20194419005

Committed 13 Dec 2025 12:36PM UTC coverage: 90.357% (-1.4%) from 91.76%

Build # 20194419005

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web-flow

Commit Message

Merge pull request #5173 from randombit/jack/ecdsa-new-blinding

Use a new strategy for blinding in ECDSA signing

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87.74

/src/lib/pubkey/ecdsa/ecdsa.cpp

/*
* ECDSA implementation
* (C) 2007 Manuel Hartl, FlexSecure GmbH
*     2007 Falko Strenzke, FlexSecure GmbH
*     2008-2010,2015,2016,2018,2024 Jack Lloyd
*     2016 René Korthaus
*
* Botan is released under the Simplified BSD License (see license.txt)
*/

#include <botan/ecdsa.h>

#include <botan/internal/keypair.h>
#include <botan/internal/pk_ops_impl.h>

#if defined(BOTAN_HAS_RFC6979_GENERATOR)
   #include <botan/internal/rfc6979.h>
#endif

namespace Botan {

namespace {

EC_AffinePoint recover_ecdsa_public_key(
   const EC_Group& group, const std::vector<uint8_t>& msg, const BigInt& r, const BigInt& s, uint8_t v) {
   if(group.has_cofactor()) {
      throw Invalid_Argument("ECDSA public key recovery only supported for prime order groups");
   }

   if(v >= 4) {
      throw Invalid_Argument("Unexpected v param for ECDSA public key recovery");
   }

   const BigInt& group_order = group.get_order();

   if(r <= 0 || r >= group_order || s <= 0 || s >= group_order) {
      throw Invalid_Argument("Out of range r/s cannot recover ECDSA public key");
   }

   const uint8_t y_odd = v % 2;
   const bool add_order = (v >> 1) == 0x01;
   const size_t p_bytes = group.get_p_bytes();

   BigInt x = r;

   if(add_order) {
      x += group_order;
   }

   if(x.bytes() <= p_bytes) {
      std::vector<uint8_t> X(p_bytes + 1);

      X[0] = 0x02 | y_odd;
      x.serialize_to(std::span{X}.subspan(1));

      if(auto R = EC_AffinePoint::deserialize(group, X)) {
         // Compute r_inv * (-eG + s*R)
         const auto ne = EC_Scalar::from_bytes_with_trunc(group, msg).negate();
         const auto ss = EC_Scalar::from_bigint(group, s);

         const auto r_inv = EC_Scalar::from_bigint(group, r).invert_vartime();

         const EC_Group::Mul2Table GR_mul(R.value());
         if(auto egsr = GR_mul.mul2_vartime(ne * r_inv, ss * r_inv)) {
            return egsr.value();
         }
      }
   }

   throw Decoding_Error("Failed to recover ECDSA public key from signature/msg pair");
}

}  // namespace

ECDSA_PublicKey::ECDSA_PublicKey(
   const EC_Group& group, const std::vector<uint8_t>& msg, const BigInt& r, const BigInt& s, uint8_t v) :
      EC_PublicKey(group, recover_ecdsa_public_key(group, msg, r, s, v)) {}

std::unique_ptr<Private_Key> ECDSA_PublicKey::generate_another(RandomNumberGenerator& rng) const {
   return std::make_unique<ECDSA_PrivateKey>(rng, domain());
}

uint8_t ECDSA_PublicKey::recovery_param(const std::vector<uint8_t>& msg, const BigInt& r, const BigInt& s) const {
   const auto this_key = this->_public_ec_point().serialize_compressed();

   for(uint8_t v = 0; v != 4; ++v) {
      try {
         const auto R = recover_ecdsa_public_key(this->domain(), msg, r, s, v);

         if(R.serialize_compressed() == this_key) {
            return v;
         }
      } catch(Decoding_Error&) {
         // try the next v
      }
   }

   throw Internal_Error("Could not determine ECDSA recovery parameter");
}

std::unique_ptr<Public_Key> ECDSA_PrivateKey::public_key() const {
   return std::make_unique<ECDSA_PublicKey>(domain(), _public_ec_point());
}

bool ECDSA_PrivateKey::check_key(RandomNumberGenerator& rng, bool strong) const {
   if(!EC_PrivateKey::check_key(rng, strong)) {
      return false;
   }

