path: root/lib/ssh/src/ssh_message.erl

%%
%% %CopyrightBegin%
%%
%% Copyright Ericsson AB 2013-2014. All Rights Reserved.
%%
%% Licensed under the Apache License, Version 2.0 (the "License");
%% you may not use this file except in compliance with the License.
%% You may obtain a copy of the License at
%%
%%     http://www.apache.org/licenses/LICENSE-2.0
%%
%% Unless required by applicable law or agreed to in writing, software
%% distributed under the License is distributed on an "AS IS" BASIS,
%% WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
%% See the License for the specific language governing permissions and
%% limitations under the License.
%%
%% %CopyrightEnd%
%%

%%

%%------------------------------------------------------------------
-module(ssh_message).

-include_lib("public_key/include/public_key.hrl").

-include("ssh.hrl").
-include("ssh_connect.hrl").
-include("ssh_auth.hrl").
-include("ssh_transport.hrl").

-export([encode/1, decode/1, encode_host_key/1, decode_keyboard_interactive_prompts/2]).

encode(#ssh_msg_global_request{
	  name = Name,
	  want_reply = Bool,
	  data = Data}) ->
    ssh_bits:encode([?SSH_MSG_GLOBAL_REQUEST,
		     Name, Bool, Data], [byte, string, boolean, '...']);
encode(#ssh_msg_request_success{data = Data}) ->
    <<?BYTE(?SSH_MSG_REQUEST_SUCCESS), Data/binary>>;
encode(#ssh_msg_request_failure{}) ->
    <<?BYTE(?SSH_MSG_REQUEST_FAILURE)>>;
encode(#ssh_msg_channel_open{
	  channel_type = Type,
	  sender_channel = Sender,
	  initial_window_size = Window,
	  maximum_packet_size = Max,
	  data = Data
	 }) ->
    ssh_bits:encode([?SSH_MSG_CHANNEL_OPEN,
		     Type, Sender, Window, Max, Data], [byte, string, uint32,
							uint32, uint32, '...']);
encode(#ssh_msg_channel_open_confirmation{
	  recipient_channel = Recipient,
	  sender_channel = Sender,
	  initial_window_size = InitWindowSize,
	  maximum_packet_size = MaxPacketSize,
	  data = Data
	 }) ->
    ssh_bits:encode([?SSH_MSG_CHANNEL_OPEN_CONFIRMATION, Recipient,
		     Sender, InitWindowSize, MaxPacketSize, Data],
		    [byte, uint32, uint32, uint32, uint32, '...']);
encode(#ssh_msg_channel_open_failure{
	  recipient_channel = Recipient,
	  reason = Reason,
	  description = Desc,
	  lang = Lang
	 }) ->
    ssh_bits:encode([?SSH_MSG_CHANNEL_OPEN_FAILURE, Recipient,
		     Reason, Desc, Lang], [byte, uint32, uint32, string, string]);
encode(#ssh_msg_channel_window_adjust{
	  recipient_channel = Recipient,
	  bytes_to_add = Bytes
	 }) ->
    ssh_bits:encode([?SSH_MSG_CHANNEL_WINDOW_ADJUST, Recipient, Bytes],
		    [byte, uint32, uint32]);
encode(#ssh_msg_channel_data{
	  recipient_channel = Recipient,
	  data = Data
	 }) ->
    ssh_bits:encode([?SSH_MSG_CHANNEL_DATA, Recipient, Data], [byte, uint32, binary]);

encode(#ssh_msg_channel_extended_data{
	  recipient_channel = Recipient,
	  data_type_code = DataType,
	  data = Data
	 }) ->
    ssh_bits:encode([?SSH_MSG_CHANNEL_EXTENDED_DATA, Recipient,
		     DataType, Data], [byte, uint32, uint32, binary]);

