socket() = gen_tcp:socket()

sslsocket() = any()

An opaque reference to the TLS/DTLS connection, may be used for equality matching.

tls_option() = tls_client_option() | tls_server_option()

tls_client_option() = 


    client_option() |


    common_option() |


    socket_option() |


    transport_option()

tls_server_option() = 


    server_option() |


    common_option() |


    socket_option() |


    transport_option()

socket_option() = 


    gen_tcp:connect_option() |


    gen_tcp:listen_option() |


    gen_udp:option()

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 TLS and not DTLS

active_msgs() = 


    {ssl, sslsocket(), Data :: binary() | list()} |


    {ssl_closed, sslsocket()} |


    {ssl_error, sslsocket(), Reason :: any()} |


    {ssl_passive, sslsocket()}

When a 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 as described above.

The ssl_passive message is sent only when the socket is in {active, N} mode and the counter dropped to 0. It indicates that the socket has transitioned to passive ({active, false}) mode.

transport_option() = 


    {cb_info,


     {CallbackModule :: atom(),


      DataTag :: atom(),


      ClosedTag :: atom(),


      ErrTag :: atom()}} |


    {cb_info,


     {CallbackModule :: atom(),


      DataTag :: atom(),


      ClosedTag :: atom(),


      ErrTag :: atom(),


      PassiveTag :: atom()}}

Defaults to {gen_tcp, tcp, tcp_closed, tcp_error, tcp_passive} for TLS (for backward compatibility a four tuple will be converted to a five tuple with the last element "second_element"_passive) and {gen_udp, udp, udp_closed, udp_error} for DTLS (might also be changed to five tuple in the future). Can be used to customize the transport layer. The tag values should be the values used by the underlying transport in its active mode messages. 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 experimental.

host() = hostname() | ip_address()

hostname() = string()

ip_address() = inet:ip_address()

protocol_version() = tls_version() | dtls_version()

tls_version() = 'tlsv1.2' | 'tlsv1.3' | tls_legacy_version()

dtls_version() = 'dtlsv1.2' | dtls_legacy_version()

tls_legacy_version() = tlsv1 | 'tlsv1.1'

dtls_legacy_version() = dtlsv1

prf_random() = client_random | server_random

verify_type() = verify_none | verify_peer

ciphers() = [erl_cipher_suite()] | string()

erl_cipher_suite() = 


    #{key_exchange := kex_algo(),


      cipher := cipher(),


      mac := hash() | aead,


      prf := hash() | default_prf}

cipher() = 


    aes_128_cbc | aes_256_cbc | aes_128_gcm | aes_256_gcm |


    aes_128_ccm | aes_256_ccm | aes_128_ccm_8 | aes_256_ccm_8 |


    chacha20_poly1305 |


    legacy_cipher()

legacy_cipher() = rc4_128 | des_cbc | '3des_ede_cbc'

cipher_filters() = 


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

hash() = sha | sha2() | legacy_hash()

sha2() = sha224 | sha256 | sha384 | sha512

legacy_hash() = md5

old_cipher_suite() = 


    {kex_algo(), cipher(), hash()} |


    {kex_algo(), cipher(), hash() | aead, hash()}

sign_algo() = rsa | dsa | ecdsa | eddsa

sign_scheme() = 


    eddsa_ed25519 | eddsa_ed448 | ecdsa_secp256r1_sha256 |


    ecdsa_secp384r1_sha384 | ecdsa_secp521r1_sha512 |


    rsassa_pss_scheme() |


    sign_scheme_legacy()

rsassa_pss_scheme() = 


    rsa_pss_rsae_sha256 | rsa_pss_rsae_sha384 |


    rsa_pss_rsae_sha512 | rsa_pss_pss_sha256 |


    rsa_pss_pss_sha384 | rsa_pss_pss_sha512

sign_scheme_legacy() = 


    rsa_pkcs1_sha256 | rsa_pkcs1_sha384 | rsa_pkcs1_sha512 |


    rsa_pkcs1_sha1 | ecdsa_sha1

group() = 


    secp256r1 | secp384r1 | secp521r1 | ffdhe2048 | ffdhe3072 |


    ffdhe4096 | ffdhe6144 | ffdhe8192

kex_algo() = 


    rsa | dhe_rsa | dhe_dss | ecdhe_ecdsa | ecdh_ecdsa |


    ecdh_rsa | srp_rsa | srp_dss | psk | dhe_psk | rsa_psk |


    dh_anon | ecdh_anon | srp_anon | any

algo_filter() = 


    fun((kex_algo() | cipher() | hash() | aead | default_prf) ->


            true | false)

