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NAME
ssl - The ssl application provides secure communication over
sockets.
DESCRIPTION
The ssl application is an implementation of the SSL/TLS protocol in Erlang.
* Supported SSL/TLS-versions are SSL-3.0, TLS-1.0, TLS-1.1, and TLS-1.2.
* For security reasons SSL-2.0 is not supported.
* For security reasons SSL-3.0 is no longer supported by default, but can be configured.
* For security reasons DES cipher suites are no longer supported by default, but can be configured.
*
Renegotiation Indication Extension RFC 5746 is supported
* Ephemeral Diffie-Hellman cipher suites are supported, but not Diffie Hellman Certificates cipher
suites.
* Elliptic Curve cipher suites are supported if the Crypto application supports it and named curves are
used.
* Export cipher suites are not supported as the U.S. lifted its export restrictions in early 2000.
* IDEA cipher suites are not supported as they have become deprecated by the latest TLS specification
so it is not motivated to implement them.
* Compression is not supported.
* CRL validation is supported.
* Policy certificate extensions are not supported.
* 'Server Name Indication' extension (RFC 6066) is supported.
* Application Layer Protocol Negotiation (ALPN) and its successor Next Protocol Negotiation (NPN) are
supported.
* It is possible to use Pre-Shared Key (PSK) and Secure Remote Password (SRP) cipher suites, but they
are not enabled by default.
DEPENDENCIES
The SSL application uses the public_key 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:protocol()<optional>:
Protocol supported by started clients and servers. If this option is not set, it defaults to all
protocols currently supported 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>:
Name of the session cache callback module that implements the ssl_session_cache_api behavior.
Defaults to ssl_session_cache.
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.
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.
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. The PEM cache has proven to be a bottleneck, until
the implementation has been improved this can be used as a workaround. 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.
ERROR LOGGER AND EVENT HANDLERS
The SSL application uses the default OTP error logger to log unexpected errors and TLS alerts. The
logging of TLS alerts may be turned off with the log_alert option.
SEE ALSO
application(3erl)