encode(#ssh_msg_channel_eof{recipient_channel = Recipient
			   }) ->
    <<?BYTE(?SSH_MSG_CHANNEL_EOF), ?UINT32(Recipient)>>;
encode(#ssh_msg_channel_close{
	   recipient_channel = Recipient
	  }) ->
    <<?BYTE(?SSH_MSG_CHANNEL_CLOSE),  ?UINT32(Recipient)>>;
encode(#ssh_msg_channel_request{
	  recipient_channel = Recipient,
	  request_type = Type,
	  want_reply = Bool,
	  data  = Data
	 }) ->
    ssh_bits:encode([?SSH_MSG_CHANNEL_REQUEST, Recipient, Type, Bool, Data],
		    [byte, uint32, string, boolean, '...']);
encode(#ssh_msg_channel_success{
	  recipient_channel = Recipient
	 }) ->
    <<?BYTE(?SSH_MSG_CHANNEL_SUCCESS), ?UINT32(Recipient)>>;
encode(#ssh_msg_channel_failure{
	  recipient_channel = Recipient
	 }) ->
    <<?BYTE(?SSH_MSG_CHANNEL_FAILURE), ?UINT32(Recipient)>>;

encode(#ssh_msg_userauth_request{
	  user = User,
	  service = Service,
	  method = Method,
	  data = Data
	 }) ->
    ssh_bits:encode([?SSH_MSG_USERAUTH_REQUEST, User, Service, Method, Data],
		    [byte, string_utf8, string, string, '...']);
encode(#ssh_msg_userauth_failure{
	  authentications = Auths,
	  partial_success = Bool
	 }) ->
    ssh_bits:encode([?SSH_MSG_USERAUTH_FAILURE, Auths, Bool],
		    [byte, string, boolean]);
encode(#ssh_msg_userauth_success{}) ->
    <<?BYTE(?SSH_MSG_USERAUTH_SUCCESS)>>;

encode(#ssh_msg_userauth_banner{
       message = Banner,
       language = Lang
      }) ->
    ssh_bits:encode([?SSH_MSG_USERAUTH_BANNER, Banner, Lang],
		    [byte, string_utf8, string]);

encode(#ssh_msg_userauth_pk_ok{
	  algorithm_name = Alg,
	  key_blob = KeyBlob
	 }) ->
    ssh_bits:encode([?SSH_MSG_USERAUTH_PK_OK, Alg, KeyBlob],
		    [byte, string, binary]);

encode(#ssh_msg_userauth_passwd_changereq{prompt = Prompt,
					  languge = Lang
					 })->
    ssh_bits:encode([?SSH_MSG_USERAUTH_PASSWD_CHANGEREQ, Prompt, Lang],
		    [byte, string, string]);

encode(#ssh_msg_userauth_info_request{
	  name = Name,
	  instruction = Inst,
	  language_tag = Lang,
	  num_prompts = NumPromtps,
	  data = Data}) ->
    ssh_bits:encode([?SSH_MSG_USERAUTH_INFO_REQUEST, Name, Inst, Lang, NumPromtps, Data],
		    [byte, string, string, string, uint32, '...']);

encode(#ssh_msg_userauth_info_response{
	  num_responses = Num,
	  data = Data}) ->
    Responses = lists:map(fun("") ->
				  <<>>;
			     (Response) ->
				  ssh_bits:encode([Response], [string])
			  end, Data),
    Start = ssh_bits:encode([?SSH_MSG_USERAUTH_INFO_RESPONSE, Num],
			    [byte, uint32]),
    iolist_to_binary([Start, Responses]);

encode(#ssh_msg_disconnect{
	  code = Code,
	  description = Desc,
	  language = Lang
	 }) ->
    ssh_bits:encode([?SSH_MSG_DISCONNECT, Code, Desc, Lang],
		    [byte, uint32, string, string]);

encode(#ssh_msg_service_request{
	  name = Service
	 }) ->
    ssh_bits:encode([?SSH_MSG_SERVICE_REQUEST, Service], [byte, string]);

