public void TestParseRC4CryptoAPIFilePassRecord()
{
byte[] rc4CryptoApiFilePassRecord = new byte[]
{
0x2F, 0x00, 0xC8, 0x00, 0x01, 0x00, 0x04, 0x00, 0x02, 0x00, 0x0C, 0x00, 0x00, 0x00, 0x7E, 0x00, 0x00,
0x00, 0x0C, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x01, 0x68, 0x00, 0x00, 0x04, 0x80, 0x00, 0x00,
0x80, 0x00, 0x00, 0x00, 0x01, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x4D,
0x00, 0x69, 0x00, 0x63, 0x00, 0x72, 0x00, 0x6F, 0x00, 0x73, 0x00, 0x6F, 0x00, 0x66, 0x00, 0x74, 0x00,
0x20, 0x00, 0x45, 0x00, 0x6E, 0x00, 0x68, 0x00, 0x61, 0x00, 0x6E, 0x00, 0x63, 0x00, 0x65, 0x00, 0x64,
0x00, 0x20, 0x00, 0x43, 0x00, 0x72, 0x00, 0x79, 0x00, 0x70, 0x00, 0x74, 0x00, 0x6F, 0x00, 0x67, 0x00,
0x72, 0x00, 0x61, 0x00, 0x70, 0x00, 0x68, 0x00, 0x69, 0x00, 0x63, 0x00, 0x20, 0x00, 0x50, 0x00, 0x72,
0x00, 0x6F, 0x00, 0x76, 0x00, 0x69, 0x00, 0x64, 0x00, 0x65, 0x00, 0x72, 0x00, 0x20, 0x00, 0x76, 0x00,
0x31, 0x00, 0x2E, 0x00, 0x30, 0x00, 0x00, 0x00, 0x10, 0x00, 0x00, 0x00, 0x98, 0xC3, 0xA1, 0xA0, 0x9A,
0xC8, 0x92, 0x3D, 0x7A, 0x5D, 0x03, 0x30, 0x34, 0xE8, 0x67, 0x64, 0xA8, 0xA9, 0x29, 0xF0, 0xA6, 0xA8,
0xB6, 0xA1, 0x1F, 0x8C, 0x6F, 0x27, 0xB6, 0xA8, 0x82, 0xEB, 0x14, 0x00, 0x00, 0x00, 0xE8, 0xAF, 0x8B,
0x67, 0x4E, 0x3F, 0xA7, 0xA1, 0x39, 0x9D, 0x9F, 0x2D, 0xDC, 0xB5, 0x1A, 0x33, 0x5D, 0x8A, 0xB2, 0x69
};
VirtualStreamReader vsr = new VirtualStreamReader(new MemoryStream(rc4CryptoApiFilePassRecord));
FilePass filePassRecord = new FilePass(vsr, (RecordType)vsr.ReadUInt16(), vsr.ReadUInt16());
byte[] filePassBytes = filePassRecord.GetBytes();
Assert.AreEqual(rc4CryptoApiFilePassRecord.Length, filePassBytes.Length);
Assert.IsFalse(filePassRecord.encryptionHeader.fDocProps);
Assert.IsFalse(filePassRecord.encryptionHeader.fCryptoAPI);
Assert.IsTrue(filePassRecord.encryptionHeader.fExternal);
Assert.IsTrue(filePassRecord.encryptionHeader.fAES);
for (int offset = 0; offset < rc4CryptoApiFilePassRecord.Length; offset += 1)
{
Assert.AreEqual(rc4CryptoApiFilePassRecord[offset], filePassBytes[offset]);
}
}
public byte[] TransformWorkbookBytes(byte[] bytes, ObfuscationMode mode, string password = XorObfuscation.DefaultPassword)
{
VirtualStreamReader vsr = new VirtualStreamReader(new MemoryStream(bytes));
MemoryStream ms = new MemoryStream();
BinaryWriter bw = new BinaryWriter(ms);
while (vsr.BaseStream.Position < vsr.BaseStream.Length)
{
BiffHeader bh;
bh.id = (RecordType)vsr.ReadUInt16();
//Handle case where RecordId is empty
if (bh.id == 0)
{
break;
}
bh.length = vsr.ReadUInt16();
//Taken from https://social.msdn.microsoft.com/Forums/en-US/3dadbed3-0e68-4f11-8b43-3a2328d9ebd5/xls-xor-data-transformation-method-1
byte XorArrayIndex = (byte)((vsr.BaseStream.Position + bh.length) % 16);
//We remove the FilePass Record for the decrypted document