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

psk_identity() = string()

srp_identity() = {Username :: string(), Password :: string()}

srp_param_type() = 


    srp_1024 | srp_1536 | srp_2048 | srp_3072 | srp_4096 |


    srp_6144 | srp_8192

app_level_protocol() = binary()

protocol_extensions() = 


    #{renegotiation_info => binary(),


      signature_algs => signature_algs(),


      alpn => app_level_protocol(),


      srp => binary(),


      next_protocol => app_level_protocol(),


      max_frag_enum => 1..4,


      ec_point_formats => [0..2],


      elliptic_curves => [public_key:oid()],


      sni => hostname()}

error_alert() = 


    {tls_alert, {tls_alert(), Description :: string()}}

tls_alert() = 


    close_notify | unexpected_message | bad_record_mac |


    record_overflow | handshake_failure | bad_certificate |


    unsupported_certificate | certificate_revoked |


    certificate_expired | certificate_unknown |


    illegal_parameter | unknown_ca | access_denied |


    decode_error | decrypt_error | export_restriction |


    protocol_version | insufficient_security | internal_error |


    inappropriate_fallback | user_canceled | no_renegotiation |


    unsupported_extension | certificate_unobtainable |


    unrecognized_name | bad_certificate_status_response |


    bad_certificate_hash_value | unknown_psk_identity |


    no_application_protocol

reason() = any()

bloom_filter_window_size() = integer()

bloom_filter_hash_functions() = integer()

bloom_filter_bits() = integer()

client_session_tickets() = disabled | manual | auto

server_session_tickets() = disabled | stateful | stateless

common_option() = 


    {protocol, protocol()} |


    {handshake, handshake_completion()} |


    {cert, cert() | [cert()]} |


    {certfile, cert_pem()} |


    {key, key()} |


    {keyfile, key_pem()} |


    {password, key_pem_password()} |


    {certs_keys, certs_keys()} |


    {ciphers, cipher_suites()} |


    {eccs, [named_curve()]} |


    {signature_algs, signature_algs()} |


    {signature_algs_cert, sign_schemes()} |


    {supported_groups, supported_groups()} |


    {secure_renegotiate, secure_renegotiation()} |


    {keep_secrets, keep_secrets()} |


    {depth, allowed_cert_chain_length()} |


    {verify_fun, custom_verify()} |


    {crl_check, crl_check()} |


    {crl_cache, crl_cache_opts()} |


    {max_handshake_size, handshake_size()} |


    {partial_chain, root_fun()} |


    {versions, protocol_versions()} |


    {user_lookup_fun, custom_user_lookup()} |


    {log_level, logging_level()} |


    {log_alert, log_alert()} |


    {hibernate_after, hibernate_after()} |


    {padding_check, padding_check()} |


    {beast_mitigation, beast_mitigation()} |


    {ssl_imp, ssl_imp()} |


    {session_tickets, session_tickets()} |


    {key_update_at, key_update_at()} |


    {receiver_spawn_opts, spawn_opts()} |


    {sender_spawn_opts, spawn_opts()}

protocol() = tls | dtls

Choose TLS or DTLS protocol for the transport layer security. Defaults to tls. For DTLS other transports than UDP are not yet supported.

handshake_completion() = 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 user certificate. Note that the cert option may also be a list of DER-encoded certificates where the first one is the user certificate, and the rest of the certificates constitutes the certificate chain. For maximum interoperability the certificates in the chain should be in the correct order, the chain will be sent as is to the peer. If chain certificates are not provided, certificates from client_cacerts(), server_cacerts(), or client_cafile(), server_cafile() are used to construct the chain. If this option is supplied, it overrides option certfile.

cert_pem() = file:filename()

Path to a file containing the user certificate on PEM format or possible several certificates where the first one is the user certificate and the rest of the certificates constitutes the certificate chain. For more details see cert(),

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 referring to a crypto engine and its key reference that optionally can be password protected, see also crypto:engine_load/3 and Crypto's Users Guide. If this option is supplied, it overrides option keyfile.

key_pem() = file:filename()

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.

key_pem_password() = iodata() | fun(() -> iodata())

