Crypto++ 8.0 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
ConstByteArrayParameter
Used to pass byte array input as part of a NameValuePairs object.
Definition: algparam.h:20
FindIfNot
InputIt FindIfNot(InputIt first, InputIt last, const T &value)
Finds first element not in a range.
Definition: misc.h:2638
Name::DigestSize
const char * DigestSize()
int, in bytes
Definition: argnames.h:79
OAEP_Base
OAEP padding base class.
Definition: oaep.h:18
RandomNumberGenerator::GenerateBlock
virtual void GenerateBlock(byte *output, size_t size)
Generate random array of bytes.
Definition: cryptlib.cpp:311
ConstByteArrayParameter::size
size_t size() const
Length of the memory block.
Definition: algparam.h:84
smartptr.h
Classes for automatic resource management.
RandomNumberGenerator
Interface for random number generators.
Definition: cryptlib.h:1383
stdcpp.h
Common C++ header files.
SecByteBlock
SecBlock<byte> typedef.
Definition: secblock.h:1058
member_ptr
Pointer that overloads operator ->
Definition: smartptr.h:36
DecodingResult
Returns a decoding results.
Definition: cryptlib.h:255
ConstByteArrayParameter::begin
const byte * begin() const
Pointer to the first byte in the memory block.
Definition: algparam.h:80
Name::EncodingParameters
const char * EncodingParameters()
ConstByteArrayParameter.
Definition: argnames.h:66
pch.h
Precompiled header file.
SaturatingSubtract
T1 SaturatingSubtract(const T1 &a, const T2 &b)
Performs a saturating subtract clamped at 0.
Definition: misc.h:972
CRYPTOPP_ASSERT
#define CRYPTOPP_ASSERT(exp)
Debugging and diagnostic assertion.
Definition: trap.h:69
oaep.h
Classes for optimal asymmetric encryption padding.
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 ...
Definition: oaep.cpp:15
CryptoPP
Crypto++ library namespace.
NameValuePairs::GetValue
bool GetValue(const char *name, T &value) const
Get a named value.
Definition: cryptlib.h:350
NameValuePairs
Interface for retrieving values given their names.
Definition: cryptlib.h:293