368 lines
12 KiB
PHP
368 lines
12 KiB
PHP
; dh_gex.inc - Diffie Hellman Group exchange
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;
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; Copyright (C) 2015-2016 Jeffrey Amelynck
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;
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; This program is free software: you can redistribute it and/or modify
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; it under the terms of the GNU General Public License as published by
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; the Free Software Foundation, either version 3 of the License, or
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; (at your option) any later version.
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;
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; This program is distributed in the hope that it will be useful,
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; but WITHOUT ANY WARRANTY; without even the implied warranty of
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; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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; GNU General Public License for more details.
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;
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; You should have received a copy of the GNU General Public License
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; along with this program. If not, see <http://www.gnu.org/licenses/>.
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; https://www.ietf.org/rfc/rfc4419.txt
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; TODO: dont convert mpints to little endian immediately.
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; Or maybe even better, not at all.
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proc dh_gex
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;----------------------------------------------
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; >> Send Diffie-Hellman Group Exchange Request
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DEBUGF 2, "Sending GEX\n"
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stdcall ssh_send_packet, con, ssh_gex_req, ssh_gex_req.length, 0
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cmp eax, -1
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je .socket_err
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;---------------------------------------------
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; << Parse Diffie-Hellman Group Exchange Group
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stdcall ssh_recv_packet, con, 0
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cmp eax, -1
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je .socket_err
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cmp [con.rx_buffer.message_code], SSH_MSG_KEX_DH_GEX_GROUP
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jne proto_err
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DEBUGF 2, "Received GEX group\n"
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mov esi, con.rx_buffer+sizeof.ssh_packet_header
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mov edi, con.dh_p
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DEBUGF 1, "DH modulus (p): "
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call mpint_to_little_endian
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stdcall mpint_print, con.dh_p
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DEBUGF 1, "DH base (g): "
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mov edi, con.dh_g
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call mpint_to_little_endian
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stdcall mpint_print, con.dh_g
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;-------------------------------------------
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; >> Send Diffie-Hellman Group Exchange Init
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; generate a random number x, where 1 < x < (p-1)/2
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mov edi, con.dh_x+4
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mov [con.dh_x], DH_PRIVATE_KEY_SIZE/8
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mov ecx, DH_PRIVATE_KEY_SIZE/8/4
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@@:
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push ecx
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call MBRandom
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pop ecx
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stosd
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dec ecx
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jnz @r
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; If the highest bit is set, add a zero byte
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shl eax, 1
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jnc @f
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mov byte[edi], 0
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inc dword[con.dh_x]
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@@:
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; Fill remaining bytes with zeros ; TO BE REMOVED ?
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if ((MAX_BITS-DH_PRIVATE_KEY_SIZE) > 0)
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mov ecx, (MAX_BITS-DH_PRIVATE_KEY_SIZE)/8/4
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xor eax, eax
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rep stosd
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end if
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DEBUGF 1, "DH x: "
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stdcall mpint_print, con.dh_x
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; Compute e = g^x mod p
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stdcall mpint_modexp, con.dh_e, con.dh_g, con.dh_x, con.dh_p
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DEBUGF 1, "DH e: "
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stdcall mpint_print, con.dh_e
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; Create group exchange init packet
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mov edi, con.tx_buffer.message_code
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mov al, SSH_MSG_KEX_DH_GEX_INIT
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stosb
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mov esi, con.dh_e
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call mpint_to_big_endian
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DEBUGF 2, "Sending GEX init\n"
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mov ecx, dword[con.tx_buffer.message_code+1]
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bswap ecx
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add ecx, 5
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stdcall ssh_send_packet, con, con.tx_buffer.message_code, ecx, 0
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cmp eax, -1
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je .socket_err
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;---------------------------------------------
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; << Parse Diffie-Hellman Group Exchange Reply