String containing the user's password or a function returning same type. Only used if the private keyfile is password-protected.

certs_keys() = [cert_key_conf()]

A list of a certificate (or possible a certificate and its chain) and the associated key of the certificate, that may be used to authenticate the client or the server. The certificate key pair that is considered best and matches negotiated parameters for the connection will be selected. Different signature algorithms are prioritized in the order eddsa, ecdsa, rsa_pss_pss, rsa and dsa . If more than one key is supplied for the same signing algorithm (which is probably an unusual use case) they will prioritized by strength unless it is a so called engine key that will be favoured over other keys. As engine keys cannot be inspected, supplying more than one engine key will make no sense. This offers flexibility to for instance configure a newer certificate that is expected to be used in most cases and an older but acceptable certificate that will only be used to communicate with legacy systems. Note that there is a trade off between the induced overhead and the flexibility so alternatives should be chosen for good reasons. If the certs_keys option is specified it overrides all single certificate and key options. For examples see the Users Guide

eddsa certificates are only supported by TLS-1.3 that does not support dsa certificates. rsa_pss_pss (RSA certificates using Probabilistic Signature Scheme) are supported in TLS-1.2 and TLS-1.3, but some TLS-1.2 implementations may not support rsa_pss_pss.

cert_key_conf() = 


    #{cert => cert(),


      key => key(),


      certfile => cert_pem(),


      keyfile => key_pem(),


      password => key_pem_password()}

A certificate (or possibly a certificate and its chain) and its associated key on one of the possible formats. For the PEM file format there may also be a password associated with the file containg the key.

cipher_suites() = ciphers()

A list of cipher suites that should be supported

The function ssl:cipher_suites/2 can be used to find all cipher suites that are supported by default and all cipher suites that may be configured.

If you compose your own cipher_suites() make sure they are filtered for cryptolib support ssl:filter_cipher_suites/2 Additionally the functions ssl:append_cipher_suites/2 , ssl:prepend_cipher_suites/2, ssl:suite_to_str/1, ssl:str_to_suite/1, and ssl:suite_to_openssl_str/1 also exist to help creating customized cipher suite lists.

Note that TLS-1.3 and TLS-1.2 cipher suites are not overlapping sets of cipher suites so to support both these versions cipher suites from both versions need to be included. Also if the supplied list does not comply with the configured versions or cryptolib so that the list becomes empty, this option will fallback on its appropriate default value for the configured versions.

Non-default cipher suites including anonymous cipher suites (PRE TLS-1.3) are supported for interop/testing purposes and may be used by adding them to your cipher suite list. Note that they must also be supported/enabled by the peer to actually be used.

signature_algs() = [{hash(), sign_algo()} | sign_scheme()]

Explicitly list acceptable signature algorithms for certificates and handshake messages in the preferred order. The client will send its list as the client hello signature_algorithm extension introduced in TLS-1.2, see Section 7.4.1.4.1 in RFC 5246. Previously these algorithms where implicitly chosen and partly derived from the cipher suite.

In TLS-1.2 a somewhat more explicit negotiation is made possible using a list of {hash(), sign_algo()} pairs.

In TLS-1.3 these algorithm pairs are replaced by so called signature schemes sign_scheme() and completely decoupled from the cipher suite.

Signature algorithms used for certificates may be overridden by the signature schemes (algorithms) supplied by the signature_algs_cert option.

TLS-1.2 default is Default_TLS_12_Alg_Pairs interleaved with rsa_pss_schemes since ssl-11.0 (OTP-25) pss_pss is prefered over pss_rsae that is prefered over rsa

Default_TLS_12_Alg_Pairs =

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

Support for {md5, rsa} was removed from the the TLS-1.2 default in ssl-8.0 (OTP-22)

rsa_pss_schemes =

[rsa_pss_pss_sha512,
rsa_pss_pss_sha384,
rsa_pss_pss_sha256,
rsa_pss_rsae_sha512,
rsa_pss_rsae_sha384,
rsa_pss_rsae_sha256]


 

TLS_13_Legacy_Schemes =

 [


 %% Legacy algorithms only applicable to certificate signatures
rsa_pkcs1_sha512, %% Corresponds to {sha512, rsa}
rsa_pkcs1_sha384, %% Corresponds to {sha384, rsa}
rsa_pkcs1_sha256, %% Corresponds to {sha256, rsa}
ecdsa_sha1,       %% Corresponds to {sha, ecdsa}
rsa_pkcs1_sha1    %% Corresponds to {sha, rsa}
]

