ssh: New option 'preferred_algorithms'

This option enables the user to define which algorithms that
are to be used as well as their precedences in the negotiation
between server and client.

6 files changed, 352 insertions, 161 deletions

diff --git a/lib/ssh/doc/src/ssh.xml b/lib/ssh/doc/src/ssh.xml
index df13442fc6..3e7726c24d 100644
--- a/lib/ssh/doc/src/ssh.xml
+++ b/lib/ssh/doc/src/ssh.xml
@@ -35,13 +35,15 @@
 
    <section>
     <title>SSH</title>
-
+    <marker id="supported"/>
     <list type="bulleted">
       <item>For application dependencies see <seealso marker="SSH_app"> ssh(6)</seealso> </item>
       <item>Supported SSH version is 2.0.</item>
+      <item>Supported public key algorithms: ssh-rsa and ssh-dss.</item>
       <item>Supported MAC algorithms: hmac-sha2-256 and hmac-sha1.</item>
       <item>Supported encryption algorithms: aes128-ctr, aes128-cb and 3des-cbc.</item>
       <item>Supported key exchange algorithms: diffie-hellman-group1-sha1.</item>
+      <item>Supported compression algorithms: none, zlib, [email protected],</item>
       <item>Supports unicode filenames if the emulator and the underlaying OS support it.
       See section DESCRIPTION in the
       <seealso marker="kernel:file">file</seealso> manual page in <c>kernel</c>
@@ -79,6 +81,18 @@
       <seealso marker="ssh_channel">ssh_channel(3)</seealso></p></item>
       <tag><c>channel_init_args() =</c></tag>
       <item><p><c>list()</c></p></item>
+
+      <tag><c>algs_list() =</c></tag>
+      <item><p><c>list( alg_entry() )</c></p></item>
+
+      <tag><c>alg_entry() =</c></tag>
+      <item><p><c>{kex, simple_algs()} | {public_key, simple_algs()} | {cipher, double_algs()} | {mac, double_algs()} | {compression, double_algs()}</c></p></item>
+
+      <tag><c>simple_algs() =</c></tag>
+      <item><p><c>list( atom() )</c></p></item>
+      
+      <tag><c>double_algs() =</c></tag>
+      <item><p><c>[{client2serverlist,simple_algs()},{server2client,simple_algs()}] | simple_algs()</c></p></item>
      </taglist>
 </section>
 
