NAME

       ssl - The ssl application provides secure communication over
         sockets.

DESCRIPTION

       The ssl application is an implementation of the SSL, TLS and DTLS protocols in Erlang.

       For current statement of standards compliance see the User's Guide.

DEPENDENCIES

       The SSL application uses the public_key, asn1 and Crypto application to handle public keys
       and encryption, hence these applications must be loaded for the SSL application  to  work.
       In  an  embedded  environment this means they must be started with application:start/[1,2]
       before the SSL application is started.

CONFIGURATION

       The application environment configuration parameters in this section are defined  for  the
       SSL   application.   For   more   information  about  configuration  parameters,  see  the
       application(3erl) manual page in Kernel.

       The environment parameters can be set on the command line, for example:

       erl -ssl protocol_version "['tlsv1.2', 'tlsv1.1']"

         protocol_version = ssl:tls_version() | [ssl:tls_version()] <optional>:
           Protocol supported by started clients and servers. If  this  option  is  not  set,  it
           defaults  to all TLS protocols currently supported, more might be configurable, by the
           SSL  application.  This  option  can  be  overridden  by   the   version   option   to
           ssl:connect/[2,3] and ssl:listen/2.

         dtls_protocol_version = ssl:dtls_version() | [ssl:dtls_version()] <optional>:
           Protocol  supported  by  started  clients  and  servers. If this option is not set, it
           defaults to all DTLS protocols currently supported, more might be configurable, by the
           SSL   application.   This   option   can  be  overridden  by  the  version  option  to
           ssl:connect/[2,3] and ssl:listen/2.

         session_lifetime = integer() <optional>:
           Maximum lifetime of the session data in seconds. Defaults to 24  hours  which  is  the
           maximum  recommended lifetime by RFC 5246. However sessions may be invalidated earlier
           due to the maximum limitation of the session cache table.

         session_cb = atom() <optional>:
           Deprecated Since OTP-23.3 replaced by client_session_cb and server_session_cb

         client_session_cb = atom() <optional>:
           Since OTP-23.3 Name client of the session cache callback module  that  implements  the
           ssl_session_cache_api behavior. Defaults to ssl_client_session_cache_db.

         server_session_cb = atom() <optional>:
           Since  OTP-23.3  Name  of the server session cache callback module that implements the
           ssl_session_cache_api behavior. Defaults to ssl_server_session_cache_db.

         session_cb_init_args = proplist:proplist() <optional>:
           Deprecated   Since    OTP-23.3    replaced    by    client_session_cb_init_args    and
           server_session_cb_init_args

         client_session_cb_init_args = proplist:proplist() <optional>:
           List  of  extra  user-defined  arguments  to  the  init  function in the session cache
           callback module. Defaults to [].

         server_session_cb_init_args = proplist:proplist() <optional>:
           List of extra user-defined arguments  to  the  init  function  in  the  session  cache
           callback module. Defaults to [].

         session_cache_client_max = integer() <optional>
           :  Limits  the  growth of the clients session cache, that is how many sessions towards
           servers that are cached to be used by new client connections. If the maximum number of
           sessions is reached, the current cache entries will be invalidated regardless of their
           remaining lifetime. Defaults to 1000. Recommended ssl-8.2.1 or later for  this  option
           to work as intended.

         session_cache_server_max = integer() <optional>:
           Limits  the  growth of the servers session cache, that is how many client sessions are
           cached by the server. If the maximum number of sessions is reached, the current  cache
           entries  will be invalidated regardless of their remaining lifetime. Defaults to 1000.
           Recommended ssl-8.2.1 or later for this option to work as intended.

         ssl_pem_cache_clean = integer() <optional>:
           Number   of   milliseconds   between   PEM   cache   validations.   Defaults   to    2
           minutes.ssl:clear_pem_cache/0

         bypass_pem_cache = boolean() <optional>:
           Introduced  in  ssl-8.0.2. Disables the PEM-cache. Can be used as a workaround for the
           PEM-cache bottleneck before ssl-8.1.1. Defaults to false.

         alert_timeout = integer() <optional>:
           Number of milliseconds between sending of a fatal alert and  closing  the  connection.
           Waiting  a  little while improves the peers chances to properly receiving the alert so
           it may shutdown gracefully. Defaults to 5000 milliseconds.

         internal_active_n = integer() <optional>:
           For TLS connections this  value  is  used  to  handle  the  internal  socket.  As  the
           implementation  was changed from an active once to an active N behavior (N = 100), for
           performance reasons, this option exist for possible tweaking or restoring of  the  old
           behavior  (internal_active_n  = 1) in unforeseen scenarios. The option will not affect
           erlang distribution over TLS that will always run in active N mode. Added  in  ssl-9.1
           (OTP-21.2).

         server_session_tickets_amount = integer() <optional>:
           Number  of  session tickets sent by the server. It must be greater than 0. Defaults to
           3.

         server_session_ticket_lifetime = integer() <optional>:
           Lifetime of session tickets sent by the server. Servers must not use any value greater
           than  604800  seconds (7 days). Expired tickets are automatically removed. Defaults to
           7200 seconds (2 hours).

         server_session_ticket_store_size = integer() <optional>:
           Sets the maximum size of the server session ticket store (stateful tickets).  Defaults
           to 1000. Size limit is enforced by dropping old tickets.

         server_session_ticket_max_early_data = integer() <optional>:
           Sets  the  maximum  size of the early data that the server accepts and also configures
           its  NewSessionTicket  messages  to  include   this   same   size   limit   in   their
           early_data_indication  extension.  Defaults  to  16384. Size limit is enforced by both
           client and server.

         client_session_ticket_lifetime = integer() <optional>:
           Lifetime  of  session  tickets  in  the  client  ticket  store.  Expired  tickets  are
           automatically removed. Defaults to 7200 seconds (2 hours).

         client_session_ticket_store_size = integer() <optional>:
           Sets the maximum size of the client session ticket store. Defaults to 1000. Size limit
           is enforced by dropping old tickets.

ERROR LOGGER AND EVENT HANDLERS

       The SSL application  uses  OTP  logger.  TLS/DTLS  alerts  are  logged  on  notice  level.
       Unexpected  errors  are logged on error level. These log entries will by default end up in
       the default Erlang log. The option log_level may be used to in run-time  to  set  the  log
       level  of  a  specific  TLS connection, which is handy when you want to use level debug to
       inspect the TLS handshake setup.

SEE ALSO

       application(3erl)