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| ; dh_gex.inc - Diffie Hellman Group exchange |
| ; |
| ; Copyright (C) 2015-2016 Jeffrey Amelynck |
| ; |
| ; This program is free software: you can redistribute it and/or modify |
| ; it under the terms of the GNU General Public License as published by |
| ; the Free Software Foundation, either version 3 of the License, or |
| ; (at your option) any later version. |
| ; |
| ; This program is distributed in the hope that it will be useful, |
| ; but WITHOUT ANY WARRANTY; without even the implied warranty of |
| ; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the |
| ; GNU General Public License for more details. |
| ; |
| ; You should have received a copy of the GNU General Public License |
| ; along with this program. If not, see <http://www.gnu.org/licenses/>. |
| |
| ; https://www.ietf.org/rfc/rfc4419.txt |
| |
| ; TODO: dont convert mpints to little endian immediately. |
| ; Or maybe even better, not at all. |
| |
| proc dh_gex |
| |
| ;---------------------------------------------- |
| ; >> Send Diffie-Hellman Group Exchange Request |
| |
| DEBUGF 1, "Sending GEX\n" |
| stdcall ssh_send_packet, [socketnum], ssh_gex_req, ssh_gex_req.length, 0 |
| cmp eax, -1 |
| je .socket_err |
| |
| ;--------------------------------------------- |
| ; << Parse Diffie-Hellman Group Exchange Group |
| |
| stdcall ssh_recv_packet, [socketnum], rx_buffer, BUFFERSIZE, 0 |
| cmp eax, -1 |
| je .socket_err |
| |
| cmp [rx_buffer+ssh_header.message_code], SSH_MSG_KEX_DH_GEX_GROUP |
| jne proto_err |
| DEBUGF 1, "Received GEX group\n" |
| |
| mov esi, rx_buffer+sizeof.ssh_header |
| mov edi, dh_p |
| DEBUGF 1, "DH modulus (p): " |
| call mpint_to_little_endian |
| stdcall mpint_print, dh_p |
| |
| DEBUGF 1, "DH base (g): " |
| mov edi, dh_g |
| call mpint_to_little_endian |
| stdcall mpint_print, dh_g |
| |
| ;------------------------------------------- |
| ; >> Send Diffie-Hellman Group Exchange Init |
| |
| ; generate a random number x, where 1 < x < (p-1)/2 |
| mov edi, dh_x+4 |
| mov [dh_x], DH_PRIVATE_KEY_SIZE/8 |
| mov ecx, DH_PRIVATE_KEY_SIZE/8/4 |
| @@: |
| push ecx |
| call MBRandom |
| pop ecx |
| stosd |
| dec ecx |
| jnz @r |
| |
| ; If the highest bit is set, add a zero byte |
| shl eax, 1 |
| jnc @f |
| mov byte[edi], 0 |
| inc dword[dh_x] |
| @@: |
| |
| ; Fill remaining bytes with zeros ; TO BE REMOVED ? |
| if ((MAX_BITS-DH_PRIVATE_KEY_SIZE) > 0) |
| mov ecx, (MAX_BITS-DH_PRIVATE_KEY_SIZE)/8/4 |
| xor eax, eax |
| rep stosd |
| end if |
| |
| DEBUGF 1, "DH x: " |
| stdcall mpint_length, dh_x;;;;;;;;;;;;; |
| stdcall mpint_print, dh_x |
| |
| ; Compute e = g^x mod p |
| stdcall mpint_modexp, dh_e, dh_g, dh_x, dh_p |
| stdcall mpint_length, dh_e |
| |
| DEBUGF 1, "DH e: " |
| stdcall mpint_print, dh_e |
| |
| ; Create group exchange init packet |
| mov edi, tx_buffer+ssh_header.message_code |
| mov al, SSH_MSG_KEX_DH_GEX_INIT |
| stosb |
| mov esi, dh_e |
| call mpint_to_big_endian |
| |
| DEBUGF 1, "Sending GEX init\n" |
| mov ecx, dword[tx_buffer+ssh_header.message_code+1] |
| bswap ecx |
| add ecx, 5 |
| stdcall ssh_send_packet, [socketnum], tx_buffer+ssh_header.message_code, ecx, 0 |
| cmp eax, -1 |
| je .socket_err |
| |
| ;--------------------------------------------- |
| ; << Parse Diffie-Hellman Group Exchange Reply |
| |
| stdcall ssh_recv_packet, [socketnum], rx_buffer, BUFFERSIZE, 0 |
| cmp eax, -1 |
| je .socket_err |
| |
| cmp [rx_buffer+ssh_header.message_code], SSH_MSG_KEX_DH_GEX_REPLY |
| jne .proto_err |
| |