@@ -160,19 +174,57 @@
 	    and <c>password</c>. However, those optins are not always desirable
 	    to use from a security point of view.</p>
 	  </item>
+
 	  <tag><c><![CDATA[{public_key_alg, 'ssh-rsa' | 'ssh-dss'}]]></c></tag>
 	  <item>
+	    <note>
+	      <p>This option is kept for compatibility. It is ignored if the <c>preferred_algorithms</c>
+	      option is used. The equivalence of <c>{public_key_alg,'ssh-dss'}</c> is 
+	      <c>{preferred_algorithms, [{public_key,['ssh-dss','ssh-rsa']}]}</c>.</p>
+	    </note>
             <p>Sets the preferred public key algorithm to use for user
 	    authentication. If the preferred algorithm fails,
 	    the other algorithm is tried. The default is
 	    to try <c><![CDATA['ssh-rsa']]></c> first.</p>
 	  </item>
+
 	  <tag><c><![CDATA[{pref_public_key_algs, list()}]]></c></tag>
 	  <item>
+	    <note>
+	      <p>This option is kept for compatibility. It is ignored if the <c>preferred_algorithms</c>
+	      option is used. The equivalence of <c>{pref_public_key_algs,['ssh-dss']}</c> is 
+	      <c>{preferred_algorithms, [{public_key,['ssh-dss']}]}</c>.</p>
+	    </note>
             <p>List of public key algorithms to try to use.
 	    <c>'ssh-rsa'</c> and <c>'ssh-dss'</c> are available.
 	    Overrides <c><![CDATA[{public_key_alg, 'ssh-rsa' | 'ssh-dss'}]]></c></p>
 	  </item>
+
+	  <tag><c><![CDATA[{preferred_algorithms, algs_list()}]]></c></tag>
+	  <item>
+            <p>List of algorithms to use in the algorithm negotiation. The default <c>algs_list()</c> can
+	    be obtained from <seealso marker="#default_algorithms/0">default_algorithms/0</seealso>.
+	    </p>
+	    <p>Here is an example of this option:</p>
+	<code>
+{preferred_algorithms, 
+ [{public_key,['ssh-rsa','ssh-dss']},
+  {cipher,[{client2server,['aes128-ctr']},
+           {server2client,['aes128-cbc','3des-cbc']}]},
+  {mac,['hmac-sha2-256','hmac-sha1']},
+  {compression,[none,zlib]}
+}
+</code>
+        <p>Note that we want different algorithms in the two directions for <c>cipher</c>, but the same in
+	both directions for <c>mac</c> and <c>compression</c>.  We keep the default for <c>kex</c> and 
+	<c>public_key</c> but has given the default value explicitly for <c>public_key</c></p>
+        <warning>
+	  <p>Changing the values can make a connection less secure. Do not change unless you
+	  know exactly what you are doing. If you do not understand the values then you
+	  are not supposed to change them</p>
+	</warning>
+	  </item>
+
 	  <tag><c><![CDATA[{connect_timeout, timeout()}]]></c></tag>
 	  <item>
 	    <p>Sets a time-out on the transport layer
@@ -341,6 +393,32 @@
               user. From a security perspective this option makes
 	      the server very vulnerable.</p>
 	  </item>
+
+	  <tag><c><![CDATA[{preferred_algorithms, algs_list()}]]></c></tag>
+	  <item>
+            <p>List of algorithms to use in the algorithm negotiation. The default <c>algs_list()</c> can
+	    be obtained from <seealso marker="#default_algorithms/0">default_algorithms/0</seealso>.
+	    </p>
+	    <p>Here is an example of this option:</p>
+	<code>
+{preferred_algorithms, 
+ [{public_key,['ssh-rsa','ssh-dss']},
+  {cipher,[{client2server,['aes128-ctr']},
+           {server2client,['aes128-cbc','3des-cbc']}]},
+  {mac,['hmac-sha2-256','hmac-sha1']},
+  {compression,[none,zlib]}
+}
+</code>
+        <p>Note that we want different algorithms in the two directions for <c>cipher</c>, but the same in
+	both directions for <c>mac</c> and <c>compression</c>.  We keep the default for <c>kex</c> and 
+	<c>public_key</c> but has given the default value explicitly for <c>public_key</c></p>
+        <warning>
+	  <p>Changing the values can make a connection less secure. Do not change unless you
+	  know exactly what you are doing. If you do not understand the values then you
+	  are not supposed to change them</p>
+	</warning>
+	  </item>
+
 	  <tag><c><![CDATA[{pwdfun, fun(User::string(), password::string()) -> boolean()}]]></c></tag>
 	  <item>
 	    <p>Provides a function for password validation. This function is called
@@ -445,6 +523,26 @@
       </desc>   
     </func>
 
+    <func>
+      <name>default_algorithms() -> algs_list()</name>
+      <fsummary>Get a list declaring the supported algorithms</fsummary>
+      <desc>
+	<p>Returns a key-value list, where the keys are the different types of algorithms and the values are the
+	algorithms themselves. An example:</p>
+	<code>
+20> ssh:default_algorithms().
+[{kex,['diffie-hellman-group1-sha1']},
+ {public_key,['ssh-rsa','ssh-dss']},
+ {cipher,[{client2server,['aes128-ctr','aes128-cbc','3des-cbc']},
+          {server2client,['aes128-ctr','aes128-cbc','3des-cbc']}]},
+ {mac,[{client2server,['hmac-sha2-256','hmac-sha1']},
+       {server2client,['hmac-sha2-256','hmac-sha1']}]},
+ {compression,[{client2server,[none,zlib]},
+               {server2client,[none,zlib]}]}]
+21> 
+</code>
+      </desc>
+    </func>
 
     <func>
       <name>shell(Host) -> </name>
diff --git a/lib/ssh/src/ssh.erl b/lib/ssh/src/ssh.erl
index a9d6f09e72..c3b0e3edc1 100644
--- a/lib/ssh/src/ssh.erl
+++ b/lib/ssh/src/ssh.erl
@@ -28,6 +28,7 @@
 -export([start/0, start/1, stop/0, connect/3, connect/4, close/1, connection_info/2,
 	 channel_info/3,
 	 daemon/1, daemon/2, daemon/3,
+	 default_algorithms/0,
 	 stop_listener/1, stop_listener/2, stop_daemon/1, stop_daemon/2,
 	 shell/1, shell/2, shell/3]).
 
@@ -208,6 +209,11 @@ shell(Host, Port, Options) ->
     end.
 