encode(#ssh_msg_service_accept{
	  name = Service
	 }) ->
    ssh_bits:encode([?SSH_MSG_SERVICE_ACCEPT, Service], [byte, string]);

encode(#ssh_msg_newkeys{}) ->
    <<?BYTE(?SSH_MSG_NEWKEYS)>>;

encode(#ssh_msg_kexinit{
	  cookie = Cookie,
	  kex_algorithms = KeyAlgs,
	  server_host_key_algorithms = HostKeyAlgs,
	  encryption_algorithms_client_to_server = EncAlgC2S,
	  encryption_algorithms_server_to_client = EncAlgS2C,
	  mac_algorithms_client_to_server = MacAlgC2S,
	  mac_algorithms_server_to_client = MacAlgS2C,
	  compression_algorithms_client_to_server = CompAlgS2C,
	  compression_algorithms_server_to_client = CompAlgC2S,
	  languages_client_to_server = LangC2S,
	  languages_server_to_client = LangS2C,
	  first_kex_packet_follows = Bool,
	  reserved = Reserved
	 }) ->
    ssh_bits:encode([?SSH_MSG_KEXINIT, Cookie, KeyAlgs, HostKeyAlgs, EncAlgC2S, EncAlgS2C,
		     MacAlgC2S, MacAlgS2C, CompAlgS2C, CompAlgC2S, LangC2S, LangS2C, Bool,
		     Reserved],
		    [byte, cookie,
		     name_list, name_list,
		     name_list, name_list,
		     name_list, name_list,
		     name_list, name_list,
		     name_list, name_list,
		     boolean, uint32]);

encode(#ssh_msg_kexdh_init{e = E}) ->
    ssh_bits:encode([?SSH_MSG_KEXDH_INIT, E], [byte, mpint]);

encode(#ssh_msg_kexdh_reply{
	  public_host_key = Key,
	  f = F,
	  h_sig = Signature
	 }) ->
    EncKey = encode_host_key(Key),
    EncSign = encode_sign(Key, Signature),
    ssh_bits:encode([?SSH_MSG_KEXDH_REPLY, EncKey, F, EncSign], [byte, binary, mpint, binary]);

encode(#ssh_msg_kex_dh_gex_request{
	  min = Min,
	  n = N,
	  max = Max
	 }) ->
    ssh_bits:encode([?SSH_MSG_KEX_DH_GEX_REQUEST, Min, N, Max],
		    [byte, uint32, uint32, uint32]);
encode(#ssh_msg_kex_dh_gex_request_old{n = N}) ->
    ssh_bits:encode([?SSH_MSG_KEX_DH_GEX_REQUEST_OLD, N],
		    [byte, uint32]);

encode(#ssh_msg_kex_dh_gex_group{p = Prime, g = Generator}) ->
    ssh_bits:encode([?SSH_MSG_KEX_DH_GEX_GROUP, Prime, Generator],
		    [byte, mpint, mpint]);

encode(#ssh_msg_kex_dh_gex_init{e = Public}) ->
    ssh_bits:encode([?SSH_MSG_KEX_DH_GEX_INIT, Public], [byte, mpint]);

encode(#ssh_msg_kex_dh_gex_reply{
	  %% Will be private key encode_host_key extracts only the public part!
	  public_host_key = Key,
	  f = F,
	  h_sig = Signature
	 }) ->
    EncKey = encode_host_key(Key),
    EncSign = encode_sign(Key, Signature),
    ssh_bits:encode([?SSH_MSG_KEX_DH_GEX_REPLY, EncKey, F, EncSign], [byte, binary, mpint, binary]);

encode(#ssh_msg_ignore{data = Data}) ->
    ssh_bits:encode([?SSH_MSG_IGNORE, Data], [byte, string]);

encode(#ssh_msg_unimplemented{sequence = Seq}) ->
    ssh_bits:encode([?SSH_MSG_UNIMPLEMENTED, Seq], [byte, uint32]);

encode(#ssh_msg_debug{always_display = Bool,
		      message = Msg,
		      language = Lang}) ->
    ssh_bits:encode([?SSH_MSG_DEBUG, Bool, Msg, Lang], [byte, boolean, string, string]).


