         path() =:
           string()

           Represents a file path.


         public_key:der_encoded() =:
           binary()

           ASN.1 DER-encoded entity as an Erlang binary.


         host() =:
           hostname() | ipaddress()

         hostname() =:
           string() - DNS hostname

         ip_address() =:
           {N1,N2,N3,N4} % IPv4 | {K1,K2,K3,K4,K5,K6,K7,K8} % IPv6

         sslsocket() =:
           opaque()

          protocol_version() =:
            ssl_tls_protocol() | dtls_protocol() sslv3 | tlsv1 | 'tlsv1.1' |
           'tlsv1.2'

          dtls_protocol() =:
           'dtlsv1' | 'dtlsv1.2'

         ciphers() =:
           = [ciphersuite()]

           Tuples and string formats accepted by versions before ssl-8.2.4 will
           be converted for backwards compatibility


         ciphersuite() =:
            #{key_exchange := key_exchange(), cipher := cipher(), mac :=
           MAC::hash() | aead, prf := PRF::hash() | default_prf}

         key_exchange()=:
           rsa | dhe_dss | dhe_rsa | dh_anon | psk | dhe_psk | rsa_psk |
           srp_anon | srp_dss | srp_rsa | ecdh_anon | ecdh_ecdsa | ecdhe_ecdsa |
           ecdh_rsa | ecdhe_rsa

         cipher() =:
           rc4_128 | des_cbc | '3des_ede_cbc' | aes_128_cbc | aes_256_cbc |
           aes_128_gcm | aes_256_gcm | chacha20_poly1305

         hash() =:
           md5 | sha | sha224 | sha256 | sha348 | sha512

         prf_random() =:
           client_random | server_random

         cipher_filters() =:
            [{key_exchange | cipher | mac | prf, algo_filter()}])

         algo_filter() =:
           fun(key_exchange() | cipher() | hash() | aead | default_prf) -> true
           | false

         srp_param_type() =:
           srp_1024 | srp_1536 | srp_2048 | srp_3072 | srp_4096 | srp_6144 |
           srp_8192

         SNIfun::fun():
           = fun(ServerName :: string()) -> [ssl_option()]

         named_curve() =:
           sect571r1 | sect571k1 | secp521r1 | brainpoolP512r1 | sect409k1 |
           sect409r1 | brainpoolP384r1 | secp384r1 | sect283k1 | sect283r1 |
           brainpoolP256r1 | secp256k1 | secp256r1 | sect239k1 | sect233k1 |
           sect233r1 | secp224k1 | secp224r1 | sect193r1 | sect193r2 | secp192k1
           | secp192r1 | sect163k1 | sect163r1 | sect163r2 | secp160k1 |
           secp160r1 | secp160r2

         hello_extensions() =:
           #{renegotiation_info => binary() | undefined, signature_algs =>
           [{hash(), ecsda| rsa| dsa}] | undefined alpn => binary() | undefined,
           next_protocol_negotiation => binary() | undefined, srp => string() |
           undefined, ec_point_formats => list() | undefined, elliptic_curves =>
           [oid] | undefined, sni => string() | undefined} }

TLS/DTLS OPTION DESCRIPTIONS - COMMON FOR SERVER AND CLIENT
       The following options have the same meaning in the client and the server:

         {protocol, tls | dtls}:
           Choose TLS or DTLS protocol for the transport layer security.
           Defaults to tls Introduced in OTP 20, DTLS support is considered
           experimental in this release. Other transports than UDP are not yet
           supported.

         {handshake, hello | full}:
           Defaults to full. If hello is specified the handshake will pause
           after the hello message and give the user a possibility make
           decisions based on hello extensions before continuing or aborting the
           handshake by calling  handshake_continue/3 or  handshake_cancel/1

         {cert, public_key:der_encoded()}:
           The DER-encoded users certificate. If this option is supplied, it
           overrides option certfile.

         {certfile, path()}:
           Path to a file containing the user certificate.

         {key, {'RSAPrivateKey'| 'DSAPrivateKey' | 'ECPrivateKey'
         |'PrivateKeyInfo', public_key:der_encoded()} | #{algorithm := rsa | dss
         | ecdsa, engine := crypto:engine_ref(), key_id := crypto:key_id(),
         password => crypto:password()}:
           The DER-encoded user's private key or a map refering to a crypto
           engine and its key reference that optionally can be password
           protected, seealso  crypto:engine_load/4  and  Crypto's Users Guide.
           If this option is supplied, it overrides option keyfile.

         {keyfile, path()}:
           Path to the file containing the user's private PEM-encoded key. As
           PEM-files can contain several entries, this option defaults to the
           same file as given by option certfile.

         {password, string()}:
           String containing the user's password. Only used if the private
           keyfile is password-protected.

         {ciphers, ciphers()}:
           Supported cipher suites. The function cipher_suites/0 can be used to
           find all ciphers that are supported by default. cipher_suites(all)
           can be called to find all available cipher suites. Pre-Shared Key
           (RFC 4279 and RFC 5487), Secure Remote Password (RFC 5054), RC4
           cipher suites, and anonymous cipher suites only work if explicitly
           enabled by this option; they are supported/enabled by the peer also.
           Anonymous cipher suites are supported for testing purposes only and
           are not be used when security matters.

