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NAME
ssl - Interface Functions for Secure Socket Layer
DESCRIPTION
This module contains interface functions to the Secure Socket Layer.
SSL
* ssl requires the crypto and public_key applications.
* Supported SSL/TLS-versions are SSL-3.0, TLS-1.0, TLS-1.1 and TLS-1.2.
* For security reasons sslv2 is not supported.
* Ephemeral Diffie-Hellman cipher suites are supported but not Diffie Hellman
Certificates cipher suites.
* Elliptic Curve cipher suites are supported if crypto 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
spec so there is not any real motivation to implement them.
* CRL and policy certificate extensions are not supported yet. However CRL verification
is supported by public_key, only not integrated in ssl yet.
* Support for 'Server Name Indication' extension client side (RFC 6066 section 3).
COMMON DATA TYPES
The following data types are used in the functions below:
boolean() = true | false
option() = socketoption() | ssloption() | transportoption()
socketoption() = proplists:property() - The default socket options are
[{mode,list},{packet, 0},{header, 0},{active, true}].
For valid options see inet(3erl) and gen_tcp(3erl).
ssloption() = {verify, verify_type()} | {verify_fun, {fun(), term()}} |
{fail_if_no_peer_cert, boolean()} {depth, integer()} | {cert, der_encoded()}| {certfile,
path()} | {key, {'RSAPrivateKey'| 'DSAPrivateKey' | 'ECPrivateKey' |'PrivateKeyInfo',
der_encoded()}} | {keyfile, path()} | {password, string()} | {cacerts, [der_encoded()]} |
{cacertfile, path()} | |{dh, der_encoded()} | {dhfile, path()} | {ciphers, ciphers()} |
{user_lookup_fun, {fun(), term()}}, {psk_identity, string()}, {srp_identity, {string(),
string()}} | {ssl_imp, ssl_imp()} | {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}
transportoption() = {cb_info, {CallbackModule::atom(), DataTag::atom(), ClosedTag::atom(),
ErrTag:atom()}} - defaults to {gen_tcp, tcp, tcp_closed, tcp_error}. Can be used to
customize the transport layer. The callback module must implement a reliable transport
protocol and behave as gen_tcp and in addition 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 will call inet directly.
CallbackModule = atom()
DataTag = atom() - tag used in socket data message.
ClosedTag = atom() - tag used in socket close message.
verify_type() = verify_none | verify_peer
path() = string() - representing a file path.
der_encoded() = binary() -Asn1 DER encoded entity as an erlang binary.
host() = hostname() | ipaddress()
hostname() = string()
ip_address() = {N1,N2,N3,N4} % IPv4 | {K1,K2,K3,K4,K5,K6,K7,K8} % IPv6
sslsocket() - opaque to the user.
protocol() = sslv3 | tlsv1 | 'tlsv1.1' | 'tlsv1.2'
ciphers() = [ciphersuite()] | string() (according to old API)
ciphersuite() = {key_exchange(), cipher(), hash()}
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
hash() = md5 | sha
prf_random() = client_random | server_random
srp_param_type() = srp_1024 | srp_1536 | srp_2048 | srp_3072 | srp_4096 | srp_6144 |
srp_8192
SSL OPTION DESCRIPTIONS - COMMON FOR SERVER AND CLIENT
Options described here are options that are have the same meaning in the client and the
server.
{cert, der_encoded()}:
The DER encoded users certificate. If this option is supplied it will override the
certfile option.
{certfile, path()}:
Path to a file containing the user's certificate.
{key, {'RSAPrivateKey'| 'DSAPrivateKey' | 'ECPrivateKey' |'PrivateKeyInfo',
der_encoded()}}:
The DER encoded users private key. If this option is supplied it will override the
keyfile option.
{keyfile, path()}:
Path to file containing user's private PEM encoded key. As PEM-files may contain
several entries this option defaults to the same file as given by certfile option.
{password, string()}:
String containing the user's password. Only used if the private keyfile is password
protected.
{cacerts, [der_encoded()]}:
The DER encoded trusted certificates. If this option is supplied it will override the
cacertfile option.
{cacertfile, path()}:
Path to file containing PEM encoded CA certificates (trusted certificates used for
verifying a peer certificate). May be omitted if you do not want to verify the peer.