 %%--------------------------------------------------------------------
+%%--------------------------------------------------------------------
+default_algorithms() -> 
+    ssh_transport:default_algorithms().
+
+%%--------------------------------------------------------------------
 %%% Internal functions
 %%--------------------------------------------------------------------
 fix_idle_time(SshOptions) ->
@@ -259,7 +265,7 @@ do_start_daemon(Host, Port, Options, SocketOptions) ->
     end.
 
 handle_options(Opts) ->
-    try handle_option(proplists:unfold(Opts), [], []) of
+    try handle_option(algs_compatibility(proplists:unfold(Opts)), [], []) of
 	{Inet, Ssh} ->
 	    {handle_ip(Inet), Ssh}
     catch
@@ -267,6 +273,35 @@ handle_options(Opts) ->
 	    Error
     end.
 
+
+algs_compatibility(Os) ->
+    %% Take care of old options 'public_key_alg' and 'pref_public_key_algs'
+    comp_pk(proplists:get_value(preferred_algorithms,Os),
+	    proplists:get_value(pref_public_key_algs,Os),
+	    proplists:get_value(public_key_alg, Os),
+	    [{K,V} || {K,V} <- Os,
+		      K =/= public_key_alg,
+		      K =/= pref_public_key_algs]
+	   ).
+
+comp_pk(undefined, undefined, undefined, Os) -> Os;
+comp_pk( PrefAlgs,         _,         _, Os) when PrefAlgs =/= undefined -> Os;
+
+comp_pk(undefined, undefined,   ssh_dsa, Os) -> comp_pk(undefined, undefined, 'ssh-dss', Os);
+comp_pk(undefined, undefined,   ssh_rsa, Os) -> comp_pk(undefined, undefined, 'ssh-rsa', Os);
+comp_pk(undefined, undefined,        PK, Os) -> 
+    PKs = [PK | ssh_transport:supported_algorithms(public_key)--[PK]],
+    [{preferred_algorithms, [{public_key,PKs}] } | Os];
+
+comp_pk(undefined, PrefPKs, _, Os) when PrefPKs =/= undefined ->
+    PKs = [case PK of
+	       ssh_dsa -> 'ssh-dss';
+	       ssh_rsa -> 'ssh-rsa';
+	       _ -> PK
+	   end || PK <- PrefPKs],
+    [{preferred_algorithms, [{public_key,PKs}]} | Os].
+
+
 handle_option([], SocketOptions, SshOptions) ->
     {SocketOptions, SshOptions};
 handle_option([{system_dir, _} = Opt | Rest], SocketOptions, SshOptions) ->
@@ -279,8 +314,6 @@ handle_option([{silently_accept_hosts, _} = Opt | Rest], SocketOptions, SshOptio
     handle_option(Rest, SocketOptions, [handle_ssh_option(Opt) | SshOptions]);
 handle_option([{user_interaction, _} = Opt | Rest], SocketOptions, SshOptions) ->
     handle_option(Rest, SocketOptions, [handle_ssh_option(Opt) | SshOptions]);
-handle_option([{public_key_alg, _} = Opt | Rest], SocketOptions, SshOptions) ->
-    handle_option(Rest, SocketOptions, [handle_ssh_option(Opt) | SshOptions]);
 handle_option([{connect_timeout, _} = Opt | Rest], SocketOptions, SshOptions) ->
     handle_option(Rest, SocketOptions, [handle_ssh_option(Opt) | SshOptions]);
 handle_option([{user, _} = Opt | Rest], SocketOptions, SshOptions) ->
@@ -329,7 +362,7 @@ handle_option([{exec, _} = Opt | Rest], SocketOptions, SshOptions) ->
     handle_option(Rest, SocketOptions, [handle_ssh_option(Opt) | SshOptions]);
 handle_option([{auth_methods, _} = Opt | Rest], SocketOptions, SshOptions) ->
     handle_option(Rest, SocketOptions, [handle_ssh_option(Opt) | SshOptions]);
-handle_option([{pref_public_key_algs, _} = Opt | Rest], SocketOptions, SshOptions) ->
+handle_option([{preferred_algorithms,_} = Opt | Rest], SocketOptions, SshOptions) ->
     handle_option(Rest, SocketOptions, [handle_ssh_option(Opt) | SshOptions]);
 handle_option([{quiet_mode, _} = Opt|Rest], SocketOptions, SshOptions) ->
     handle_option(Rest, SocketOptions, [handle_ssh_option(Opt) | SshOptions]);
@@ -365,19 +398,8 @@ handle_ssh_option({silently_accept_hosts, Value} = Opt) when is_boolean(Value) -
     Opt;
 handle_ssh_option({user_interaction, Value} = Opt) when is_boolean(Value) ->
     Opt;
-handle_ssh_option({public_key_alg, ssh_dsa}) ->
-    {public_key_alg, 'ssh-dss'};
-handle_ssh_option({public_key_alg, ssh_rsa})  ->
-    {public_key_alg, 'ssh-rsa'};
-handle_ssh_option({public_key_alg, Value} = Opt) when Value == 'ssh-rsa'; Value == 'ssh-dss' ->
-    Opt;
-handle_ssh_option({pref_public_key_algs, Value} = Opt) when is_list(Value), length(Value) >= 1 ->
-    case handle_pref_algs(Value, []) of
-	{true, NewOpts} ->
-	    NewOpts;
-	_ ->
-	    throw({error, {eoptions, Opt}})
-    end;
+handle_ssh_option({preferred_algorithms,[_|_]} = Opt) -> 
+    handle_pref_algs(Opt);
 handle_ssh_option({connect_timeout, Value} = Opt) when is_integer(Value); Value == infinity ->
     Opt;
 handle_ssh_option({max_sessions, Value} = Opt) when is_integer(Value), Value>0 ->
@@ -463,23 +485,83 @@ handle_inet_option({reuseaddr, _} = Opt) ->
 %% Option verified by inet
 handle_inet_option(Opt) ->
     Opt.
+
+
 %% Check preferred algs
-handle_pref_algs([], Acc) ->
-    {true, lists:reverse(Acc)};
-handle_pref_algs([H|T], Acc) ->
-    case H of
-	ssh_dsa ->
-	    handle_pref_algs(T, ['ssh-dss'| Acc]);
-	ssh_rsa ->
-	    handle_pref_algs(T, ['ssh-rsa'| Acc]);
-	'ssh-dss' ->
-	    handle_pref_algs(T, ['ssh-dss'| Acc]);
-	'ssh-rsa' ->
-	    handle_pref_algs(T, ['ssh-rsa'| Acc]);
-	_ ->
-	    false
+
+handle_pref_algs({preferred_algorithms,Algs}) ->
+    try alg_duplicates(Algs, [], []) of
+	[] ->
+	    {preferred_algorithms,
+	     [try ssh_transport:supported_algorithms(Key)
+	      of
+		  DefAlgs -> handle_pref_alg(Key,Vals,DefAlgs)
+	      catch
+		  _:_ -> throw({error, {{eoptions, {preferred_algorithms,Key}}, 
+					"Bad preferred_algorithms key"}})
+	      end  || {Key,Vals} <- Algs]
+	    };
+		    
+	Dups ->
+	    throw({error, {{eoptions, {preferred_algorithms,Dups}}, "Duplicates found"}})
+    catch
+	_:_ ->
+	    throw({error, {{eoptions, preferred_algorithms}, "Malformed"}})
     end.
 
