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-rw-r--r--CryptoPP/elgamal.h121
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diff --git a/CryptoPP/elgamal.h b/CryptoPP/elgamal.h
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+#ifndef CRYPTOPP_ELGAMAL_H
+#define CRYPTOPP_ELGAMAL_H
+
+#include "modexppc.h"
+#include "dsa.h"
+
+NAMESPACE_BEGIN(CryptoPP)
+
+class CRYPTOPP_NO_VTABLE ElGamalBase : public DL_KeyAgreementAlgorithm_DH<Integer, NoCofactorMultiplication>,
+ public DL_KeyDerivationAlgorithm<Integer>,
+ public DL_SymmetricEncryptionAlgorithm
+{
+public:
+ void Derive(const DL_GroupParameters<Integer> &groupParams, byte *derivedKey, size_t derivedLength, const Integer &agreedElement, const Integer &ephemeralPublicKey, const NameValuePairs &derivationParams) const
+ {
+ agreedElement.Encode(derivedKey, derivedLength);
+ }
+
+ size_t GetSymmetricKeyLength(size_t plainTextLength) const
+ {
+ return GetGroupParameters().GetModulus().ByteCount();
+ }
+
+ size_t GetSymmetricCiphertextLength(size_t plainTextLength) const
+ {
+ unsigned int len = GetGroupParameters().GetModulus().ByteCount();
+ if (plainTextLength <= GetMaxSymmetricPlaintextLength(len))
+ return len;
+ else
+ return 0;
+ }
+
+ size_t GetMaxSymmetricPlaintextLength(size_t cipherTextLength) const
+ {
+ unsigned int len = GetGroupParameters().GetModulus().ByteCount();
+ if (cipherTextLength == len)
+ return STDMIN(255U, len-3);
+ else
+ return 0;
+ }
+
+ void SymmetricEncrypt(RandomNumberGenerator &rng, const byte *key, const byte *plainText, size_t plainTextLength, byte *cipherText, const NameValuePairs &parameters) const
+ {
+ const Integer &p = GetGroupParameters().GetModulus();
+ unsigned int modulusLen = p.ByteCount();
+
+ SecByteBlock block(modulusLen-1);
+ rng.GenerateBlock(block, modulusLen-2-plainTextLength);
+ memcpy(block+modulusLen-2-plainTextLength, plainText, plainTextLength);
+ block[modulusLen-2] = (byte)plainTextLength;
+
+ a_times_b_mod_c(Integer(key, modulusLen), Integer(block, modulusLen-1), p).Encode(cipherText, modulusLen);
+ }
+
+ DecodingResult SymmetricDecrypt(const byte *key, const byte *cipherText, size_t cipherTextLength, byte *plainText, const NameValuePairs &parameters) const
+ {
+ const Integer &p = GetGroupParameters().GetModulus();
+ unsigned int modulusLen = p.ByteCount();
+
+ if (cipherTextLength != modulusLen)
+ return DecodingResult();
+
+ Integer m = a_times_b_mod_c(Integer(cipherText, modulusLen), Integer(key, modulusLen).InverseMod(p), p);
+
+ m.Encode(plainText, 1);
+ unsigned int plainTextLength = plainText[0];
+ if (plainTextLength > GetMaxSymmetricPlaintextLength(modulusLen))
+ return DecodingResult();
+ m >>= 8;
+ m.Encode(plainText, plainTextLength);
+ return DecodingResult(plainTextLength);
+ }
+
+ virtual const DL_GroupParameters_GFP & GetGroupParameters() const =0;
+};
+
+template <class BASE, class SCHEME_OPTIONS, class KEY>
+class ElGamalObjectImpl : public DL_ObjectImplBase<BASE, SCHEME_OPTIONS, KEY>, public ElGamalBase
+{
+public:
+ size_t FixedMaxPlaintextLength() const {return this->MaxPlaintextLength(FixedCiphertextLength());}
+ size_t FixedCiphertextLength() const {return this->CiphertextLength(0);}
+
+ const DL_GroupParameters_GFP & GetGroupParameters() const {return this->GetKey().GetGroupParameters();}
+
+ DecodingResult FixedLengthDecrypt(RandomNumberGenerator &rng, const byte *cipherText, byte *plainText) const
+ {return Decrypt(rng, cipherText, FixedCiphertextLength(), plainText);}
+
+protected:
+ const DL_KeyAgreementAlgorithm<Integer> & GetKeyAgreementAlgorithm() const {return *this;}
+ const DL_KeyDerivationAlgorithm<Integer> & GetKeyDerivationAlgorithm() const {return *this;}
+ const DL_SymmetricEncryptionAlgorithm & GetSymmetricEncryptionAlgorithm() const {return *this;}
+};
+
+struct ElGamalKeys
+{
+ typedef DL_CryptoKeys_GFP::GroupParameters GroupParameters;
+ typedef DL_PrivateKey_GFP_OldFormat<DL_CryptoKeys_GFP::PrivateKey> PrivateKey;
+ typedef DL_PublicKey_GFP_OldFormat<DL_CryptoKeys_GFP::PublicKey> PublicKey;
+};
+
+//! ElGamal encryption scheme with non-standard padding
+struct ElGamal
+{
+ typedef DL_CryptoSchemeOptions<ElGamal, ElGamalKeys, int, int, int> SchemeOptions;
+
+ static const char * StaticAlgorithmName() {return "ElgamalEnc/Crypto++Padding";}
+
+ typedef SchemeOptions::GroupParameters GroupParameters;
+ //! implements PK_Encryptor interface
+ typedef PK_FinalTemplate<ElGamalObjectImpl<DL_EncryptorBase<Integer>, SchemeOptions, SchemeOptions::PublicKey> > Encryptor;
+ //! implements PK_Decryptor interface
+ typedef PK_FinalTemplate<ElGamalObjectImpl<DL_DecryptorBase<Integer>, SchemeOptions, SchemeOptions::PrivateKey> > Decryptor;
+};
+
+typedef ElGamal::Encryptor ElGamalEncryptor;
+typedef ElGamal::Decryptor ElGamalDecryptor;
+
+NAMESPACE_END
+
+#endif