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Interface Functions for Secure Socket Layer


This module contains interface functions to the Secure Socket Layer.


This manual page describes functions that are defined in the ssl module and represents the new ssl implementation that coexists with the old one, as the new implementation is not yet compleat enough to replace the old one.

The new implementation can be accessed by providing the option {ssl_imp, new} to the ssl:connect and ssl:listen functions.

The new implementation is Erlang based and all logic is in Erlang and only payload encryption calculations are done in C via the crypto application. The main reason for making a new implementation is that the old solution was very crippled as the control of the ssl-socket was deep down in openssl making it hard if not impossible to support all inet options, ipv6 and upgrade of a tcp connection to a ssl connection. The alfa version has a few limitations that will be removed before the ssl-4.0 release. Main differences and limitations in the alfa are listed below.


The following data types are used in the functions below:

boolean() = true | false
option() = socketoption() | ssloption()
socketoption() - [{property(), value()}], property() = atom(),
      value() = term(), defaults to
      [{mode,list},{packet, 0},{header, 0},{active, true}].

For valid options see inet(3) and gen_tcp(3) .

ssloption() = {verify, verify_code()} | {depth, integer()} |
      {certfile, path()} | {keyfile, path()} | {password, string()} |
      {cacertfile, path()} | {ciphers, ciphers()} | {ssl_imp, ssl_imp()}
      | {reuse_sessions, boolean()}
path() = string() - representing a file path.
verify_code() = 0 | 1 | 2
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'
ciphers() = [ciphersuite()] | sting() (according to old API)
chiphersuite() =
      {key_exchange(), chipher(), hash(), exportable()}
key_exchange() =  rsa | dh_dss | dh_rsa | dh_anon | dhe_dss
      | dhe_rsa | krb5 | KeyExchange_export
cipher() = rc4_128 | idea_cbc | des_cbc | '3des_ede_cbc'
      des40_cbc | dh_dss | aes_128_cbc | aes_256_cbc |
      rc2_cbc_40 | rc4_40  
hash() = md5 | sha
exportable() = export | no_export | ignore
ssl_imp() = new | old - default is old.


{verify, verify_code()}
Specifies type of verification: 0 = do not verify peer; 1 = verify peer, 2 = verify peer, fail if no peer certificate. The default value is 0.
{depth, integer()}
Specifies the maximum verification depth, i.e. how far in a chain of certificates the verification process can proceed before the verification is considered to fail. Peer certificate = 0, CA certificate = 1, higher level CA certificate = 2, etc. The value 2 thus means that a chain can at most contain peer cert, CA cert, next CA cert, and an additional CA cert. The default value is 1.
{certfile, path()}
Path to a file containing the user's certificate.
{keyfile, path()}
Path to file containing user's private PEM encoded key.
{password, string()}
String containing the user's password. Only used if the private keyfile is password protected.
{cacertfile, path()}
Path to file containing PEM encoded CA certificates (trusted certificates used for verifying a peer certificate).
{ciphers, ciphers()}
The function ciphers_suites/0 can be used to find all availabe ciphers.
{ssl_imp, ssl_imp()}
Specify which ssl implementation you want to use.
{reuse_sessions, boolean()}
Specifies if ssl sessions should be reused when possible.


When a 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:

A Timeout argument specifies a timeout in milliseconds. The default value for a Timeout argument is infinity.


cipher_suites() ->
cipher_suites(Type) -> ciphers()


Type = erlang | openssl

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.

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


Socket = socket()
SslOptions = [ssloption()]
Timeout = integer() | infinity
SslSocket = sslsocket()
Reason = term()

Upgrades a gen_tcp, or equivalent, connected socket to a ssl socket e.i performs the client-side ssl handshake.

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


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}


SslSocket = sslsocket()
Reason = term()

Close a ssl connection.

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


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

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

connection_info(SslSocket) -> {ok, {ProtocolVersion, CipherSuite}} | {error, Reason}


CipherSuite = ciphersuite()
ProtocolVersion = protocol()

Returns the negotiated protocol version and cipher suite.

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


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

Get the value of the specified socket options, if no options are specified all options are returned.

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


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

Creates a ssl listen socket.

peercert(Socket) ->
peercert(Socket, Opts) -> {ok, Cert} | {ok, Subject} | {error, Reason}


Socket = sslsocket()
Opts = [] | [pkix] | [ssl] | [pkix, subject] | [ssl, subject]
Cert = term()
Subject = term()

peercert(Cert) is equivalent to peercert(Cert, []).

The form of the returned certificate depends on the options.

If the options list is empty the certificate is returned as a DER encoded binary.

The options pkix and ssl implies that the certificate is returned as a parsed ASN.1 structure in the form of an Erlang term.

The ssl option gives a more elaborate return structure, with more explicit information. In particular object identifiers are replaced by atoms.

The option subject implies that only the subject's distinguished name part of the peer certificate is returned.

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


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}


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.

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


Socket = sslsocket()
Data = iolist() | binary()

Writes Data to Socket.

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

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


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

Sets options according to Options for the socket Socket.

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


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}


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}


ListenSocket = socket()
SslOptions = ssloptions()
Timeout = integer()
Reason = term()

Upgrades a gen_tcp, or equivalent, socket to a ssl socket e.i performs the ssl server-side handshake.

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


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

Returns the local address and port number of the socket Socket.

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


Type = permanent | transient | temporary

Starts the Ssl application. Default type is temporary. application(3)

stop() -> ok

Stops the Ssl application. application(3)

transport_accept(Socket) ->
transport_accept(Socket, Timeout) -> {ok, NewSocket} | {error, Reason}


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.


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}]


SslAppVer = string()
SupportedSslVer = [protocol()]
AvailableSslVsn = [protocol()]

Returns version information relevant for the ssl application.


inet(3) and gen_tcp(3)

ssl 3.9
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