+alg_duplicates([{K,V}|KVs], Ks, Dups0) ->
+    Dups =
+	case lists:member(K,Ks) of
+	    true ->
+		[K|Dups0];
+	    false ->
+		Dups0
+	end,
+    case V--lists:usort(V) of
+	[] ->
+	    alg_duplicates(KVs, [K|Ks], Dups);
+	Ds ->
+	    alg_duplicates(KVs, [K|Ks], Dups++Ds)
+    end;
+alg_duplicates([], _Ks, Dups) ->
+    Dups.
+
+handle_pref_alg(Key,
+		Vs=[{client2server,C2Ss=[_|_]},{server2client,S2Cs=[_|_]}],
+		[{client2server,Sup_C2Ss},{server2client,Sup_S2Cs}]
+	       ) ->
+    chk_alg_vs(Key, C2Ss, Sup_C2Ss),
+    chk_alg_vs(Key, S2Cs, Sup_S2Cs),
+    {Key, Vs};
+
+handle_pref_alg(Key,
+		Vs=[{server2client,[_|_]},{client2server,[_|_]}],
+		Sup=[{client2server,_},{server2client,_}]
+	       ) ->
+    handle_pref_alg(Key, lists:reverse(Vs), Sup);
+
+handle_pref_alg(Key, 
+		Vs=[V|_],
+		Sup=[{client2server,_},{server2client,_}]
+	       ) when is_atom(V) ->
+    handle_pref_alg(Key, [{client2server,Vs},{server2client,Vs}], Sup);
+
+handle_pref_alg(Key, 
+		Vs=[V|_],
+		Sup=[S|_]
+	       ) when is_atom(V), is_atom(S) ->
+    chk_alg_vs(Key, Vs, Sup),
+    {Key, Vs};
+
+handle_pref_alg(Key, Vs, _) ->
+    throw({error, {{eoptions, {preferred_algorithms,[{Key,Vs}]}}, "Badly formed list"}}).
+
+chk_alg_vs(OptKey, Values, SupportedValues) ->
+    case (Values -- SupportedValues) of
+	[] -> Values;
+	Bad -> throw({error, {{eoptions, {OptKey,Bad}}, "Unsupported value(s) found"}})
+    end.
+	    
 handle_ip(Inet) -> %% Default to ipv4
     case lists:member(inet, Inet) of
 	true ->
diff --git a/lib/ssh/src/ssh_auth.erl b/lib/ssh/src/ssh_auth.erl
index 45c4d52d7e..197808754c 100644
--- a/lib/ssh/src/ssh_auth.erl
+++ b/lib/ssh/src/ssh_auth.erl
@@ -30,7 +30,8 @@
 -export([publickey_msg/1, password_msg/1, keyboard_interactive_msg/1,
 	 service_request_msg/1, init_userauth_request_msg/1,
 	 userauth_request_msg/1, handle_userauth_request/3,
-	 handle_userauth_info_request/3, handle_userauth_info_response/2
+	 handle_userauth_info_request/3, handle_userauth_info_response/2,
+	 default_public_key_algorithms/0
 	]).
 