   if(!strong) {
      return true;
   }

   return KeyPair::signature_consistency_check(rng, *this, "SHA-256");
}

namespace {

/**
* ECDSA signature operation
*/
class ECDSA_Signature_Operation final : public PK_Ops::Signature_with_Hash {
   public:
      ECDSA_Signature_Operation(const ECDSA_PrivateKey& ecdsa, std::string_view padding, RandomNumberGenerator& rng) :
            PK_Ops::Signature_with_Hash(padding),
            m_group(ecdsa.domain()),
            m_x(ecdsa._private_key()),
            m_b(EC_Scalar::random(m_group, rng)) {
#if defined(BOTAN_HAS_RFC6979_GENERATOR)
         m_rfc6979 = std::make_unique<RFC6979_Nonce_Generator>(
            this->rfc6979_hash_function(), m_group.get_order_bits(), ecdsa._private_key());
#endif
      }

      size_t signature_length() const override { return 2 * m_group.get_order_bytes(); }

      std::vector<uint8_t> raw_sign(std::span<const uint8_t> msg, RandomNumberGenerator& rng) override;

      AlgorithmIdentifier algorithm_identifier() const override;

   private:
      const EC_Group m_group;
      const EC_Scalar m_x;

#if defined(BOTAN_HAS_RFC6979_GENERATOR)
      std::unique_ptr<RFC6979_Nonce_Generator> m_rfc6979;
#endif

      EC_Scalar m_b;
};

AlgorithmIdentifier ECDSA_Signature_Operation::algorithm_identifier() const {
   const std::string full_name = "ECDSA/" + hash_function();
   const OID oid = OID::from_string(full_name);
   return AlgorithmIdentifier(oid, AlgorithmIdentifier::USE_EMPTY_PARAM);
}

std::vector<uint8_t> ECDSA_Signature_Operation::raw_sign(std::span<const uint8_t> msg, RandomNumberGenerator& rng) {
   const auto m = EC_Scalar::from_bytes_with_trunc(m_group, msg);

#if defined(BOTAN_HAS_RFC6979_GENERATOR)
   const auto k = m_rfc6979->nonce_for(m_group, m);
#else
   const auto k = EC_Scalar::random(m_group, rng);
#endif

   const auto r = EC_Scalar::gk_x_mod_order(k, rng);

   /*
   * Blind the inputs
   *
   * Here we are computing (x*r+m)/k
   *
   * Instead have a random b and compute (k*b)^-1
   *
   * Then compute (x*r+m) as (x*r*b + m*b)
   *
   * Finally (x*r*b + m*b)/(k*b) = (x*r+m)/k
   *
   * This effectively blinds both the inversion as well as the various scalar
   * multiplications. All of these operations should be constant-time anyway but
   * blinding is very cheap and may help if either the compiler introduces
   * variable-time behavior, or for the case of EM/power side channel attacks [1].
   *
   * [1] But note that such attacks are currently outside of Botan's threat model.
   *
   */
   const auto k_inv = (m_b * k).invert();

   const auto xr_m = ((m_x * m_b) * r) + (m * m_b);

   const auto s = (k_inv * xr_m);

   // Generate the next blinding value via modular squaring
   m_b.square_self();

   // With overwhelming probability, a bug rather than actual zero r/s
   if(r.is_zero() || s.is_zero()) {
      throw Internal_Error("During ECDSA signature generated zero r/s");
   }

   return EC_Scalar::serialize_pair(r, s);
}

/**
* ECDSA verification operation
*/
class ECDSA_Verification_Operation final : public PK_Ops::Verification_with_Hash {
   public:
      ECDSA_Verification_Operation(const ECDSA_PublicKey& ecdsa, std::string_view padding) :
            PK_Ops::Verification_with_Hash(padding), m_group(ecdsa.domain()), m_gy_mul(ecdsa._public_ec_point()) {}

      ECDSA_Verification_Operation(const ECDSA_PublicKey& ecdsa, const AlgorithmIdentifier& alg_id) :
            PK_Ops::Verification_with_Hash(alg_id, "ECDSA", true),
            m_group(ecdsa.domain()),
            m_gy_mul(ecdsa._public_ec_point()) {}

      bool verify(std::span<const uint8_t> msg, std::span<const uint8_t> sig) override;

   private:
      const EC_Group m_group;
      const EC_Group::Mul2Table m_gy_mul;
};

bool ECDSA_Verification_Operation::verify(std::span<const uint8_t> msg, std::span<const uint8_t> sig) {
   if(auto rs = EC_Scalar::deserialize_pair(m_group, sig)) {
      const auto& [r, s] = rs.value();

      if(r.is_nonzero() && s.is_nonzero()) {
         const auto m = EC_Scalar::from_bytes_with_trunc(m_group, msg);

         const auto w = s.invert_vartime();

