ssl: Add option signature_algs

In TLS-1.2 The signature algorithm and the hash function algorithm
used to produce the digest that is used when creating the digital signature
may be negotiated through the signature algorithm extension RFC 5246.

We want to make these algorithm pairs configurable.
In connections using lower versions of TLS these algorithms are
implicit defined and can not be negotiated or configured.

DTLS is updated to not cause dialyzer errors, but needs to get a real
implementation later.

1 files changed, 46 insertions, 3 deletions

diff --git a/lib/ssl/doc/src/ssl.xml b/lib/ssl/doc/src/ssl.xml
index 82bede69d0..17842c71ad 100644
--- a/lib/ssl/doc/src/ssl.xml
+++ b/lib/ssl/doc/src/ssl.xml
@@ -421,7 +421,6 @@ fun(srp, Username :: string(), UserState :: term()) ->
 
         <warning><p>Using <c>{padding_check, boolean()}</c> makes TLS
 	vulnerable to the Poodle attack.</p></warning>
-
   </section>
   
   <section>
@@ -522,9 +521,45 @@ fun(srp, Username :: string(), UserState :: term()) ->
 	 be supported by the server for the prevention to work.
 	</p></warning>
       </item>
-    </taglist>
+      <tag><marker id="client_signature_algs"/><c>{signature_algs, [{hash(), ecdsa | rsa | dsa}]}</c></tag>
+	<item>
+	<p>In addition to the algorithms negotiated by the cipher
+	suite used for key exchange, payload encryption, message
+	authentication and pseudo random calculation, the TLS signature
+	algorithm extension <url
+	href="http://www.ietf.org/rfc/rfc5246.txt">Section 7.4.1.4.1 in RFC 5246</url> may be
+	used, from TLS 1.2, to negotiate which signature algorithm to use during the
+	TLS handshake. If no lower TLS versions than 1.2 are supported,
+	the client will send a TLS signature algorithm extension
+	with the algorithms specified by this option.
+	Defaults to
+	
+	<code>[
+%% SHA2
+{sha512, ecdsa},
+{sha512, rsa},
+{sha384, ecdsa},
+{sha384, rsa},
+{sha256, ecdsa},
+{sha256, rsa},
+{sha224, ecdsa},
+{sha224, rsa},
+%% SHA
+{sha, ecdsa},
+{sha, rsa},
+{sha, dsa},
+%% MD5
+{md5, rsa}
+]</code>
+	
+	The algorithms should be in the preferred order.
+	Selected signature algorithm can restrict which hash functions
+	that may be selected.
+	</p>
+	</item>
+      </taglist>
    </section>
-
+   
   <section>
     <title>SSL OPTION DESCRIPTIONS - SERVER SIDE</title>
 
@@ -651,6 +686,14 @@ fun(srp, Username :: string(), UserState :: term()) ->
       <item>If true, use the server's preference for cipher selection. If false
       (the default), use the client's preference.
       </item>
+      
+      <tag><c>{signature_algs, [{hash(), ecdsa | rsa | dsa}]}</c></tag>
+      <item><p> The algorithms specified by
+      this option will be the ones accepted by the server in a signature algorithm
+      negotiation, introduced in TLS-1.2. The algorithms will also be offered to the client if a
+      client certificate is requested. For more details see the <seealso marker="#client_signature_algs">corresponding client option</seealso>.
+      </p> </item>
+
     </taglist>
   </section>