Default_TLS_13_Schemes =

 [


 %% EDDSA
eddsa_ed25519,
eddsa_ed448
%% ECDSA
ecdsa_secp521r1_sha512,
ecdsa_secp384r1_sha384,
ecdsa_secp256r1_sha256] ++
%% RSASSA-PSS
rsa_pss_schemes()


 

EDDSA was made highest priority in ssl-11.0 (OTP-25)

TLS-1.3 default is

Default_TLS_13_Schemes ++ Legacy_TLS_13_Schemes 

If both TLS-1.3 and TLS-1.2 are supported the default will be

Default_TLS_13_Schemes ++ Default_TLS_12_Alg_Pairs 

so appropriate algorithms can be chosen for the negotiated version.

TLS-1.2 algorithms will not be negotiated for TLS-1.3, but TLS-1.3 RSASSA-PSS rsassa_pss_scheme() signature schemes may be negotiated also for TLS-1.2 from 24.1 (fully working from 24.1.3). However if TLS-1.3 is negotiated when both TLS-1.3 and TLS-1.2 is supported using defaults, the corresponding TLS-1.2 algorithms to the TLS-1.3 legacy signature schemes will be considered as the legacy schemes and applied only to certificate signatures.

sign_schemes() = [sign_scheme()]

Explicitly list acceptable signature schemes (algorithms) in the preferred order. Overrides the algorithms supplied in signature_algs option for certificates.

In addition to the signature_algorithms extension from TLS 1.2, TLS 1.3 (RFC 5246 Section 4.2.3) adds the signature_algorithms_cert extension which enables having special requirements on the signatures used in the certificates that differs from the requirements on digital signatures as a whole. If this is not required this extension is not need.

The client will send a signature_algorithms_cert extension (in the client hello message), if TLS version 1.2 (back-ported to TLS 1.2 in 24.1) or later is used, and the signature_algs_cert option is explicitly specified. By default, only the signature_algs extension is sent.

Note that supported signature schemes for TLS-1.2 are sign_scheme_legacy() and rsassa_pss_scheme()

supported_groups() = [group()]

TLS 1.3 introduces the "supported_groups" extension that is used for negotiating the Diffie-Hellman parameters in a TLS 1.3 handshake. Both client and server can specify a list of parameters that they are willing to use.

If it is not specified it will use a default list ([x25519, x448, secp256r1, secp384r1]) that is filtered based on the installed crypto library version.

secure_renegotiation() = 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.

allowed_cert_chain_length() = 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 10.

custom_verify() = 


    {Verifyfun :: function(), InitialUserState :: any()}

The verification fun is to be defined as follows:

fun(OtpCert :: #'OTPCertificate'{},


    Event, InitialUserState :: term()) ->
	{valid, UserState :: term()} |
	{fail, Reason :: term()} | {unknown, UserState :: term()}.
fun(OtpCert :: #'OTPCertificate'{}, DerCert :: public_key:der_encoded(),


    Event, InitialUserState :: term()) ->
	{valid, UserState :: term()} |
	{fail, Reason :: term()} | {unknown, UserState :: term()}.
Types:


      Event = {bad_cert, Reason :: atom() |


              {revoked, atom()}} |
	      {extension, #'Extension'{}} |


              valid |


              valid_peer
	

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 Event argument to the verification fun. See the public_key User's Guide for definition of #'OTPCertificate'{} and #'Extension'{}.

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:

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.

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_opts() = 


    {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:

root_fun() = function()

fun(Chain::[public_key:der_encoded()]) ->
	{trusted_ca, DerCert::public_key:der_encoded()} | 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.

protocol_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, supported by the SSL application. See also ssl(7).

custom_user_lookup() = 


    {Lookupfun :: function(), UserState :: any()}

The lookup fun is to defined as follows:

fun(psk, PSKIdentity :: binary(), UserState :: term()) ->
	{ok, SharedSecret :: binary()} | error;
fun(srp, Username :: binary(), 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])])

session_id() = binary()

Identifies a TLS session.

log_alert() = boolean()

If set to false, TLS/DTLS Alert reports are not displayed. Deprecated in OTP 22, use {log_level, logging_level()} instead.

logging_level() = logger:level() | none | all

Specifies the log level for a TLS/DTLS connection. Alerts are logged on notice level, which is the default level. The level debug triggers verbose logging of TLS/DTLS protocol messages. See also ssl(7)

hibernate_after() = timeout()

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.

handshake_size() = integer()

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

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.