         // Check if r == x_coord(g*w*m + y*w*r) % n
         return m_gy_mul.mul2_vartime_x_mod_order_eq(r, w, m, r);
      }
   }

   return false;
}

}  // namespace

std::unique_ptr<PK_Ops::Verification> ECDSA_PublicKey::create_verification_op(std::string_view params,
                                                                              std::string_view provider) const {
   if(provider == "base" || provider.empty()) {
      return std::make_unique<ECDSA_Verification_Operation>(*this, params);
   }

   throw Provider_Not_Found(algo_name(), provider);
}

std::unique_ptr<PK_Ops::Verification> ECDSA_PublicKey::create_x509_verification_op(
   const AlgorithmIdentifier& signature_algorithm, std::string_view provider) const {
   if(provider == "base" || provider.empty()) {
      return std::make_unique<ECDSA_Verification_Operation>(*this, signature_algorithm);
   }

   throw Provider_Not_Found(algo_name(), provider);
}

std::unique_ptr<PK_Ops::Signature> ECDSA_PrivateKey::create_signature_op(RandomNumberGenerator& rng,
                                                                         std::string_view params,
                                                                         std::string_view provider) const {
   if(provider == "base" || provider.empty()) {
      return std::make_unique<ECDSA_Signature_Operation>(*this, params, rng);
   }

