Modified source engine (2017) developed by valve and leaked in 2020. Not for commercial purporses
You can not select more than 25 topics Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
 
 
 
 
 
 

304 lines
13 KiB

// elgamal.h - originally written and placed in the public domain by Wei Dai
/// \file elgamal.h
/// \brief Classes and functions for ElGamal key agreement and encryption schemes
#ifndef CRYPTOPP_ELGAMAL_H
#define CRYPTOPP_ELGAMAL_H
#include "cryptlib.h"
#include "modexppc.h"
#include "integer.h"
#include "gfpcrypt.h"
#include "pubkey.h"
#include "misc.h"
#include "oids.h"
#include "dsa.h"
#include "asn.h"
NAMESPACE_BEGIN(CryptoPP)
/// \brief ElGamal key agreement and encryption schemes base class
/// \since Crypto++ 1.0
class CRYPTOPP_NO_VTABLE ElGamalBase :
public DL_KeyAgreementAlgorithm_DH<Integer, NoCofactorMultiplication>,
public DL_KeyDerivationAlgorithm<Integer>,
public DL_SymmetricEncryptionAlgorithm
{
public:
virtual ~ElGamalBase() {}
void Derive(const DL_GroupParameters<Integer> &groupParams, byte *derivedKey, size_t derivedLength, const Integer &agreedElement, const Integer &ephemeralPublicKey, const NameValuePairs &derivationParams) const
{
CRYPTOPP_UNUSED(groupParams); CRYPTOPP_UNUSED(ephemeralPublicKey);
CRYPTOPP_UNUSED(derivationParams);
agreedElement.Encode(derivedKey, derivedLength);
}
size_t GetSymmetricKeyLength(size_t plainTextLength) const
{
CRYPTOPP_UNUSED(plainTextLength);
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();
CRYPTOPP_ASSERT(len >= 3);
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
{
CRYPTOPP_UNUSED(parameters);
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
{
CRYPTOPP_UNUSED(parameters);
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;
};
/// \brief ElGamal key agreement and encryption schemes default implementation
/// \tparam BASE Base class implementation
/// \tparam SCHEME_OPTIONS Scheme options
/// \tparam KEY ElGamal key classes
/// \since Crypto++ 1.0
template <class BASE, class SCHEME_OPTIONS, class KEY>
class ElGamalObjectImpl :
public DL_ObjectImplBase<BASE, SCHEME_OPTIONS, KEY>,
public ElGamalBase
{
public:
virtual ~ElGamalObjectImpl() {}
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;}
};
/// \brief ElGamal Public Key adapter
/// \tparam BASE PublicKey derived class
/// \details DL_PublicKey_ElGamal provides an override for GetAlgorithmID()
/// to utilize 1.3.14.7.2.1.1. Prior to DL_PublicKey_ElGamal, the ElGamal
/// keys [mistakenly] used the OID from DSA due to DL_GroupParmaters_GFP().
/// If you need to <tt>Load</tt> an ElGamal key with the wrong OID then
/// see <A HREF="https://www.cryptopp.com/wiki/ElGamal">ElGamal</A> on
/// the Crypto++ wiki.
/// \sa <A HREF="https://github.com/weidai11/cryptopp/issues/876">Issue 876</A>,
/// <A HREF="https://github.com/weidai11/cryptopp/issues/567">Issue 567</A>
/// \since Crypto++ 8.3
template <class BASE>
struct DL_PublicKey_ElGamal : public BASE
{
virtual ~DL_PublicKey_ElGamal() {}
/// \brief Retrieves the OID of the algorithm
/// \returns OID of the algorithm
/// \details DL_PrivateKey_ElGamal provides an override for GetAlgorithmID()
/// to utilize 1.3.14.7.2.1.1. Prior to DL_PrivateKey_ElGamal, the ElGamal
/// keys [mistakenly] used the OID from DSA due to DL_GroupParmaters_GFP().
/// If you need to <tt>Load</tt> an ElGamal key with the wrong OID then
/// see <A HREF="https://www.cryptopp.com/wiki/ElGamal">ElGamal</A> on
/// the Crypto++ wiki.