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stdcall ssh_recv_packet, con, 0
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cmp eax, -1
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je .socket_err
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cmp [con.rx_buffer.message_code], SSH_MSG_KEX_DH_GEX_REPLY
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jne .proto_err
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DEBUGF 2, "Received GEX Reply\n"
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;--------------------------------
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; HASH: string K_S, the host key
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mov esi, con.rx_buffer+sizeof.ssh_packet_header
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mov edx, [esi]
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bswap edx
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add edx, 4
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lea ebx, [esi+edx]
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push ebx
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invoke sha256_update, con.temp_ctx, esi, edx
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;--------------------------------------------------------------------------
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; HASH: uint32 min, minimal size in bits of an acceptable group
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; uint32 n, preferred size in bits of the group the server will send
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; uint32 max, maximal size in bits of an acceptable group
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invoke sha256_update, con.temp_ctx, ssh_gex_req+sizeof.ssh_packet_header-ssh_packet_header.message_code, 12
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;----------------------------
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; HASH: mpint p, safe prime
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mov esi, con.dh_p
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mov edi, con.mpint_tmp
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call mpint_to_big_endian
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lea edx, [eax+4]
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invoke sha256_update, con.temp_ctx, con.mpint_tmp, edx
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;----------------------------------------
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; HASH: mpint g, generator for subgroup
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mov esi, con.dh_g
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mov edi, con.mpint_tmp
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call mpint_to_big_endian
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lea edx, [eax+4]
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invoke sha256_update, con.temp_ctx, con.mpint_tmp, edx
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;---------------------------------------------------
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; HASH: mpint e, exchange value sent by the client
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mov esi, con.tx_buffer+sizeof.ssh_packet_header
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mov edx, [esi]
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bswap edx
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add edx, 4
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invoke sha256_update, con.temp_ctx, esi, edx
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;---------------------------------------------------
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; HASH: mpint f, exchange value sent by the server
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mov esi, [esp]
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mov edx, [esi]
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bswap edx
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add edx, 4
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invoke sha256_update, con.temp_ctx, esi, edx
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pop esi
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mov edi, con.dh_f
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call mpint_to_little_endian
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DEBUGF 1, "DH f: "
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stdcall mpint_print, con.dh_f
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mov edi, con.dh_signature
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call mpint_to_little_endian
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DEBUGF 1, "DH signature: "
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stdcall mpint_print, con.dh_signature
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;--------------------------------------
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; Calculate shared secret K = f^x mod p
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stdcall mpint_modexp, con.rx_buffer, con.dh_f, con.dh_x, con.dh_p
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DEBUGF 1, "DH K: "
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stdcall mpint_print, con.rx_buffer
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; We always need it in big endian order, so store it as such.
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mov edi, con.dh_K
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mov esi, con.rx_buffer
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call mpint_to_big_endian
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mov [con.dh_K_length], eax
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;-----------------------------------
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; HASH: mpint K, the shared secret
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mov edx, [con.dh_K_length]
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add edx, 4
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invoke sha256_update, con.temp_ctx, con.dh_K, edx
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;-------------------------------
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; Finalize the exchange hash (H)
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invoke sha256_final, con.temp_ctx
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mov esi, con.temp_ctx.hash
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mov edi, con.dh_H
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mov ecx, SHA256_HASH_SIZE/4
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rep movsd
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DEBUGF 1, "Exchange hash H: "
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stdcall dump_hex, con.dh_H, 8
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; TODO: skip this block when re-keying
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mov esi, con.dh_H
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mov edi, con.session_id
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mov ecx, SHA256_HASH_SIZE/4
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rep movsd
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;---------------
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; Calculate keys
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; First, calculate partial hash of K and H so we can re-use it for every key.
