Crypto++ 8.2 Free C++ class library of cryptographic schemes

elgamal.h
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1 // elgamal.h - originally written and placed in the public domain by Wei Dai
2
3 /// \file elgamal.h
4 /// \brief Classes and functions for ElGamal key agreement and encryption schemes
5
6 #ifndef CRYPTOPP_ELGAMAL_H
7 #define CRYPTOPP_ELGAMAL_H
8
9 #include "cryptlib.h"
10 #include "modexppc.h"
11 #include "integer.h"
12 #include "gfpcrypt.h"
13 #include "pubkey.h"
14 #include "misc.h"
15 #include "oids.h"
16 #include "dsa.h"
17 #include "asn.h"
18
19 NAMESPACE_BEGIN(CryptoPP)
20
21 /// \brief ElGamal key agreement and encryption schemes base class
22 /// \since Crypto++ 1.0
23 class CRYPTOPP_NO_VTABLE ElGamalBase :
24 public DL_KeyAgreementAlgorithm_DH<Integer, NoCofactorMultiplication>,
25 public DL_KeyDerivationAlgorithm<Integer>,
26 public DL_SymmetricEncryptionAlgorithm
27 {
28 public:
29 virtual ~ElGamalBase() {}
30
31 void Derive(const DL_GroupParameters<Integer> &groupParams, byte *derivedKey, size_t derivedLength, const Integer &agreedElement, const Integer &ephemeralPublicKey, const NameValuePairs &derivationParams) const
32 {
33 CRYPTOPP_UNUSED(groupParams); CRYPTOPP_UNUSED(ephemeralPublicKey);
34 CRYPTOPP_UNUSED(derivationParams);
35 agreedElement.Encode(derivedKey, derivedLength);
36 }
37
38 size_t GetSymmetricKeyLength(size_t plainTextLength) const
39 {
40 CRYPTOPP_UNUSED(plainTextLength);
41 return GetGroupParameters().GetModulus().ByteCount();
42 }
43
44 size_t GetSymmetricCiphertextLength(size_t plainTextLength) const
45 {
46 unsigned int len = GetGroupParameters().GetModulus().ByteCount();
47 if (plainTextLength <= GetMaxSymmetricPlaintextLength(len))
48 return len;
49 else
50 return 0;
51 }
52
53 size_t GetMaxSymmetricPlaintextLength(size_t cipherTextLength) const
54 {
55 unsigned int len = GetGroupParameters().GetModulus().ByteCount();
56 CRYPTOPP_ASSERT(len >= 3);
57
58 if (cipherTextLength == len)
59 return STDMIN(255U, len-3);
60 else
61 return 0;
62 }
63
64 void SymmetricEncrypt(RandomNumberGenerator &rng, const byte *key, const byte *plainText, size_t plainTextLength, byte *cipherText, const NameValuePairs &parameters) const
65 {
66 CRYPTOPP_UNUSED(parameters);
67 const Integer &p = GetGroupParameters().GetModulus();
68 unsigned int modulusLen = p.ByteCount();
69
70 SecByteBlock block(modulusLen-1);
71 rng.GenerateBlock(block, modulusLen-2-plainTextLength);
72 memcpy(block+modulusLen-2-plainTextLength, plainText, plainTextLength);
73 block[modulusLen-2] = (byte)plainTextLength;
74
75 a_times_b_mod_c(Integer(key, modulusLen), Integer(block, modulusLen-1), p).Encode(cipherText, modulusLen);
76 }
77
78 DecodingResult SymmetricDecrypt(const byte *key, const byte *cipherText, size_t cipherTextLength, byte *plainText, const NameValuePairs &parameters) const
79 {
80 CRYPTOPP_UNUSED(parameters);
81 const Integer &p = GetGroupParameters().GetModulus();
82 unsigned int modulusLen = p.ByteCount();
83
84 if (cipherTextLength != modulusLen)
85 return DecodingResult();
86
