Botan 1.10.17

emsa4.cpp
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1 /*
2 * EMSA4
3 * (C) 1999-2007 Jack Lloyd
4 *
5 * Distributed under the terms of the Botan license
6 */
7
8 #include <botan/emsa4.h>
9 #include <botan/mgf1.h>
10 #include <botan/internal/bit_ops.h>
11
12 namespace Botan {
13
14 /*
15 * EMSA4 Update Operation
16 */
17 void EMSA4::update(const byte input[], size_t length)
18 {
19 hash->update(input, length);
20 }
21
22 /*
23 * Return the raw (unencoded) data
24 */
25 SecureVector<byte> EMSA4::raw_data()
26 {
27 return hash->final();
28 }
29
30 /*
31 * EMSA4 Encode Operation
32 */
33 SecureVector<byte> EMSA4::encoding_of(const MemoryRegion<byte>& msg,
34 size_t output_bits,
35 RandomNumberGenerator& rng)
36 {
37 const size_t HASH_SIZE = hash->output_length();
38
39 if(msg.size() != HASH_SIZE)
40 throw Encoding_Error("EMSA4::encoding_of: Bad input length");
41 if(output_bits < 8*HASH_SIZE + 8*SALT_SIZE + 9)
42 throw Encoding_Error("EMSA4::encoding_of: Output length is too small");
43
44 const size_t output_length = (output_bits + 7) / 8;
45
46 SecureVector<byte> salt = rng.random_vec(SALT_SIZE);
47
48 for(size_t j = 0; j != 8; ++j)
49 hash->update(0);
50 hash->update(msg);
51 hash->update(salt, SALT_SIZE);
52 SecureVector<byte> H = hash->final();
53
54 SecureVector<byte> EM(output_length);
55
56 EM[output_length - HASH_SIZE - SALT_SIZE - 2] = 0x01;
57 EM.copy(output_length - 1 - HASH_SIZE - SALT_SIZE, salt, SALT_SIZE);
58 mgf->mask(H, HASH_SIZE, EM, output_length - HASH_SIZE - 1);
59 EM[0] &= 0xFF >> (8 * ((output_bits + 7) / 8) - output_bits);
60 EM.copy(output_length - 1 - HASH_SIZE, H, HASH_SIZE);
61 EM[output_length-1] = 0xBC;
62
63 return EM;
64 }
65
66 /*
67 * EMSA4 Decode/Verify Operation
68 */
69 bool EMSA4::verify(const MemoryRegion<byte>& const_coded,
70 const MemoryRegion<byte>& raw, size_t key_bits)
71 {
72 const size_t HASH_SIZE = hash->output_length();
73 const size_t KEY_BYTES = (key_bits + 7) / 8;
74
75 if(key_bits < 8*HASH_SIZE + 9)
76 return false;
77
78 if(raw.size() != HASH_SIZE)
79 return false;
80
81 if(const_coded.size() > KEY_BYTES || const_coded.size() <= 1)
82 return false;
83
84 if(const_coded[const_coded.size()-1] != 0xBC)
85 return false;
86
87 SecureVector<byte> coded = const_coded;
88 if(coded.size() < KEY_BYTES)
89 {
90 SecureVector<byte> temp(KEY_BYTES);
91 temp.copy(KEY_BYTES - coded.size(), coded, coded.size());
92 coded = temp;
93 }
94
95 const size_t TOP_BITS = 8 * ((key_bits + 7) / 8) - key_bits;
96 if(TOP_BITS > 8 - high_bit(coded[0]))
97 return false;
98
99 SecureVector<byte> DB(&coded[0], coded.size() - HASH_SIZE - 1);
100 SecureVector<byte> H(&coded[coded.size() - HASH_SIZE - 1], HASH_SIZE);
101
102 mgf->mask(H, H.size(), DB, coded.size() - H.size() - 1);
103 DB[0] &= 0xFF >> TOP_BITS;
104
105 size_t salt_offset = 0;
106 for(size_t j = 0; j != DB.size(); ++j)
107 {
108 if(DB[j] == 0x01)
109 { salt_offset = j + 1; break; }
110 if(DB[j])
111 return false;
112 }
113 if(salt_offset == 0)
114 return false;
115
116 SecureVector<byte> salt(&DB[salt_offset], DB.size() - salt_offset);
117
118 for(size_t j = 0; j != 8; ++j)
119 hash->update(0);
120 hash->update(raw);
121 hash->update(salt);
122 SecureVector<byte> H2 = hash->final();
123
124 return (H == H2);
125 }
126
127 /*
128 * EMSA4 Constructor
129 */
130 EMSA4::EMSA4(HashFunction* h) :
131 SALT_SIZE(h->output_length()), hash(h)
132 {
133 mgf = new MGF1(hash->clone());
134 }
135
136 /*
137 * EMSA4 Constructor
138 */
139 EMSA4::EMSA4(HashFunction* h, size_t salt_size) :
140 SALT_SIZE(salt_size), hash(h)
141 {
142 mgf = new MGF1(hash->clone());
143 }
144
145 }
Botan::EMSA4::EMSA4
EMSA4(HashFunction *hash)
Definition: emsa4.cpp:130
Botan::HashFunction::clone
virtual HashFunction * clone() const =0
Botan::byte
unsigned char byte
Definition: types.h:22
Botan::MGF::mask
virtual void mask(const byte in[], size_t in_len, byte out[], size_t out_len) const =0
Botan::Buffered_Computation::update
void update(const byte in[], size_t length)
Definition: buf_comp.h:33
Botan::high_bit
size_t high_bit(T n)
Definition: bit_ops.h:33
Botan
Definition: algo_base.h:14
Botan::Buffered_Computation::final
void final(byte out[])
Definition: buf_comp.h:80
Botan::HashFunction
Definition: hash.h:20
Botan::Buffered_Computation::output_length
virtual size_t output_length() const =0
Botan::MGF1
Definition: mgf1.h:19