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