87 Integer m = a_times_b_mod_c(Integer(cipherText, modulusLen), Integer(key, modulusLen).InverseMod(p), p);
88
89 m.Encode(plainText, 1);
90 unsigned int plainTextLength = plainText[0];
91 if (plainTextLength > GetMaxSymmetricPlaintextLength(modulusLen))
92 return DecodingResult();
93 m >>= 8;
94 m.Encode(plainText, plainTextLength);
95 return DecodingResult(plainTextLength);
96 }
97
98 virtual const DL_GroupParameters_GFP & GetGroupParameters() const =0;
99 };
100
101 /// \brief ElGamal key agreement and encryption schemes default implementation
102 /// \tparam BASE Base class implementation
103 /// \tparam SCHEME_OPTIONS Scheme options
104 /// \tparam KEY ElGamal key classes
105 /// \since Crypto++ 1.0
106 template <class BASE, class SCHEME_OPTIONS, class KEY>
107 class ElGamalObjectImpl :
108 public DL_ObjectImplBase<BASE, SCHEME_OPTIONS, KEY>,
109 public ElGamalBase
110 {
111 public:
112 virtual ~ElGamalObjectImpl() {}
113
114 size_t FixedMaxPlaintextLength() const {return this->MaxPlaintextLength(FixedCiphertextLength());}
115 size_t FixedCiphertextLength() const {return this->CiphertextLength(0);}
116
117 const DL_GroupParameters_GFP & GetGroupParameters() const {return this->GetKey().GetGroupParameters();}
118
119 DecodingResult FixedLengthDecrypt(RandomNumberGenerator &rng, const byte *cipherText, byte *plainText) const
120 {return Decrypt(rng, cipherText, FixedCiphertextLength(), plainText);}
121
122 protected:
123 const DL_KeyAgreementAlgorithm<Integer> & GetKeyAgreementAlgorithm() const {return *this;}
124 const DL_KeyDerivationAlgorithm<Integer> & GetKeyDerivationAlgorithm() const {return *this;}
125 const DL_SymmetricEncryptionAlgorithm & GetSymmetricEncryptionAlgorithm() const {return *this;}
126 };
127
128 /// \brief ElGamal Public Key adapter
129 /// \tparam BASE PublicKey derived class
130 /// \details DL_PublicKey_ElGamal provides an override for GetAlgorithmID()
131 /// to utilize 1.3.14.7.2.1.1. Prior to DL_PublicKey_ElGamal, the ElGamal
132 /// keys [mistakenly] used the OID from DSA due to DL_GroupParmaters_GFP().
133 /// If you need to <tt>Load</tt> an ElGamal key with the wrong OID then
134 /// see <A HREF="https://www.cryptopp.com/wiki/ElGamal">ElGamal</A> on
135 /// the Crypto++ wiki.
136 /// \sa <A HREF="https://github.com/weidai11/cryptopp/issues/876">Issue 876</A>,
137 /// <A HREF="https://github.com/weidai11/cryptopp/issues/567">Issue 567</A>
138 /// \since Crypto++ 8.3
139 template <class BASE>
140 struct DL_PublicKey_ElGamal : public BASE
141 {
142 virtual ~DL_PublicKey_ElGamal() {}
143
144 /// \brief Retrieves the OID of the algorithm
145 /// \return OID of the algorithm
146 /// \details DL_PrivateKey_ElGamal provides an override for GetAlgorithmID()
147 /// to utilize 1.3.14.7.2.1.1. Prior to DL_PrivateKey_ElGamal, the ElGamal
148 /// keys [mistakenly] used the OID from DSA due to DL_GroupParmaters_GFP().
149 /// If you need to <tt>Load</tt> an ElGamal key with the wrong OID then
150 /// see <A HREF="https://www.cryptopp.com/wiki/ElGamal">ElGamal</A> on
151 /// the Crypto++ wiki.