if (mode == ObfuscationMode.Decrypt && bh.id == RecordType.FilePass)
{
//Skip the remaining FilePass bytes
ushort encryptionMode = vsr.ReadUInt16();
if (encryptionMode != 0)
{
throw new NotImplementedException("FilePass EncryptionMode of " + encryptionMode +
" is unsupported.");
}
ushort key = vsr.ReadUInt16();
ushort verify = vsr.ReadUInt16();
ushort passwordVerify = CreatePasswordVerifier_Method1(password);
if (verify != passwordVerify)
{
throw new ArgumentException(
"Incorrect decryption password. Try bruteforcing the password with another tool.");
}
continue;
}
;
bw.Write(Convert.ToUInt16(bh.id));
bw.Write(Convert.ToUInt16(bh.length));
//If we're encrypting, then use the byte writer for our current position rather than the read stream
if (mode == ObfuscationMode.Encrypt)
{
XorArrayIndex = (byte)((bw.BaseStream.Position + bh.length) % 16);
}
//Nothing to decrypt for 0 length
if (bh.length == 0)
{
continue;
}
switch (bh.id)
{
case RecordType.BOF:
case RecordType.FilePass:
case RecordType.UsrExcl:
case RecordType.FileLock:
case RecordType.InterfaceHdr:
case RecordType.RRDInfo:
case RecordType.RRDHead:
byte[] recordBytes = vsr.ReadBytes(bh.length);
bw.Write(recordBytes);
//If this is the first BOF record, we inject the appropriate FilePass record
if (mode == ObfuscationMode.Encrypt &&
bh.id == RecordType.BOF &&
vsr.BaseStream.Position == (bh.length + 4))
{
ushort key = CreateXorKey_Method1(password);
ushort verify = CreatePasswordVerifier_Method1(password);
FilePass filePass = new FilePass(key, verify);
byte[] filePassBytes = filePass.GetBytes();
bw.Write(filePassBytes);
}
continue;
case RecordType.BoundSheet8:
//Special Case - don't encrypt/decrypt the lbPlyPos Field
uint lbPlyPos = vsr.ReadUInt32();
//For encryption we need to adjust this by the added FilePass record length
//Decryption we auto-fix afterwards, but encrypted entries don't auto-fix well
// if (mode == ObfuscationMode.Encrypt)
// {
// lbPlyPos += 10;
// }
bw.Write(lbPlyPos);
//Since we are skipping lbPlyPos, we need to update the XorArrayIndex offset as well
XorArrayIndex = (byte)((XorArrayIndex + 4) % 16);
byte[] remainingBytes = vsr.ReadBytes(bh.length - 4);
if (mode == ObfuscationMode.Decrypt)
{
byte[] decryptedBytes = DecryptData_Method1(password, remainingBytes, XorArrayIndex);
bw.Write(decryptedBytes);
}
else
{
byte[] encryptedBytes = EncryptData_Method1(password, remainingBytes, XorArrayIndex);
bw.Write(encryptedBytes);
}
continue;
default:
byte[] preTransformBytes = vsr.ReadBytes(bh.length);
if (mode == ObfuscationMode.Decrypt)
{
byte[] decBytes = DecryptData_Method1(password, preTransformBytes, XorArrayIndex);
bw.Write(decBytes);
}
else
{
byte[] encBytes = EncryptData_Method1(password, preTransformBytes, XorArrayIndex);
bw.Write(encBytes);
}
continue;
}
}
return(bw.GetBytesWritten());
}