{ciphers, ciphers()}:
The cipher suites that should be supported. The function cipher_suites/0 can be used
to find all ciphers that are supported by default. cipher_suites(all) may be called to
find all available cipher suites. Pre-Shared Key (RFC 4279 and RFC 5487), Secure
Remote Password (RFC 5054) and anonymous cipher suites only work if explicitly enabled
by this option and they are supported/enabled by the peer also. Note that anonymous
cipher suites are supported for testing purposes only and should not be used when
security matters.
{ssl_imp, new | old}:
No longer has any meaning as the old implementation has been removed, it will be
ignored.
{secure_renegotiate, boolean()}:
Specifies if to reject renegotiation attempt that does not live up to RFC 5746. By
default secure_renegotiate is set to false i.e. secure renegotiation will be used if
possible but it will fallback to unsecure renegotiation if the peer does not support
RFC 5746.
{depth, integer()}:
The depth is the maximum number of non-self-issued intermediate certificates that may
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 it is 2 PEER, CA, CA, ROOT-CA and so on. The default value is 1.
{verify_fun, {Verifyfun :: fun(), InitialUserState :: term()}}:
The verification fun should be defined as:
fun(OtpCert :: #'OTPCertificate'{}, Event :: {bad_cert, Reason :: atom()} |
{extension, #'Extension'{}}, InitialUserState :: term()) ->
{valid, UserState :: term()} | {valid_peer, UserState :: term()} |
{fail, Reason :: term()} | {unknown, UserState :: term()}.
The verify fun will be called during the X509-path validation when an error or an
extension unknown to the ssl application is encountered. Additionally it will be
called when a certificate is considered valid by the path validation to allow access
to each certificate in the path to the user application. Note that it will
differentiate between the peer certificate and CA certificates by using valid_peer or
valid as the second argument to the verify 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 and an alert is sent to the peer and the TLS/SSL handshake is
terminated. If the verify callback fun returns {valid, UserState}, the verification
process is continued. If the verify callback fun always returns {valid, UserState},
the TLS/SSL handshake will not be terminated with respect to verification failures and
the connection will be established. If called with an extension unknown to the user
application the return value {unknown, UserState} should be used.
The default verify_fun option in verify_peer mode:
{fun(_,{bad_cert, _} = Reason, _) ->
{fail, Reason};
(_,{extension, _}, UserState) ->
{unknown, UserState};
(_, valid, UserState) ->
{valid, UserState};
(_, valid_peer, UserState) ->
{valid, UserState}
end, []}
The default verify_fun option in verify_none mode:
{fun(_,{bad_cert, _}, UserState) ->
{valid, UserState};
(_,{extension, _}, UserState) ->
{unknown, UserState};
(_, valid, UserState) ->
{valid, UserState};
(_, valid_peer, UserState) ->
{valid, UserState}
end, []}
Possible path validation errors:
{bad_cert, cert_expired}, {bad_cert, invalid_issuer}, {bad_cert, invalid_signature},
{bad_cert, unknown_ca},{bad_cert, selfsigned_peer}, {bad_cert, name_not_permitted},
{bad_cert, missing_basic_constraint}, {bad_cert, invalid_key_usage}
{versions, [protocol()]}:
TLS protocol versions that will be supported by started clients and servers. This
option overrides the application environment option protocol_version. If the
environment option is not set it defaults to all versions supported by the SSL
application. See also ssl(7)
{hibernate_after, integer()|undefined}:
When an integer-value is specified, the ssl_connection will go 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 will never
go into hibernation.
{user_lookup_fun, {Lookupfun :: fun(), UserState :: term()}}:
The lookup fun should be defined as:
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 will be called by the client
and server to determine the shared secret. When called by the client, PSKIdentity will
be set to the hint presented by the server or undefined. When called by the server,
PSKIdentity is the identity presented by the client.
For Secure Remote Password (SRP), the fun will only be used by the server to obtain
parameters that it will use to generate its session keys. DerivedKey should be derived
according to RFC 2945 and RFC 5054: crypto:sha([Salt, crypto:sha([Username, <<$:>>,
Password])])
{padding_check, boolean()}:
This option only affects TLS-1.0 connections. If set to false it disables the block
cipher padding check to be able to interoperate with legacy software.
Warning:
Using this option makes TLS vulnerable to the Poodle attack
SSL OPTION DESCRIPTIONS - CLIENT SIDE
Options described here are client specific or has a slightly different meaning in the
client than in the server.
{verify, verify_type()}:
In verify_none mode the default behavior will be to allow all x509-path validation
errors. See also the verify_fun option.