| DEBUGF 1, "Received GEX Reply\n" |
| |
| ;-------------------------------- |
| ; HASH: string K_S, the host key |
| mov esi, rx_buffer+sizeof.ssh_header |
| mov edx, [esi] |
| bswap edx |
| add edx, 4 |
| lea ebx, [esi+edx] |
| push ebx |
| call sha256_update |
| |
| ;-------------------------------------------------------------------------- |
| ; HASH: uint32 min, minimal size in bits of an acceptable group |
| ; uint32 n, preferred size in bits of the group the server will send |
| ; uint32 max, maximal size in bits of an acceptable group |
| mov esi, ssh_gex_req+sizeof.ssh_header-ssh_header.message_code |
| mov edx, 12 |
| call sha256_update |
| |
| ;---------------------------- |
| ; HASH: mpint p, safe prime |
| mov esi, dh_p |
| mov edi, mpint_tmp |
| call mpint_to_big_endian |
| lea edx, [eax+4] |
| mov esi, mpint_tmp |
| call sha256_update |
| |
| ;---------------------------------------- |
| ; HASH: mpint g, generator for subgroup |
| mov esi, dh_g |
| mov edi, mpint_tmp |
| call mpint_to_big_endian |
| lea edx, [eax+4] |
| mov esi, mpint_tmp |
| call sha256_update |
| |
| ;--------------------------------------------------- |
| ; HASH: mpint e, exchange value sent by the client |
| mov esi, tx_buffer+sizeof.ssh_header |
| mov edx, [esi] |
| bswap edx |
| add edx, 4 |
| call sha256_update |
| |
| ;--------------------------------------------------- |
| ; HASH: mpint f, exchange value sent by the server |
| mov esi, [esp] |
| mov edx, [esi] |
| bswap edx |
| add edx, 4 |
| call sha256_update |
| pop esi |
| |
| mov edi, dh_f |
| call mpint_to_little_endian |
| |
| DEBUGF 1, "DH f: " |
| stdcall mpint_print, dh_f |
| |
| mov edi, dh_signature |
| call mpint_to_little_endian |
| |
| DEBUGF 1, "DH signature: " |
| stdcall mpint_print, dh_signature |
| |
| ;-------------------------------------- |
| ; Calculate shared secret K = f^x mod p |
| stdcall mpint_modexp, rx_buffer, dh_f, dh_x, dh_p |
| stdcall mpint_length, rx_buffer |
| |
| DEBUGF 1, "DH K: " |
| stdcall mpint_print, rx_buffer |
| |
| ; We always need it in big endian order, so store it as such. |
| mov edi, dh_K |
| mov esi, rx_buffer |
| call mpint_to_big_endian |
| mov [dh_K.length], eax |
| |
| ;----------------------------------- |
| ; HASH: mpint K, the shared secret |
| mov edx, [dh_K.length] |
| add edx, 4 |
| mov esi, dh_K |
| call sha256_update |
| |
| ;------------------------------- |
| ; Finalize the exchange hash (H) |
| mov edi, dh_H |
| call sha256_final |
| |
| DEBUGF 1, "Exchange hash H: " |
| stdcall dump_256bit_hex, dh_H |
| |
| ; TODO: skip this block when re-keying |
| mov esi, dh_H |
| mov edi, session_id |
| mov ecx, 32/4 |
| rep movsd |
| |
| ;--------------- |
| ; Calculate keys |
| |
| ; TODO: re-use partial hash of K and H |
| |
| ;--------------------------------------------------------------- |
| ; Initial IV client to server: HASH(K || H || "A" || session_id) |
| |
| call sha256_init |
| mov edx, [dh_K.length] |
| add edx, 4 |
| mov esi, dh_K |
| call sha256_update |
| mov edx, 32 |
| mov esi, dh_H |
| call sha256_update |
| mov edx, 1 |
| mov esi, str_A |
| call sha256_update |
| mov edx, 32 |
| mov esi, session_id |
| call sha256_update |
| mov edi, tx_iv |
| call sha256_final |
| |
| DEBUGF 1, "Remote IV: " |
| stdcall dump_256bit_hex, tx_iv |
| |
| ;--------------------------------------------------------------- |
| ; Initial IV server to client: HASH(K || H || "B" || session_id) |
| |
| call sha256_init |
| mov edx, [dh_K.length] |
| add edx, 4 |
| mov esi, dh_K |
| call sha256_update |
| mov edx, 32 |