/// \sa <A HREF="https://github.com/weidai11/cryptopp/issues/876">Issue 876</A>,
/// <A HREF="https://github.com/weidai11/cryptopp/issues/567">Issue 567</A>
virtual OID GetAlgorithmID() const {
return ASN1::elGamal();
}
};
/// \brief ElGamal Private Key adapter
/// \tparam BASE PrivateKey derived class
/// \details DL_PrivateKey_ElGamal provides an override for GetAlgorithmID()
/// to utilize 1.3.14.7.2.1.1. Prior to DL_PrivateKey_ElGamal, the ElGamal
/// keys [mistakenly] used the OID from DSA due to DL_GroupParmaters_GFP().
/// If you need to <tt>Load</tt> an ElGamal key with the wrong OID then
/// see <A HREF="https://www.cryptopp.com/wiki/ElGamal">ElGamal</A> on
/// the Crypto++ wiki.
/// \sa <A HREF="https://github.com/weidai11/cryptopp/issues/876">Issue 876</A>,
/// <A HREF="https://github.com/weidai11/cryptopp/issues/567">Issue 567</A>
/// \since Crypto++ 8.3
template <class BASE>
struct DL_PrivateKey_ElGamal : public BASE
{
virtual ~DL_PrivateKey_ElGamal() {}
/// \brief Retrieves the OID of the algorithm
/// \returns OID of the algorithm
/// \details DL_PrivateKey_ElGamal provides an override for GetAlgorithmID()
/// to utilize 1.3.14.7.2.1.1. Prior to DL_PrivateKey_ElGamal, the ElGamal
/// keys [mistakenly] used the OID from DSA due to DL_GroupParmaters_GFP().
/// If you need to <tt>Load</tt> an ElGamal key with the wrong OID then
/// see <A HREF="https://www.cryptopp.com/wiki/ElGamal">ElGamal</A> on
/// the Crypto++ wiki.
/// \sa <A HREF="https://github.com/weidai11/cryptopp/issues/876">Issue 876</A>,
/// <A HREF="https://github.com/weidai11/cryptopp/issues/567">Issue 567</A>
virtual OID GetAlgorithmID() const {
return ASN1::elGamal();
}
/// \brief Check the key for errors
/// \param rng RandomNumberGenerator for objects which use randomized testing
/// \param level level of thoroughness
/// \return true if the tests succeed, false otherwise
/// \details There are four levels of thoroughness:
/// <ul>
/// <li>0 - using this object won't cause a crash or exception
/// <li>1 - this object will probably function, and encrypt, sign, other
/// operations correctly
/// <li>2 - ensure this object will function correctly, and perform
/// reasonable security checks
/// <li>3 - perform reasonable security checks, and do checks that may
/// take a long time
/// </ul>
/// \details Level 0 does not require a RandomNumberGenerator. A NullRNG() can
/// be used for level 0. Level 1 may not check for weak keys and such.
/// Levels 2 and 3 are recommended.
bool Validate(RandomNumberGenerator &rng, unsigned int level) const
{
// Validate() formerly used DL_PrivateKey_GFP implementation through
// inheritance. However, it would reject keys from other libraries
// like BouncyCastle. The failure was x < q. According to ElGamal's
// paper and the HAC, the private key is selected in over [1,p-1],
// Later Tsiounis and Yung showed the lower limit as [1,q-1] in
// "On the Security of EIGamal Based Encryption". As such, Crypto++
// will generate a key in the range [1,q-1], but accept a key
// in [1,p-1]. Thanks to JPM for finding the reference. Also see
// https://github.com/weidai11/cryptopp/commit/a5a684d92986.
CRYPTOPP_ASSERT(this->GetAbstractGroupParameters().Validate(rng, level));
bool pass = this->GetAbstractGroupParameters().Validate(rng, level);
const Integer &p = this->GetGroupParameters().GetModulus();
const Integer &q = this->GetAbstractGroupParameters().GetSubgroupOrder();
const Integer &x = this->GetPrivateExponent();
// Changed to x < p-1 based on ElGamal's paper and the HAC.
