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/***************************************************************************
* fqterm, a terminal emulator for both BBS and *nix. *
* Copyright (C) 2008 fqterm development group. *
* *
* 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 2 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, write to the *
* Free Software Foundation, Inc., *
* 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. *
***************************************************************************/
#include "fqterm_trace.h"
#include "fqterm_ssh_buffer.h"
#include "fqterm_ssh2_packet.h"
#include "fqterm_serialization.h"
#include "crc32.h"
namespace FQTerm {
//==============================================================================
//FQTermSSH2PacketSender
//==============================================================================
// 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
//==============================================================================
void FQTermSSH2PacketSender::makePacket() {
FQ_TRACE("ssh2packet", 9) << "----------------------------Send "
<< (is_encrypt_ ? "Encrypted": "plain")
<< " Packet---->>>>>>>";
// 0. compress
if (is_compressed_) {
FQ_VERIFY(false);
}
// 1. compute the padding length for padding.
int non_padding_len = 4 + 1 + buffer_->len();
int padding_block_len = 8;
if (is_encrypt_ && 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;
delete output_buffer_;
output_buffer_ = new FQTermSSHBuffer(total_len);
// 3. Fill the output buffer.
int packet_len = 1 + buffer_->len() + padding_len;
output_buffer_->putInt(packet_len);
output_buffer_->putByte(padding_len);
output_buffer_->putRawData((const char*)buffer_->data(), buffer_->len());
u_int32_t rand_val = 0;
for (int i = 0; i < padding_len; i++) {
if (i % 4 == 0) {
rand_val = rand(); // FIXME: rand() doesn't range from 0 to 2^32.
}
output_buffer_->putByte(rand_val & 0xff);
rand_val >>= 8;
}
// 4. Add MAC on the entire unencrypted packet,
// including two length fields, 'payload' and 'random padding'.
if (is_mac_) {
const unsigned char *packet = output_buffer_->data();
int len = output_buffer_->len();
FQTermSSHBuffer buffer(4 + len);
buffer.putInt(sequence_no_);
buffer.putRawData((const char *)packet, len);
std::vector<u_char> digest(mac->dgstSize);
mac->getmac(mac, buffer.data(), buffer.len(), &digest[0]);
FQ_TRACE("ssh2packet", 9) << "Making packets...";
FQ_TRACE("ssh2packet", 9) << "Append MAC with sequence_no_" << sequence_no_;
FQ_TRACE("ssh2packet", 9) << "Compute MAC with "
<< buffer.len() << " bytes data:\n"
<< dumpHexString << std::string((char *)buffer.data(), buffer.len());
FQ_TRACE("ssh2packet", 9) << "MAC data "
<< digest.size() << " bytes:\n"
<< dumpHexString << std::string((const char *)&digest[0], digest.size());
output_buffer_->putRawData((const char *)&digest[0], digest.size());
}
if (is_compressed_) {
FQ_VERIFY(false);
}
if (is_encrypt_) {
// 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.
u_char *data = output_buffer_->data();
int len = output_buffer_->len() - mac->dgstSize;
FQ_TRACE("ssh2packet", 9) << "An packet (without MAC) to be encrypted:"
<< len << " bytes:\n"
<< dumpHexString << std::string((const char *)data, len);
FQ_VERIFY(cipher->crypt(cipher, data, data, len)==1);
FQ_TRACE("ssh2packet", 9) << "An encrypted packet (without MAC) made:"
<< len << " bytes:\n"
<< dumpHexString << std::string((const char *)data, len);
}
++sequence_no_;
}
//==============================================================================
//FQTermSSH2PacketReceiver
//==============================================================================
void FQTermSSH2PacketReceiver::parseData(FQTermSSHBuffer *input) {
FQ_TRACE("ssh2packet", 9) << "----------------------------Receive "
<< (is_decrypt_ ? "Encrypted": "plain")
<< " Packet----<<<<<<<";
while (input->len() > 0) {
// 1. Check the ssh packet
if (input->len() < 16
|| (is_decrypt_ && input->len() < cipher->blkSize)
|| input->len() < last_expected_input_length_
) {
FQ_TRACE("ssh2packet", 3)
<< "Got an incomplete packet. Wait for more data.";
return ;
}
if (last_expected_input_length_ == 0) {
if (is_decrypt_) {
// decrypte the first block to get the packet_length field.
FQ_VERIFY(cipher->crypt(cipher, input->data(), input->data(), cipher->blkSize)==1);
}
} else {
// last_expected_input_length_ != 0
// indicates an incomplete ssh2 packet received last time,
// the first block of data is already decrypted at that time,
// so it must not be decrypted again.
}
int packet_len = ntohu32(input->data());
if (packet_len > SSH_BUFFER_MAX) {
emit packetError(tr("parseData: packet too big"));
return ;
}
int expected_input_len = 4 + packet_len + (is_mac_ ? mac->dgstSize : 0);
if (input->len() < (long)expected_input_len) {
FQ_TRACE("ssh2packet", 3)
<< "The packet is too small. Wait for more data.";
last_expected_input_length_ = expected_input_len;
return ;
} else {
last_expected_input_length_ = 0;
}
// 2. decrypte data.
if (is_decrypt_) {
// decrypte blocks left.
unsigned char *tmp = input->data() + cipher->blkSize;
int left_len = expected_input_len - cipher->blkSize - mac->dgstSize;
FQ_VERIFY(cipher->crypt(cipher, tmp, tmp, left_len)==1);
}
// 3. check MAC
if (is_mac_) {
int digest_len = mac->dgstSize;
std::vector<u_char> digest(digest_len);
FQTermSSHBuffer buffer(4 + expected_input_len - digest_len);
buffer.putInt(sequence_no_);
buffer.putRawData((const char *)input->data(), expected_input_len - digest_len);
mac->getmac(mac, buffer.data(), buffer.len(), &digest[0]);
u_char *received_digest = input->data() + expected_input_len - digest_len;
if (memcmp(&digest[0], received_digest, digest_len) != 0) {
emit packetError("incorrect MAC.");
return ;
}
}
// 4. get every field of the ssh packet.
packet_len = input->getInt();
std::vector<u_char> data(packet_len);
input->getRawData((char*)&data[0], packet_len);
if (is_mac_)
input->consume(mac->dgstSize);
int padding_len = data[0];
real_data_len_ = packet_len - 1 - padding_len;
buffer_->clear();
buffer_->putRawData((char*)&data[0] + 1, real_data_len_);
FQ_TRACE("ssh2packet", 9) << "Receive " << real_data_len_ << " bytes payload:\n"
<< dumpHexString << std::string((char *)&data[0] + 1, real_data_len_);
// 5. notify others a ssh packet is parsed successfully.
packet_type_ = buffer_->getByte();
real_data_len_ -= 1;
emit packetAvaliable(packet_type_);
++sequence_no_;
}
}
} // namespace FQTerm
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