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hidnplayr |
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; 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 . |
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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 1, "Sending GEX\n" |
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stdcall ssh_send_packet, [socketnum], 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, [socketnum], rx_buffer, BUFFERSIZE, 0 |
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cmp eax, -1 |
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je .socket_err |
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cmp [rx_buffer+ssh_header.message_code], SSH_MSG_KEX_DH_GEX_GROUP |
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jne proto_err |
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DEBUGF 1, "Received GEX group\n" |
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mov esi, rx_buffer+sizeof.ssh_header |
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mov edi, 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, dh_p |
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DEBUGF 1, "DH base (g): " |
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mov edi, dh_g |
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call mpint_to_little_endian |
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stdcall mpint_print, 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, dh_x+4 |
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mov [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[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_length, dh_x;;;;;;;;;;;;; |
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stdcall mpint_print, dh_x |
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; Compute e = g^x mod p |
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stdcall mpint_modexp, dh_e, dh_g, dh_x, dh_p |
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stdcall mpint_length, dh_e |
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DEBUGF 1, "DH e: " |
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stdcall mpint_print, dh_e |
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; Create group exchange init packet |
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mov edi, tx_buffer+ssh_header.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, dh_e |
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call mpint_to_big_endian |
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DEBUGF 1, "Sending GEX init\n" |
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mov ecx, dword[tx_buffer+ssh_header.message_code+1] |
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bswap ecx |
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add ecx, 5 |
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stdcall ssh_send_packet, [socketnum], tx_buffer+ssh_header.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, [socketnum], rx_buffer, BUFFERSIZE, 0 |
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cmp eax, -1 |
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je .socket_err |
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cmp [rx_buffer+ssh_header.message_code], SSH_MSG_KEX_DH_GEX_REPLY |
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jne .proto_err |
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DEBUGF 1, "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, rx_buffer+sizeof.ssh_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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call sha256_update |
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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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mov esi, ssh_gex_req+sizeof.ssh_header-ssh_header.message_code |
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mov edx, 12 |
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call sha256_update |
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;---------------------------- |
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; HASH: mpint p, safe prime |
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mov esi, dh_p |
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mov edi, mpint_tmp |
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call mpint_to_big_endian |
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lea edx, [eax+4] |
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mov esi, mpint_tmp |
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call sha256_update |
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;---------------------------------------- |
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; HASH: mpint g, generator for subgroup |
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mov esi, dh_g |
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mov edi, mpint_tmp |
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call mpint_to_big_endian |
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lea edx, [eax+4] |
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mov esi, mpint_tmp |
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call sha256_update |
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;--------------------------------------------------- |
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; HASH: mpint e, exchange value sent by the client |
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mov esi, tx_buffer+sizeof.ssh_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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call sha256_update |
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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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call sha256_update |
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pop esi |
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mov edi, 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, dh_f |
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mov edi, 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, 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, rx_buffer, dh_f, dh_x, dh_p |
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stdcall mpint_length, rx_buffer |
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DEBUGF 1, "DH K: " |
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stdcall mpint_print, 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, dh_K |
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mov esi, rx_buffer |
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call mpint_to_big_endian |
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mov [dh_K.length], eax |
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;----------------------------------- |
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; HASH: mpint K, the shared secret |
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mov edx, [dh_K.length] |
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add edx, 4 |
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mov esi, dh_K |
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call sha256_update |
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;------------------------------- |
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; Finalize the exchange hash (H) |
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mov edi, dh_H |
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call sha256_final |
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DEBUGF 1, "Exchange hash H: " |
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stdcall dump_256bit_hex, dh_H |
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; TODO: skip this block when re-keying |
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mov esi, dh_H |
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mov edi, session_id |
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mov ecx, 32/4 |
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rep movsd |
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;--------------- |
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; Calculate keys |
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; TODO: re-use partial hash of K and H |
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;--------------------------------------------------------------- |
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; Initial IV client to server: HASH(K || H || "A" || session_id) |
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call sha256_init |
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mov edx, [dh_K.length] |
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add edx, 4 |
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mov esi, dh_K |
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call sha256_update |
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mov edx, 32 |
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mov esi, dh_H |
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call sha256_update |
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mov edx, 1 |
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mov esi, str_A |
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call sha256_update |
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mov edx, 32 |
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mov esi, session_id |
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call sha256_update |
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mov edi, tx_iv |
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call sha256_final |
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DEBUGF 1, "Remote IV: " |
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stdcall dump_256bit_hex, tx_iv |
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;--------------------------------------------------------------- |
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; Initial IV server to client: HASH(K || H || "B" || session_id) |
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call sha256_init |
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mov edx, [dh_K.length] |
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add edx, 4 |
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mov esi, dh_K |
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call sha256_update |
