k256/
point.rs

1use core::{
2    iter::Sum,
3    ops::{Mul, MulAssign},
4};
5
6use elliptic_curve::{
7    bigint::{ArrayEncoding, U256},
8    ops::{LinearCombination, MulByGenerator},
9    point::{AffineCoordinates, DecompactPoint, DecompressPoint},
10    rand_core::RngCore,
11    sec1::{FromEncodedPoint, ToEncodedPoint},
12    subtle::{Choice, ConditionallySelectable, ConstantTimeEq, CtOption},
13    zeroize::DefaultIsZeroes,
14    FieldBytesEncoding,
15};
16use openvm_algebra_guest::IntMod;
17use openvm_ecc_guest::{
18    weierstrass::{IntrinsicCurve, WeierstrassPoint},
19    CyclicGroup,
20};
21
22use crate::{
23    internal::{Secp256k1Coord, Secp256k1Point, Secp256k1Scalar},
24    EncodedPoint, Secp256k1,
25};
26
27// --- Implement elliptic_curve traits on Secp256k1Point ---
28
29/// secp256k1 (K-256) field element serialized as bytes.
30///
31/// Byte array containing a serialized field element value (base field or scalar).
32pub type FieldBytes = elliptic_curve::FieldBytes<Secp256k1>;
33
34impl FieldBytesEncoding<Secp256k1> for U256 {
35    fn decode_field_bytes(field_bytes: &FieldBytes) -> Self {
36        U256::from_be_byte_array(*field_bytes)
37    }
38
39    fn encode_field_bytes(&self) -> FieldBytes {
40        self.to_be_byte_array()
41    }
42}
43
44impl AffineCoordinates for Secp256k1Point {
45    type FieldRepr = FieldBytes;
46
47    fn x(&self) -> FieldBytes {
48        *FieldBytes::from_slice(&<Self as WeierstrassPoint>::x(self).to_be_bytes())
49    }
50
51    fn y_is_odd(&self) -> Choice {
52        (self.y().as_le_bytes()[0] & 1).into()
53    }
54}
55
56impl Copy for Secp256k1Point {}
57
58impl ConditionallySelectable for Secp256k1Point {
59    fn conditional_select(
60        a: &Secp256k1Point,
61        b: &Secp256k1Point,
62        choice: Choice,
63    ) -> Secp256k1Point {
64        Secp256k1Point::from_xy_unchecked(
65            Secp256k1Coord::conditional_select(
66                <Self as WeierstrassPoint>::x(a),
67                <Self as WeierstrassPoint>::x(b),
68                choice,
69            ),
70            Secp256k1Coord::conditional_select(a.y(), b.y(), choice),
71        )
72    }
73}
74
75impl ConstantTimeEq for Secp256k1Point {
76    fn ct_eq(&self, other: &Secp256k1Point) -> Choice {
77        <Self as WeierstrassPoint>::x(self).ct_eq(<Self as WeierstrassPoint>::x(other))
78            & self.y().ct_eq(other.y())
79    }
80}
81
82impl Default for Secp256k1Point {
83    fn default() -> Self {
84        <Self as WeierstrassPoint>::IDENTITY
85    }
86}
87
88impl DefaultIsZeroes for Secp256k1Point {}
89
90impl Sum for Secp256k1Point {
91    fn sum<I: Iterator<Item = Self>>(iter: I) -> Self {
92        iter.fold(<Self as WeierstrassPoint>::IDENTITY, |a, b| a + b)
93    }
94}
95
96impl<'a> Sum<&'a Secp256k1Point> for Secp256k1Point {
97    fn sum<I: Iterator<Item = &'a Secp256k1Point>>(iter: I) -> Self {
98        iter.cloned().sum()
99    }
100}
101
102impl Mul<Secp256k1Scalar> for Secp256k1Point {
103    type Output = Secp256k1Point;
104
105    fn mul(self, other: Secp256k1Scalar) -> Secp256k1Point {
106        Secp256k1::msm(&[other], &[self])
107    }
108}
109
110impl Mul<&Secp256k1Scalar> for &Secp256k1Point {
111    type Output = Secp256k1Point;
112
113    fn mul(self, other: &Secp256k1Scalar) -> Secp256k1Point {
114        Secp256k1::msm(&[*other], &[*self])
115    }
116}
117
118impl Mul<&Secp256k1Scalar> for Secp256k1Point {
119    type Output = Secp256k1Point;
120
121    fn mul(self, other: &Secp256k1Scalar) -> Secp256k1Point {
122        Secp256k1::msm(&[*other], &[self])
123    }
124}
125
126impl MulAssign<Secp256k1Scalar> for Secp256k1Point {
127    fn mul_assign(&mut self, rhs: Secp256k1Scalar) {
128        *self = Secp256k1::msm(&[rhs], &[*self]);
129    }
130}
131
132impl MulAssign<&Secp256k1Scalar> for Secp256k1Point {
133    fn mul_assign(&mut self, rhs: &Secp256k1Scalar) {
134        *self = Secp256k1::msm(&[*rhs], &[*self]);
135    }
136}
137
138impl elliptic_curve::Group for Secp256k1Point {
139    type Scalar = Secp256k1Scalar;
140
141    fn random(mut _rng: impl RngCore) -> Self {