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

beast_mitigation() = one_n_minus_one | zero_n | disabled

Affects 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.

Using {beast_mitigation, disabled} makes TLS-1.0 vulnerable to the BEAST attack.

ssl_imp() = new | old

Deprecated since OTP-17, has no effect.

session_tickets() = 


    client_session_tickets() | server_session_tickets()

Configures the session ticket functionality in TLS 1.3 client and server.

key_update_at() = integer() >= 1

Configures the maximum amount of bytes that can be sent on a TLS 1.3 connection before an automatic key update is performed.

There are cryptographic limits on the amount of plaintext which can be safely encrypted under a given set of keys. The current default ensures that data integrity will not be breached with probability greater than 1/2^57. For more information see Limits on Authenticated Encryption Use in TLS.

The default value of this option shall provide the above mentioned security guarantees and it shall be reasonable for most applications (~353 TB).

middlebox_comp_mode() = boolean()

Configures the middlebox compatibility mode on a TLS 1.3 connection.

A significant number of middleboxes misbehave when a TLS 1.3 connection is negotiated. Implementations can increase the chance of making connections through those middleboxes by making the TLS 1.3 handshake more like a TLS 1.2 handshake.

The middlebox compatibility mode is enabled (true) by default.

spawn_opts() = [erlang:spawn_opt_option()]

Configures spawn options of TLS sender and receiver processes.

Setting up garbage collection options can be helpful for trade-offs between CPU usage and Memory usage. See erlang:spawn_opt/2.

For dist connections, default sender option is [...{priority, max}], this priority option cannot be changed. For all connections, ...link is added to receiver and cannot be changed.

keep_secrets() = boolean()

Configures a TLS 1.3 connection for keylogging

In order to retrieve keylog information on a TLS 1.3 connection, it must be configured in advance to keep the client_random and various handshake secrets.

The keep_secrets functionality is disabled (false) by default.

Added in OTP 23.2

client_option() = 


    {verify, client_verify_type()} |


    {reuse_session, client_reuse_session()} |


    {reuse_sessions, client_reuse_sessions()} |


    {cacerts, client_cacerts()} |


    {cacertfile, client_cafile()} |


    {alpn_advertised_protocols, client_alpn()} |


    {client_preferred_next_protocols,


     client_preferred_next_protocols()} |


    {psk_identity, client_psk_identity()} |


    {srp_identity, client_srp_identity()} |


    {server_name_indication, sni()} |


    {max_fragment_length, max_fragment_length()} |


    {customize_hostname_check, customize_hostname_check()} |


    {fallback, fallback()} |


    {middlebox_comp_mode, middlebox_comp_mode()} |


    {certificate_authorities, client_certificate_authorities()} |


    {session_tickets, client_session_tickets()} |


    {use_ticket, use_ticket()} |


    {early_data, client_early_data()}

client_verify_type() = verify_type()

Defaults to verify_none as additional options are needed to be able to perform the certificate verification. A warning will be emitted unless verify_none is explicitly configured. Usually the applications will want to configure verify_peer together with an appropriate cacert or cacertfile option. For example an HTTPS client would normally use the option {cacerts, public_key:cacerts_get()} (available since OTP-25) to access the CA certificates provided by the OS. Using verify_none means that all x509-certificate path validation errors will be ignored. See also option verify_fun.

client_reuse_session() = 


    session_id() | {session_id(), SessionData :: binary()}

Reuses a specific session. The session should be referred by its session id if it is earlier saved with the option {reuse_sessions, save} since OTP-21.3 or explicitly specified by its session id and associated data since OTP-22.3. See also SSL's Users Guide, Session Reuse pre TLS 1.3.

client_reuse_sessions() = boolean() | save

When save is specified a new connection will be negotiated and saved for later reuse. The session ID can be fetched with connection_information/2 and used with the client option reuse_session The boolean value true specifies that if possible, automated session reuse will be performed. If a new session is created, and is unique in regard to previous stored sessions, it will be saved for possible later reuse. Since OTP-21.3.

client_certificate_authorities() = boolean()

If set to true, sends the certificate authorities extension in TLS-1.3 client hello. The default is false. Note that setting it to true may result in a big overhead if you have many trusted CA certificates. Since OTP-24.3.

client_cacerts() = 


    [public_key:der_encoded()] | [public_key:combined_cert()]

The DER-encoded trusted certificates. If this option is supplied it overrides option cacertfile.

client_cafile() = file:filename()

Path to a file containing PEM-encoded CA certificates. The CA certificates are used during server authentication and when building the client certificate chain.