| mov esi, dh_H |
| call sha256_update |
| mov edx, 1 |
| mov esi, str_B |
| call sha256_update |
| mov edx, 32 |
| mov esi, session_id |
| call sha256_update |
| mov edi, rx_iv |
| call sha256_final |
| |
| DEBUGF 1, "Local IV: " |
| stdcall dump_256bit_hex, rx_iv |
| |
| ;------------------------------------------------------------------- |
| ; Encryption key client to server: HASH(K || H || "C" || session_id) |
| |
| call sha256_init |
| mov edx, [dh_K.length] |
| add edx, 4 |
| mov esi, dh_K |
| call sha256_update |
| mov edx, 32 |
| mov esi, dh_H |
| call sha256_update |
| mov edx, 1 |
| mov esi, str_C |
| call sha256_update |
| mov edx, 32 |
| mov esi, session_id |
| call sha256_update |
| mov edi, tx_enc_key |
| call sha256_final |
| |
| DEBUGF 1, "Remote key: " |
| stdcall dump_256bit_hex, tx_enc_key |
| |
| ;------------------------------------------------------------------- |
| ; Encryption key server to client: HASH(K || H || "D" || session_id) |
| |
| call sha256_init |
| mov edx, [dh_K.length] |
| add edx, 4 |
| mov esi, dh_K |
| call sha256_update |
| mov edx, 32 |
| mov esi, dh_H |
| call sha256_update |
| mov edx, 1 |
| mov esi, str_D |
| call sha256_update |
| mov edx, 32 |
| mov esi, session_id |
| call sha256_update |
| mov edi, rx_enc_key |
| call sha256_final |
| |
| DEBUGF 1, "Local key: " |
| stdcall dump_256bit_hex, rx_enc_key |
| |
| ;------------------------------------------------------------------ |
| ; Integrity key client to server: HASH(K || H || "E" || session_id) |
| |
| call sha256_init |
| mov edx, [dh_K.length] |
| add edx, 4 |
| mov esi, dh_K |
| call sha256_update |
| mov edx, 32 |
| mov esi, dh_H |
| call sha256_update |
| mov edx, 1 |
| mov esi, str_E |
| call sha256_update |
| mov edx, 32 |
| mov esi, session_id |
| call sha256_update |
| mov edi, tx_int_key |
| call sha256_final |
| |
| DEBUGF 1, "Remote Integrity key: " |
| stdcall dump_256bit_hex, tx_int_key |
| |
| ;------------------------------------------------------------------ |
| ; Integrity key server to client: HASH(K || H || "F" || session_id) |
| |
| call sha256_init |
| mov edx, [dh_K.length] |
| add edx, 4 |
| mov esi, dh_K |
| call sha256_update |
| mov edx, 32 |
| mov esi, dh_H |
| call sha256_update |
| mov edx, 1 |
| mov esi, str_F |
| call sha256_update |
| mov edx, 32 |
| mov esi, session_id |
| call sha256_update |
| mov edi, rx_int_key |
| call sha256_final |
| |
| DEBUGF 1, "Local Integrity key: " |
| stdcall dump_256bit_hex, rx_int_key |
| |
| ;------------------------------------- |
| ; << Parse Diffie-Hellman New Keys MSG |
| |
| stdcall ssh_recv_packet, [socketnum], rx_buffer, BUFFERSIZE, 0 |
| cmp eax, -1 |
| je .socket_err |
| |
| cmp [rx_buffer+ssh_header.message_code], SSH_MSG_NEWKEYS |
| jne .proto_err |
| |
| DEBUGF 1, "Received New Keys\n" |
| |
| ;------------------------------- |
| ; >> Reply with New Keys message |
| |
| stdcall ssh_send_packet, [socketnum], ssh_new_keys, ssh_new_keys.length, 0 |
| |
| xor eax, eax |
| ret |
| |
| .socket_err: |
| DEBUGF 2, "Socket error during key exchange!\n" |
| mov eax, 1 |
| ret |
| |
| .proto_err: |
| DEBUGF 2, "Protocol error during key exchange!\n" |
| mov eax, 2 |
| ret |
| |
| endp |
| |
| proc dump_256bit_hex _ptr |
| pushad |
| |
| mov esi, [_ptr] |
| mov ecx, 8 |
| .next_dword: |
| lodsd |
| bswap eax |
| DEBUGF 1,'%x',eax |
| loop .next_dword |
| DEBUGF 1,'\n' |
| |
| popad |
| ret |
| endp |
| |
| iglobal |
| |
| str_A db 'A' |
| str_B db 'B' |
| str_C db 'C' |
| str_D db 'D' |
| str_E db 'E' |
| str_F db 'F' |
| |
| endg |