152 /// \sa <A HREF="https://github.com/weidai11/cryptopp/issues/876">Issue 876</A>,
153 /// <A HREF="https://github.com/weidai11/cryptopp/issues/567">Issue 567</A>
154 virtual OID GetAlgorithmID() const {
155 return ASN1::elGamal();
156 }
157 };
158
159 /// \brief ElGamal Private Key adapter
160 /// \tparam BASE PrivateKey derived class
161 /// \details DL_PrivateKey_ElGamal provides an override for GetAlgorithmID()
162 /// to utilize 1.3.14.7.2.1.1. Prior to DL_PrivateKey_ElGamal, the ElGamal
163 /// keys [mistakenly] used the OID from DSA due to DL_GroupParmaters_GFP().
164 /// If you need to <tt>Load</tt> an ElGamal key with the wrong OID then
165 /// see <A HREF="https://www.cryptopp.com/wiki/ElGamal">ElGamal</A> on
166 /// the Crypto++ wiki.
167 /// \sa <A HREF="https://github.com/weidai11/cryptopp/issues/876">Issue 876</A>,
168 /// <A HREF="https://github.com/weidai11/cryptopp/issues/567">Issue 567</A>
169 /// \since Crypto++ 8.3
170 template <class BASE>
171 struct DL_PrivateKey_ElGamal : public BASE
172 {
173 virtual ~DL_PrivateKey_ElGamal() {}
174
175 /// \brief Retrieves the OID of the algorithm
176 /// \return OID of the algorithm
177 /// \details DL_PrivateKey_ElGamal provides an override for GetAlgorithmID()
178 /// to utilize 1.3.14.7.2.1.1. Prior to DL_PrivateKey_ElGamal, the ElGamal
179 /// keys [mistakenly] used the OID from DSA due to DL_GroupParmaters_GFP().
180 /// If you need to <tt>Load</tt> an ElGamal key with the wrong OID then
181 /// see <A HREF="https://www.cryptopp.com/wiki/ElGamal">ElGamal</A> on
182 /// the Crypto++ wiki.
183 /// \sa <A HREF="https://github.com/weidai11/cryptopp/issues/876">Issue 876</A>,
184 /// <A HREF="https://github.com/weidai11/cryptopp/issues/567">Issue 567</A>
185 virtual OID GetAlgorithmID() const {
186 return ASN1::elGamal();
187 }
188
189 /// \brief Check the key for errors
190 /// \param rng RandomNumberGenerator for objects which use randomized testing
191 /// \param level level of thoroughness
192 /// \return true if the tests succeed, false otherwise
193 /// \details There are four levels of thoroughness:
194 /// <ul>
195 /// <li>0 - using this object won't cause a crash or exception
196 /// <li>1 - this object will probably function, and encrypt, sign, other
197 /// operations correctly
198 /// <li>2 - ensure this object will function correctly, and perform
199 /// reasonable security checks
200 /// <li>3 - perform reasonable security checks, and do checks that may
201 /// take a long time
202 /// </ul>
203 /// \details Level 0 does not require a RandomNumberGenerator. A NullRNG() can
204 /// be used for level 0. Level 1 may not check for weak keys and such.
205 /// Levels 2 and 3 are recommended.
206 bool Validate(RandomNumberGenerator &rng, unsigned int level) const
207 {
208 // Validate() formerly used DL_PrivateKey_GFP implementation through
209 // inheritance. However, it would reject keys from other libraries
210 // like BouncyCastle. The failure was x < q. According to ElGamal's
211 // paper and the HAC, the private key is selected in over [1,p-1],
212 // Later Tsiounis and Yung showed the lower limit as [1,q-1] in
213 // "On the Security of EIGamal Based Encryption". As such, Crypto++
214 // will generate a key in the range [1,q-1], but accept a key
215 // in [1,p-1]. Thanks to JPM for finding the reference. Also see
216 // https://github.com/weidai11/cryptopp/commit/a5a684d92986.