%% Connection Messages
decode(<<?BYTE(?SSH_MSG_GLOBAL_REQUEST), ?UINT32(Len), Name:Len/binary,
	 ?BYTE(Bool), Data/binary>>) ->
    #ssh_msg_global_request{
       name = Name,
       want_reply = erl_boolean(Bool),
       data = Data
      };
decode(<<?BYTE(?SSH_MSG_REQUEST_SUCCESS), Data/binary>>) ->
    #ssh_msg_request_success{data = Data};
decode(<<?BYTE(?SSH_MSG_REQUEST_FAILURE)>>) ->
    #ssh_msg_request_failure{};
decode(<<?BYTE(?SSH_MSG_CHANNEL_OPEN),
	 ?UINT32(Len), Type:Len/binary,
	 ?UINT32(Sender), ?UINT32(Window), ?UINT32(Max),
	 Data/binary>>) ->
    #ssh_msg_channel_open{
       channel_type = binary_to_list(Type),
       sender_channel = Sender,
       initial_window_size = Window,
       maximum_packet_size = Max,
       data = Data
      };
decode(<<?BYTE(?SSH_MSG_CHANNEL_OPEN_CONFIRMATION), ?UINT32(Recipient), ?UINT32(Sender),
	 ?UINT32(InitWindowSize), ?UINT32(MaxPacketSize),
	 Data/binary>>) ->
    #ssh_msg_channel_open_confirmation{
       recipient_channel = Recipient,
       sender_channel = Sender,
       initial_window_size = InitWindowSize,
       maximum_packet_size = MaxPacketSize,
       data = Data
      };
decode(<<?BYTE(?SSH_MSG_CHANNEL_OPEN_FAILURE),  ?UINT32(Recipient), ?UINT32(Reason),
	 ?UINT32(Len0), Desc:Len0/binary,  ?UINT32(Len1), Lang:Len1/binary >>) ->
    #ssh_msg_channel_open_failure{
       recipient_channel = Recipient,
       reason = Reason,
       description = unicode:characters_to_list(Desc),
       lang = Lang
      };
decode(<<?BYTE(?SSH_MSG_CHANNEL_WINDOW_ADJUST), ?UINT32(Recipient), ?UINT32(Bytes)>>) ->
    #ssh_msg_channel_window_adjust{
       recipient_channel = Recipient,
       bytes_to_add = Bytes
    };

decode(<<?BYTE(?SSH_MSG_CHANNEL_DATA), ?UINT32(Recipient), ?UINT32(Len), Data:Len/binary>>) ->
    #ssh_msg_channel_data{
       recipient_channel = Recipient,
       data = Data
    };
decode(<<?BYTE(?SSH_MSG_CHANNEL_EXTENDED_DATA), ?UINT32(Recipient), 
	 ?UINT32(DataType), ?UINT32(Len), Data:Len/binary>>) ->
    #ssh_msg_channel_extended_data{
       recipient_channel = Recipient,
       data_type_code = DataType,
       data = Data
      };
decode(<<?BYTE(?SSH_MSG_CHANNEL_EOF), ?UINT32(Recipient)>>) ->
    #ssh_msg_channel_eof{
       recipient_channel = Recipient
      };
decode(<<?BYTE(?SSH_MSG_CHANNEL_CLOSE),  ?UINT32(Recipient)>>) ->
    #ssh_msg_channel_close{
       recipient_channel = Recipient
      };
decode(<<?BYTE(?SSH_MSG_CHANNEL_REQUEST), ?UINT32(Recipient),
	 ?UINT32(Len), RequestType:Len/binary,
	 ?BYTE(Bool), Data/binary>>) ->
    #ssh_msg_channel_request{
       recipient_channel = Recipient,
       request_type = unicode:characters_to_list(RequestType),
       want_reply = erl_boolean(Bool),
       data  = Data
      };
decode(<<?BYTE(?SSH_MSG_CHANNEL_SUCCESS),  ?UINT32(Recipient)>>) ->
    #ssh_msg_channel_success{
       recipient_channel = Recipient
      };
decode(<<?BYTE(?SSH_MSG_CHANNEL_FAILURE),  ?UINT32(Recipient)>>) ->
    #ssh_msg_channel_failure{
       recipient_channel = Recipient
      };

