Botan: src/math/ec_gfp/curve_gfp.h Source File

Botan 1.10.16

curve_gfp.h
Go to the documentation of this file.
1 /*
2 * Elliptic curves over GF(p)
3 *
4 * (C) 2007 Martin Doering, Christoph Ludwig, Falko Strenzke
5 * 2010-2011 Jack Lloyd
6 *
7 * Distributed under the terms of the Botan license
8 */
9
10 #ifndef BOTAN_GFP_CURVE_H__
11 #define BOTAN_GFP_CURVE_H__
12
13 #include <botan/numthry.h>
14
15 namespace Botan {
16
17 /**
18 * This class represents an elliptic curve over GF(p)
19 */
20 class BOTAN_DLL CurveGFp
21 {
22 public:
23
24 /**
25 * Create an uninitialized CurveGFp
26 */
27 CurveGFp() : p_words(0), p_dash(0) {}
28
29 /**
30 * Construct the elliptic curve E: y^2 = x^3 + ax + b over GF(p)
31 * @param p prime number of the field
32 * @param a first coefficient
33 * @param b second coefficient
34 */
35 CurveGFp(const BigInt& p, const BigInt& a, const BigInt& b) :
36 p(p), a(a), b(b), p_words(p.sig_words())
37 {
38 BigInt r(BigInt::Power2, p_words * BOTAN_MP_WORD_BITS);
39
40 p_dash = (((r * inverse_mod(r, p)) - 1) / p).word_at(0);
41
42 r2 = (r * r) % p;
43 a_r = (a * r) % p;
44 b_r = (b * r) % p;
45 }
46
47 // CurveGFp(const CurveGFp& other) = default;
48 // CurveGFp& operator=(const CurveGFp& other) = default;
49
50 /**
51 * @return curve coefficient a
52 */
53 const BigInt& get_a() const { return a; }
54
55 /**
56 * @return curve coefficient b
57 */
58 const BigInt& get_b() const { return b; }
59
60 /**
61 * Get prime modulus of the field of the curve
62 * @return prime modulus of the field of the curve
63 */
64 const BigInt& get_p() const { return p; }
65
66 /**
67 * @return Montgomery parameter r^2 % p
68 */
69 const BigInt& get_r2() const { return r2; }
70
71 /**
72 * @return a * r mod p
73 */
74 const BigInt& get_a_r() const { return a_r; }
75
76 /**
77 * @return b * r mod p
78 */
79 const BigInt& get_b_r() const { return b_r; }
80
81 /**
82 * @return Montgomery parameter p-dash
83 */
84 word get_p_dash() const { return p_dash; }
85
86 /**
87 * @return p.sig_words()
88 */
89 size_t get_p_words() const { return p_words; }
90
91 /**
92 * swaps the states of *this and other, does not throw
93 * @param other curve to swap values with
94 */
95 void swap(CurveGFp& other)
96 {
97 std::swap(p, other.p);
98
99 std::swap(a, other.a);
100 std::swap(b, other.b);
101
102 std::swap(a_r, other.a_r);
103 std::swap(b_r, other.b_r);
104
105 std::swap(p_words, other.p_words);
106
107 std::swap(r2, other.r2);
108 std::swap(p_dash, other.p_dash);
109 }
110
111 /**
112 * Equality operator
113 * @param other curve to compare with
114 * @return true iff this is the same curve as other
115 */
116 bool operator==(const CurveGFp& other) const
117 {
118 /*
119 Relies on choice of R, but that is fixed by constructor based
120 on size of p
121 */
122 return (p == other.p && a_r == other.a_r && b_r == other.b_r);
123 }
124
125 private:
126 // Curve parameters
127 BigInt p, a, b;
128
129 size_t p_words; // cache of p.sig_words()
130
131 // Montgomery parameters
132 BigInt r2, a_r, b_r;
133 word p_dash;
134 };
135
136 /**
137 * Equality operator
138 * @param lhs a curve
139 * @param rhs a curve
140 * @return true iff lhs is not the same as rhs
141 */
142 inline bool operator!=(const CurveGFp& lhs, const CurveGFp& rhs)
143 {
144 return !(lhs == rhs);
145 }
146
147 }
148
149 namespace std {
150
151 template<> inline
152 void swap<Botan::CurveGFp>(Botan::CurveGFp& curve1,
153 Botan::CurveGFp& curve2)
154 {
155 curve1.swap(curve2);
156 }
157
158 } // namespace std
159
160 #endif
Botan::operator!=
bool operator!=(const OctetString &s1, const OctetString &s2)
Definition: symkey.cpp:106
Botan::BigInt
Definition: bigint.h:22
Botan::CurveGFp::CurveGFp
CurveGFp(const BigInt &p, const BigInt &a, const BigInt &b)
Definition: curve_gfp.h:35
Botan::CurveGFp::get_p_words
size_t get_p_words() const
Definition: curve_gfp.h:89
std
Definition: secmem.h:422
Botan::CurveGFp::CurveGFp
CurveGFp()
Definition: curve_gfp.h:27
Botan::CurveGFp::get_p_dash
word get_p_dash() const
Definition: curve_gfp.h:84
Botan::CurveGFp::get_b_r
const BigInt & get_b_r() const
Definition: curve_gfp.h:79
Botan::CurveGFp::operator==
bool operator==(const CurveGFp &other) const
Definition: curve_gfp.h:116
Botan::CurveGFp::swap
void swap(CurveGFp &other)
Definition: curve_gfp.h:95
Botan
Definition: algo_base.h:14
Botan::CurveGFp::get_b
const BigInt & get_b() const
Definition: curve_gfp.h:58
Botan::inverse_mod
BigInt inverse_mod(const BigInt &n, const BigInt &mod)
Definition: numthry.cpp:314
Botan::CurveGFp::get_a
const BigInt & get_a() const
Definition: curve_gfp.h:53
Botan::CurveGFp::get_r2
const BigInt & get_r2() const
Definition: curve_gfp.h:69
Botan::CurveGFp::get_a_r
const BigInt & get_a_r() const
Definition: curve_gfp.h:74
std::swap
void swap(Botan::MemoryRegion< T > &x, Botan::MemoryRegion< T > &y)
Definition: secmem.h:425
Botan::BigInt::Power2
Definition: bigint.h:38
Botan::CurveGFp::get_p
const BigInt & get_p() const
Definition: curve_gfp.h:64
Botan::CurveGFp
Definition: curve_gfp.h:20