Botan  2.8.0
Crypto and TLS for C++11
ecgdsa.cpp
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1 /*
2 * ECGDSA (BSI-TR-03111, version 2.0)
3 * (C) 2016 RenĂ© Korthaus
4 * (C) 2018 Jack Lloyd
5 *
6 * Botan is released under the Simplified BSD License (see license.txt)
7 */
8 
9 #include <botan/ecgdsa.h>
10 #include <botan/keypair.h>
11 #include <botan/reducer.h>
12 #include <botan/internal/pk_ops_impl.h>
13 #include <botan/internal/point_mul.h>
14 
15 namespace Botan {
16 
18  bool strong) const
19  {
20  if(!public_point().on_the_curve())
21  return false;
22 
23  if(!strong)
24  return true;
25 
26  return KeyPair::signature_consistency_check(rng, *this, "EMSA1(SHA-256)");
27  }
28 
29 namespace {
30 
31 /**
32 * ECGDSA signature operation
33 */
34 class ECGDSA_Signature_Operation final : public PK_Ops::Signature_with_EMSA
35  {
36  public:
37 
38  ECGDSA_Signature_Operation(const ECGDSA_PrivateKey& ecgdsa,
39  const std::string& emsa) :
40  PK_Ops::Signature_with_EMSA(emsa),
41  m_group(ecgdsa.domain()),
42  m_x(ecgdsa.private_value())
43  {
44  }
45 
46  secure_vector<uint8_t> raw_sign(const uint8_t msg[], size_t msg_len,
47  RandomNumberGenerator& rng) override;
48 
49  size_t signature_length() const override { return 2*m_group.get_order_bytes(); }
50 
51  size_t max_input_bits() const override { return m_group.get_order_bits(); }
52 
53  private:
54  const EC_Group m_group;
55  const BigInt& m_x;
56  std::vector<BigInt> m_ws;
57  };
58 
59 secure_vector<uint8_t>
60 ECGDSA_Signature_Operation::raw_sign(const uint8_t msg[], size_t msg_len,
61  RandomNumberGenerator& rng)
62  {
63  const BigInt m(msg, msg_len, m_group.get_order_bits());
64 
65  const BigInt k = m_group.random_scalar(rng);
66 
67  const BigInt r = m_group.mod_order(
68  m_group.blinded_base_point_multiply_x(k, rng, m_ws));
69 
70  const BigInt kr = m_group.multiply_mod_order(k, r);
71 
72  const BigInt s = m_group.multiply_mod_order(m_x, kr - m);
73 
74  // With overwhelming probability, a bug rather than actual zero r/s
75  if(r.is_zero() || s.is_zero())
76  throw Internal_Error("During ECGDSA signature generated zero r/s");
77 
78  return BigInt::encode_fixed_length_int_pair(r, s, m_group.get_order_bytes());
79  }
80 
81 /**
82 * ECGDSA verification operation
83 */
84 class ECGDSA_Verification_Operation final : public PK_Ops::Verification_with_EMSA
85  {
86  public:
87 
88  ECGDSA_Verification_Operation(const ECGDSA_PublicKey& ecgdsa,
89  const std::string& emsa) :
90  PK_Ops::Verification_with_EMSA(emsa),
91  m_group(ecgdsa.domain()),
92  m_gy_mul(m_group.get_base_point(), ecgdsa.public_point())
93  {
94  }
95 
96  size_t max_input_bits() const override { return m_group.get_order_bits(); }
97 
98  bool with_recovery() const override { return false; }
99 
100  bool verify(const uint8_t msg[], size_t msg_len,
101  const uint8_t sig[], size_t sig_len) override;
102  private:
103  const EC_Group m_group;
104  const PointGFp_Multi_Point_Precompute m_gy_mul;
105  };
106 
107 bool ECGDSA_Verification_Operation::verify(const uint8_t msg[], size_t msg_len,
108  const uint8_t sig[], size_t sig_len)
109  {
110  if(sig_len != m_group.get_order_bytes() * 2)
111  return false;
112 
113  const BigInt e(msg, msg_len, m_group.get_order_bits());
114 
115  const BigInt r(sig, sig_len / 2);
116  const BigInt s(sig + sig_len / 2, sig_len / 2);
117 
118  if(r <= 0 || r >= m_group.get_order() || s <= 0 || s >= m_group.get_order())
119  return false;
120 
121  const BigInt w = m_group.inverse_mod_order(r);
122 
123  const BigInt u1 = m_group.multiply_mod_order(e, w);
124  const BigInt u2 = m_group.multiply_mod_order(s, w);
125  const PointGFp R = m_gy_mul.multi_exp(u1, u2);
126 
127  if(R.is_zero())
128  return false;
129 
130  const BigInt v = m_group.mod_order(R.get_affine_x());
131  return (v == r);
132  }
133 
134 }
135 
136 std::unique_ptr<PK_Ops::Verification>
138  const std::string& provider) const
139  {
140  if(provider == "base" || provider.empty())
141  return std::unique_ptr<PK_Ops::Verification>(new ECGDSA_Verification_Operation(*this, params));
142  throw Provider_Not_Found(algo_name(), provider);
143  }
144 
145 std::unique_ptr<PK_Ops::Signature>
147  const std::string& params,
148  const std::string& provider) const
149  {
150  if(provider == "base" || provider.empty())
151  return std::unique_ptr<PK_Ops::Signature>(new ECGDSA_Signature_Operation(*this, params));
152  throw Provider_Not_Found(algo_name(), provider);
153  }
154 
155 }
std::string algo_name() const override
Definition: ecgdsa.h:44
PointGFp multi_exp(const BigInt &k1, const BigInt &k2) const
Definition: point_mul.cpp:341
std::unique_ptr< PK_Ops::Signature > create_signature_op(RandomNumberGenerator &rng, const std::string &params, const std::string &provider) const override
Definition: ecgdsa.cpp:146
const PointGFp & public_point() const
Definition: ecc_key.h:57
int(* final)(unsigned char *, CTX *)
std::unique_ptr< PK_Ops::Verification > create_verification_op(const std::string &params, const std::string &provider) const override
Definition: ecgdsa.cpp:137
bool signature_consistency_check(RandomNumberGenerator &rng, const Private_Key &private_key, const Public_Key &public_key, const std::string &padding)
Definition: keypair.cpp:49
Definition: alg_id.cpp:13
bool check_key(RandomNumberGenerator &rng, bool) const override
Definition: ecgdsa.cpp:17
static secure_vector< uint8_t > encode_fixed_length_int_pair(const BigInt &n1, const BigInt &n2, size_t bytes)
Definition: big_code.cpp:145