%%% Auth Messages
decode(<<?BYTE(?SSH_MSG_USERAUTH_REQUEST),
	 ?UINT32(Len0), User:Len0/binary,
	 ?UINT32(Len1), Service:Len1/binary,
	 ?UINT32(Len2), Method:Len2/binary,
	 Data/binary>>) ->
    #ssh_msg_userauth_request{
       user = unicode:characters_to_list(User),
       service = unicode:characters_to_list(Service),
       method = unicode:characters_to_list(Method),
       data = Data
      };

decode(<<?BYTE(?SSH_MSG_USERAUTH_FAILURE),
	 ?UINT32(Len0), Auths:Len0/binary,
	 ?BYTE(Bool)>>) ->
    #ssh_msg_userauth_failure {
       authentications = unicode:characters_to_list(Auths),
       partial_success = erl_boolean(Bool)
      };

decode(<<?BYTE(?SSH_MSG_USERAUTH_SUCCESS)>>) ->
    #ssh_msg_userauth_success{};

decode(<<?BYTE(?SSH_MSG_USERAUTH_BANNER),
	       ?UINT32(Len0), Banner:Len0/binary,
	       ?UINT32(Len1), Lang:Len1/binary>>) ->
    #ssh_msg_userauth_banner{
       message = Banner,
       language = Lang
      };

decode(<<?BYTE(?SSH_MSG_USERAUTH_INFO_REQUEST), ?UINT32(Len0), Name:Len0/binary,
	 ?UINT32(Len1), Inst:Len1/binary, ?UINT32(Len2), Lang:Len2/binary,
	 ?UINT32(NumPromtps), Data/binary>>) ->
    #ssh_msg_userauth_info_request{
       name = Name,
       instruction = Inst,
       language_tag = Lang,
       num_prompts = NumPromtps,
       data = Data};

%%% Unhandled message, also masked by same 1:st byte value as ?SSH_MSG_USERAUTH_INFO_REQUEST:
decode(<<?BYTE(?SSH_MSG_USERAUTH_PASSWD_CHANGEREQ), ?UINT32(Len0), Prompt:Len0/binary,
	 ?UINT32(Len1), Lang:Len1/binary>>) ->
    #ssh_msg_userauth_passwd_changereq{
       prompt = Prompt,
       languge = Lang
      };

%%% Unhandled message, also masked by same 1:st byte value as ?SSH_MSG_USERAUTH_INFO_REQUEST:
decode(<<?BYTE(?SSH_MSG_USERAUTH_PK_OK), ?UINT32(Len), Alg:Len/binary, KeyBlob/binary>>) ->
    #ssh_msg_userauth_pk_ok{
       algorithm_name = Alg,
       key_blob = KeyBlob
      };

decode(<<?BYTE(?SSH_MSG_USERAUTH_INFO_RESPONSE), ?UINT32(Num), Data/binary>>) ->
    #ssh_msg_userauth_info_response{
       num_responses = Num,
       data = Data};