 %%--------------------------------------------------------------------
@@ -115,33 +116,16 @@ init_userauth_request_msg(#ssh{opts = Opts} = Ssh) ->
 					    service = "ssh-connection",
 					    method = "none",
 					    data = <<>>},
-	    case proplists:get_value(pref_public_key_algs, Opts, false) of
-		false ->
-		    FirstAlg = proplists:get_value(public_key_alg, Opts, ?PREFERRED_PK_ALG),
-		    SecondAlg = other_alg(FirstAlg),
-		    Prefs = method_preference(FirstAlg, SecondAlg),
-		    ssh_transport:ssh_packet(Msg, Ssh#ssh{user = User,
-							  userauth_preference = Prefs,
-							  userauth_methods = none,
-							  service = "ssh-connection"});
-		Algs ->
-		    FirstAlg = lists:nth(1, Algs),
-		    case length(Algs) =:= 2 of
-			true ->
-			    SecondAlg = other_alg(FirstAlg),
-			    Prefs = method_preference(FirstAlg, SecondAlg),
-			    ssh_transport:ssh_packet(Msg, Ssh#ssh{user = User,
-								  userauth_preference = Prefs,
-								  userauth_methods = none,
-								  service = "ssh-connection"});
-			_ ->
-			    Prefs = method_preference(FirstAlg),
-			    ssh_transport:ssh_packet(Msg, Ssh#ssh{user = User,
-								  userauth_preference = Prefs,
-								  userauth_methods = none,
-								  service = "ssh-connection"})
-		    end
-	    end;
+
+
+	    Algs = proplists:get_value(public_key, 
+				       proplists:get_value(preferred_algorithms, Opts, []),
+				       default_public_key_algorithms()),
+	    Prefs = method_preference(Algs),
+	    ssh_transport:ssh_packet(Msg, Ssh#ssh{user = User,
+						  userauth_preference = Prefs,
+						  userauth_methods = none,
+						  service = "ssh-connection"});
 	{error, no_user} ->
 	    ErrStr = "Could not determine the users name",
 	    throw(#ssh_msg_disconnect{code = ?SSH_DISCONNECT_ILLEGAL_USER_NAME,
@@ -287,20 +271,20 @@ handle_userauth_info_response(#ssh_msg_userauth_info_response{},
 			      "keyboard-interactive",
 			      language = "en"}).
 
+
+default_public_key_algorithms() -> ?PREFERRED_PK_ALGS.
+
 %%--------------------------------------------------------------------
 %%% Internal functions
 %%--------------------------------------------------------------------
-method_preference(Alg1, Alg2) ->
-    [{"publickey", ?MODULE, publickey_msg, [Alg1]},
-     {"publickey", ?MODULE, publickey_msg,[Alg2]},
-     {"password", ?MODULE, password_msg, []},
-     {"keyboard-interactive", ?MODULE, keyboard_interactive_msg, []}
-    ].
-method_preference(Alg1) ->
-    [{"publickey", ?MODULE, publickey_msg, [Alg1]},
-     {"password", ?MODULE, password_msg, []},
-     {"keyboard-interactive", ?MODULE, keyboard_interactive_msg, []}
-    ].
+method_preference(Algs) ->
+    lists:foldr(fun(A, Acc) ->
+		       [{"publickey", ?MODULE, publickey_msg, [A]} | Acc]
+	       end, 
+	       [{"password", ?MODULE, password_msg, []},
+		{"keyboard-interactive", ?MODULE, keyboard_interactive_msg, []}
+	       ],
+	       Algs).
 
 user_name(Opts) ->
     Env = case os:type() of
@@ -418,10 +402,6 @@ keyboard_interact_fun(KbdInteractFun, Name, Instr,  PromptInfos, NumPrompts) ->
 				       language = "en"}})
     end.
 
