ssl(3)

MODULE
ssl - Interface Functions for Secure Socket Layer

DESCRIPTION

This module contains interface functions to the Secure Socket Layer.

GENERAL

The reader is advised to also read the ssl(6) manual page describing the SSL application.

  Warning:

It is strongly advised to seed the random generator after the ssl application has been started (see seed/1 below), and before any connections are established. Although the port program interfacing to the ssl libraries does a "random" seeding of its own in order to make everything work properly, that seeding is by no means random for the world since it has a constant value which is known to everyone reading the source code of the port program.

COMMON DATA TYPES

The following datatypes are used in the functions below:

    *   options() = [option()]

    *   option() = socketoption() | ssloption()

    *   socketoption() = {mode, list} | {mode, binary} | binary | {packet, packettype()} | {header, integer()} | {nodelay, boolean()} | {active, activetype()} | {backlog, integer()} | {ip, ipaddress()} | {port, integer()}

    *   ssloption() = {verify, code()} | {depth, depth()} | {certfile, path()} | {keyfile, path()} | {password, string()} | {cacertfile, path()} | {ciphers, string()}

    *   packettype() (see inet(3))

    *   activetype() (see inet(3))

    *   reason() = atom() | {atom(), string()}

    *   bytes() = [byte()]

    *   string() = [byte()]

    *   byte() = 0 | 1 | 2 | ... | 255

    *   code() = 0 | 1 | 2

    *   depth() = byte()

    *   address() = hostname() | ipstring() | ipaddress()

    *   ipaddress() = ipstring() | iptuple()

    *   hostname() = string()

    *   ipstring() = string()

    *   iptuple() = {byte(), byte(), byte(), byte()}

    *   sslsocket()

    *   protocol() = sslv2 | sslv3 | tlsv1

    *

The socket option {backlog, integer()} is for listen/2 only, and the option {port, integer()} is for connect/3/4 only.

The following socket options are set by default: {mode, list}, {packet, 0}, {header, 0}, {nodelay, false}, {active, true}, {backlog, 5}, {ip, {0, 0, 0, 0}}, and {port, 0}.

Note that the options {mode, binary} and binary are equivalent. Similarly {mode, list} and the absence of option binary are equivalent.

The ssl options are for setting specific SSL parameters as follows:

    *   {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, depth()} 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. chain of PEM encoded certificates.

    *   {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, string()} String of ciphers as a colon separated list of ciphers. The function ciphers/0 can be used to find all availabe ciphers.

The type sslsocket() is opaque to the user.

The owner of a socket is the one that created it by a call to transport_accept (or accept/1), connect/3/4/, or listen/2.

When a 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.

Functions listed below may return the value {error, closed}, which only indicates that the SSL socket is considered closed for the operation in question. It is for instance possible to have {error, closed} returned from an call to send/2, and a subsequent call to recv/3 returning {ok, Data}.

Hence a return value of {error, closed} must not be interpreted as if the socket was completely closed. On the contrary, in order to free all resources occupied by an SSL socket, close/1 must be called, or else the process owning the socket has to terminate.

For each SSL socket there is an Erlang process representing the socket. When a socket is opened, that process links to the calling client process. Implementations that want to detect abnormal exits from the socket process by receiving {'EXIT', Pid, Reason} messages, should use the function pid/1 to retreive the process identifier from the socket, in order to be able to match exit messages properly.

EXPORTS

accept(ListenSocket) -> {ok, Socket} | {error, Reason}
accept(ListenSocket, Timeout) -> {ok, Socket} | {error, Reason}

    Types
        ListenSocket = Socket = sslsocket()
        Timeout = integer()

    Accepts an incoming connection request on a listen socket. ListenSocket must be a socket returned from listen/2.

    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.

  Warning:

This call is obsolete and should be avoided. It calls both the unix system call accept and the SSL call SSL_accept. The latter can take time, and if a non-SSL client is connected to the socket, it can hang the server. A server using ssl:accept should use the two calls transport_accept and ssl_accept instead. For documentation of these, see below.

ciphers() -> {ok, string()} | {error, enotstarted}

    Returns a string constisting of colon separated cipher designations that are supported by the current SSL library implementation.

    The SSL application has to be started to return the string of ciphers.

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

    Types
        Socket = sslsocket()

    Closes a socket returned by accept/1/2, connect/3/4, or listen/2

connect(Address, Port, Options) -> {ok, Socket} | {error, Reason}
connect(Address, Port, Options, Timeout) -> {ok, Socket} | {error, Reason}

    Types
        Address = address()
        Port = integer()
        Options = [connect_option()]
        connect_option() = {mode, list} | {mode, binary} | binary | {packet, packettype()} | {header, integer()} | {nodelay, boolean()} | {active, activetype()} | {ip, ipaddress()} | {port, integer()} | {verify, code()} | {depth, depth()} | {certfile, path()} | {keyfile, path()} | {password, string()} | {cacertfile, path()} | {ciphers, string()}
        Timeout = integer()
        Socket = sslsocket()

    Connects to Port at Address. If the optional Timeout argument is specified, and a connection could not be established within the given time, {error, timeout} is returned. The default value for Timeout is infinity.

    The ip and port options are for binding to a particular local address and port, respectively.

connection_info(Socket) -> {ok, {Protocol, Cipher}} | {error, Reason}

    Types
        Socket = sslsocket()
        Protocol = protocol()
        Cipher = string()

    Gets the chosen protocol version and cipher for an established connection (accepted och connected).

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

    Types
        Socket = sslsocket()
        NewOwner = pid()

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

format_error(ErrorCode) -> string()

    Types
        ErrorCode = term()

    Returns a diagnostic string describing an error.