%%% Keyexchange messages
decode(<<?BYTE(?SSH_MSG_KEXINIT), Cookie:128, Data/binary>>) ->
    decode_kex_init(Data, [Cookie, ssh_msg_kexinit], 10);

decode(<<?BYTE(?SSH_MSG_KEXDH_INIT), ?UINT32(Len), E:Len/big-signed-integer-unit:8>>) ->
    #ssh_msg_kexdh_init{e = E
		       };
decode(<<?BYTE(?SSH_MSG_KEX_DH_GEX_REQUEST), ?UINT32(Min), ?UINT32(N), ?UINT32(Max)>>) ->
    #ssh_msg_kex_dh_gex_request{
       min = Min,
       n = N,
       max = Max
      };
decode(<<?BYTE(?SSH_MSG_KEX_DH_GEX_REQUEST_OLD), ?UINT32(N)>>) ->
    #ssh_msg_kex_dh_gex_request_old{
       n = N
      };
decode(<<?BYTE(?SSH_MSG_KEX_DH_GEX_GROUP),  
	 ?UINT32(Len0), Prime:Len0/big-signed-integer-unit:8,
	 ?UINT32(Len1), Generator:Len1/big-signed-integer-unit:8>>) ->
    #ssh_msg_kex_dh_gex_group{
       p = Prime,
       g = Generator
      };
decode(<<?BYTE(?SSH_MSG_KEX_DH_GEX_INIT), ?UINT32(Len), E:Len/big-signed-integer-unit:8>>) ->
    #ssh_msg_kex_dh_gex_init{
       e = E
      };
decode(<<?BYTE(?SSH_MSG_KEX_DH_GEX_REPLY), 
	 ?UINT32(Len0), Key:Len0/binary,
	 ?UINT32(Len1), F:Len1/big-signed-integer-unit:8,
	 ?UINT32(Len2), Hashsign:Len2/binary>>) ->
    #ssh_msg_kex_dh_gex_reply{
       public_host_key = decode_host_key(Key),
       f = F,
       h_sig = decode_sign(Hashsign)
      };
decode(<<?BYTE(?SSH_MSG_KEXDH_REPLY), ?UINT32(Len0), Key:Len0/binary,
	 ?UINT32(Len1), F:Len1/big-signed-integer-unit:8,
	 ?UINT32(Len2), Hashsign:Len2/binary>>) ->
    #ssh_msg_kexdh_reply{
       public_host_key = decode_host_key(Key),
       f = F,
       h_sig = decode_sign(Hashsign)
      };

decode(<<?SSH_MSG_SERVICE_REQUEST, ?UINT32(Len0), Service:Len0/binary>>) ->
    #ssh_msg_service_request{
       name = unicode:characters_to_list(Service)
      };

decode(<<?SSH_MSG_SERVICE_ACCEPT, ?UINT32(Len0), Service:Len0/binary>>) ->
    #ssh_msg_service_accept{
       name = unicode:characters_to_list(Service)
      };

decode(<<?BYTE(?SSH_MSG_DISCONNECT), ?UINT32(Code),
       ?UINT32(Len0), Desc:Len0/binary, ?UINT32(Len1), Lang:Len1/binary>>) ->
    #ssh_msg_disconnect{
       code = Code,
       description = unicode:characters_to_list(Desc),
       language = Lang
      };

%% Accept bad disconnects from ancient openssh clients that doesn't send language tag.  Use english as a work-around.
decode(<<?BYTE(?SSH_MSG_DISCONNECT), ?UINT32(Code),
       ?UINT32(Len0), Desc:Len0/binary>>) ->
    #ssh_msg_disconnect{
       code = Code,
       description = unicode:characters_to_list(Desc),
       language = <<"en">>
      };

decode(<<?SSH_MSG_NEWKEYS>>) ->
    #ssh_msg_newkeys{};

decode(<<?BYTE(?SSH_MSG_IGNORE), ?UINT32(Len), Data:Len/binary>>) ->
    #ssh_msg_ignore{data = Data};

decode(<<?BYTE(?SSH_MSG_UNIMPLEMENTED), ?UINT32(Seq)>>) ->
    #ssh_msg_unimplemented{sequence = Seq};

decode(<<?BYTE(?SSH_MSG_DEBUG), ?BYTE(Bool), ?UINT32(Len0), Msg:Len0/binary,
	 ?UINT32(Len1), Lang:Len1/binary>>) ->
    #ssh_msg_debug{always_display = erl_boolean(Bool),
		   message = Msg,
		   language = Lang}.