         {eccs, [named_curve()]}:
           Allows to specify the order of preference for named curves and to
           restrict their usage when using a cipher suite supporting them.

         {secure_renegotiate, boolean()}:
           Specifies if to reject renegotiation attempt that does not live up to
           RFC 5746. By default secure_renegotiate is set to true, that is,
           secure renegotiation is enforced. If set to false secure
           renegotiation will still be used if possible, but it falls back to
           insecure renegotiation if the peer does not support RFC 5746.

         {depth, integer()}:
           Maximum number of non-self-issued intermediate certificates that can
           follow the peer certificate in a valid certification path. So, if
           depth is 0 the PEER must be signed by the trusted ROOT-CA directly;
           if 1 the path can be PEER, CA, ROOT-CA; if 2 the path can be PEER,
           CA, CA, ROOT-CA, and so on. The default value is 1.

         {verify_fun, {Verifyfun :: fun(), InitialUserState :: term()}}:
           The verification fun is to be defined as follows:

         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()}.


           The verification fun is called during the X509-path validation when
           an error or an extension unknown to the SSL application is
           encountered. It is also called when a certificate is considered valid
           by the path validation to allow access to each certificate in the
           path to the user application. It differentiates between the peer
           certificate and the CA certificates by using valid_peer or valid as
           second argument to the verification fun. See the public_key User's
           Guide for definition of #'OTPCertificate'{} and #'Extension'{}.


           * If the verify callback fun returns {fail, Reason}, the verification
             process is immediately stopped, an alert is sent to the peer, and
             the TLS/DTLS handshake terminates.

           * If the verify callback fun returns {valid, UserState}, the
             verification process continues.

           * If the verify callback fun always returns {valid, UserState}, the
             TLS/DTLS handshake does not terminate regarding verification
             failures and the connection is established.

           * If called with an extension unknown to the user application, return
             value {unknown, UserState} is to be used.

             Note that if the fun returns unknown for an extension marked as
             critical, validation will fail.


           Default option verify_fun in verify_peer mode:


         {fun(_,{bad_cert, _} = Reason, _) ->
               {fail, Reason};
             (_,{extension, _}, UserState) ->
               {unknown, UserState};
             (_, valid, UserState) ->
               {valid, UserState};
             (_, valid_peer, UserState) ->
                  {valid, UserState}
          end, []}


           Default option verify_fun in mode verify_none:


         {fun(_,{bad_cert, _}, UserState) ->
               {valid, UserState};
             (_,{extension, #'Extension'{critical = true}}, UserState) ->
               {valid, UserState};
             (_,{extension, _}, UserState) ->
               {unknown, UserState};
             (_, valid, UserState) ->
               {valid, UserState};
             (_, valid_peer, UserState) ->
                  {valid, UserState}
          end, []}


           The possible path validation errors are given on form {bad_cert,
           Reason} where Reason is:


           unknown_ca:
             No trusted CA was found in the trusted store. The trusted CA is
             normally a so called ROOT CA, which is a self-signed certificate.
             Trust can be claimed for an intermediate CA (trusted anchor does
             not have to be self-signed according to X-509) by using option
             partial_chain.

           selfsigned_peer:
             The chain consisted only of one self-signed certificate.

           PKIX X-509-path validation error:
             For possible reasons, see public_key:pkix_path_validation/3

         {crl_check, boolean() | peer | best_effort }:
           Perform CRL (Certificate Revocation List) verification
           (public_key:pkix_crls_validate/3) on all the certificates during the
           path validation (public_key:pkix_path_validation/3)  of the
           certificate chain. Defaults to false.

           peer:
             check is only performed on the peer certificate.

           best_effort:
             if certificate revocation status can not be determined it will be
             accepted as valid.

           The CA certificates specified for the connection will be used to
           construct the certificate chain validating the CRLs.


           The CRLs will be fetched from a local or external cache. See
           ssl_crl_cache_api(3erl).


         {crl_cache, {Module :: atom(), {DbHandle :: internal | term(), Args ::
         list()}}}:
           Specify how to perform lookup and caching of certificate revocation
           lists. Module defaults to ssl_crl_cache with  DbHandle  being
           internal and an empty argument list.

           There are two implementations available:


           ssl_crl_cache:
             This module maintains a cache of CRLs. CRLs can be added to the
             cache using the function ssl_crl_cache:insert/1, and optionally
             automatically fetched through HTTP if the following argument is
             specified:

             {http, timeout()}:
               Enables fetching of CRLs specified as http URIs inX509
               certificate extensions. Requires the OTP inets application.

           ssl_crl_hash_dir:
             This module makes use of a directory where CRLs are stored in files
             named by the hash of the issuer name.

             The file names consist of eight hexadecimal digits followed by .rN,
             where N is an integer, e.g. 1a2b3c4d.r0. For the first version of
             the CRL, N starts at zero, and for each new version, N is
             incremented by one. The OpenSSL utility c_rehash creates symlinks
             according to this pattern.


