k256/
scalar.rs

1use alloc::vec::Vec;
2use core::{cmp::Ordering, ops::ShrAssign};
3
4use elliptic_curve::{
5    bigint::{ArrayEncoding, Encoding, U256},
6    ops::{Invert, Reduce},
7    rand_core::RngCore,
8    scalar::{FromUintUnchecked, IsHigh},
9    subtle::{Choice, ConditionallySelectable, ConstantTimeEq, CtOption},
10    zeroize::DefaultIsZeroes,
11    Field, PrimeField, ScalarPrimitive,
12};
13use hex_literal::hex;
14use openvm_algebra_guest::IntMod;
15
16use crate::{
17    internal::{seven_le, Secp256k1Scalar},
18    point::FieldBytes,
19    Secp256k1, ORDER_HEX,
20};
21
22impl Secp256k1Scalar {
23    /// Returns the SEC1 encoding of this scalar.
24    pub fn to_bytes(&self) -> FieldBytes {
25        self.to_be_bytes().into()
26    }
27}
28// --- Implement elliptic_curve traits on Secp256k1Scalar ---
29
30impl Copy for Secp256k1Scalar {}
31
32impl From<u64> for Secp256k1Scalar {
33    fn from(value: u64) -> Self {
34        Self::from_u64(value)
35    }
36}
37
38impl Default for Secp256k1Scalar {
39    fn default() -> Self {
40        <Self as IntMod>::ZERO
41    }
42}
43
44// Requires canonical form
45impl ConstantTimeEq for Secp256k1Scalar {
46    fn ct_eq(&self, other: &Self) -> Choice {
47        self.as_le_bytes().ct_eq(other.as_le_bytes())
48    }
49}
50
51impl ConditionallySelectable for Secp256k1Scalar {
52    fn conditional_select(
53        a: &Secp256k1Scalar,
54        b: &Secp256k1Scalar,
55        choice: Choice,
56    ) -> Secp256k1Scalar {
57        Secp256k1Scalar::from_le_bytes_unchecked(
58            &a.as_le_bytes()
59                .iter()
60                .zip(b.as_le_bytes().iter())
61                .map(|(a, b)| u8::conditional_select(a, b, choice))
62                .collect::<Vec<_>>(),
63        )
64    }
65}
66
67impl Field for Secp256k1Scalar {
68    const ZERO: Self = <Self as IntMod>::ZERO;
69    const ONE: Self = <Self as IntMod>::ONE;
70
71    fn random(mut _rng: impl RngCore) -> Self {
72        unimplemented!()
73    }
74
75    #[must_use]
76    fn square(&self) -> Self {
77        self * self
78    }
79
80    #[must_use]
81    fn double(&self) -> Self {
82        self + self
83    }
84
85    fn invert(&self) -> CtOption<Self> {
86        // needs to be in canonical form for ct_eq
87        self.assert_reduced();
88        let is_zero = self.ct_eq(&<Self as IntMod>::ZERO);
89        CtOption::new(
90            <Secp256k1Scalar as openvm_algebra_guest::Field>::invert(self),
91            !is_zero,
92        )
93    }
94
95    #[allow(clippy::many_single_char_names)]
96    fn sqrt(&self) -> CtOption<Self> {
97        match <Self as openvm_algebra_guest::Sqrt>::sqrt(self) {
98            Some(sqrt) => CtOption::new(sqrt, 1.into()),
99            None => CtOption::new(<Self as Field>::ZERO, 0.into()),
100        }
101    }
102
103    fn sqrt_ratio(num: &Self, div: &Self) -> (Choice, Self) {
104        ff::helpers::sqrt_ratio_generic(num, div)
105    }
106}
107
108impl PrimeField for Secp256k1Scalar {
109    type Repr = FieldBytes;
110
111    const MODULUS: &'static str = ORDER_HEX;
112    const NUM_BITS: u32 = 256;
113    const CAPACITY: u32 = 255;
114    const TWO_INV: Self = Self::from_const_bytes(hex!(
115        "a1201b68462fe9df1d50a457736e575dffffffffffffffffffffffffffffff7f"
116    ));
117    const MULTIPLICATIVE_GENERATOR: Self = Self::from_const_bytes(seven_le());
118    const S: u32 = 6;
119    const ROOT_OF_UNITY: Self = Self::from_const_bytes(hex!(
120        "f252b002544b2f9945607580b6eabd98a883c4fba37998df8619a9e760c01d0c"
121    ));
122    const ROOT_OF_UNITY_INV: Self = Self::from_const_bytes(hex!(
123        "1c0d4f88a030fbb6c313a40a9175a27772bb8c5bc7b0c7ef96702df181e13afd"
124    ));
125    const DELTA: Self = Self::from_const_bytes(hex!(
126        "0176bbc0c81794191e34e180e7783bd6c86145fe21bc0c000000000000000000"
127    ));
128
129    /// Attempts to parse the given byte array as an SEC1-encoded scalar.
