ssl: Fix encoding/decoding of the SRP extension

The encoded value of the SRP extension length was bigger than the
actual length of the extension. This could cause interoperability
problems with third party SSL implementations.

This commit corrects the encoding and decoding of the SRP extension
length.

Change-Id: I78d118faab7f5d02b755a7d1e2e8561b86f5a15c

2 files changed, 30 insertions, 3 deletions

diff --git a/lib/ssl/src/ssl_handshake.erl b/lib/ssl/src/ssl_handshake.erl
index 14df1d2e02..be0b241017 100644
--- a/lib/ssl/src/ssl_handshake.erl
+++ b/lib/ssl/src/ssl_handshake.erl
@@ -610,7 +610,7 @@ encode_hello_extensions([#ec_point_formats{ec_point_format_list = ECPointFormats
 				 ?UINT16(Len), ?BYTE(ListLen), ECPointFormatList/binary, Acc/binary>>);
 encode_hello_extensions([#srp{username = UserName} | Rest], Acc) ->
     SRPLen = byte_size(UserName),
-    Len = SRPLen + 2,
+    Len = SRPLen + 1,
     encode_hello_extensions(Rest, <<?UINT16(?SRP_EXT), ?UINT16(Len), ?BYTE(SRPLen),
 				    UserName/binary, Acc/binary>>);
 encode_hello_extensions([#hash_sign_algos{hash_sign_algos = HashSignAlgos} | Rest], Acc) ->
@@ -1941,7 +1941,7 @@ dec_hello_extensions(<<?UINT16(?RENEGOTIATION_EXT), ?UINT16(Len), Info:Len/binar
 										RenegotiateInfo}});
 
 dec_hello_extensions(<<?UINT16(?SRP_EXT), ?UINT16(Len), ?BYTE(SRPLen), SRP:SRPLen/binary, Rest/binary>>, Acc)
-  when Len == SRPLen + 2 ->
+  when Len == SRPLen + 1 ->
     dec_hello_extensions(Rest,  Acc#hello_extensions{srp = #srp{username = SRP}});
 
 dec_hello_extensions(<<?UINT16(?SIGNATURE_ALGORITHMS_EXT), ?UINT16(Len),
diff --git a/lib/ssl/test/ssl_handshake_SUITE.erl b/lib/ssl/test/ssl_handshake_SUITE.erl
index b8b9989d30..1fa6029963 100644
--- a/lib/ssl/test/ssl_handshake_SUITE.erl
+++ b/lib/ssl/test/ssl_handshake_SUITE.erl
@@ -25,6 +25,7 @@
 -compile(export_all).
 
 -include_lib("common_test/include/ct.hrl").
+-include("ssl_handshake.hrl").
 -include("ssl_internal.hrl").
 -include("tls_handshake.hrl").
 -include_lib("public_key/include/public_key.hrl").
@@ -41,7 +42,8 @@ all() -> [decode_hello_handshake,
 	  decode_empty_server_sni_correctly,
 	  select_proper_tls_1_2_rsa_default_hashsign,
 	  ignore_hassign_extension_pre_tls_1_2,
-          unorded_chain].
+	  unorded_chain,
+	  encode_decode_srp].
 
 %%--------------------------------------------------------------------
 init_per_suite(Config) ->
@@ -192,6 +194,31 @@ unorded_chain(Config) when is_list(Config) ->
     {ok, _, OrderedChain} = 
         ssl_certificate:certificate_chain(PeerCert, ets:new(foo, []), ExtractedCerts, UnordedChain).
 
+encode_decode_srp(_Config) ->
+    Exts = #hello_extensions{
+              srp = #srp{username = <<"foo">>},
+              sni = #sni{hostname = "bar"},
+              renegotiation_info = undefined,
+              signature_algs = undefined,
+              alpn = undefined,
+              next_protocol_negotiation = undefined,
+              ec_point_formats = undefined,
+              elliptic_curves = undefined
+             },
+    EncodedExts = <<0,20,          % Length
+                    0,0,           % SNI extension
+                    0,8,           % Length
+                    0,6,           % ServerNameLength
+                    0,             % NameType (host_name)
+                    0,3,           % HostNameLength
+                    98,97,114,     % hostname = "bar"
+                    0,12,          % SRP extension
+                    0,4,           % Length
+                    3,             % srp_I length
+                    102,111,111>>, % username = "foo"
+    EncodedExts = ssl_handshake:encode_hello_extensions(Exts),
+    Exts = ssl_handshake:decode_hello_extensions({client, EncodedExts}).
+
 
 %%--------------------------------------------------------------------
 %% Internal functions ------------------------------------------------