             For a given hash value, this module finds all consecutive .r* files
             starting from zero, and those files taken together make up the
             revocation list. CRL files whose nextUpdate fields are in the past,
             or that are issued by a different CA that happens to have the same
             name hash, are excluded.


             The following argument is required:


             {dir, string()}:
               Specifies the directory in which the CRLs can be found.

           max_handshake_size:
             Integer (24 bits unsigned). Used to limit the size of valid TLS
             handshake packets to avoid DoS attacks. Defaults to 256*1024.

         {partial_chain, fun(Chain::[DerCert]) -> {trusted_ca, DerCert} |
         unknown_ca }:
           Claim an intermediate CA in the chain as trusted. TLS then performs
           public_key:pkix_path_validation/3 with the selected CA as trusted
           anchor and the rest of the chain.

         {versions, [protocol_version()]}:
           TLS protocol versions supported by started clients and servers. This
           option overrides the application environment option protocol_version
           and dtls_protocol_version. If the environment option is not set, it
           defaults to all versions, except SSL-3.0, supported by the SSL
           application. See also ssl(7).

         {hibernate_after, integer()|undefined}:
           When an integer-value is specified, TLS/DTLS-connection goes into
           hibernation after the specified number of milliseconds of inactivity,
           thus reducing its memory footprint. When undefined is specified (this
           is the default), the process never goes into hibernation.

         {user_lookup_fun, {Lookupfun :: fun(), UserState :: term()}}:
           The lookup fun is to defined as follows:

         fun(psk, PSKIdentity ::string(), UserState :: term()) ->
              {ok, SharedSecret :: binary()} | error;
         fun(srp, Username :: string(), UserState :: term()) ->
              {ok, {SRPParams :: srp_param_type(), Salt :: binary(), DerivedKey :: binary()}} | error.


           For Pre-Shared Key (PSK) cipher suites, the lookup fun is called by
           the client and server to determine the shared secret. When called by
           the client, PSKIdentity is set to the hint presented by the server or
           to undefined. When called by the server, PSKIdentity is the identity
           presented by the client.


           For Secure Remote Password (SRP), the fun is only used by the server
           to obtain parameters that it uses to generate its session keys.
           DerivedKey is to be derived according to  RFC 2945 and  RFC 5054:
           crypto:sha([Salt, crypto:sha([Username, <<$:>>, Password])])


         {padding_check, boolean()}:
           Affects TLS-1.0 connections only. If set to false, it disables the
           block cipher padding check to be able to interoperate with legacy
           software.

     Warning:
         Using {padding_check, boolean()} makes TLS vulnerable to the Poodle
         attack.


         {beast_mitigation, one_n_minus_one | zero_n | disabled}:
           Affects SSL-3.0 and TLS-1.0 connections only. Used to change the
           BEAST mitigation strategy to interoperate with legacy software.
           Defaults to one_n_minus_one.

           one_n_minus_one - Perform 1/n-1 BEAST mitigation.


           zero_n - Perform 0/n BEAST mitigation.


           disabled - Disable BEAST mitigation.


     Warning:
         Using {beast_mitigation, disabled} makes SSL or TLS vulnerable to the
         BEAST attack.


TLS/DTLS OPTION DESCRIPTIONS - CLIENT SIDE
       The following options are client-specific or have a slightly different
       meaning in the client than in the server:

         {verify, verify_type()}:
           In mode verify_none the default behavior is to allow all x509-path
           validation errors. See also option verify_fun.

         {reuse_sessions, boolean()}:
           Specifies if the client is to try to reuse sessions when possible.

         {cacerts, [public_key:der_encoded()]}:
           The DER-encoded trusted certificates. If this option is supplied it
           overrides option cacertfile.

         {cacertfile, path()}:
           Path to a file containing PEM-encoded CA certificates. The CA
           certificates are used during server authentication and when building
           the client certificate chain.

         {alpn_advertised_protocols, [binary()]}:
           The list of protocols supported by the client to be sent to the
           server to be used for an Application-Layer Protocol Negotiation
           (ALPN). If the server supports ALPN then it will choose a protocol
           from this list; otherwise it will fail the connection with a
           "no_application_protocol" alert. A server that does not support ALPN
           will ignore this value.

           The list of protocols must not contain an empty binary.


           The negotiated protocol can be retrieved using the
           negotiated_protocol/1 function.


         {client_preferred_next_protocols, {Precedence :: server | client,
         ClientPrefs :: [binary()]}}
           {client_preferred_next_protocols, {Precedence :: server | client,
           ClientPrefs :: [binary()], Default :: binary()}}: Indicates that the
           client is to try to perform Next Protocol Negotiation.

           If precedence is server, the negotiated protocol is the first
           protocol to be shown on the server advertised list, which is also on
           the client preference list.


           If precedence is client, the negotiated protocol is the first
           protocol to be shown on the client preference list, which is also on
           the server advertised list.


           If the client does not support any of the server advertised protocols
           or the server does not advertise any protocols, the client falls back
           to the first protocol in its list or to the default protocol (if a
           default is supplied). If the server does not support Next Protocol
           Negotiation, the connection terminates if no default protocol is
           supplied.