   throw Provider_Not_Found(algo_name(), provider);
}

}  // namespace Botan

1	/*
2	* ECDSA implementation
3	* (C) 2007 Manuel Hartl, FlexSecure GmbH
4	* 2007 Falko Strenzke, FlexSecure GmbH
5	* 2008-2010,2015,2016,2018,2024 Jack Lloyd
6	* 2016 René Korthaus
7	*
8	* Botan is released under the Simplified BSD License (see license.txt)
9	*/
10
11	#include <botan/ecdsa.h>
12
13	#include <botan/internal/keypair.h>
14	#include <botan/internal/pk_ops_impl.h>
15
16	#if defined(BOTAN_HAS_RFC6979_GENERATOR)
17	#include <botan/internal/rfc6979.h>
18	#endif
19
20	namespace Botan {
21
22	namespace {
23
24	EC_AffinePoint recover_ecdsa_public_key(	29✔
25	const EC_Group& group, const std::vector<uint8_t>& msg, const BigInt& r, const BigInt& s, uint8_t v) {
26	if(group.has_cofactor()) {	29✔
27	throw Invalid_Argument("ECDSA public key recovery only supported for prime order groups");	×
28	}
29
30	if(v >= 4) {	29✔
31	throw Invalid_Argument("Unexpected v param for ECDSA public key recovery");	×
32	}
33
34	const BigInt& group_order = group.get_order();	29✔
35
36	if(r <= 0 \|\| r >= group_order \|\| s <= 0 \|\| s >= group_order) {	116✔
37	throw Invalid_Argument("Out of range r/s cannot recover ECDSA public key");	×
38	}
39
40	const uint8_t y_odd = v % 2;	29✔
41	const bool add_order = (v >> 1) == 0x01;	29✔
42	const size_t p_bytes = group.get_p_bytes();	29✔
43
44	BigInt x = r;	29✔
45
46	if(add_order) {	29✔
47	x += group_order;	×
48	}
49
50	if(x.bytes() <= p_bytes) {	29✔
51	std::vector<uint8_t> X(p_bytes + 1);	29✔
52
53	X[0] = 0x02 \| y_odd;	29✔
54	x.serialize_to(std::span{X}.subspan(1));	29✔
55
56	if(auto R = EC_AffinePoint::deserialize(group, X)) {	29✔
57	// Compute r_inv * (-eG + s*R)
58	const auto ne = EC_Scalar::from_bytes_with_trunc(group, msg).negate();	29✔
59	const auto ss = EC_Scalar::from_bigint(group, s);	29✔
60
61	const auto r_inv = EC_Scalar::from_bigint(group, r).invert_vartime();	29✔
62
63	const EC_Group::Mul2Table GR_mul(R.value());	29✔
64	if(auto egsr = GR_mul.mul2_vartime(ne * r_inv, ss * r_inv)) {	29✔
65	return egsr.value();	58✔
66	}	×
67	}	58✔
68	}	×
69
70	throw Decoding_Error("Failed to recover ECDSA public key from signature/msg pair");	×
71	}	58✔
72
73	} // namespace
74
75	ECDSA_PublicKey::ECDSA_PublicKey(	12✔
76	const EC_Group& group, const std::vector<uint8_t>& msg, const BigInt& r, const BigInt& s, uint8_t v) :	12✔
77	EC_PublicKey(group, recover_ecdsa_public_key(group, msg, r, s, v)) {}	12✔
78
79	std::unique_ptr<Private_Key> ECDSA_PublicKey::generate_another(RandomNumberGenerator& rng) const {	28✔
80	return std::make_unique<ECDSA_PrivateKey>(rng, domain());	56✔
81	}
82
83	uint8_t ECDSA_PublicKey::recovery_param(const std::vector<uint8_t>& msg, const BigInt& r, const BigInt& s) const {	12✔
84	const auto this_key = this->_public_ec_point().serialize_compressed();	12✔
85
86	for(uint8_t v = 0; v != 4; ++v) {	17✔
87	try {	17✔
88	const auto R = recover_ecdsa_public_key(this->domain(), msg, r, s, v);	17✔
89
90	if(R.serialize_compressed() == this_key) {	34✔
91	return v;	24✔
92	}
93	} catch(Decoding_Error&) {	17✔
94	// try the next v
95	}	×
96	}
97
98	throw Internal_Error("Could not determine ECDSA recovery parameter");	×
99	}	12✔
100
101	std::unique_ptr<Public_Key> ECDSA_PrivateKey::public_key() const {	487✔
102	return std::make_unique<ECDSA_PublicKey>(domain(), _public_ec_point());	487✔
103	}
104
105	bool ECDSA_PrivateKey::check_key(RandomNumberGenerator& rng, bool strong) const {	32✔
106	if(!EC_PrivateKey::check_key(rng, strong)) {	32✔
107	return false;
108	}
109
110	if(!strong) {	32✔
111	return true;
112	}
113
114	return KeyPair::signature_consistency_check(rng, *this, "SHA-256");	31✔
115	}
116
117	namespace {
118
119	/**
120	* ECDSA signature operation
121	*/
122	class ECDSA_Signature_Operation final : public PK_Ops::Signature_with_Hash {	×
123	public:
124	ECDSA_Signature_Operation(const ECDSA_PrivateKey& ecdsa, std::string_view padding, RandomNumberGenerator& rng) :	2,183✔
125	PK_Ops::Signature_with_Hash(padding),
126	m_group(ecdsa.domain()),	2,183✔
127	m_x(ecdsa._private_key()),	2,183✔
128	m_b(EC_Scalar::random(m_group, rng)) {	4,366✔
129	#if defined(BOTAN_HAS_RFC6979_GENERATOR)
130	m_rfc6979 = std::make_unique<RFC6979_Nonce_Generator>(	6,549✔
131	this->rfc6979_hash_function(), m_group.get_order_bits(), ecdsa._private_key());	4,366✔
132	#endif
133	}	2,183✔
134
135	size_t signature_length() const override { return 2 * m_group.get_order_bytes(); }	127✔
136
137	std::vector<uint8_t> raw_sign(std::span<const uint8_t> msg, RandomNumberGenerator& rng) override;
138
139	AlgorithmIdentifier algorithm_identifier() const override;
140
141	private:
142	const EC_Group m_group;
143	const EC_Scalar m_x;
144
145	#if defined(BOTAN_HAS_RFC6979_GENERATOR)
