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/*
Copyright (C) 2019-2025 Selwin van Dijk
This file is part of signalbackup-tools.
signalbackup-tools 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.
signalbackup-tools 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 signalbackup-tools. If not, see <https://www.gnu.org/licenses/>.
*/
#include "filedecryptor.ih"
std::unique_ptr<BackupFrame> FileDecryptor::bruteForceFrom(std::ifstream &file, uint64_t filepos, uint32_t previousframelength)
{
Logger::message("Starting bruteforcing offset to next valid frame... starting after: ", filepos);
uint64_t skip = 1;
std::unique_ptr<BackupFrame> ret(nullptr);
while (filepos + skip < d_filesize)
{
file.clear();
if (skip % 10 == 0)
Logger::message_overwrite("Checking offset ", skip, " bytes");
file.seekg(filepos + skip, std::ios_base::beg);
ret.reset(getFrameBrute(file, skip++, previousframelength).release());
if (ret)
{
Logger::message("Got frame, breaking");
break;
}
}
return ret;
}
std::unique_ptr<BackupFrame> FileDecryptor::getFrameBrute(std::ifstream &file, uint64_t offset, uint32_t previousframelength)
{
if (static_cast<uint64_t>(file.tellg()) == d_filesize)
{
Logger::message("Read entire backup file...");
return std::unique_ptr<BackupFrame>(nullptr);
}
if (d_headerframe)
{
file.seekg(4 + d_headerframe->dataSize());
std::unique_ptr<BackupFrame> frame(d_headerframe.release());
return frame;
}
uint32_t encryptedframelength = getNextFrameBlockSize(file);
if (encryptedframelength > 3145728/*= 3MB*/ /*115343360 / * =110MB*/ || encryptedframelength < 11)
{
//std::cout << "Framesize too big to be real" << std::endl;
return std::unique_ptr<BackupFrame>(nullptr);
}
std::unique_ptr<unsigned char[]> encryptedframe(new unsigned char[encryptedframelength]);
if (!getNextFrameBlock(file, encryptedframe.get(), encryptedframelength))
return std::unique_ptr<BackupFrame>(nullptr);
// check hash
unsigned int digest_size = SHA256_DIGEST_LENGTH;
unsigned char hash[SHA256_DIGEST_LENGTH];
HMAC(EVP_sha256(), d_mackey, d_mackey_size, encryptedframe.get(), encryptedframelength - MACSIZE, hash, &digest_size);
if (std::memcmp(encryptedframe.get() + (encryptedframelength - MACSIZE), hash, MACSIZE) != 0)
return std::unique_ptr<BackupFrame>(nullptr);
else
{
Logger::message("\nGOT GOOD MAC AT OFFSET ", offset, " BYTES!");
Logger::message("Now let's try and find out how many frames we skipped to get here....");
d_badmac = false;
}
// decode
unsigned int skippedframes = 0;
std::unique_ptr<BackupFrame> frame(nullptr);
while (!frame)
{
if (skippedframes > offset / 10) // a frame is at least 10 bytes? -> could probably safely set this higher. MAC alone is 10 bytes, there is also actual data
{
Logger::message("\nNo valid frame found at maximum frameskip for this offset...");
return std::unique_ptr<BackupFrame>(nullptr);
}
Logger::message_overwrite("Checking if we skipped ", skippedframes, " frames... ");
uintToFourBytes(d_iv, d_counter + skippedframes);
// create context
std::unique_ptr<EVP_CIPHER_CTX, decltype(&::EVP_CIPHER_CTX_free)> ctx(EVP_CIPHER_CTX_new(), &::EVP_CIPHER_CTX_free);
// disable padding
EVP_CIPHER_CTX_set_padding(ctx.get(), 0);
if (EVP_DecryptInit_ex(ctx.get(), EVP_aes_256_ctr(), nullptr, d_cipherkey, d_iv) != 1)
{
Logger::error("CTX INIT FAILED");
return std::unique_ptr<BackupFrame>(nullptr);
}
int decodedframelength = encryptedframelength - MACSIZE;
unsigned char *decodedframe = new unsigned char[decodedframelength];
if (EVP_DecryptUpdate(ctx.get(), decodedframe, &decodedframelength, encryptedframe.get(), encryptedframelength - MACSIZE) != 1)
{
Logger::error("Failed to decrypt data");
delete[] decodedframe;
return std::unique_ptr<BackupFrame>(nullptr);
}
DEBUGOUT("Decoded hex : ", bepaald::bytesToHexString(decodedframe, decodedframelength));
frame.reset(initBackupFrame(decodedframe, decodedframelength, d_framecount + skippedframes));
delete[] decodedframe;
++skippedframes;
if (!frame)
{
Logger::message_overwrite("Checking if we skipped ", skippedframes, " frames... nope! :(");
//if (skipped >
}
else
{
if (frame->validate(d_filesize - file.tellg()) &&
frame->frameType() != BackupFrame::FRAMETYPE::HEADER && // it is impossible to get in this function without the headerframe, and there is only one
(frame->frameType() != BackupFrame::FRAMETYPE::END || static_cast<uint64_t>(file.tellg()) == d_filesize))
{
d_counter += skippedframes;
d_framecount += skippedframes;
Logger::message_overwrite("Checking if we skipped ", skippedframes, " frames... YEAH! :)", Logger::Control::ENDOVERWRITE);
if (d_assumebadframesize && skippedframes == 1 /*NOTE, skippedframes was already upped*/)
{
Logger::message("\n ! CORRECT FRAME_NUMBER:SIZE = ", frame->frameNumber() - 1, ":",
offset - previousframelength - MACSIZE - 4, "\n");
}
Logger::message("Good frame at offset ", offset, ". Frame number: ", frame->frameNumber(), " (Type: ", frame->frameTypeString(), ")");
frame->printInfo();
delete[] encryptedframe.release();
break;
}
Logger::message_overwrite("Checking if we skipped ", skippedframes, " frames... nope! :(");
frame.reset();
}
}
//frame->printInfo();
//std::cout << "HEADERTYPE: " << frame->frameType() << std::endl;
uint32_t attsize = 0;
if (!d_badmac && (attsize = frame->attachmentSize()) > 0 &&
(frame->frameType() == BackupFrame::FRAMETYPE::ATTACHMENT ||
frame->frameType() == BackupFrame::FRAMETYPE::AVATAR ||
frame->frameType() == BackupFrame::FRAMETYPE::STICKER))
{
if (d_verbose) [[unlikely]]
Logger::message("Trying to read attachment (bruteforce)");
uintToFourBytes(d_iv, d_counter++);
//reinterpret_cast<FrameWithAttachment *>(frame.get())->setLazyData(d_iv, d_iv_size, d_mackey, d_mackey_size, d_cipherkey, d_cipherkey_size, attsize, d_filename, file.tellg());
reinterpret_cast<FrameWithAttachment *>(frame.get())->setReader(new AndroidAttachmentReader(d_iv, d_iv_size, d_mackey, d_mackey_size, d_cipherkey, d_cipherkey_size, attsize, d_filename, file.tellg()));
file.seekg(attsize + MACSIZE, std::ios_base::cur);
}
//std::cout << "FILEPOS: " << d_file.tellg() << std::endl;
//delete frame;
return frame;
}
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