217
218 CRYPTOPP_ASSERT(this->GetAbstractGroupParameters().Validate(rng, level));
219 bool pass = this->GetAbstractGroupParameters().Validate(rng, level);
220
221 const Integer &p = this->GetGroupParameters().GetModulus();
222 const Integer &q = this->GetAbstractGroupParameters().GetSubgroupOrder();
223 const Integer &x = this->GetPrivateExponent();
224
225 // Changed to x < p-1 based on ElGamal's paper and the HAC.
226 CRYPTOPP_ASSERT(x.IsPositive());
227 CRYPTOPP_ASSERT(x < p-1);
228 pass = pass && x.IsPositive() && x < p-1;
229
230 if (level >= 1)
231 {
232 // Minimum security level due to Tsiounis and Yung.
233 CRYPTOPP_ASSERT(Integer::Gcd(x, q) == Integer::One());
234 pass = pass && Integer::Gcd(x, q) == Integer::One();
235 }
236 return pass;
237 }
238 };
239
240 /// \brief ElGamal key agreement and encryption schemes keys
241 /// \details ElGamalKeys provide the algorithm implementation ElGamal key
242 /// agreement and encryption schemes.
243 /// \details The ElGamalKeys class used <tt>DL_PrivateKey_GFP_OldFormat</tt>
244 /// and <tt>DL_PublicKey_GFP_OldFormat</tt> for the <tt>PrivateKey</tt> and
245 /// <tt>PublicKey</tt> from about Crypto++ 1.0 through Crypto++ 5.6.5. At
246 /// Crypto++ 6.0 the serialization format was cutover to standard PKCS8 and
247 /// X509 encodings.
248 /// \details The ElGamalKeys class [mistakenly] used the OID for DSA from
249 /// about Crypto++ 1.0 through Crypto++ 8.2. At Crypto++ 8.3 the OID was
250 /// fixed and now uses ElGamal encryption, which is 1.3.14.7.2.1.1.
251 /// If you need to <tt>Load</tt> an ElGamal key with the wrong OID then
252 /// see <A HREF="https://www.cryptopp.com/wiki/ElGamal">ElGamal</A> on
253 /// the Crypto++ wiki.
254 /// \sa <A HREF="https://github.com/weidai11/cryptopp/issues/876">Issue 876</A>,
255 /// <A HREF="https://github.com/weidai11/cryptopp/issues/567">Issue 567</A>
256 /// \since Crypto++ 1.0
257 struct ElGamalKeys
258 {
259 /// \brief Implements DL_GroupParameters interface
260 typedef DL_CryptoKeys_GFP::GroupParameters GroupParameters;
261 /// \brief Implements DL_PrivateKey interface
262 typedef DL_PrivateKey_ElGamal<DL_CryptoKeys_GFP::PrivateKey> PrivateKey;
263 /// \brief Implements DL_PublicKey interface
264 typedef DL_PublicKey_ElGamal<DL_CryptoKeys_GFP::PublicKey> PublicKey;
265 };
266
267 /// \brief ElGamal encryption scheme with non-standard padding
268 /// \details ElGamal provide the algorithm implementation ElGamal key
269 /// agreement and encryption schemes.
270 /// \details The ElGamal class [mistakenly] used the OID for DSA from about
271 /// Crypto++ 1.0 through Crypto++ 8.2. At Crypto++ 8.3 the OID was fixed
272 /// and now uses ElGamal encryption, which is 1.3.14.7.2.1.1.
273 /// If you need to <tt>Load</tt> an ElGamal key with the wrong OID then
274 /// see <A HREF="https://www.cryptopp.com/wiki/ElGamal">ElGamal</A> on
275 /// the Crypto++ wiki.