{reuse_sessions, boolean()}:
Specifies if client should try to reuse sessions when possible.
{client_preferred_next_protocols, {Precedence :: server | client, ClientPrefs ::
[binary()]}}:
{client_preferred_next_protocols, {Precedence :: server | client, ClientPrefs ::
[binary()], Default :: binary()}}:
Indicates the client will try to perform Next Protocol Negotiation.
If precedence is server the negotiated protocol will be the first protocol that
appears on the server advertised list that is also on the client preference list.
If precedence is client the negotiated protocol will be the first protocol that
appears on the client preference list that 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 will fallback to the first protocol in its
list or if a default is supplied it will fallback to that instead. If the server does
not support Next Protocol Negotiation the connection will be aborted 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 the user_look_fun.
{srp_identity, {Username :: string(), Password :: string()}:
Specifies the Username and Password to use to authenticate to the server.
{server_name_indication, hostname()}:
{server_name_indication, disable}:
This option can be specified when upgrading a TCP socket to a TLS socket to use the
TLS Server Name Indication extension.
When starting a TLS connection without upgrade the Server Name Indication extension
will be sent if possible, this option may also be used to disable that behavior.
SSL OPTION DESCRIPTIONS - SERVER SIDE
Options described here are server specific or has a slightly different meaning in the
server than in the client.
{dh, der_encoded()}:
The DER encoded Diffie Hellman parameters. If this option is supplied it will override
the dhfile option.
{dhfile, path()}:
Path to file containing PEM encoded Diffie Hellman parameters, for the server to use
if a cipher suite using Diffie Hellman key exchange is negotiated. If not specified
default parameters will be used.
{verify, verify_type()}:
Servers only do the x509-path validation in verify_peer mode, as it then will send a
certificate request to the client (this message is not sent if the verify option is
verify_none) and you may then also want to specify the option fail_if_no_peer_cert.
{fail_if_no_peer_cert, boolean()}:
Used together with {verify, verify_peer} by an ssl server. If set to true, the server
will fail if the client does not have a certificate to send, i.e. sends a empty
certificate, if set to false it will only fail if the client sends an invalid
certificate (an empty certificate is considered valid).
{reuse_sessions, boolean()}:
Specifies if the server should agree to reuse sessions when the clients request to do
so. See also the reuse_session option.
{reuse_session, fun(SuggestedSessionId, PeerCert, Compression, CipherSuite) ->
boolean()}:
Enables the ssl server to have a local policy for deciding if a session should be
reused or not, only meaningful 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().
{next_protocols_advertised, Protocols :: [binary()]}:
The list of protocols to send to the client if the client indicates it supports the
Next Protocol extension. The client may 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 negotiated_next_protocol/1 method.
{psk_identity, string()}:
Specifies the server identity hint the server presents to the client.
{log_alert, boolean()}:
If false, error reports will not be displayed.
GENERAL
When an ssl 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 timeout in milliseconds. The default value for a Timeout
argument is infinity.
EXPORTS
cipher_suites() ->
cipher_suites(Type) -> ciphers()
Types:
Type = erlang | openssl | all
Returns a list of supported cipher suites. cipher_suites() is equivalent to
cipher_suites(erlang). Type openssl is provided for backwards compatibility with
old ssl that used openssl. cipher_suites(all) returns all available cipher suites.
The cipher suites not present in cipher_suites(erlang) but in included in
cipher_suites(all) will not be used unless explicitly configured by the user.
connect(Socket, SslOptions) ->
connect(Socket, SslOptions, Timeout) -> {ok, SslSocket} | {error, Reason}
Types:
Socket = socket()
SslOptions = [ssloption()]
Timeout = integer() | infinity
SslSocket = sslsocket()
Reason = term()
Upgrades a gen_tcp, or equivalent, connected socket to an ssl socket i.e. performs
the client-side ssl handshake.
connect(Host, Port, Options) ->
connect(Host, Port, Options, Timeout) -> {ok, SslSocket} | {error, Reason}
Types:
Host = host()
Port = integer()
Options = [option()]
Timeout = integer() | infinity
SslSocket = sslsocket()
Reason = term()
Opens an ssl connection to Host, Port.
close(SslSocket) -> ok | {error, Reason}
Types:
SslSocket = sslsocket()
Reason = term()
Close an ssl connection.