decode_keyboard_interactive_prompts(<<>>, Acc) ->
    lists:reverse(Acc);
decode_keyboard_interactive_prompts(<<?UINT32(Len), Prompt:Len/binary, ?BYTE(Bool), Bin/binary>>,
				    Acc) ->
    decode_keyboard_interactive_prompts(Bin, [{Prompt, erl_boolean(Bool)} | Acc]).

erl_boolean(0) ->
    false;
erl_boolean(1) ->
    true.

decode_kex_init(<<?BYTE(Bool), ?UINT32(X)>>, Acc, 0) ->
    list_to_tuple(lists:reverse([X, erl_boolean(Bool) | Acc]));
decode_kex_init(<<?BYTE(Bool)>>, Acc, 0) ->
    %% The mandatory trailing UINT32 is missing. Assume the value it anyhow must have
    %% See rfc 4253 7.1
    X = 0,
    list_to_tuple(lists:reverse([X, erl_boolean(Bool) | Acc]));
decode_kex_init(<<?UINT32(Len), Data:Len/binary, Rest/binary>>, Acc, N) ->
    Names = string:tokens(unicode:characters_to_list(Data), ","),
    decode_kex_init(Rest, [Names | Acc], N -1).



decode_sign(<<?UINT32(Len), _Alg:Len/binary, ?UINT32(_), Signature/binary>>) ->
    Signature.

decode_host_key(<<?UINT32(Len), Alg:Len/binary, Rest/binary>>) ->
    decode_host_key(Alg, Rest).

decode_host_key(<<"ssh-rsa">>, <<?UINT32(Len0), E:Len0/big-signed-integer-unit:8,
				 ?UINT32(Len1), N:Len1/big-signed-integer-unit:8>>) ->
    #'RSAPublicKey'{publicExponent = E,
		    modulus = N};

decode_host_key(<<"ssh-dss">>,
		<<?UINT32(Len0), P:Len0/big-signed-integer-unit:8,
		  ?UINT32(Len1), Q:Len1/big-signed-integer-unit:8,
		  ?UINT32(Len2), G:Len2/big-signed-integer-unit:8,
		  ?UINT32(Len3), Y:Len3/big-signed-integer-unit:8>>) ->
    {Y, #'Dss-Parms'{p = P,
		     q = Q,
		     g = G}}.

encode_host_key(#'RSAPublicKey'{modulus = N, publicExponent = E}) ->
    ssh_bits:encode(["ssh-rsa", E, N], [string, mpint, mpint]);
encode_host_key({Y,  #'Dss-Parms'{p = P, q = Q, g = G}}) ->
    ssh_bits:encode(["ssh-dss", P, Q, G, Y],
		    [string, mpint, mpint, mpint, mpint]);
encode_host_key(#'RSAPrivateKey'{modulus = N, publicExponent = E}) ->
    ssh_bits:encode(["ssh-rsa", E, N], [string, mpint, mpint]);
encode_host_key(#'DSAPrivateKey'{y = Y, p = P, q = Q, g = G}) ->
    ssh_bits:encode(["ssh-dss", P, Q, G, Y],
		    [string, mpint, mpint, mpint, mpint]).
encode_sign(#'RSAPrivateKey'{}, Signature) ->
    ssh_bits:encode(["ssh-rsa", Signature],[string, binary]);
encode_sign(#'DSAPrivateKey'{}, Signature) ->
    ssh_bits:encode(["ssh-dss", Signature],[string, binary]).