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/*
* ssh_packet.c: SSH packet maker
* Copyright (C) 2018 Iru Cai <mytbk920423@gmail.com>
*
* This library is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License as published by the Free Software Foundation; either
* version 2.1 of the License, or (at your option) any later version.
*
* This library 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
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with this library; if not, write to the Free Software
* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
*/
#include "ssh_packet.h"
#include "crc32.h"
#include "ssh_error.h"
//==============================================================================
//
// SSH1 Packet Structure:
// --------------------------------------------------------------------------
// | length | padding | type | data | crc32 |
// --------------------------------------------------------------------------
// | uint32 | 1-7bytes | uchar | | 4bytes|
// --------------------------------------------------------------------------
// encrypt = padding + type + data + crc32
// length = type + data + crc32
//
//==============================================================================
void make_ssh1_packet(buffer *orig_data, buffer *data_to_send,
SSH_CIPHER *cipher)
{
int len, padding_len;
uint32_t padding[2];
uint8_t *data = buffer_data(orig_data);
size_t data_len = buffer_len(orig_data);
len = data_len + 4; //CRC32
padding_len = 8 - (len % 8);
padding[0] = rand();
padding[1] = rand();
buffer_clear(data_to_send);
buffer_append_be32(data_to_send, len);
buffer_append(data_to_send, (const uint8_t *)padding, padding_len);
buffer_append(data_to_send, data, data_len);
buffer_append_be32(data_to_send,
ssh_crc32(buffer_data(data_to_send) + 4,
buffer_len(data_to_send) - 4));
if (cipher->started) {
cipher->crypt(cipher, buffer_data(data_to_send) + 4,
buffer_data(data_to_send) + 4,
buffer_len(data_to_send) - 4);
}
}
//==============================================================================
// SSH2 Packet Structure:
// uint32 packet_length
// byte padding_length
// byte[n1] payload; n1 = packet_length - padding_length - 1
// byte[n2] random padding; n2 = padding_length
// byte[m] mac (Message Authentication Code - MAC); m = mac_length
//==============================================================================
int make_ssh2_packet(buffer *orig_data, buffer *data_to_send,
SSH_CIPHER *cipher, SSH_MAC *mac, bool is_mac_,
uint32_t *seq)
{
// 1. compute the padding length for padding.
int non_padding_len = 4 + 1 + buffer_len(orig_data);
int padding_block_len = 8;
if (cipher->started && cipher->blkSize > padding_block_len)
padding_block_len = cipher->blkSize;
int padding_len =
padding_block_len - (non_padding_len % padding_block_len);
if (padding_len < 4)
padding_len += padding_block_len;
// 2. renew the output buffer.
int total_len = non_padding_len + padding_len;
if (is_mac_)
total_len += mac->dgstSize;
buffer_clear(data_to_send);
// 3. Fill the output buffer.
int packet_len = 1 + buffer_len(orig_data) + padding_len;
buffer_append_be32(data_to_send, packet_len);
buffer_append_byte(data_to_send, padding_len);
buffer_append(data_to_send, buffer_data(orig_data),
buffer_len(orig_data));
uint32_t padding[8]; /* padding at most 256 bits */
for (int i = 0; i < 8; i++)
padding[i] = rand();
buffer_append(data_to_send, (const uint8_t *)padding, padding_len);
// 4. Add MAC on the entire unencrypted packet,
// including two length fields, 'payload' and 'random padding'.
if (is_mac_) {
const unsigned char *packet = buffer_data(data_to_send);
int len = buffer_len(data_to_send);
uint8_t digest[MAX_DGSTLEN];
buffer mbuffer;
buffer_init(&mbuffer);
buffer_append_be32(&mbuffer, *seq);
buffer_append(&mbuffer, packet, len);
mac->getmac(mac, buffer_data(&mbuffer), buffer_len(&mbuffer),
digest);
buffer_deinit(&mbuffer);
buffer_append(data_to_send, digest, mac->dgstSize);
}
if (cipher->started) {
// as RFC 4253:
// When encryption is in effect, the packet length, padding
// length, payload, and padding fields of each packet MUST be encrypted
// with the given algorithm.
uint8_t *data = buffer_data(data_to_send);
int len = buffer_len(data_to_send) - mac->dgstSize;
if (cipher->crypt(cipher, data, data, len) != 1)
return -ECRYPT;
}
*seq = *seq + 1;
return 0;
}
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