-other_alg('ssh-rsa') ->
-    'ssh-dss';
-other_alg('ssh-dss') ->
-    'ssh-rsa'.
 decode_public_key_v2(<<?UINT32(Len0), _:Len0/binary,
 		       ?UINT32(Len1), BinE:Len1/binary,
 		       ?UINT32(Len2), BinN:Len2/binary>>
diff --git a/lib/ssh/src/ssh_auth.hrl b/lib/ssh/src/ssh_auth.hrl
index 6cd8e6bf14..764c9f4246 100644
--- a/lib/ssh/src/ssh_auth.hrl
+++ b/lib/ssh/src/ssh_auth.hrl
@@ -23,7 +23,7 @@
 
 -define(SUPPORTED_AUTH_METHODS, "publickey,keyboard-interactive,password").
 
--define(PREFERRED_PK_ALG, 'ssh-rsa').
+-define(PREFERRED_PK_ALGS, ['ssh-rsa','ssh-dss']).
 
 -define(SSH_MSG_USERAUTH_REQUEST,  50).
 -define(SSH_MSG_USERAUTH_FAILURE,  51).
diff --git a/lib/ssh/src/ssh_connection_handler.erl b/lib/ssh/src/ssh_connection_handler.erl
index 65208ae158..ca63d2194f 100644
--- a/lib/ssh/src/ssh_connection_handler.erl
+++ b/lib/ssh/src/ssh_connection_handler.erl
@@ -33,7 +33,7 @@
 -include("ssh_transport.hrl").
 -include("ssh_auth.hrl").
 -include("ssh_connect.hrl").
-
+-compile(export_all).
 -export([start_link/3]).
 
 %% Internal application API
@@ -1156,54 +1156,38 @@ init_ssh(server = Role, Vsn, Version, Options, Socket) ->
 
 supported_host_keys(client, _, Options) ->
     try
-	case extract_algs(proplists:get_value(pref_public_key_algs, Options, false), []) of
-	    false ->
-		["ssh-rsa", "ssh-dss"];
-	    Algs ->
-		Algs
+	case proplists:get_value(public_key, 
+				 proplists:get_value(preferred_algorithms,Options,[])
+				) of
+	    undefined -> 
+		ssh_auth:default_public_key_algorithms();
+	    L ->
+		L -- (L--ssh_auth:default_public_key_algorithms())
 	end
+    of
+	[] ->
+	    {stop, {shutdown, "No public key algs"}};
+	Algs ->
+	    [atom_to_list(A) || A<-Algs]
     catch
 	exit:Reason ->
 	    {stop, {shutdown, Reason}}
     end;
 supported_host_keys(server, KeyCb, Options) ->
-    lists:foldl(fun(Type, Acc) ->
-			case available_host_key(KeyCb, Type, Options) of
-			    {error, _} ->
-				Acc;
-			    Alg ->
-				[Alg | Acc]
-			end
-		end, [],
-		%% Prefered alg last so no need to reverse
-		["ssh-dss", "ssh-rsa"]).
-extract_algs(false, _) ->
-    false;
-extract_algs([],[]) ->
-    false;
-extract_algs([], NewList) ->
-    lists:reverse(NewList);
-extract_algs([H|T], NewList) ->
-    case H of
-	'ssh-dss' ->
-	    extract_algs(T, ["ssh-dss"|NewList]);
-	'ssh-rsa' ->
-	    extract_algs(T, ["ssh-rsa"|NewList])
-    end.
-available_host_key(KeyCb, "ssh-dss"= Alg, Opts) ->
-    case KeyCb:host_key('ssh-dss', Opts) of
-	{ok, _} ->
-	    Alg;
-	Other ->
-	    Other
-    end;
-available_host_key(KeyCb, "ssh-rsa" = Alg, Opts) ->
-    case KeyCb:host_key('ssh-rsa', Opts) of
-	{ok, _} ->
-	    Alg;
-	Other ->
-	    Other
-    end.
+    Algs=
+    [atom_to_list(A) || A <- proplists:get_value(public_key, 
+						 proplists:get_value(preferred_algorithms,Options,[]),
+						 ssh_auth:default_public_key_algorithms()
+						),
+			available_host_key(KeyCb, A, Options)
+    ],
+    Algs.
+
+
+%% Alg :: atom()
+available_host_key(KeyCb, Alg, Opts) ->
+    element(1, catch KeyCb:host_key(Alg, Opts)) == ok.
+
 