146	std::unique_ptr<RFC6979_Nonce_Generator> m_rfc6979;
147	#endif
148
149	EC_Scalar m_b;
150	};
151
152	AlgorithmIdentifier ECDSA_Signature_Operation::algorithm_identifier() const {	1,643✔
153	const std::string full_name = "ECDSA/" + hash_function();	3,286✔
154	const OID oid = OID::from_string(full_name);	1,643✔
155	return AlgorithmIdentifier(oid, AlgorithmIdentifier::USE_EMPTY_PARAM);	1,643✔
156	}	1,643✔
157
158	std::vector<uint8_t> ECDSA_Signature_Operation::raw_sign(std::span<const uint8_t> msg, RandomNumberGenerator& rng) {	5,947✔
159	const auto m = EC_Scalar::from_bytes_with_trunc(m_group, msg);	5,947✔
160
161	#if defined(BOTAN_HAS_RFC6979_GENERATOR)
162	const auto k = m_rfc6979->nonce_for(m_group, m);	5,947✔
163	#else
164	const auto k = EC_Scalar::random(m_group, rng);
165	#endif
166
167	const auto r = EC_Scalar::gk_x_mod_order(k, rng);	5,947✔
168
169	/*
170	* Blind the inputs
171	*
172	* Here we are computing (x*r+m)/k
173	*
174	* Instead have a random b and compute (k*b)^-1
175	*
176	* Then compute (xr+m) as (xrb + mb)
177	*
178	* Finally (xrb + mb)/(kb) = (x*r+m)/k
179	*
180	* This effectively blinds both the inversion as well as the various scalar
181	* multiplications. All of these operations should be constant-time anyway but
182	* blinding is very cheap and may help if either the compiler introduces
183	* variable-time behavior, or for the case of EM/power side channel attacks [1].
184	*
185	* [1] But note that such attacks are currently outside of Botan's threat model.
186	*
187	*/
188	const auto k_inv = (m_b * k).invert();	5,947✔
189
190	const auto xr_m = ((m_x * m_b) * r) + (m * m_b);	5,947✔
191
192	const auto s = (k_inv * xr_m);	5,947✔
193
194	// Generate the next blinding value via modular squaring
195	m_b.square_self();	5,947✔
196
197	// With overwhelming probability, a bug rather than actual zero r/s
198	if(r.is_zero() \|\| s.is_zero()) {	5,947✔
199	throw Internal_Error("During ECDSA signature generated zero r/s");	×
200	}
201
202	return EC_Scalar::serialize_pair(r, s);	11,894✔
203	}	5,947✔
204
205	/**
206	* ECDSA verification operation
207	*/
208	class ECDSA_Verification_Operation final : public PK_Ops::Verification_with_Hash {	×
209	public:
210	ECDSA_Verification_Operation(const ECDSA_PublicKey& ecdsa, std::string_view padding) :	12,783✔
211	PK_Ops::Verification_with_Hash(padding), m_group(ecdsa.domain()), m_gy_mul(ecdsa._public_ec_point()) {}	12,783✔
212
213	ECDSA_Verification_Operation(const ECDSA_PublicKey& ecdsa, const AlgorithmIdentifier& alg_id) :	4,456✔
214	PK_Ops::Verification_with_Hash(alg_id, "ECDSA", true),
215	m_group(ecdsa.domain()),	4,456✔
216	m_gy_mul(ecdsa._public_ec_point()) {}	8,912✔
217
218	bool verify(std::span<const uint8_t> msg, std::span<const uint8_t> sig) override;
219
220	private:
221	const EC_Group m_group;
222	const EC_Group::Mul2Table m_gy_mul;
223	};
224
225	bool ECDSA_Verification_Operation::verify(std::span<const uint8_t> msg, std::span<const uint8_t> sig) {	28,599✔
226	if(auto rs = EC_Scalar::deserialize_pair(m_group, sig)) {	28,599✔
227	const auto& [r, s] = rs.value();	24,161✔
228
229	if(r.is_nonzero() && s.is_nonzero()) {	48,312✔
230	const auto m = EC_Scalar::from_bytes_with_trunc(m_group, msg);	24,142✔
231
232	const auto w = s.invert_vartime();	24,142✔
233
234	// Check if r == x_coord(gwm + ywr) % n
235	return m_gy_mul.mul2_vartime_x_mod_order_eq(r, w, m, r);	24,142✔
236	}	24,142✔
237	}	24,142✔
238
239	return false;	4,457✔
240	}
241
242	} // namespace
243
244	std::unique_ptr<PK_Ops::Verification> ECDSA_PublicKey::create_verification_op(std::string_view params,	49,485✔
245	std::string_view provider) const {
246	if(provider == "base" \|\| provider.empty()) {	61,731✔
247	return std::make_unique<ECDSA_Verification_Operation>(*this, params);	12,783✔
248	}
249
250	throw Provider_Not_Found(algo_name(), provider);	73,404✔
251	}
252
253	std::unique_ptr<PK_Ops::Verification> ECDSA_PublicKey::create_x509_verification_op(	4,456✔
254	const AlgorithmIdentifier& signature_algorithm, std::string_view provider) const {
255	if(provider == "base" \|\| provider.empty()) {	4,456✔
256	return std::make_unique<ECDSA_Verification_Operation>(*this, signature_algorithm);	4,456✔
257	}
258
259	throw Provider_Not_Found(algo_name(), provider);	×
260	}
261
262	std::unique_ptr<PK_Ops::Signature> ECDSA_PrivateKey::create_signature_op(RandomNumberGenerator& rng,	2,495✔
263	std::string_view params,
264	std::string_view provider) const {
265	if(provider == "base" \|\| provider.empty()) {	2,601✔
266	return std::make_unique<ECDSA_Signature_Operation>(*this, params, rng);	2,183✔
267	}
268
269	throw Provider_Not_Found(algo_name(), provider);	624✔
270	}
271
272	} // namespace Botan

randombit / botan / 20194419005

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