         {psk_identity, string()}:
           Specifies the identity the client presents to the server. The
           matching secret is found by calling user_lookup_fun.

         {srp_identity, {Username :: string(), Password :: string()} :
           Specifies the username and password to use to authenticate to the
           server.

         {server_name_indication, HostName :: hostname()}:
           Specify the hostname to be used in TLS Server Name Indication
           extension. If not specified it will default to the Host argument of
           connect/[3,4] unless it is of type inet:ipaddress().

           The HostName will also be used in the hostname verification of the
           peer certificate using public_key:pkix_verify_hostname/2.


         {server_name_indication, disable}:
           Prevents the Server Name Indication extension from being sent and
           disables the hostname verification check
           public_key:pkix_verify_hostname/2

         {customize_hostname_check, Options::list()}:
           Customizes the hostname verification of the peer certificate, as
           different protocols that use TLS such as HTTP or LDAP may want to do
           it differently, for possible options see
           public_key:pkix_verify_hostname/3

         {fallback, boolean()}:
           Send special cipher suite TLS_FALLBACK_SCSV to avoid undesired TLS
           version downgrade. Defaults to false

     Warning:
         Note this option is not needed in normal TLS usage and should not be
         used to implement new clients. But legacy clients that retries
         connections in the following manner

          ssl:connect(Host, Port, [...{versions, ['tlsv2', 'tlsv1.1', 'tlsv1',
         'sslv3']}])

          ssl:connect(Host, Port, [...{versions, [tlsv1.1', 'tlsv1', 'sslv3']},
         {fallback, true}])

          ssl:connect(Host, Port, [...{versions, ['tlsv1', 'sslv3']}, {fallback,
         true}])

          ssl:connect(Host, Port, [...{versions, ['sslv3']}, {fallback, true}])

         may use it to avoid undesired TLS version downgrade. Note that
         TLS_FALLBACK_SCSV must also be supported by the server for the
         prevention to work.


         {signature_algs, [{hash(), ecdsa | rsa | dsa}]}:
           In addition to the algorithms negotiated by the cipher suite used for
           key exchange, payload encryption, message authentication and pseudo
           random calculation, the TLS signature algorithm extension Section
           7.4.1.4.1 in RFC 5246 may be used, from TLS 1.2, to negotiate which
           signature algorithm to use during the TLS handshake. If no lower TLS
           versions than 1.2 are supported, the client will send a TLS signature
           algorithm extension with the algorithms specified by this option.
           Defaults to

         [
         %% SHA2
         {sha512, ecdsa},
         {sha512, rsa},
         {sha384, ecdsa},
         {sha384, rsa},
         {sha256, ecdsa},
         {sha256, rsa},
         {sha224, ecdsa},
         {sha224, rsa},
         %% SHA
         {sha, ecdsa},
         {sha, rsa},
         {sha, dsa},
         ]

           The algorithms should be in the preferred order. Selected signature
           algorithm can restrict which hash functions that may be selected.
           Default support for {md5, rsa} removed in ssl-8.0


TLS/DTLS OPTION DESCRIPTIONS - SERVER SIDE
       The following options are server-specific or have a slightly different
       meaning in the server than in the client:

         {cacerts, [public_key:der_encoded()]}:
           The DER-encoded trusted certificates. If this option is supplied it
           overrides option cacertfile.

         {cacertfile, path()}:
           Path to a file containing PEM-encoded CA certificates. The CA
           certificates are used to build the server certificate chain and for
           client authentication. The CAs are also used in the list of
           acceptable client CAs passed to the client when a certificate is
           requested. Can be omitted if there is no need to verify the client
           and if there are no intermediate CAs for the server certificate.

         {dh, public_key:der_encoded()}:
           The DER-encoded Diffie-Hellman parameters. If specified, it overrides
           option dhfile.

         {dhfile, path()}:
           Path to a file containing PEM-encoded Diffie Hellman parameters to be
           used by the server if a cipher suite using Diffie Hellman key
           exchange is negotiated. If not specified, default parameters are
           used.

         {verify, verify_type()}:
           A server only does x509-path validation in mode verify_peer, as it
           then sends a certificate request to the client (this message is not
           sent if the verify option is verify_none). You can then also want to
           specify option fail_if_no_peer_cert.

         {fail_if_no_peer_cert, boolean()}:
           Used together with {verify, verify_peer} by an TLS/DTLS server. If
           set to true, the server fails if the client does not have a
           certificate to send, that is, sends an empty certificate. If set to
           false, it fails only if the client sends an invalid certificate (an
           empty certificate is considered valid). Defaults to false.

         {reuse_sessions, boolean()}:
           Specifies if the server is to agree to reuse sessions when requested
           by the clients. See also option reuse_session.

         {reuse_session, fun(SuggestedSessionId, PeerCert, Compression,
         CipherSuite) -> boolean()}:
           Enables the TLS/DTLS server to have a local policy for deciding if a
           session is to be reused or not. Meaningful only if reuse_sessions is
           set to true. SuggestedSessionId is a binary(), PeerCert is a DER-
           encoded certificate, Compression is an enumeration integer, and
           CipherSuite is of type ciphersuite().