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_info(SslSocket) -> {ok, {ProtocolVersion, CipherSuite}} | {error, Reason}
Types:
CipherSuite = ciphersuite()
ProtocolVersion = protocol()
Returns the negotiated protocol version and cipher suite.
format_error(Reason) -> string()
Types:
Reason = term()
Presents the error returned by an ssl function as a printable string.
getopts(Socket, OptionNames) -> {ok, [socketoption()]} | {error, Reason}
Types:
Socket = sslsocket()
OptionNames = [atom()]
Get the value of the specified socket options.
listen(Port, Options) -> {ok, ListenSocket} | {error, Reason}
Types:
Port = integer()
Options = options()
ListenSocket = sslsocket()
Creates an ssl listen socket.
peercert(Socket) -> {ok, Cert} | {error, Reason}
Types:
Socket = 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(Socket) -> {ok, {Address, Port}} | {error, Reason}
Types:
Socket = sslsocket()
Address = ipaddress()
Port = integer()
Returns the address and port number of the peer.
recv(Socket, Length) ->
recv(Socket, Length, Timeout) -> {ok, Data} | {error, Reason}
Types:
Socket = sslsocket()
Length = integer()
Timeout = integer()
Data = [char()] | binary()
This function receives a packet from a socket in passive mode. A closed socket is
indicated by a return value {error, closed}.
The Length argument is only meaningful when the socket is in raw mode 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.
The optional Timeout parameter specifies a timeout in milliseconds. The default
value is infinity.
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()
Use the pseudo random function (PRF) of a TLS session to generate additional key
material. It either takes user generated values for Secret and Seed or atoms
directing it use a specific value from the session security parameters.
This function can only be used with TLS connections, {error, undefined} is returned
for SSLv3 connections.
renegotiate(Socket) -> ok | {error, Reason}
Types:
Socket = 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(Socket, Data) -> ok | {error, Reason}
Types:
Socket = sslsocket()
Data = iodata()
Writes Data to Socket.
A notable return value is {error, closed} indicating that the socket is closed.
setopts(Socket, Options) -> ok | {error, Reason}
Types:
Socket = sslsocket()
Options = [socketoption]()
Sets options according to Options for the socket Socket.
shutdown(Socket, How) -> ok | {error, Reason}
Types:
Socket = sslsocket()
How = read | write | read_write
Reason = reason()
Immediately close 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, the
{exit_on_close, false} option is useful.
ssl_accept(ListenSocket) ->
ssl_accept(ListenSocket, Timeout) -> ok | {error, Reason}
Types:
ListenSocket = sslsocket()
Timeout = integer()
Reason = term()
The ssl_accept function establish the SSL connection on the server side. It should
be called directly after transport_accept, in the spawned server-loop.
ssl_accept(ListenSocket, SslOptions) ->
ssl_accept(ListenSocket, SslOptions, Timeout) -> {ok, Socket} | {error, Reason}
Types:
ListenSocket = socket()
SslOptions = ssloptions()
Timeout = integer()
Reason = term()
Upgrades a gen_tcp, or equivalent, socket to an ssl socket i.e. performs the ssl
server-side handshake.
Warning:
Note that the listen socket should be in {active, false} mode before telling the
client that the server is ready to upgrade and calling this function, otherwise the
upgrade may or may not succeed depending on timing.
sockname(Socket) -> {ok, {Address, Port}} | {error, Reason}
Types:
Socket = sslsocket()
Address = ipaddress()
Port = integer()
Returns the local address and port number of the socket Socket.
start() ->
start(Type) -> ok | {error, Reason}
Types:
Type = permanent | transient | temporary
Starts the Ssl application. Default type is temporary. application(3erl)
stop() -> ok
Stops the Ssl application. application(3erl)
transport_accept(Socket) ->
transport_accept(Socket, Timeout) -> {ok, NewSocket} | {error, Reason}
Types:
Socket = NewSocket = 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 should be passed to ssl_accept
to complete ssl handshaking and establishing the connection.
Warning:
The socket returned can only be used with ssl_accept, no traffic can be sent or
received before that call.
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() -> [{SslAppVer, SupportedSslVer, AvailableSslVsn}]
Types:
SslAppVer = string()
SupportedSslVer = [protocol()]
AvailableSslVsn = [protocol()]
Returns version information relevant for the ssl application.
negotiated_next_protocol(Socket) -> {ok, Protocol} | {error, next_protocol_not_negotiated}
Types:
Socket = sslsocket()
Protocol = binary()
Returns the Next Protocol negotiated.
SEE ALSO
inet(3erl) and gen_tcp(3erl)