%%
%% %CopyrightBegin%
%%
%% Copyright Ericsson AB 2005-2011. All Rights Reserved.
%%
%% The contents of this file are subject to the Erlang Public License,
%% Version 1.1, (the "License"); you may not use this file except in
%% compliance with the License. You should have received a copy of the
%% Erlang Public License along with this software. If not, it can be
%% retrieved online at http://www.erlang.org/.
%%
%% Software distributed under the License is distributed on an "AS IS"
%% basis, WITHOUT WARRANTY OF ANY KIND, either express or implied. See
%% the License for the specific language governing rights and limitations
%% under the License.
%%
%% %CopyrightEnd%
%%
%%
%%% Description: dsa public-key sign and verify
-module(ssh_dsa).
-export([verify/3]).
-export([sign/2]).
-export([alg_name/0]).
-include("ssh.hrl").
%% start() ->
%% crypto:start().
%% sign_file(File, Opts) ->
%% start(),
%% {ok,Bin} = file:read_file(File),
%% {ok,Key} = ssh_file:private_host_dsa_key(user, Opts),
%% sign(Key, Bin).
%% verify_file(File, Sig) ->
%% start(),
%% {ok,Bin} = file:read_file(File),
%% {ok,Key} = ssh_file:public_host_key(user, dsa),
%% verify(Key, Bin, Sig).
sign(_Private=#ssh_key { private={P,Q,G,X} },Mb) ->
K = ssh_bits:irandom(160) rem Q,
R = ssh_math:ipow(G, K, P) rem Q,
Ki = ssh_math:invert(K, Q),
<<M:160/big-unsigned-integer>> = crypto:sha(Mb),
S = (Ki * (M + X*R)) rem Q,
<<R:160/big-unsigned-integer, S:160/big-unsigned-integer>>.
%% the paramiko client sends a bad sig sometimes,
%% instead of crashing, we nicely return error, the
%% typcally manifests itself as Sb being 39 bytes
%% instead of 40.
verify(Public, Mb, Sb) ->
case catch xverify(Public, Mb, Sb) of
{'EXIT', _Reason} ->
%store({Public, Mb, Sb, _Reason}),
{error, inconsistent_key};
ok ->
%store({Public, Mb, Sb, ok})
ok
end.
%% store(Term) ->
%% {ok, Fd} = file:open("/tmp/dsa", [append]),
%% io:format(Fd, "~p~n~n~n", [Term]),
%% file:close(Fd).
xverify(_Public=#ssh_key { public={P,Q,G,Y} },Mb,Sb) ->
<<R0:160/big-unsigned-integer, S0:160/big-unsigned-integer>> = Sb,
?ssh_assert(R0 >= 0 andalso R0 < Q andalso
S0 >= 0 andalso S0 < Q, out_of_range),
W = ssh_math:invert(S0,Q),
<<M0:160/big-unsigned-integer>> = crypto:sha(Mb),
U1 = (M0*W) rem Q,
U2 = (R0*W) rem Q,
T1 = ssh_math:ipow(G,U1,P),
T2 = ssh_math:ipow(Y,U2,P),
V = ((T1*T2) rem P) rem Q,
if V == R0 ->
ok;
true ->
{error, inconsistent_key}
end.
alg_name() ->
"ssh-dss".