         {alpn_preferred_protocols, [binary()]}:
           Indicates the server will try to perform Application-Layer Protocol
           Negotiation (ALPN).

           The list of protocols is in order of preference. The protocol
           negotiated will be the first in the list that matches one of the
           protocols advertised by the client. If no protocol matches, the
           server will fail the connection with a "no_application_protocol"
           alert.


           The negotiated protocol can be retrieved using the
           negotiated_protocol/1 function.


         {next_protocols_advertised, Protocols :: [binary()]}:
           List of protocols to send to the client if the client indicates that
           it supports the Next Protocol extension. The client can select a
           protocol that is not on this list. The list of protocols must not
           contain an empty binary. If the server negotiates a Next Protocol, it
           can be accessed using the negotiated_next_protocol/1 method.

         {psk_identity, string()}:
           Specifies the server identity hint, which the server presents to the
           client.

         {log_alert, boolean()}:
           If set to false, error reports are not displayed.

         {honor_cipher_order, boolean()}:
           If set to true, use the server preference for cipher selection. If
           set to false (the default), use the client preference.

         {sni_hosts, [{hostname(), [ssl_option()]}]}:
           If the server receives a SNI (Server Name Indication) from the client
           matching a host listed in the sni_hosts option, the specific options
           for that host will override previously specified options. The option
           sni_fun, and sni_hosts are mutually exclusive.

         {sni_fun, SNIfun::fun()}:
           If the server receives a SNI (Server Name Indication) from the
           client, the given function will be called to retrieve [ssl_option()]
           for the indicated server. These options will be merged into
           predefined [ssl_option()]. The function should be defined as:
           fun(ServerName :: string()) -> [ssl_option()] and can be specified as
           a fun or as named fun module:function/1 The option sni_fun, and
           sni_hosts are mutually exclusive.

         {client_renegotiation, boolean()}:
           In protocols that support client-initiated renegotiation, the cost of
           resources of such an operation is higher for the server than the
           client. This can act as a vector for denial of service attacks. The
           SSL application already takes measures to counter-act such attempts,
           but client-initiated renegotiation can be strictly disabled by
           setting this option to false. The default value is true. Note that
           disabling renegotiation can result in long-lived connections becoming
           unusable due to limits on the number of messages the underlying
           cipher suite can encipher.

         {honor_cipher_order, boolean()}:
           If true, use the server's preference for cipher selection. If false
           (the default), use the client's preference.

         {honor_ecc_order, boolean()}:
           If true, use the server's preference for ECC curve selection. If
           false (the default), use the client's preference.

         {signature_algs, [{hash(), ecdsa | rsa | dsa}]}:
           The algorithms specified by this option will be the ones accepted by
           the server in a signature algorithm negotiation, introduced in
           TLS-1.2. The algorithms will also be offered to the client if a
           client certificate is requested. For more details see the
           corresponding client option.

GENERAL
       When an TLS/DTLS socket is in active mode (the default), data from the
       socket is delivered to the owner of the socket in the form of messages:

         * {ssl, Socket, Data}

         * {ssl_closed, Socket}

         * {ssl_error, Socket, Reason}

       A Timeout argument specifies a time-out in milliseconds. The default
       value for argument Timeout is infinity.

EXPORTS
       append_cipher_suites(Deferred, Suites) -> ciphers()

              Types:

                 Deferred = ciphers() | cipher_filters()
                 Suites = ciphers()

              Make Deferred suites become the least preferred suites, that is
              put them at the end of the cipher suite list Suites after removing
              them from Suites if present. Deferred may be a list of cipher
              suits or a list of filters in which case the filters are use on
              Suites to extract the Deferred cipher list.


       cipher_suites() ->
       cipher_suites(Type) -> old_ciphers()

              Types:

                 Type = erlang | openssl | all

              Deprecated in OTP 21, use cipher_suites/2 instead.


       cipher_suites(Supported, Version) -> ciphers()

              Types:

                  Supported = default | all | anonymous
                  Version = protocol_version()

              Returns all default or all supported (except anonymous), or all
              anonymous cipher suites for a TLS version


       eccs() ->
       eccs(protocol_version()) -> [named_curve()]

              Returns a list of supported ECCs. eccs() is equivalent to calling
              eccs(Protocol) with all supported protocols and then deduplicating
              the output.


       clear_pem_cache() -> ok

              PEM files, used by ssl API-functions, are cached. The cache is
              regularly checked to see if any cache entries should be
              invalidated, however this function provides a way to
              unconditionally clear the whole cache.


       connect(Socket, SslOptions) ->
       connect(Socket, SslOptions, Timeout) -> {ok, SslSocket} | {ok, SslSocket,
       Ext} | {error, Reason}

              Types:

                 Socket = socket()
                 SslOptions = [{handshake, hello| full} | ssl_option()]
                 Timeout = integer() | infinity
                 SslSocket = sslsocket()
                 Ext = hello_extensions()
                 Reason = term()

              Upgrades a gen_tcp, or equivalent, connected socket to an TLS
              socket, that is, performs the client-side TLS handshake.