When PEM caching is enabled, files provided with this option will be checked for updates at fixed time intervals specified by the ssl_pem_cache_clean environment parameter.

Alternatively, CA certificates can be provided as a DER-encoded binary with client_cacerts option.

client_alpn() = [app_level_protocol()]

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 :: [app_level_protocol()]} |


    {Precedence :: server | client,


     ClientPrefs :: [app_level_protocol()],


     Default :: app_level_protocol()}

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.

max_fragment_length() = undefined | 512 | 1024 | 2048 | 4096

Specifies the maximum fragment length the client is prepared to accept from the server. See RFC 6066

client_psk_identity() = psk_identity()

Specifies the identity the client presents to the server. The matching secret is found by calling user_lookup_fun

client_srp_identity() = srp_identity()

Specifies the username and password to use to authenticate to the server.

sni() = hostname() | disable

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.

The special value 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() = 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

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']}])

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

ssl:connect(Host, Port, [...{versions, ['tlsv1']}, {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.

client_session_tickets() = disabled | manual | auto

Configures the session ticket functionality. Allowed values are disabled, manual and auto. If it is set to manual the client will send the ticket information to user process in a 3-tuple:

{ssl, session_ticket, {SNI, TicketData}}

where SNI is the ServerNameIndication and TicketData is the extended ticket data that can be used in subsequent session resumptions.

If it is set to auto, the client automatically handles received tickets and tries to use them when making new TLS connections (session resumption with pre-shared keys).

This option is supported by TLS 1.3 and above. See also SSL's Users Guide, Session Tickets and Session Resumption in TLS 1.3

use_ticket() = [binary()]

Configures the session tickets to be used for session resumption. It is a mandatory option in manual mode (session_tickets = manual).

Session tickets are only sent to user if option session_tickets is set to manual

This option is supported by TLS 1.3 and above. See also SSL's Users Guide, Session Tickets and Session Resumption in TLS 1.3

client_early_data() = binary()

Configures the early data to be sent by the client.

In order to be able to verify that the server has the intention to process the early data, the following 3-tuple is sent to the user process:

{ssl, SslSocket, {early_data, Result}}

where Result is either accepted or rejected.

It is the responsibility of the user to handle a rejected Early Data and to resend when it is appropriate.

server_option() = 


    {cacerts, server_cacerts()} |


    {cacertfile, server_cafile()} |


    {dh, dh_der()} |


    {dhfile, dh_file()} |


    {verify, server_verify_type()} |


    {fail_if_no_peer_cert, fail_if_no_peer_cert()} |


    {certificate_authorities, server_certificate_authorities()} |


    {reuse_sessions, server_reuse_sessions()} |


    {reuse_session, server_reuse_session()} |


    {alpn_preferred_protocols, server_alpn()} |


    {next_protocols_advertised, server_next_protocol()} |


    {psk_identity, server_psk_identity()} |


    {sni_hosts, sni_hosts()} |


    {sni_fun, sni_fun()} |


    {honor_cipher_order, honor_cipher_order()} |


    {honor_ecc_order, honor_ecc_order()} |


    {client_renegotiation, client_renegotiation()} |


    {session_tickets, server_session_tickets()} |


    {anti_replay, anti_replay()} |


    {cookie, cookie()} |


    {early_data, server_early_data()}

server_cacerts() = 


    [public_key:der_encoded()] | [public_key:combined_cert()]

The DER-encoded trusted certificates. If this option is supplied it overrides option cacertfile.

server_certificate_authorities() = boolean()

Determines if a TLS-1.3 server should include the authorities extension in its certificate request message that will be sent if the option verify is set to verify_peer. Defaults to true.

A reason to exclude the extension would be if the server wants to communicate with clients incapable of sending complete certificate chains that adhere to the extension, but the server still has the capability to recreate a chain that it can verify.

server_cafile() = file:filename()

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.

