Method SymmetricDecrypt

src/cryptopp/gfpcrypt.h:839–873

		mac.Final(ciphertext + plaintextLength);
	}
	DecodingResult SymmetricDecrypt(const byte *key, const byte *ciphertext, size_t ciphertextLength, byte *plaintext, const NameValuePairs &parameters) const
	{
		size_t plaintextLength = GetMaxSymmetricPlaintextLength(ciphertextLength);
		const byte *cipherKey, *macKey;
		if (DHAES_MODE)
		{
			macKey = key;
			cipherKey = key + MAC::DEFAULT_KEYLENGTH;
		}
		else
		{
			cipherKey = key;
			macKey = key + plaintextLength;
		}

		ConstByteArrayParameter encodingParameters;
		parameters.GetValue(Name::EncodingParameters(), encodingParameters);

		MAC mac(macKey);
		mac.Update(ciphertext, plaintextLength);
		mac.Update(encodingParameters.begin(), encodingParameters.size());
		if (DHAES_MODE)
		{
			byte L[8];
			PutWord(false, BIG_ENDIAN_ORDER, L, (LABEL_OCTETS ? word64(encodingParameters.size()) : 8 * word64(encodingParameters.size())));
			mac.Update(L, 8);
		}
		if (!mac.Verify(ciphertext + plaintextLength))
			return DecodingResult();

		if (plaintextLength)	// Coverity finding
			xorbuf(plaintext, ciphertext, cipherKey, plaintextLength);

		return DecodingResult(plaintextLength);
	}
};

//! _