Crypto++ 8.4 Free C++ class library of cryptographic schemes

oaep.cpp
1 // oaep.cpp - originally written and placed in the public domain by Wei Dai
2
3 #include "pch.h"
4
5 #ifndef CRYPTOPP_IMPORTS
6
7 #include "oaep.h"
8 #include "stdcpp.h"
9 #include "smartptr.h"
10
11 NAMESPACE_BEGIN(CryptoPP)
12
13 // ********************************************************
14
15 size_t OAEP_Base::MaxUnpaddedLength(size_t paddedLength) const
16 {
17 return SaturatingSubtract(paddedLength/8, 1+2*DigestSize());
18 }
19
20 void OAEP_Base::Pad(RandomNumberGenerator &rng, const byte *input, size_t inputLength, byte *oaepBlock, size_t oaepBlockLen, const NameValuePairs &parameters) const
21 {
22 CRYPTOPP_ASSERT (inputLength <= MaxUnpaddedLength(oaepBlockLen));
23
24 // convert from bit length to byte length
25 if (oaepBlockLen % 8 != 0)
26 {
27 oaepBlock[0] = 0;
28 oaepBlock++;
29 }
30 oaepBlockLen /= 8;
31
32 member_ptr<HashTransformation> pHash(NewHash());
33 const size_t hLen = pHash->DigestSize();
34 const size_t seedLen = hLen, dbLen = oaepBlockLen-seedLen;
35 byte *const maskedSeed = oaepBlock;
36 byte *const maskedDB = oaepBlock+seedLen;
37
38 ConstByteArrayParameter encodingParameters;
39 parameters.GetValue(Name::EncodingParameters(), encodingParameters);
40
41 // DB = pHash || 00 ... || 01 || M
42 pHash->CalculateDigest(maskedDB, encodingParameters.begin(), encodingParameters.size());
43 memset(maskedDB+hLen, 0, dbLen-hLen-inputLength-1);
44 maskedDB[dbLen-inputLength-1] = 0x01;
45 memcpy(maskedDB+dbLen-inputLength, input, inputLength);
46
47 rng.GenerateBlock(maskedSeed, seedLen);
48 member_ptr<MaskGeneratingFunction> pMGF(NewMGF());
49 pMGF->GenerateAndMask(*pHash, maskedDB, dbLen, maskedSeed, seedLen);
50 pMGF->GenerateAndMask(*pHash, maskedSeed, seedLen, maskedDB, dbLen);
51 }
52
53 DecodingResult OAEP_Base::Unpad(const byte *oaepBlock, size_t oaepBlockLen, byte *output, const NameValuePairs &parameters) const
54 {
55 bool invalid = false;
56
57 // convert from bit length to byte length
58 if (oaepBlockLen % 8 != 0)
59 {
60 invalid = (oaepBlock[0] != 0) || invalid;
61 oaepBlock++;
62 }
63 oaepBlockLen /= 8;
64
65 member_ptr<HashTransformation> pHash(NewHash());
66 const size_t hLen = pHash->DigestSize();
67 const size_t seedLen = hLen, dbLen = oaepBlockLen-seedLen;
68
69 invalid = (oaepBlockLen < 2*hLen+1) || invalid;
70
71 SecByteBlock t(oaepBlock, oaepBlockLen);
72 byte *const maskedSeed = t;
73 byte *const maskedDB = t+seedLen;
74
75 member_ptr<MaskGeneratingFunction> pMGF(NewMGF());
76 pMGF->GenerateAndMask(*pHash, maskedSeed, seedLen, maskedDB, dbLen);
77 pMGF->GenerateAndMask(*pHash, maskedDB, dbLen, maskedSeed, seedLen);
78
79 ConstByteArrayParameter encodingParameters;
80 parameters.GetValue(Name::EncodingParameters(), encodingParameters);
81
82 // DB = pHash' || 00 ... || 01 || M
83 byte *M = std::find(maskedDB+hLen, maskedDB+dbLen, 0x01);
84 invalid = (M == maskedDB+dbLen) || invalid;
85 invalid = (FindIfNot(maskedDB+hLen, M, byte(0)) != M) || invalid;
86 invalid = !pHash->VerifyDigest(maskedDB, encodingParameters.begin(), encodingParameters.size()) || invalid;
87
88 if (invalid)
89 return DecodingResult();
90
91 M++;
92 memcpy(output, M, maskedDB+dbLen-M);
93 return DecodingResult(maskedDB+dbLen-M);
94 }
95
96 NAMESPACE_END
97
98 #endif
oaep.h
Classes for optimal asymmetric encryption padding.
ConstByteArrayParameter::size
size_t size() const
Length of the memory block.
Definition: algparam.h:88
member_ptr
Pointer that overloads operator ->
Definition: smartptr.h:37
SecByteBlock
SecBlock<byte> typedef.
Definition: secblock.h:1115
CRYPTOPP_ASSERT
#define CRYPTOPP_ASSERT(exp)
Debugging and diagnostic assertion.
Definition: trap.h:68
smartptr.h
Classes for automatic resource management.
pch.h
Precompiled header file.
OAEP_Base::MaxUnpaddedLength
size_t MaxUnpaddedLength(size_t paddedLength) const
max size of unpadded message in bytes, given max size of padded message in bits (1 less than size of ...
RandomNumberGenerator
Interface for random number generators.
Definition: cryptlib.h:1417
DecodingResult
Returns a decoding results.
Definition: cryptlib.h:277
stdcpp.h
Common C++ header files.
RandomNumberGenerator::GenerateBlock
virtual void GenerateBlock(byte *output, size_t size)
Generate random array of bytes.
FindIfNot
InputIt FindIfNot(InputIt first, InputIt last, const T &value)
Finds first element not in a range.
Definition: misc.h:2724
ConstByteArrayParameter::begin
const byte * begin() const
Pointer to the first byte in the memory block.
Definition: algparam.h:84
CryptoPP
Crypto++ library namespace.
NameValuePairs::GetValue
bool GetValue(const char *name, T &value) const
Get a named value.
Definition: cryptlib.h:379
SaturatingSubtract
T1 SaturatingSubtract(const T1 &a, const T2 &b)
Performs a saturating subtract clamped at 0.
Definition: misc.h:1073
NameValuePairs
Interface for retrieving values given their names.
Definition: cryptlib.h:321
ConstByteArrayParameter
Used to pass byte array input as part of a NameValuePairs object.
Definition: algparam.h:24