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mov edx, 32 |
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mov esi, dh_H |
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call sha256_update |
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mov edx, 1 |
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mov esi, str_B |
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call sha256_update |
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mov edx, 32 |
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mov esi, session_id |
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call sha256_update |
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mov edi, rx_iv |
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call sha256_final |
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DEBUGF 1, "Local IV: " |
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stdcall dump_256bit_hex, rx_iv |
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;------------------------------------------------------------------- |
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; Encryption key client to server: HASH(K || H || "C" || session_id) |
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call sha256_init |
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mov edx, [dh_K.length] |
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add edx, 4 |
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mov esi, dh_K |
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call sha256_update |
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mov edx, 32 |
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mov esi, dh_H |
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call sha256_update |
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mov edx, 1 |
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mov esi, str_C |
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call sha256_update |
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mov edx, 32 |
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mov esi, session_id |
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call sha256_update |
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mov edi, tx_enc_key |
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call sha256_final |
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DEBUGF 1, "Remote key: " |
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stdcall dump_256bit_hex, tx_enc_key |
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;------------------------------------------------------------------- |
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; Encryption key server to client: HASH(K || H || "D" || session_id) |
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call sha256_init |
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mov edx, [dh_K.length] |
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add edx, 4 |
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mov esi, dh_K |
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call sha256_update |
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mov edx, 32 |
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mov esi, dh_H |
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call sha256_update |
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mov edx, 1 |
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mov esi, str_D |
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call sha256_update |
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mov edx, 32 |
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mov esi, session_id |
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call sha256_update |
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mov edi, rx_enc_key |
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call sha256_final |
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DEBUGF 1, "Local key: " |
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stdcall dump_256bit_hex, rx_enc_key |
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;------------------------------------------------------------------ |
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; Integrity key client to server: HASH(K || H || "E" || session_id) |
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call sha256_init |
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mov edx, [dh_K.length] |
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add edx, 4 |
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mov esi, dh_K |
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call sha256_update |
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mov edx, 32 |
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mov esi, dh_H |
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call sha256_update |
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mov edx, 1 |
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mov esi, str_E |
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call sha256_update |
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mov edx, 32 |
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mov esi, session_id |
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call sha256_update |
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mov edi, tx_int_key |
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call sha256_final |
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DEBUGF 1, "Remote Integrity key: " |
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stdcall dump_256bit_hex, tx_int_key |
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;------------------------------------------------------------------ |
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; Integrity key server to client: HASH(K || H || "F" || session_id) |
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call sha256_init |
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mov edx, [dh_K.length] |
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add edx, 4 |
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mov esi, dh_K |
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call sha256_update |
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mov edx, 32 |
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mov esi, dh_H |
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call sha256_update |
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mov edx, 1 |
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mov esi, str_F |
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call sha256_update |
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mov edx, 32 |
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mov esi, session_id |
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call sha256_update |
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mov edi, rx_int_key |
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call sha256_final |
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DEBUGF 1, "Local Integrity key: " |
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stdcall dump_256bit_hex, rx_int_key |
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;------------------------------------- |
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366 |
; << Parse Diffie-Hellman New Keys MSG |
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367 |
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stdcall ssh_recv_packet, [socketnum], rx_buffer, BUFFERSIZE, 0 |
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cmp eax, -1 |
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je .socket_err |
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371 |
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cmp [rx_buffer+ssh_header.message_code], SSH_MSG_NEWKEYS |
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jne .proto_err |
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374 |
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DEBUGF 1, "Received New Keys\n" |
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376 |
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;------------------------------- |
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; >> Reply with New Keys message |
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379 |
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stdcall ssh_send_packet, [socketnum], 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 2, "Socket error during key exchange!\n" |
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mov eax, 1 |
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ret |
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389 |
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.proto_err: |
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DEBUGF 2, "Protocol error during key exchange!\n" |
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mov eax, 2 |
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ret |
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394 |
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endp |
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proc dump_256bit_hex _ptr |
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398 |
pushad |
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399 |
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mov esi, [_ptr] |
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mov ecx, 8 |
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.next_dword: |
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lodsd |
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bswap eax |
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DEBUGF 1,'%x',eax |
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loop .next_dword |
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DEBUGF 1,'\n' |
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408 |
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popad |
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ret |
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endp |
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413 |
iglobal |
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414 |
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|
415 |
str_A db 'A' |
|
|
416 |
str_B db 'B' |
|
|
417 |
str_C db 'C' |
|
|
418 |
str_D db 'D' |
|
|
419 |
str_E db 'E' |
|
|
420 |
str_F db 'F' |
|
|
421 |
|
|
|
422 |
endg |