CRYPTOPP_ASSERT(x.IsPositive());
CRYPTOPP_ASSERT(x < p-1);
pass = pass && x.IsPositive() && x < p-1;
if (level >= 1)
{
// Minimum security level due to Tsiounis and Yung.
CRYPTOPP_ASSERT(Integer::Gcd(x, q) == Integer::One());
pass = pass && Integer::Gcd(x, q) == Integer::One();
}
return pass;
}
};
/// \brief ElGamal key agreement and encryption schemes keys
/// \details ElGamalKeys provide the algorithm implementation ElGamal key
/// agreement and encryption schemes.
/// \details The ElGamalKeys class used <tt>DL_PrivateKey_GFP_OldFormat</tt>
/// and <tt>DL_PublicKey_GFP_OldFormat</tt> for the <tt>PrivateKey</tt> and
/// <tt>PublicKey</tt> from about Crypto++ 1.0 through Crypto++ 5.6.5. At
/// Crypto++ 6.0 the serialization format was cutover to standard PKCS8 and
/// X509 encodings.
/// \details The ElGamalKeys class [mistakenly] used the OID for DSA from
/// about Crypto++ 1.0 through Crypto++ 8.2. At Crypto++ 8.3 the OID was
/// fixed and now uses ElGamal encryption, which is 1.3.14.7.2.1.1.
/// If you need to <tt>Load</tt> an ElGamal key with the wrong OID then
/// see <A HREF="https://www.cryptopp.com/wiki/ElGamal">ElGamal</A> on
/// the Crypto++ wiki.
/// \sa <A HREF="https://github.com/weidai11/cryptopp/issues/876">Issue 876</A>,
/// <A HREF="https://github.com/weidai11/cryptopp/issues/567">Issue 567</A>
/// \since Crypto++ 1.0
struct ElGamalKeys
{
/// \brief Implements DL_GroupParameters interface
typedef DL_CryptoKeys_GFP::GroupParameters GroupParameters;
/// \brief Implements DL_PrivateKey interface
typedef DL_PrivateKey_ElGamal<DL_CryptoKeys_GFP::PrivateKey> PrivateKey;
/// \brief Implements DL_PublicKey interface
typedef DL_PublicKey_ElGamal<DL_CryptoKeys_GFP::PublicKey> PublicKey;
};
/// \brief ElGamal encryption scheme with non-standard padding
/// \details ElGamal provide the algorithm implementation ElGamal key
/// agreement and encryption schemes.
/// \details The ElGamal class [mistakenly] used the OID for DSA from about
/// Crypto++ 1.0 through Crypto++ 8.2. At Crypto++ 8.3 the OID was fixed
/// and now uses ElGamal encryption, which is 1.3.14.7.2.1.1.
/// If you need to <tt>Load</tt> an ElGamal key with the wrong OID then
/// see <A HREF="https://www.cryptopp.com/wiki/ElGamal">ElGamal</A> on
/// the Crypto++ wiki.
/// \sa <A HREF="https://github.com/weidai11/cryptopp/issues/876">Issue 876</A>,
/// <A HREF="https://github.com/weidai11/cryptopp/issues/567">Issue 567</A>
/// \since Crypto++ 1.0
struct ElGamal
{
typedef DL_CryptoSchemeOptions<ElGamal, ElGamalKeys, int, int, int> SchemeOptions;
typedef SchemeOptions::PrivateKey PrivateKey;
typedef SchemeOptions::PublicKey PublicKey;
/// \brief The algorithm name
/// \returns the algorithm name
/// \details StaticAlgorithmName returns the algorithm's name as a static
/// member function.
CRYPTOPP_STATIC_CONSTEXPR const char* StaticAlgorithmName() {return "ElgamalEnc/Crypto++Padding";}
/// \brief Implements DL_GroupParameters interface
typedef SchemeOptions::GroupParameters GroupParameters;
/// \brief Implements PK_Encryptor interface
typedef PK_FinalTemplate<ElGamalObjectImpl<DL_EncryptorBase<Integer>, SchemeOptions, SchemeOptions::PublicKey> > Encryptor;
/// \brief Implements PK_Encryptor interface
typedef PK_FinalTemplate<ElGamalObjectImpl<DL_DecryptorBase<Integer>, SchemeOptions, SchemeOptions::PrivateKey> > Decryptor;
};
typedef ElGamal::Encryptor ElGamalEncryptor;
typedef ElGamal::Decryptor ElGamalDecryptor;
NAMESPACE_END
#endif