          Note:
              If the option verify is set to verify_peer the option
              server_name_indication shall also be specified, if it is not no
              Server Name Indication extension will be sent, and
              public_key:pkix_verify_hostname/2 will be called with the IP-
              address of the connection as ReferenceID, which is proably not
              what you want.


              If the option {handshake, hello} is used the handshake is paused
              after receiving the server hello message and the success response
              is {ok, SslSocket, Ext} instead of {ok, SslSocket}. Thereafter the
              handshake is continued or canceled by calling handshake_continue/3
              or handshake_cancel/1.


       connect(Host, Port, Options) ->
       connect(Host, Port, Options, Timeout) -> {ok, SslSocket}| {ok, SslSocket,
       Ext} | {error, Reason}

              Types:

                 Host = host()
                 Port = integer()
                 Options = [option()]
                 Timeout = integer() | infinity
                 SslSocket = sslsocket()
                 Reason = term()

              Opens an TLS/DTLS connection to Host, Port.

              When the option verify is set to verify_peer the check
              public_key:pkix_verify_hostname/2 will be performed in addition to
              the usual x509-path validation checks. If the check fails the
              error {bad_cert, hostname_check_failed} will be propagated to the
              path validation fun verify_fun, where it is possible to do
              customized checks by using the full possibilities of the
              public_key:pkix_verify_hostname/3 API. When the option
              server_name_indication is provided, its value (the DNS name) will
              be used as ReferenceID to public_key:pkix_verify_hostname/2. When
              no server_name_indication option is given, the Host argument will
              be used as Server Name Indication extension. The Host argument
              will also be used for the public_key:pkix_verify_hostname/2 check
              and if the Host argument is an inet:ip_address() the ReferenceID
              used for the check will be {ip, Host} otherwise dns_id will be
              assumed with a fallback to ip if that fails.

          Note:
              According to good practices certificates should not use IP-
              addresses as "server names". It would be very surprising if this
              happen outside a closed network.


              If the option {handshake, hello} is used the handshake is paused
              after receiving the server hello message and the success response
              is {ok, SslSocket, Ext} instead of {ok, SslSocket}. Thereafter the
              handshake is continued or canceled by calling handshake_continue/3
              or handshake_cancel/1.


       close(SslSocket) -> ok | {error, Reason}

              Types:

                 SslSocket = sslsocket()
                 Reason = term()

              Closes an TLS/DTLS connection.


       close(SslSocket, How) -> ok | {ok, port()} | {error, Reason}

              Types:

                 SslSocket = sslsocket()
                 How = timeout() | {NewController::pid(), timeout()}
                 Reason = term()

              Closes or downgrades an TLS connection. In the latter case the
              transport connection will be handed over to the NewController
              process after receiving the TLS close alert from the peer. The
              returned transport socket will have the following options set:
              [{active, false}, {packet, 0}, {mode, binary}]


       controlling_process(SslSocket, NewOwner) -> ok | {error, Reason}

              Types:

                 SslSocket = sslsocket()
                 NewOwner = pid()
                 Reason = term()

              Assigns a new controlling process to the SSL socket. A controlling
              process is the owner of an SSL socket, and receives all messages
              from the socket.


       connection_information(SslSocket) -> {ok, Result} | {error, Reason}

              Types:

                 SslSocket = sslsocket()
                 Item = protocol | selected_cipher_suite | sni_hostname | ecc |
                 session_id | atom()
                   Meaningful atoms, not specified above, are the ssl option
                   names.
                 Result = [{Item::atom(), Value::term()}]
                 Reason = term()

              Returns the most relevant information about the connection, ssl
              options that are undefined will be filtered out. Note that values
              that affect the security of the connection will only be returned
              if explicitly requested by connection_information/2.

          Note:
              The legacy Item = cipher_suite is still supported and returns the
              cipher suite on its (undocumented) legacy format. It should be
              replaced by selected_cipher_suite.



       connection_information(SslSocket, Items) -> {ok, Result} | {error,
       Reason}

              Types:

                 SslSocket = sslsocket()
                 Items = [Item]
                 Item = protocol | cipher_suite | sni_hostname | ecc |
                 session_id | client_random | server_random | master_secret |
                 atom()
                   Note that client_random, server_random and master_secret are
                   values that affect the security of connection. Meaningful
                   atoms, not specified above, are the ssl option names.
                 Result = [{Item::atom(), Value::term()}]
                 Reason = term()

              Returns the requested information items about the connection, if
              they are defined.