 send_msg(Msg, #state{socket = Socket, transport_cb = Transport}) ->
     Transport:send(Socket, Msg).
diff --git a/lib/ssh/src/ssh_transport.erl b/lib/ssh/src/ssh_transport.erl
index d6414bab6c..95840c94ad 100644
--- a/lib/ssh/src/ssh_transport.erl
+++ b/lib/ssh/src/ssh_transport.erl
@@ -31,6 +31,8 @@
 
 -export([versions/2, hello_version_msg/1]).
 -export([next_seqnum/1, decrypt_first_block/2, decrypt_blocks/3,
+	 supported_algorithms/0, supported_algorithms/1,
+	 default_algorithms/0, default_algorithms/1,
 	 is_valid_mac/3,
 	 handle_hello_version/1,
 	 key_exchange_init_msg/1,
@@ -42,6 +44,68 @@
 	 unpack/3, decompress/2, ssh_packet/2, pack/2, msg_data/1,
 	 sign/3, verify/4]).
 
+%%%----------------------------------------------------------------------------
+%%%
+%%% There is a difference between supported and default algorithms. The
+%%% SUPPORTED algorithms can be handled (maybe untested...). The DEFAULT ones
+%%% are announced in ssh_msg_kexinit and in ssh:default_algorithms/0 to the
+%%% user.
+%%%
+%%% A supported algorithm can be requested in the option 'preferred_algorithms',
+%%% but may give unexpected results because of being promoted to default.
+%%%
+%%% This makes it possible to add experimental algorithms (in supported_algorithms)
+%%% and test them without letting the default users know about them.
+%%%
+
+default_algorithms() -> [{K,default_algorithms(K)} || K <- algo_classes()].
+
+algo_classes() -> [kex, public_key, cipher, mac, compression].
+
+default_algorithms(compression) ->
+    %% Do not announce '[email protected]' because there seem to be problems
+    supported_algorithms(compression, same(['[email protected]']));
+default_algorithms(Alg) ->
+    supported_algorithms(Alg).
+
+
+supported_algorithms() -> [{K,supported_algorithms(K)} || K <- algo_classes()].
+
+supported_algorithms(kex) ->
+    ['diffie-hellman-group1-sha1'];
+supported_algorithms(public_key) ->
+    ssh_auth:default_public_key_algorithms();
+supported_algorithms(cipher) ->
+    Supports = crypto:supports(),
+    CipherAlgos = [{aes_ctr, 'aes128-ctr'}, {aes_cbc128, 'aes128-cbc'}, {des3_cbc, '3des-cbc'}],
+    Algs = [SshAlgo ||
+	       {CryptoAlgo, SshAlgo} <- CipherAlgos,
+	       lists:member(CryptoAlgo, proplists:get_value(ciphers, Supports, []))],
+    same(Algs);
+supported_algorithms(mac) ->
+    Supports = crypto:supports(),
+    HashAlgos = [{sha256, 'hmac-sha2-256'}, {sha, 'hmac-sha1'}],
+    Algs = [SshAlgo ||
+	       {CryptoAlgo, SshAlgo} <- HashAlgos,
+	       lists:member(CryptoAlgo, proplists:get_value(hashs, Supports, []))],
+    same(Algs);
+supported_algorithms(compression) ->
+    same(['none','zlib','[email protected]']).
+
+
+supported_algorithms(Key, [{client2server,BL1},{server2client,BL2}]) ->
+    [{client2server,As1},{server2client,As2}] = supported_algorithms(Key),
+    [{client2server,As1--BL1},{server2client,As2--BL2}];
+supported_algorithms(Key, BlackList) ->
+    supported_algorithms(Key) -- BlackList.
+
+    
+
+
+same(Algs) ->  [{client2server,Algs}, {server2client,Algs}].
+
+
+%%%----------------------------------------------------------------------------
 versions(client, Options)->
     Vsn = proplists:get_value(vsn, Options, ?DEFAULT_CLIENT_VERSION),
     {Vsn, format_version(Vsn, software_version(Options))};
@@ -128,62 +192,45 @@ key_exchange_init_msg(Ssh0) ->
 
 kex_init(#ssh{role = Role, opts = Opts, available_host_keys = HostKeyAlgs}) ->
     Random = ssh_bits:random(16),
-    Compression = case proplists:get_value(compression, Opts, none) of
-		      openssh_zlib -> ["[email protected]", "none"];
-		      zlib -> ["zlib", "none"];
-		      none -> ["none", "zlib"]
-		  end,
-    kexinit_messsage(Role, Random, Compression, HostKeyAlgs).
+    PrefAlgs =
+	case proplists:get_value(preferred_algorithms,Opts) of
+	    undefined -> 
+		default_algorithms();
+	    Algs0 ->
+		Algs0
+	end,
+    kexinit_message(Role, Random, PrefAlgs, HostKeyAlgs).
 