130    ///
131    /// Returns None if the byte array does not contain a big-endian integer in the range
132    /// [0, p).
133    fn from_repr(bytes: FieldBytes) -> CtOption<Self> {
134        let ret = Self::from_be_bytes_unchecked(bytes.as_slice());
135        CtOption::new(ret, (ret.is_reduced() as u8).into())
136    }
137
138    // Endianness should match from_repr
139    fn to_repr(&self) -> FieldBytes {
140        *FieldBytes::from_slice(&self.to_be_bytes())
141    }
142
143    fn is_odd(&self) -> Choice {
144        (self.as_le_bytes()[0] & 1).into()
145    }
146}
147
148impl ShrAssign<usize> for Secp256k1Scalar {
149    fn shr_assign(&mut self, _rhs: usize) {
150        // I don't think this is used anywhere
151        unimplemented!()
152    }
153}
154
155impl Reduce<U256> for Secp256k1Scalar {
156    type Bytes = FieldBytes;
157
158    fn reduce(w: U256) -> Self {
159        <Self as openvm_algebra_guest::Reduce>::reduce_le_bytes(&w.to_le_bytes())
160    }
161
162    #[inline]
163    fn reduce_bytes(bytes: &FieldBytes) -> Self {
164        Self::reduce(U256::from_be_byte_array(*bytes))
165    }
166}
167
168impl PartialOrd for Secp256k1Scalar {
169    // requires self and other to be in canonical form
170    fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
171        self.assert_reduced();
172        other.assert_reduced();
173        Some(
174            self.to_be_bytes()
175                .iter()
176                .zip(other.to_be_bytes().iter())
177                .map(|(a, b)| a.cmp(b))
178                .find(|ord| *ord != Ordering::Equal)
179                .unwrap_or(Ordering::Equal),
180        )
181    }
182}
183
184impl IsHigh for Secp256k1Scalar {
185    fn is_high(&self) -> Choice {
186        // self > n/2
187        // iff self + self overflows
188        // iff self + self < self
189        ((self + self < *self) as u8).into()
190    }
191}
192
193impl Invert for Secp256k1Scalar {
194    type Output = CtOption<Self>;
195
196    fn invert(&self) -> CtOption<Self> {
197        <Self as Field>::invert(self)
198    }
199}
200
201impl FromUintUnchecked for Secp256k1Scalar {
202    type Uint = U256;
203
204    fn from_uint_unchecked(uint: Self::Uint) -> Self {
205        Self::from_le_bytes_unchecked(&uint.to_le_bytes())
206    }
207}
208
209impl From<ScalarPrimitive<Secp256k1>> for Secp256k1Scalar {
210    fn from(scalar: ScalarPrimitive<Secp256k1>) -> Self {
211        Self::from_le_bytes_unchecked(&scalar.as_uint().to_le_bytes())
212    }
213}
214
215impl From<Secp256k1Scalar> for ScalarPrimitive<Secp256k1> {
216    fn from(scalar: Secp256k1Scalar) -> ScalarPrimitive<Secp256k1> {
217        ScalarPrimitive::from_slice(&scalar.to_be_bytes()).unwrap()
218    }
219}
220
221impl DefaultIsZeroes for Secp256k1Scalar {}
222
223impl AsRef<Secp256k1Scalar> for Secp256k1Scalar {
224    fn as_ref(&self) -> &Secp256k1Scalar {
225        self
226    }
227}
228
229impl From<Secp256k1Scalar> for U256 {
230    fn from(scalar: Secp256k1Scalar) -> Self {
231        U256::from_be_slice(&scalar.to_be_bytes())
232    }
233}
234
235impl From<Secp256k1Scalar> for FieldBytes {
236    fn from(scalar: Secp256k1Scalar) -> Self {
237        *FieldBytes::from_slice(&scalar.to_be_bytes())
238    }
239}
k256/scalar.rs

k256/
scalar.rs