          Note:
              If only undefined options are requested the resulting list can be
              empty.



       filter_cipher_suites(Suites, Filters) -> ciphers()

              Types:

                  Suites = ciphers()
                  Filters = cipher_filters()

              Removes cipher suites if any of the filter functions returns false
              for any part of the cipher suite. This function also calls default
              filter functions to make sure the cipher suites are supported by
              crypto. If no filter function is supplied for some part the
              default behaviour is fun(Algorithm) -> true.


       format_error(Reason) -> string()

              Types:

                 Reason = term()

              Presents the error returned by an SSL function as a printable
              string.


       getopts(SslSocket, OptionNames) -> {ok, [socketoption()]} | {error,
       Reason}

              Types:

                 Socket = sslsocket()
                 OptionNames = [atom()]

              Gets the values of the specified socket options.


       getstat(SslSocket) -> {ok, OptionValues} | {error, inet:posix()}
       getstat(SslSocket, OptionNames) -> {ok, OptionValues} | {error,
       inet:posix()}

              Types:

                 SslSocket = sslsocket()
                 OptionNames = [atom()]
                 OptionValues = [{inet:stat_option(), integer()}]

              Gets one or more statistic options for the underlying TCP socket.

              See inet:getstat/2 for statistic options description.


       handshake(HsSocket) ->
       handshake(HsSocket, Timeout) -> {ok, SslSocket} | {error, Reason}

              Types:

                 HsSocket = SslSocket = sslsocket()
                 Timeout = integer()
                 Reason = term()

              Performs the SSL/TLS/DTLS server-side handshake.

              Returns a new TLS/DTLS socket if the handshake is successful.


       handshake(Socket, SslOptions) ->
       handshake(Socket, SslOptions, Timeout) -> {ok, SslSocket} | {ok,
       SslSocket, Ext} | {error, Reason}

              Types:

                 Socket = socket() | sslsocket()
                 SslSocket = sslsocket()
                 Ext = hello_extensions()
                 SslOptions = [{handshake, hello| full} | ssl_option()]
                 Timeout = integer()
                 Reason = term()

              If Socket is a ordinary socket(): upgrades a gen_tcp, or
              equivalent, socket to an SSL socket, that is, performs the SSL/TLS
              server-side handshake and returns a TLS socket.

          Warning:
              The Socket shall be in passive mode ({active, false}) before
              calling this function or else the behavior of this function is
              undefined.


              If Socket is an sslsocket(): provides extra SSL/TLS/DTLS options
              to those specified in listen/2  and then performs the SSL/TLS/DTLS
              handshake. Returns a new TLS/DTLS socket if the handshake is
              successful.

              If option {handshake, hello} is specified the handshake is paused
              after receiving the client hello message and the success response
              is {ok, SslSocket, Ext} instead of {ok, SslSocket}. Thereafter the
              handshake is continued or canceled by calling handshake_continue/3
              or handshake_cancel/1.


       handshake_cancel(SslSocket) -> ok

              Types:

                 SslSocket = sslsocket()

              Cancel the handshake with a fatal USER_CANCELED alert.


       handshake_continue(HsSocket, SSLOptions) -> {ok, SslSocket} | {error,
       Reason}
       handshake_continue(HsSocket, SSLOptions, Timeout) -> {ok, SslSocket} |
       {error, Reason}

              Types:

                 HsSocket = SslSocket = sslsocket()
                 SslOptions = [ssl_option()]
                 Timeout = integer()
                 Reason = term()

              Continue the SSL/TLS handshake possiby with new, additional or
              changed options.


       listen(Port, Options) -> {ok, ListenSocket} | {error, Reason}

              Types:

                 Port = integer()
                 Options = options()
                 ListenSocket = sslsocket()

              Creates an SSL listen socket.


       negotiated_protocol(SslSocket) -> {ok, Protocol} | {error,
       protocol_not_negotiated}

              Types:

                 SslSocket = sslsocket()
                 Protocol = binary()

              Returns the protocol negotiated through ALPN or NPN extensions.


       peercert(SslSocket) -> {ok, Cert} | {error, Reason}

              Types:

                 SslSocket = sslsocket()
                 Cert = binary()

              The peer certificate is returned as a DER-encoded binary. The
              certificate can be decoded with public_key:pkix_decode_cert/2


       peername(SslSocket) -> {ok, {Address, Port}} | {error, Reason}

              Types:

                 SslSocket = sslsocket()
                 Address = ipaddress()
                 Port = integer()

              Returns the address and port number of the peer.


       prepend_cipher_suites(Preferred, Suites) -> ciphers()

              Types:

                 Preferred = ciphers() | cipher_filters()
                 Suites = ciphers()

              Make Preferred suites become the most preferred suites that is put
              them at the head of the cipher suite list Suites after removing
              them from Suites if present. Preferred may be a list of cipher
              suits or a list of filters in which case the filters are use on
              Suites to extract the preferred cipher list.


       prf(Socket, Secret, Label, Seed, WantedLength) -> {ok, binary()} |
       {error, reason()}

              Types:

                 Socket = sslsocket()
                 Secret = binary() | master_secret
                 Label = binary()
                 Seed = [binary() | prf_random()]
                 WantedLength = non_neg_integer()

              Uses the Pseudo-Random Function (PRF) of a TLS session to generate
              extra key material. It either takes user-generated values for
              Secret and Seed or atoms directing it to use a specific value from
              the session security parameters.

              Can only be used with TLS/DTLS connections; {error, undefined} is
              returned for SSLv3 connections.


       recv(SslSocket, Length) ->
       recv(SslSocket, Length, Timeout) -> {ok, Data} | {error, Reason}

              Types:

                 SslSocket = sslsocket()
                 Length = integer()
                 Timeout = integer()
                 Data = [char()] | binary()

              Receives a packet from a socket in passive mode. A closed socket
              is indicated by return value {error, closed}.