 key_init(client, Ssh, Value) ->
     Ssh#ssh{c_keyinit = Value};
 key_init(server, Ssh, Value) ->
     Ssh#ssh{s_keyinit = Value}.
 
-available_ssh_algos() ->
-    Supports = crypto:supports(),
-    CipherAlgos = [{aes_ctr, "aes128-ctr"}, {aes_cbc128, "aes128-cbc"}, {des3_cbc, "3des-cbc"}],
-    Ciphers = [SshAlgo ||
-	{CryptoAlgo, SshAlgo} <- CipherAlgos,
-	lists:member(CryptoAlgo, proplists:get_value(ciphers, Supports, []))],
-    HashAlgos = [{sha256, "hmac-sha2-256"}, {sha, "hmac-sha1"}],
-    Hashs = [SshAlgo ||
-	{CryptoAlgo, SshAlgo} <- HashAlgos,
-	lists:member(CryptoAlgo, proplists:get_value(hashs, Supports, []))],
-    {Ciphers, Hashs}.
-
-kexinit_messsage(client, Random, Compression, HostKeyAlgs) ->
-    {CipherAlgs, HashAlgs} = available_ssh_algos(),
-    #ssh_msg_kexinit{ 
-		  cookie = Random,
-		  kex_algorithms = ["diffie-hellman-group1-sha1"],
-		  server_host_key_algorithms = HostKeyAlgs,
-		  encryption_algorithms_client_to_server = CipherAlgs,
-		  encryption_algorithms_server_to_client = CipherAlgs,
-		  mac_algorithms_client_to_server = HashAlgs,
-		  mac_algorithms_server_to_client = HashAlgs,
-		  compression_algorithms_client_to_server = Compression,
-		  compression_algorithms_server_to_client = Compression,
-		  languages_client_to_server = [],
-		  languages_server_to_client = []
-		 };
 
-kexinit_messsage(server, Random, Compression, HostKeyAlgs) ->
-    {CipherAlgs, HashAlgs} = available_ssh_algos(),
+kexinit_message(_Role, Random, Algs, HostKeyAlgs) ->
     #ssh_msg_kexinit{
 		  cookie = Random,
-		  kex_algorithms = ["diffie-hellman-group1-sha1"],
+		  kex_algorithms = to_strings( get_algs(kex,Algs) ),
 		  server_host_key_algorithms = HostKeyAlgs,
-		  encryption_algorithms_client_to_server = CipherAlgs,
-		  encryption_algorithms_server_to_client = CipherAlgs,
-		  mac_algorithms_client_to_server = HashAlgs,
-		  mac_algorithms_server_to_client = HashAlgs,
-		  compression_algorithms_client_to_server = Compression,
-		  compression_algorithms_server_to_client = Compression,
+		  encryption_algorithms_client_to_server = c2s(cipher,Algs),
+		  encryption_algorithms_server_to_client = s2c(cipher,Algs),
+		  mac_algorithms_client_to_server = c2s(mac,Algs),
+		  mac_algorithms_server_to_client = s2c(mac,Algs),
+		  compression_algorithms_client_to_server = c2s(compression,Algs),
+		  compression_algorithms_server_to_client = s2c(compression,Algs),
 		  languages_client_to_server = [],
 		  languages_server_to_client = []
 		 }.
 
+c2s(Key, Algs) -> x2y(client2server, Key, Algs).
+s2c(Key, Algs) -> x2y(server2client, Key, Algs).
+
+x2y(DirectionKey, Key, Algs) -> to_strings(proplists:get_value(DirectionKey, get_algs(Key,Algs))).
+
+get_algs(Key, Algs) -> proplists:get_value(Key, Algs, default_algorithms(Key)).
+
+to_strings(L) -> lists:map(fun erlang:atom_to_list/1, L).
+
 new_keys_message(Ssh0) ->
     {SshPacket, Ssh} = 
 	ssh_packet(#ssh_msg_newkeys{}, Ssh0),