Erlang -- Using the SSL API

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Secure Socket Layer
User's Guide
Version 5.1

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Chapters

- Transport Layer Security (TLS) and its predecessor, Secure Socket Layer (SSL)
  - Top of chapter
  - Security overview
  - Data Privacy and Integrity
  - Digital Certificates
  - Authentication of Sender
  - TLS Sessions
- Using the SSL API
  - Top of chapter
  - General information
  - Setting up connections
- Using SSL for Erlang Distribution
  - Top of chapter
  - Introduction
  - Building boot scripts including the SSL application
  - Specifying distribution module for net_kernel
  - Specifying SSL options
  - Setting up environment to always use SSL

# 2 Using the SSL API

### 2.1 General information

To see relevant version information for ssl you can call ssl:versions/0

To see all supported cipher suites call ssl:cipher_suites/0. Note that available cipher suites for a connection will depend on your certificate. It is also possible to specify a specific cipher suite(s) that you want your connection to use. Default is to use the strongest available.

### 2.2 Setting up connections

Here follows some small example of how to set up client/server connections using the erlang shell. The returned value of the sslsocket has been abbreviated with [...] as it can be fairly large and is opaque.

#### Minmal example

Note

The minimal setup is not the most secure setup of ssl.

Start server side

    1 server> ssl:start().
    ok

Create an ssl listen socket

    2 server> {ok, ListenSocket} =
    ssl:listen(9999, [{certfile, "cert.pem"}, {keyfile, "key.pem"},{reuseaddr, true}]).
    {ok,{sslsocket, [...]}}

Do a transport accept on the ssl listen socket

    3 server> {ok, Socket} = ssl:transport_accept(ListenSocket).
    {ok,{sslsocket, [...]}}

Start client side

    1 client> ssl:start().
    ok

    2 client> {ok, Socket} = ssl:connect("localhost", 9999,  [], infinity).
    {ok,{sslsocket, [...]}}

Do the ssl handshake

    4 server> ok = ssl:ssl_accept(Socket).
    ok

Send a messag over ssl

    5 server> ssl:send(Socket, "foo").
    ok

Flush the shell message queue to see that we got the message sent on the server side

    3 client> flush().
    Shell got {ssl,{sslsocket,[...]},"foo"}
    ok

#### Upgrade example

Note

To upgrade a TCP/IP connection to an ssl connection the client and server have to aggre to do so. Agreement may be accompliced by using a protocol such the one used by HTTP specified in RFC 2817.

Start server side

    1 server> ssl:start().
    ok

Create a normal tcp listen socket

    2 server> {ok, ListenSocket} = gen_tcp:listen(9999, [{reuseaddr, true}]).
    {ok, #Port<0.475>}

Accept client connection

    3 server> {ok, Socket} = gen_tcp:accept(ListenSocket).
    {ok, #Port<0.476>}

Start client side

    1 client> ssl:start().
    ok

    2 client> {ok, Socket} = gen_tcp:connect("localhost", 9999,  [], infinity).

Make sure active is set to false before trying to upgrade a connection to an ssl connection, otherwhise ssl handshake messages may be deliverd to the wrong process.

    4 server> inet:setopts(Socket, [{active, false}]).
    ok

Do the ssl handshake.

    5 server> {ok, SSLSocket} = ssl:ssl_accept(Socket, [{cacertfile, "cacerts.pem"},
    {certfile, "cert.pem"}, {keyfile, "key.pem"}]).
    {ok,{sslsocket,[...]}}

Upgrade to an ssl connection. Note that the client and server must agree upon the upgrade and the server must call ssl:accept/2 before the client calls ssl:connect/3.

    3 client>{ok, SSLSocket} = ssl:connect(Socket, [{cacertfile, "cacerts.pem"},
    {certfile, "cert.pem"}, {keyfile, "key.pem"}], infinity).
    {ok,{sslsocket,[...]}}

Send a messag over ssl

    4 client> ssl:send(SSLSocket, "foo").
    ok

Set active true on the ssl socket

    4 server> ssl:setopts(SSLSocket, [{active, true}]).
    ok

Flush the shell message queue to see that we got the message sent on the client side

    5 server> flush().
    Shell got {ssl,{sslsocket,[...]},"foo"}
    ok