              Argument Length is meaningful only when the socket is in mode raw
              and denotes the number of bytes to read. If Length = 0, all
              available bytes are returned. If Length > 0, exactly Length bytes
              are returned, or an error; possibly discarding less than Length
              bytes of data when the socket gets closed from the other side.

              Optional argument Timeout specifies a time-out in milliseconds.
              The default value is infinity.


       renegotiate(SslSocket) -> ok | {error, Reason}

              Types:

                 SslSocket = sslsocket()

              Initiates a new handshake. A notable return value is {error,
              renegotiation_rejected} indicating that the peer refused to go
              through with the renegotiation, but the connection is still active
              using the previously negotiated session.


       send(SslSocket, Data) -> ok | {error, Reason}

              Types:

                 SslSocket = sslsocket()
                 Data = iodata()

              Writes Data to Socket.

              A notable return value is {error, closed} indicating that the
              socket is closed.


       setopts(SslSocket, Options) -> ok | {error, Reason}

              Types:

                 SslSocket = sslsocket()
                 Options = [socketoption]()

              Sets options according to Options for socket Socket.


       shutdown(SslSocket, How) -> ok | {error, Reason}

              Types:

                 SslSocket = sslsocket()
                 How = read | write | read_write
                 Reason = reason()

              Immediately closes a socket in one or two directions.

              How == write means closing the socket for writing, reading from it
              is still possible.

              To be able to handle that the peer has done a shutdown on the
              write side, option {exit_on_close, false} is useful.


       ssl_accept(SslSocket) ->
       ssl_accept(SslSocket, Timeout) -> ok | {error, Reason}

              Types:

                 SslSocket = sslsocket()
                 Timeout = integer()
                 Reason = term()

              Deprecated in OTP 21, use handshake/[1,2] instead.

          Note:
              handshake/[1,2] always returns a new socket.



       ssl_accept(Socket, SslOptions) ->
       ssl_accept(Socket, SslOptions, Timeout) -> {ok, Socket} | ok | {error,
       Reason}

              Types:

                 Socket = socket() | sslsocket()
                 SslOptions = [ssl_option()]
                 Timeout = integer()
                 Reason = term()

              Deprecated in OTP 21, use handshake/[2,3] instead.

          Note:
              handshake/[2,3] always returns a new socket.



       sockname(SslSocket) -> {ok, {Address, Port}} | {error, Reason}

              Types:

                 SslSocket = sslsocket()
                 Address = ipaddress()
                 Port = integer()

              Returns the local address and port number of socket Socket.


       start() ->
       start(Type) -> ok | {error, Reason}

              Types:

                 Type = permanent | transient | temporary

              Starts the SSL application. Default type is temporary.


       stop() -> ok

              Stops the SSL application.


       suite_to_str(CipherSuite) -> String

              Types:

                 CipherSuite = erl_cipher_suite()
                 String = string()

              Returns the string representation of a cipher suite.


       transport_accept(ListenSocket) ->
       transport_accept(ListenSocket, Timeout) -> {ok, SslSocket} | {error,
       Reason}

              Types:

                 ListenSocket = SslSocket = sslsocket()
                 Timeout = integer()
                 Reason = reason()

              Accepts an incoming connection request on a listen socket.
              ListenSocket must be a socket returned from  listen/2. The socket
              returned is to be passed to  handshake/[2,3] to complete
              handshaking, that is, establishing the SSL/TLS/DTLS connection.

          Warning:
              Most API functions require that the TLS/DTLS connection is
              established to work as expected.


              The accepted socket inherits the options set for ListenSocket in
              listen/2.

              The default value for Timeout is infinity. If Timeout is specified
              and no connection is accepted within the given time, {error,
              timeout} is returned.


       versions() -> [versions_info()]

              Types:

                 versions_info() = {app_vsn, string()} | {supported | available,
                 [ssl_tls_protocol()]} | {supported_dtls | available_dtls,
                 [dtls_protocol()]}

              Returns version information relevant for the SSL application.

                app_vsn:
                  The application version of the SSL application.

                supported:
                  SSL/TLS versions supported by default. Overridden by a version
                  option on  connect/[2,3,4],  listen/2, and ssl_accept/[1,2,3].
                  For the negotiated SSL/TLS version, see
                  connection_information/1 .

                supported_dtls:
                  DTLS versions supported by default. Overridden by a version
                  option on  connect/[2,3,4],  listen/2, and ssl_accept/[1,2,3].
                  For the negotiated DTLS version, see connection_information/1
                  .

                available:
                  All SSL/TLS versions supported by the SSL application. TLS 1.2
                  requires sufficient support from the Crypto application.

                available_dtls:
                  All DTLS versions supported by the SSL application. DTLS 1.2
                  requires sufficient support from the Crypto application.


SEE ALSO
       inet(3erl) and gen_tcp(3erl) gen_udp(3erl)



Ericsson AB                         ssl 9.1.2                          ssl(3erl)