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Diffstat (limited to '')
| -rw-r--r-- | CryptoPP/elgamal.h | 121 |
1 files changed, 121 insertions, 0 deletions
diff --git a/CryptoPP/elgamal.h b/CryptoPP/elgamal.h new file mode 100644 index 000000000..9afc30eee --- /dev/null +++ b/CryptoPP/elgamal.h @@ -0,0 +1,121 @@ +#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 ¶meters) 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 ¶meters) 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 |