Botan 1.10.17

dsa_gen.cpp
Go to the documentation of this file.
1 /*
2 * DSA Parameter Generation
3 * (C) 1999-2007 Jack Lloyd
4 *
5 * Distributed under the terms of the Botan license
6 */
7
8 #include <botan/numthry.h>
9 #include <botan/algo_factory.h>
10 #include <botan/hash.h>
11 #include <botan/parsing.h>
12 #include <algorithm>
13 #include <memory>
14
15 namespace Botan {
16
17 namespace {
18
19 /*
20 * Check if this size is allowed by FIPS 186-3
21 */
22 bool fips186_3_valid_size(size_t pbits, size_t qbits)
23 {
24 if(qbits == 160)
25 return (pbits == 512 || pbits == 768 || pbits == 1024);
26
27 if(qbits == 224)
28 return (pbits == 2048);
29
30 if(qbits == 256)
31 return (pbits == 2048 || pbits == 3072);
32
33 return false;
34 }
35
36 }
37
38 /*
39 * Attempt DSA prime generation with given seed
40 */
41 bool generate_dsa_primes(RandomNumberGenerator& rng,
42 Algorithm_Factory& af,
43 BigInt& p, BigInt& q,
44 size_t pbits, size_t qbits,
45 const MemoryRegion<byte>& seed_c)
46 {
47 if(!fips186_3_valid_size(pbits, qbits))
48 throw Invalid_Argument(
49 "FIPS 186-3 does not allow DSA domain parameters of " +
50 to_string(pbits) + "/" + to_string(qbits) + " bits long");
51
52 if(seed_c.size() * 8 < qbits)
53 throw Invalid_Argument(
54 "Generating a DSA parameter set with a " + to_string(qbits) +
55 "long q requires a seed at least as many bits long");
56
57 std::auto_ptr<HashFunction> hash(
58 af.make_hash_function("SHA-" + to_string(qbits)));
59
60 const size_t HASH_SIZE = hash->output_length();
61
62 class Seed
63 {
64 public:
65 Seed(const MemoryRegion<byte>& s) : seed(s) {}
66
67 operator MemoryRegion<byte>& () { return seed; }
68
69 Seed& operator++()
70 {
71 for(size_t j = seed.size(); j > 0; --j)
72 if(++seed[j-1])
73 break;
74 return (*this);
75 }
76 private:
77 SecureVector<byte> seed;
78 };
79
80 Seed seed(seed_c);
81
82 q.binary_decode(hash->process(seed));
83 q.set_bit(qbits-1);
84 q.set_bit(0);
85
86 if(!check_prime(q, rng))
87 return false;
88
89 const size_t n = (pbits-1) / (HASH_SIZE * 8),
90 b = (pbits-1) % (HASH_SIZE * 8);
91
92 BigInt X;
93 SecureVector<byte> V(HASH_SIZE * (n+1));
94
95 for(size_t j = 0; j != 4096; ++j)
96 {
97 for(size_t k = 0; k <= n; ++k)
98 {
99 ++seed;
100 hash->update(seed);
101 hash->final(&V[HASH_SIZE * (n-k)]);
102 }
103
104 X.binary_decode(&V[HASH_SIZE - 1 - b/8],
105 V.size() - (HASH_SIZE - 1 - b/8));
106 X.set_bit(pbits-1);
107
108 p = X - (X % (2*q) - 1);
109
110 if(p.bits() == pbits && check_prime(p, rng))
111 return true;
112 }
113 return false;
114 }
115
116 /*
117 * Generate DSA Primes
118 */
119 SecureVector<byte> generate_dsa_primes(RandomNumberGenerator& rng,
120 Algorithm_Factory& af,
121 BigInt& p, BigInt& q,
122 size_t pbits, size_t qbits)
123 {
124 while(true)
125 {
126 SecureVector<byte> seed = rng.random_vec(qbits / 8);
127
128 if(generate_dsa_primes(rng, af, p, q, pbits, qbits, seed))
129 return seed;
130 }
131 }
132
133 }
Botan::Algorithm_Factory
Definition: algo_factory.h:34
Botan::BigInt
Definition: bigint.h:22
Botan::RandomNumberGenerator
Definition: rng.h:20
Botan::RandomNumberGenerator::random_vec
SecureVector< byte > random_vec(size_t bytes)
Definition: rng.h:40
Botan::BigInt::bits
size_t bits() const
Definition: bigint.cpp:254
Botan::BigInt::binary_decode
void binary_decode(const byte buf[], size_t length)
Definition: bigint.cpp:351
Botan::BigInt::set_bit
void set_bit(size_t n)
Definition: bigint.cpp:206
Botan::Invalid_Argument
std::invalid_argument Invalid_Argument
Definition: exceptn.h:20
Botan::MemoryRegion< byte >
Botan
Definition: algo_base.h:14
Botan::Algorithm_Factory::make_hash_function
HashFunction * make_hash_function(const std::string &algo_spec, const std::string &provider="")
Definition: algo_factory.cpp:274
Botan::MemoryRegion::size
size_t size() const
Definition: secmem.h:29
Botan::to_string
std::string to_string(u64bit n, size_t min_len)
Definition: parsing.cpp:42
Botan::SecureVector< byte >
Botan::generate_dsa_primes
bool generate_dsa_primes(RandomNumberGenerator &rng, Algorithm_Factory &af, BigInt &p, BigInt &q, size_t pbits, size_t qbits, const MemoryRegion< byte > &seed_c)
Definition: dsa_gen.cpp:41
Botan::check_prime
bool check_prime(const BigInt &n, RandomNumberGenerator &rng)
Definition: numthry.h:143