276 /// \sa <A HREF="https://github.com/weidai11/cryptopp/issues/876">Issue 876</A>,
277 /// <A HREF="https://github.com/weidai11/cryptopp/issues/567">Issue 567</A>
278 /// \since Crypto++ 1.0
279 struct ElGamal
280 {
281 typedef DL_CryptoSchemeOptions<ElGamal, ElGamalKeys, int, int, int> SchemeOptions;
282 typedef SchemeOptions::PrivateKey PrivateKey;
283 typedef SchemeOptions::PublicKey PublicKey;
284
285 /// \brief The algorithm name
286 /// \return the algorithm name
287 /// \details StaticAlgorithmName returns the algorithm's name as a static
288 /// member function.
289 CRYPTOPP_STATIC_CONSTEXPR const char* StaticAlgorithmName() {return "ElgamalEnc/Crypto++Padding";}
290
291 /// \brief Implements DL_GroupParameters interface
292 typedef SchemeOptions::GroupParameters GroupParameters;
293 /// \brief Implements PK_Encryptor interface
294 typedef PK_FinalTemplate<ElGamalObjectImpl<DL_EncryptorBase<Integer>, SchemeOptions, SchemeOptions::PublicKey> > Encryptor;
295 /// \brief Implements PK_Encryptor interface
296 typedef PK_FinalTemplate<ElGamalObjectImpl<DL_DecryptorBase<Integer>, SchemeOptions, SchemeOptions::PrivateKey> > Decryptor;
297 };
298
299 typedef ElGamal::Encryptor ElGamalEncryptor;
300 typedef ElGamal::Decryptor ElGamalDecryptor;
301
302 NAMESPACE_END
303
304 #endif
ElGamal::Encryptor
PK_FinalTemplate< ElGamalObjectImpl< DL_EncryptorBase< Integer >, SchemeOptions, SchemeOptions::PublicKey > > Encryptor
Implements PK_Encryptor interface.
Definition: elgamal.h:294
DL_PublicKey_ElGamal
ElGamal Public Key adapter.
Definition: elgamal.h:140
DL_KeyAgreementAlgorithm_DH
Diffie-Hellman key agreement algorithm.
Definition: pubkey.h:2131
misc.h
Utility functions for the Crypto++ library.
DL_GroupParameters_GFP
GF(p) group parameters.
Definition: gfpcrypt.h:224
ElGamalObjectImpl
ElGamal key agreement and encryption schemes default implementation.
Definition: elgamal.h:107
RandomNumberGenerator::GenerateBlock
virtual void GenerateBlock(byte *output, size_t size)
Generate random array of bytes.
Definition: cryptlib.cpp:311
pubkey.h
This file contains helper classes/functions for implementing public key algorithms.
ElGamalKeys::GroupParameters
DL_CryptoKeys_GFP::GroupParameters GroupParameters
Implements DL_GroupParameters interface.
Definition: elgamal.h:260
Integer::Gcd
static Integer CRYPTOPP_API Gcd(const Integer &a, const Integer &n)
Calculate greatest common divisor.
Definition: integer.cpp:4416
DL_GroupParameters< Integer >
ElGamal::GroupParameters
SchemeOptions::GroupParameters GroupParameters
Implements DL_GroupParameters interface.
Definition: elgamal.h:292
EnumToType
Converts an enumeration to a type suitable for use as a template parameter.
Definition: cryptlib.h:135
cryptlib.h
Abstract base classes that provide a uniform interface to this library.
DL_GroupParameters_GFP_DefaultSafePrime
GF(p) group parameters that default to safe primes.
Definition: gfpcrypt.h:274
oids.h
ASN.1 object identifiers for algorthms and schemes.
DL_KeyDerivationAlgorithm
Interface for key derivation algorithms used in DL cryptosystems.
Definition: pubkey.h:1487
RandomNumberGenerator
Interface for random number generators.
Definition: cryptlib.h:1413
SecByteBlock
SecBlock<byte> typedef.