When PEM caching is enabled, files provided with this option will be checked for updates at fixed time intervals specified by the ssl_pem_cache_clean environment parameter.

Alternatively, CA certificates can be provided as a DER-encoded binary with server_cacerts option.

dh_der() = binary()

The DER-encoded Diffie-Hellman parameters. If specified, it overrides option dhfile.

The dh_der option is not supported by TLS 1.3. Use the supported_groups option instead.

dh_file() = file:filename()

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.

The dh_file option is not supported by TLS 1.3. Use the supported_groups option instead.

server_verify_type() = verify_type()

Client certificates are an optional part of the TLS protocol. A server only does x509-certificate path validation in mode verify_peer. By default the server is in verify_none mode an hence will not send an certificate request to the client. When using verify_peer you may also want to specify the options fail_if_no_peer_cert and certificate_authorities.

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.

server_reuse_sessions() = boolean()

The boolean value true specifies that the server will agree to reuse sessions. Setting it to false will result in an empty session table, that is no sessions will be reused. See also option reuse_session.

server_reuse_session() = function()

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().

server_alpn() = [app_level_protocol()]

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.

server_next_protocol() = [app_level_protocol()]

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.

server_psk_identity() = psk_identity()

Specifies the server identity hint, which the server presents to the client.

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(), [server_option() | common_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() = function()

If the server receives a SNI (Server Name Indication) from the client, the given function will be called to retrieve [server_option()] for the indicated server. These options will be merged into predefined [server_option()] list. The function should be defined as: fun(ServerName :: string()) -> [server_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.

server_session_tickets() = disabled | stateful | stateless

Configures the session ticket functionality. Allowed values are disabled, stateful and stateless.

If it is set to stateful or stateless, session resumption with pre-shared keys is enabled and the server will send stateful or stateless session tickets to the client after successful connections.

A stateful session ticket is a database reference to internal state information. A stateless session ticket is a self-encrypted binary that contains both cryptographic keying material and state data.

This option is supported by TLS 1.3 and above. See also SSL's Users Guide, Session Tickets and Session Resumption in TLS 1.3

anti_replay() = 


    '10k' | '100k' |


    {bloom_filter_window_size(),


     bloom_filter_hash_functions(),


     bloom_filter_bits()}

Configures the server's built-in anti replay feature based on Bloom filters.

Allowed values are the pre-defined '10k', '100k' or a custom 3-tuple that defines the properties of the bloom filters: {WindowSize, HashFunctions, Bits}. WindowSize is the number of seconds after the current Bloom filter is rotated and also the window size used for freshness checks. HashFunctions is the number hash functions and Bits is the number of bits in the bit vector. '10k' and '100k' are simple defaults with the following properties:

This option is supported by TLS 1.3 and above and only with stateless session tickets. Ticket lifetime, the number of tickets sent by the server and the maximum number of tickets stored by the server in stateful mode are configured by application variables. See also SSL's Users Guide, Anti-Replay Protection in TLS 1.3

cookie() = boolean()

If true (default), the server sends a cookie extension in its HelloRetryRequest messages.

The cookie extension has two main purposes. It allows the server to force the client to demonstrate reachability at their apparent network address (thus providing a measure of DoS protection). This is primarily useful for non-connection-oriented transports. It also allows to offload the server's state to the client. The cookie extension is enabled by default as it is a mandatory extension in RFC8446.

server_early_data() = disabled | enabled

Configures if the server accepts (enabled) or rejects (rejects) early data sent by a client. The default value is disabled.

This option is a placeholder, early data is not yet implemented on the server side.

connection_info() = 


    [common_info() |


     curve_info() |


     ssl_options_info() |


     security_info()]

common_info() = 


    {protocol, protocol_version()} |


    {session_id, session_id()} |


    {session_resumption, boolean()} |


    {selected_cipher_suite, erl_cipher_suite()} |


    {sni_hostname, term()} |


    {srp_username, term()}

curve_info() = {ecc, {named_curve, term()}}

ssl_options_info() = tls_option()

security_info() = 


    {client_random, binary()} |


    {server_random, binary()} |


    {master_secret, binary()}

connection_info_items() = [connection_info_item()]

connection_info_item() = 


    protocol | session_id | session_resumption |


    selected_cipher_suite | sni_hostname | srp_username | ecc |


    client_random | server_random | master_secret | keylog |


    tls_options_name()

tls_options_name() = atom()