const UInt32 decryptionMultKey = 0x0019660D; // 1664525
private byte[] DecryptArchiveHeader(FileStream fileStream)
{
fileStream.Seek(0, SeekOrigin.Begin);
UInt32 encryptedHeaderSize = fileStream.ReadUInt32LE(0);
UInt32 headerSize = (encryptedHeaderSize ^ decryptionAddKey);
var fileEnd = fileStream.Seek(0, SeekOrigin.End);
if (headerSize > fileEnd)
{
throw new Exception("Header size is larger than file, something went wrong");
}
var headerBuffer = CopyHeader(fileStream, headerSize, 4);
UInt32 currentKey = 0;
byte[] copyBuffer = new byte[4];
UInt32 value = 0;
int offset = 0;
for (uint i = 0; i < headerSize; i++)
{
offset = (int)i * 4;
currentKey += decryptionAddKey;
copyBuffer[0] = headerBuffer[offset];
copyBuffer[1] = headerBuffer[offset + 1];
copyBuffer[2] = headerBuffer[offset + 2];
copyBuffer[3] = headerBuffer[offset + 3];
value = BitConverter.ToUInt32(copyBuffer, 0);
value = value ^ currentKey;
value.CopyToByteArrayLE(headerBuffer, offset);
currentKey *= decryptionMultKey;
}
return(headerBuffer);
}