Definition: secblock.h:1097
ElGamalKeys
ElGamal key agreement and encryption schemes keys.
Definition: elgamal.h:257
DL_CryptoSchemeOptions
Discrete Log (DL) crypto scheme options.
Definition: pubkey.h:1934
ElGamalKeys::PublicKey
DL_PublicKey_ElGamal< DL_CryptoKeys_GFP::PublicKey > PublicKey
Implements DL_PublicKey interface.
Definition: elgamal.h:264
PrivateKey
Interface for private keys.
Definition: cryptlib.h:2519
Integer::IsPositive
bool IsPositive() const
Determines if the Integer is positive.
Definition: integer.h:345
Integer::One
static const Integer &CRYPTOPP_API One()
Integer representing 1.
Definition: integer.cpp:4868
ElGamal
ElGamal encryption scheme with non-standard padding.
Definition: elgamal.h:279
Integer::ByteCount
unsigned int ByteCount() const
Determines the number of bytes required to represent the Integer.
Definition: integer.cpp:3339
DL_PrivateKey_ElGamal
ElGamal Private Key adapter.
Definition: elgamal.h:171
DecodingResult
Returns a decoding results.
Definition: cryptlib.h:277
Integer
Multiple precision integer with arithmetic operations.
Definition: integer.h:49
DL_ObjectImplBase
Discrete Log (DL) base object implementation.
Definition: pubkey.h:1946
DL_PrivateKey_ElGamal::GetAlgorithmID
virtual OID GetAlgorithmID() const
Retrieves the OID of the algorithm.
Definition: elgamal.h:185
gfpcrypt.h
Classes and functions for schemes based on Discrete Logs (DL) over GF(p)
dsa.h
Classes for the DSA signature algorithm.
DL_PublicKey_ElGamal::GetAlgorithmID
virtual OID GetAlgorithmID() const
Retrieves the OID of the algorithm.
Definition: elgamal.h:154
STDMIN
const T & STDMIN(const T &a, const T &b)
Replacement function for std::min.
Definition: misc.h:635
CRYPTOPP_ASSERT
#define CRYPTOPP_ASSERT(exp)
Debugging and diagnostic assertion.
Definition: trap.h:68
asn.h
Classes and functions for working with ANS.1 objects.
Integer::Encode
void Encode(byte *output, size_t outputLen, Signedness sign=UNSIGNED) const
Encode in big-endian format.
Definition: integer.cpp:3411
ElGamalKeys::PrivateKey
DL_PrivateKey_ElGamal< DL_CryptoKeys_GFP::PrivateKey > PrivateKey
Implements DL_PrivateKey interface.
Definition: elgamal.h:262
integer.h
Multiple precision integer with arithmetic operations.
ElGamalBase
ElGamal key agreement and encryption schemes base class.
Definition: elgamal.h:23
DL_PrivateKey_ElGamal::Validate
bool Validate(RandomNumberGenerator &rng, unsigned int level) const
Check the key for errors.
Definition: elgamal.h:206
PublicKey
Interface for public keys.
Definition: cryptlib.h:2514
CryptoPP
Crypto++ library namespace.
DL_SymmetricEncryptionAlgorithm
Interface for symmetric encryption algorithms used in DL cryptosystems.
Definition: pubkey.h:1498
ElGamal::Decryptor
PK_FinalTemplate< ElGamalObjectImpl< DL_DecryptorBase< Integer >, SchemeOptions, SchemeOptions::PrivateKey > > Decryptor
Implements PK_Encryptor interface.
Definition: elgamal.h:296
OID
Object Identifier.
Definition: asn.h:264
DL_KeyAgreementAlgorithm< Integer >
NameValuePairs
Interface for retrieving values given their names.
Definition: cryptlib.h:321
PK_FinalTemplate
Template implementing constructors for public key algorithm classes.
Definition: pubkey.h:2187