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invoke sha256_init, con.k_h_ctx
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mov edx, [con.dh_K_length]
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add edx, 4
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invoke sha256_update, con.k_h_ctx, con.dh_K, edx
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invoke sha256_update, con.k_h_ctx, con.dh_H, 32
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;---------------------------------------------------------------
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; Initial IV client to server: HASH(K || H || "A" || session_id)
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mov esi, con.k_h_ctx
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mov edi, con.temp_ctx
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mov ecx, sizeof.ctx_sha224256/4
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rep movsd
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mov [con.session_id_prefix], 'A'
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invoke sha256_update, con.temp_ctx, con.session_id_prefix, 32+1
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invoke sha256_final, con.temp_ctx.hash
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mov edi, con.tx_iv
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mov esi, con.temp_ctx
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mov ecx, SHA256_HASH_SIZE/4
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rep movsd
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DEBUGF 1, "Remote IV: "
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stdcall dump_hex, con.tx_iv, 8
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;---------------------------------------------------------------
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; Initial IV server to client: HASH(K || H || "B" || session_id)
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mov esi, con.k_h_ctx
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mov edi, con.temp_ctx
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mov ecx, sizeof.ctx_sha224256/4
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rep movsd
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inc [con.session_id_prefix]
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invoke sha256_update, con.temp_ctx, con.session_id_prefix, 32+1
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invoke sha256_final, con.temp_ctx
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mov edi, con.rx_iv
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mov esi, con.temp_ctx
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mov ecx, SHA256_HASH_SIZE/4
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rep movsd
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DEBUGF 1, "Local IV: "
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stdcall dump_hex, con.rx_iv, 8
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;-------------------------------------------------------------------
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; Encryption key client to server: HASH(K || H || "C" || session_id)
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mov esi, con.k_h_ctx
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mov edi, con.temp_ctx
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mov ecx, sizeof.ctx_sha224256/4
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rep movsd
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inc [con.session_id_prefix]
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invoke sha256_update, con.temp_ctx, con.session_id_prefix, 32+1
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invoke sha256_final, con.temp_ctx
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mov edi, con.tx_enc_key
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mov esi, con.temp_ctx
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mov ecx, SHA256_HASH_SIZE/4
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rep movsd
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DEBUGF 1, "Remote key: "
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stdcall dump_hex, con.tx_enc_key, 8
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;-------------------------------------------------------------------
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; Encryption key server to client: HASH(K || H || "D" || session_id)
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mov esi, con.k_h_ctx
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mov edi, con.temp_ctx
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mov ecx, sizeof.ctx_sha224256/4
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rep movsd
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inc [con.session_id_prefix]
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invoke sha256_update, con.temp_ctx, con.session_id_prefix, 32+1
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invoke sha256_final, con.temp_ctx
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mov edi, con.rx_enc_key
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mov esi, con.temp_ctx
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mov ecx, SHA256_HASH_SIZE/4
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rep movsd
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DEBUGF 1, "Local key: "
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stdcall dump_hex, con.rx_enc_key, 8
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;------------------------------------------------------------------
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; Integrity key client to server: HASH(K || H || "E" || session_id)
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mov esi, con.k_h_ctx
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mov edi, con.temp_ctx
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mov ecx, sizeof.ctx_sha224256/4
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rep movsd
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inc [con.session_id_prefix]
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invoke sha256_update, con.temp_ctx, con.session_id_prefix, 32+1
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invoke sha256_final, con.temp_ctx
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mov edi, con.tx_int_key
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mov esi, con.temp_ctx
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mov ecx, SHA256_HASH_SIZE/4
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rep movsd
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DEBUGF 1, "Remote Integrity key: "
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stdcall dump_hex, con.tx_int_key, 8
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;------------------------------------------------------------------
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; Integrity key server to client: HASH(K || H || "F" || session_id)
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mov esi, con.k_h_ctx
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mov edi, con.temp_ctx
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mov ecx, sizeof.ctx_sha224256/4
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rep movsd
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inc [con.session_id_prefix]
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invoke sha256_update, con.temp_ctx, con.session_id_prefix, 32+1
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invoke sha256_final, con.temp_ctx
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mov edi, con.rx_int_key
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mov esi, con.temp_ctx
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mov ecx, SHA256_HASH_SIZE/4
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rep movsd
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DEBUGF 1, "Local Integrity key: "
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stdcall dump_hex, con.rx_int_key, 8
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;-------------------------------------
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; << Parse Diffie-Hellman New Keys MSG
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stdcall ssh_recv_packet, con, 0
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cmp eax, -1
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je .socket_err
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cmp [con.rx_buffer.message_code], SSH_MSG_NEWKEYS
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jne .proto_err
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DEBUGF 2, "Received New Keys\n"
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;-------------------------------
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; >> Reply with New Keys message
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stdcall ssh_send_packet, con, ssh_new_keys, ssh_new_keys.length, 0
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xor eax, eax
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ret
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.socket_err:
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DEBUGF 3, "Socket error during key exchange!\n"
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mov eax, 1
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ret
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.proto_err:
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DEBUGF 3, "Protocol error during key exchange!\n"
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mov eax, 2
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ret
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endp
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