142        // Self::GENERATOR * Self::Scalar::random(&mut rng)
143        unimplemented!()
144    }
145
146    fn identity() -> Self {
147        <Self as WeierstrassPoint>::IDENTITY
148    }
149
150    fn generator() -> Self {
151        Self::GENERATOR
152    }
153
154    fn is_identity(&self) -> Choice {
155        (<Self as openvm_ecc_guest::Group>::is_identity(self) as u8).into()
156    }
157
158    fn double(&self) -> Self {
159        self + self
160    }
161}
162
163impl elliptic_curve::group::Curve for Secp256k1Point {
164    type AffineRepr = Secp256k1Point;
165
166    fn to_affine(&self) -> Secp256k1Point {
167        *self
168    }
169}
170
171impl LinearCombination for Secp256k1Point {
172    fn lincomb(x: &Self, k: &Self::Scalar, y: &Self, l: &Self::Scalar) -> Self {
173        Secp256k1::msm(&[*k, *l], &[*x, *y])
174    }
175}
176
177// default implementation
178impl MulByGenerator for Secp256k1Point {}
179
180impl DecompressPoint<Secp256k1> for Secp256k1Point {
181    /// Note that this is not constant time
182    fn decompress(x_bytes: &FieldBytes, y_is_odd: Choice) -> CtOption<Self> {
183        use openvm_ecc_guest::weierstrass::FromCompressed;
184
185        let x = Secp256k1Coord::from_be_bytes_unchecked(x_bytes.as_slice());
186        let rec_id = y_is_odd.unwrap_u8();
187        CtOption::new(x, (x.is_reduced() as u8).into()).and_then(|x| {
188            let y = <Secp256k1Point as FromCompressed<Secp256k1Coord>>::decompress(x, &rec_id);
189            match y {
190                Some(point) => CtOption::new(point, 1.into()),
191                None => CtOption::new(Secp256k1Point::default(), 0.into()),
192            }
193        })
194    }
195}
196
197// Taken from https://docs.rs/k256/latest/src/k256/arithmetic/affine.rs.html#207
198impl DecompactPoint<Secp256k1> for Secp256k1Point {
199    fn decompact(x_bytes: &FieldBytes) -> CtOption<Self> {
200        Self::decompress(x_bytes, Choice::from(0))
201    }
202}
203
204impl FromEncodedPoint<Secp256k1> for Secp256k1Point {
205    /// Attempts to parse the given [`EncodedPoint`] as an SEC1-encoded [`Secp256k1Point`].
206    ///
207    /// # Returns
208    ///
209    /// `None` value if `encoded_point` is not on the secp256k1 curve.
210    fn from_encoded_point(encoded_point: &EncodedPoint) -> CtOption<Self> {
211        match openvm_ecc_guest::ecdsa::VerifyingKey::<Secp256k1>::from_sec1_bytes(
212            encoded_point.as_bytes(),
213        ) {
214            Ok(verifying_key) => CtOption::new(*verifying_key.as_affine(), 1.into()),
215            Err(_) => CtOption::new(Secp256k1Point::default(), 0.into()),
216        }
217    }
218}
219
220impl ToEncodedPoint<Secp256k1> for Secp256k1Point {
221    fn to_encoded_point(&self, compress: bool) -> EncodedPoint {
222        EncodedPoint::conditional_select(
223            &EncodedPoint::from_affine_coordinates(
224                &<Self as WeierstrassPoint>::x(self).to_be_bytes().into(),
225                &<Self as WeierstrassPoint>::y(self).to_be_bytes().into(),
226                compress,
227            ),
228            &EncodedPoint::identity(),
229            elliptic_curve::Group::is_identity(self),
230        )
231    }
232}
233
234impl TryFrom<EncodedPoint> for Secp256k1Point {
235    type Error = elliptic_curve::Error;
236
237    fn try_from(point: EncodedPoint) -> elliptic_curve::Result<Secp256k1Point> {
238        Secp256k1Point::try_from(&point)
239    }
240}
241
242impl TryFrom<&EncodedPoint> for Secp256k1Point {
243    type Error = elliptic_curve::Error;
244
245    fn try_from(point: &EncodedPoint) -> elliptic_curve::Result<Secp256k1Point> {
246        Option::from(Secp256k1Point::from_encoded_point(point)).ok_or(elliptic_curve::Error)
247    }
248}
249
250impl From<Secp256k1Point> for EncodedPoint {
251    fn from(affine_point: Secp256k1Point) -> EncodedPoint {
252        EncodedPoint::from(&affine_point)
253    }
254}
255
256impl From<&Secp256k1Point> for EncodedPoint {
257    fn from(affine_point: &Secp256k1Point) -> EncodedPoint {
258        affine_point.to_encoded_point(true)
259    }
260}
k256/point.rs

k256/
point.rs