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

    Types
        Socket = sslsocket()
        OptionTags = [optiontag()]()

    Returns the options the tags of which are OptionTags for for the socket Socket.

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

    Types
        Port = integer()
        Options = [listen_option()]
        listen_option() = {mode, list} | {mode, binary} | binary | {packet, packettype()} | {header, integer()} | {active, activetype()} | {backlog, integer()} | {ip, ipaddress()} | {verify, code()} | {depth, depth()} | {certfile, path()} | {keyfile, path()} | {password, string()} | {cacertfile, path()} | {ciphers, string()}
        ListenSocket = sslsocket()

    Sets up a socket to listen on port Port at the local host. If Port is zero, listen/2 picks an available port number (use port/1 to retreive it).

    The listen queue size defaults to 5. If a different value is wanted, the option {backlog, Size} should be added to the list of options.

    An empty Options list is considered an error, and {error, enooptions} is returned.

    The returned ListenSocket can only be used in calls to accept/1/2.

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

    Types
        Socket = sslsocket()
        Opts = [pkix | 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 options pkix, and ssl are mutually exclusive.

    The option subject implies that only the subject's distinguished name part of the peer certificate is returned. It can only be used together with the option pkix or the option ssl.

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

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

    Returns the address and port number of the peer.

pid(Socket) -> pid()

    Types
        Socket = sslsocket()

    Returns the pid of the socket process. The returned pid should only be used for receiving exit messages.

recv(Socket, Length) -> {ok, Data} | {error, Reason}
recv(Socket, Length, Timeout) -> {ok, Data} | {error, Reason}

    Types
        Socket = sslsocket()
        Length = integer() >= 0
        Timeout = integer()
        Data = bytes() | binary()

    Receives data on socket Socket when the socket is in passive mode, i.e. when the option {active, false} has been specified.

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

    A positive value of the Length argument is only valid when the socket is in raw mode (option {packet, 0} is set, and the option binary is not set); otherwise it should be set to 0, whence all available bytes are returned.

    If the optional Timeout parameter is specified, and no data was available within the given time, {error, timeout} is returned. The default value for Timeout is infinity.

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

    Types
        Data = iolist() | binary()

    Seeds the ssl random generator.

    It is strongly advised to seed the random generator after the ssl application has been started, and before any connections are established. Although the port program interfacing to the OpenSSL libraries does a "random" seeding of its own in order to make everything work properly, that seeding is by no means random for the world since it has a constant value which is known to everyone reading the source code of the seeding.

    A notable return value is {error, edata}} indicating that Data was not a binary nor an iolist.

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

    Types
        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}

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

    Sets options according to Options for the socket Socket.

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

    Types
        Socket = sslsocket()
        Timeout = integer()
        Reason = atom()

    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.

    Note that the ssl connection is not complete until ssl_accept has returned true, and if an error is returned, the socket is unavailable and for instance close/1 will crash.

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.

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

    Types
        Socket = NewSocket = sslsocket()
        Timeout = integer()
        Reason = atom()

    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.

version() -> {ok, {SSLVsn, CompVsn, LibVsn}}

    Types
        SSLVsn = CompVsn = LibVsn = string()()

    Returns the SSL application version (SSLVsn), the library version used when compiling the SSL application port program (CompVsn), and the actual library version used when dynamically linking in runtime (LibVsn).

    If the SSL application has not been started, CompVsn and LibVsn are empty strings.

ERRORS

The possible error reasons and the corresponding diagnostic strings returned by format_error/1 are either the same as those defined in the inet(3) reference manual, or as follows:

    closed:
        Connection closed for the operation in question.

    ebadsocket:
        Connection not found (internal error).

    ebadstate:
        Connection not in connect state (internal error).

    ebrokertype:
        Wrong broker type (internal error).

    ecacertfile:
        Own CA certificate file is invalid.

    ecertfile:
        Own certificate file is invalid.

    echaintoolong:
        The chain of certificates provided by peer is too long.

    ecipher:
        Own list of specified ciphers is invalid.

    ekeyfile:
        Own private key file is invalid.

    ekeymismatch:
        Own private key does not match own certificate.

    enoissuercert:
        Cannot find certificate of issuer of certificate provided by peer.

    enoservercert:
        Attempt to do accept without having set own certificate.

    enotlistener:
        Attempt to accept on a non-listening socket.

    enoproxysocket:
        No proxy socket found (internal error).

    enooptions:
        The list of options is empty.

    enotstarted:
        The SSL application has not been started.

    eoptions:
        Invalid list of options.

    epeercert:
        Certificate provided by peer is in error.

    epeercertexpired:
        Certificate provided by peer has expired.

    epeercertinvalid:
        Certificate provided by peer is invalid.

    eselfsignedcert:
        Certificate provided by peer is self signed.

    esslaccept:
        Server SSL handshake procedure between client and server failed.

    esslconnect:
        Client SSL handshake procedure between client and server failed.

    esslerrssl:
        SSL protocol failure. Typically because of a fatal alert from peer.

    ewantconnect:
        Protocol wants to connect, which is not supported in this version of the SSL application.

    ex509lookup:
        Protocol wants X.509 lookup, which is not supported in this version of the SSL application.

    {badcall, Call}:
        Call not recognized for current mode (active or passive) and state of socket.

    {badcast, Cast}:
        Call not recognized for current mode (active or passive) and state of socket.

    {badinfo, Info}:
        Call not recognized for current mode (active or passive) and state of socket.

SEE ALSO

gen_tcp(3), inet(3)