1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
// -*- mode: rust; -*-
//
// This file is part of schnorrkel.
// Copyright (c) 2019 Web 3 Foundation
// See LICENSE for licensing information.
//
// Authors:
// - Jeff Burdges <jeff@web3.foundation>

//! ### Ristretto point tooling
//!
//! We provide a `RistrettoBoth` type that contains both an uncompressed
//! `RistrettoPoint` alongside its matching `CompressedRistretto`,
//! which helps several protocols avoid duplicate ristretto compressions
//! and/or decompressions.

// We're discussing including some variant in curve25519-dalek directly in
// https://github.com/dalek-cryptography/curve25519-dalek/pull/220


use core::fmt::{Debug};

use curve25519_dalek::ristretto::{CompressedRistretto,RistrettoPoint};
use subtle::{ConstantTimeEq,Choice};
// use curve25519_dalek::scalar::Scalar;

use crate::errors::{SignatureError,SignatureResult};


/// Compressed Ristretto point length
pub const RISTRETTO_POINT_LENGTH: usize = 32;


/// A `RistrettoBoth` contains both an uncompressed `RistrettoPoint`
/// as well as the corresponding `CompressedRistretto`.  It provides
/// a convenient middle ground for protocols that both hash compressed
/// points to derive scalars for use with uncompressed points.
#[derive(Copy, Clone, Default, Eq)]  // PartialEq optimized below
pub struct RistrettoBoth {
    compressed: CompressedRistretto,
    point: RistrettoPoint,
}

impl Debug for RistrettoBoth {
    fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
        write!(f, "RistrettoPoint( {:?} )", self.compressed)
    }
}

impl ConstantTimeEq for RistrettoBoth {
    fn ct_eq(&self, other: &RistrettoBoth) -> Choice {
       self.compressed.ct_eq(&other.compressed)
    }
}

impl RistrettoBoth {
    const DESCRIPTION : &'static str = "A ristretto point represented as a 32-byte compressed point";

    // I dislike getter methods, and prefer direct field access, but doing
    // getters here permits the fields being private, and gives us faster
    // equality comparisons.

    /// Access the compressed Ristretto form
    pub fn as_compressed(&self) -> &CompressedRistretto { &self.compressed }

    /// Extract the compressed Ristretto form
    pub fn into_compressed(self) -> CompressedRistretto { self.compressed }

    /// Access the point form
    pub fn as_point(&self) -> &RistrettoPoint { &self.point }

    /// Extract the point form
    pub fn into_point(self) -> RistrettoPoint { self.point }

    /// Decompress into the `RistrettoBoth` format that also retains the
    /// compressed form.
    pub fn from_compressed(compressed: CompressedRistretto) -> SignatureResult<RistrettoBoth> {
        Ok(RistrettoBoth {
            point: compressed.decompress().ok_or(SignatureError::PointDecompressionError) ?,
            compressed,
        })
    }

    /// Compress into the `RistrettoBoth` format that also retains the
    /// uncompressed form.
    pub fn from_point(point: RistrettoPoint) -> RistrettoBoth {
        RistrettoBoth {
            compressed: point.compress(),
            point,
        }
    }

    /// Convert this public key to a byte array.
    #[inline]
    pub fn to_bytes(&self) -> [u8; RISTRETTO_POINT_LENGTH] {
        self.compressed.to_bytes()
    }

    /// Construct a `RistrettoBoth` from a slice of bytes.
    ///
    /// # Example
    ///
    /// ```
    /// use schnorrkel::points::RistrettoBoth;
    /// use schnorrkel::PUBLIC_KEY_LENGTH;
    /// use schnorrkel::SignatureError;
    ///
    /// # fn doctest() -> Result<RistrettoBoth, SignatureError> {
    /// let public_key_bytes: [u8; PUBLIC_KEY_LENGTH] = [
    ///    215,  90, 152,   1, 130, 177,  10, 183, 213,  75, 254, 211, 201, 100,   7,  58,
    ///     14, 225, 114, 243, 218, 166,  35,  37, 175,   2,  26, 104, 247,   7,   81, 26];
    ///
    /// let public_key = RistrettoBoth::from_bytes(&public_key_bytes)?;
    /// #
    /// # Ok(public_key)
    /// # }
    /// #
    /// # fn main() {
    /// #     doctest();
    /// # }
    /// ```
    ///
    /// # Returns
    ///
    /// A `Result` whose okay value is an EdDSA `RistrettoBoth` or whose error value
    /// is an `SignatureError` describing the error that occurred.
    #[inline]
    pub fn from_bytes(bytes: &[u8]) -> SignatureResult<RistrettoBoth> {
        RistrettoBoth::from_bytes_ser("RistrettoPoint",RistrettoBoth::DESCRIPTION,bytes)
    }

    /// Variant of `RistrettoBoth::from_bytes` that propagates more informative errors.
    #[inline]
    pub fn from_bytes_ser(name: &'static str, description: &'static str, bytes: &[u8]) -> SignatureResult<RistrettoBoth> {
        if bytes.len() != RISTRETTO_POINT_LENGTH {
            return Err(SignatureError::BytesLengthError{
                name, description, length: RISTRETTO_POINT_LENGTH,
            });
        }
        let mut compressed = CompressedRistretto([0u8; RISTRETTO_POINT_LENGTH]);
        compressed.0.copy_from_slice(&bytes[..32]);
        RistrettoBoth::from_compressed(compressed)
    }
}

serde_boilerplate!(RistrettoBoth);

/// We hide fields largely so that only comparing the compressed forms works.
impl PartialEq<Self> for RistrettoBoth {
    fn eq(&self, other: &Self) -> bool {
        let r = self.compressed.eq(&other.compressed);
        debug_assert_eq!(r, self.point.eq(&other.point));
        r
    }
}

impl PartialOrd<RistrettoBoth> for RistrettoBoth {
    fn partial_cmp(&self, other: &RistrettoBoth) -> Option<::core::cmp::Ordering> {
        Some(self.cmp(other))
    }
}

impl Ord for RistrettoBoth {
    fn cmp(&self, other: &Self) -> core::cmp::Ordering {
        self.compressed.0.cmp(&other.compressed.0)
    }
}

impl core::hash::Hash for RistrettoBoth {
    fn hash<H: core::hash::Hasher>(&self, state: &mut H) {
        self.compressed.0.hash(state);
    }
}