bp-pp 0.1.1

Rust library for Bulletproofs++ - range-proof protocol in discret loggarithm setting
Documentation 
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
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217

#![allow(non_snake_case)]

//! Definition and implementation of the reciprocal range-proof protocol based on arithmetic circuits protocol.

use std::ops::{Add, Mul};
use k256::{AffinePoint, ProjectivePoint, Scalar};
use k256::elliptic_curve::ops::Invert;
use k256::elliptic_curve::rand_core::{CryptoRng, RngCore};
use merlin::Transcript;
use serde::{Deserialize, Serialize};
use crate::util::*;
use crate::{circuit, transcript};
use crate::circuit::{ArithmeticCircuit, PartitionType};

/// Represents reciprocal range-proof protocol witness.
#[derive(Clone, Debug)]
pub struct Witness {
    /// Private value in range [0..dim_np^dim_nd).
    pub x: Scalar,
    /// Blinding value
    pub s: Scalar,
    /// Witness vector: value multiplicities: i-th element corresponds to the 'i-digit' multiplicity
    pub m: Vec<Scalar>,
    /// Witness vector: value digits.
    pub digits: Vec<Scalar>,
}

/// Represents reciprocal range-proof: zk-proof that committed value lies in [0..dim_np^dim_nd) range.
#[derive(Clone, Debug)]
pub struct Proof {
    pub circuit_proof: circuit::Proof,
    pub r: ProjectivePoint,
}

/// Represent serializable version of reciprocal proof (uses AffinePoint instead of ProjectivePoint
/// and serialized version of circuit proof).
#[derive(Serialize, Deserialize, Clone, Debug)]
pub struct SerializableProof {
    pub circuit_proof: circuit::SerializableProof,
    pub r: AffinePoint,
}

impl From<&SerializableProof> for Proof {
    fn from(value: &SerializableProof) -> Self {
        Proof {
            circuit_proof: circuit::Proof::from(&value.circuit_proof),
            r: ProjectivePoint::from(value.r),
        }
    }
}

impl From<&Proof> for SerializableProof {
    fn from(value: &Proof) -> Self {
        SerializableProof {
            circuit_proof: circuit::SerializableProof::from(&value.circuit_proof),
            r: value.r.to_affine(),
        }
    }
}

/// Represents public reciprocal range proof protocol information. Using this information and challenge
/// both prover and verifier can derive the arithmetic circuit.
#[derive(Clone, Debug)]
pub struct ReciprocalRangeProofProtocol {
    /// Count of private proles (size of committed value). Equals to: `dim_nm`. Also, `dim_nv = 1 + dim_nd`.
    pub dim_nd: usize,
    /// Count of public poles (number system base). Equals to: `dim_no`.
    pub dim_np: usize,

    /// Will be used for the value commitment: `commitment = x*g + s*h_vec[0]`
    pub g: ProjectivePoint,

    /// Dimension: `dim_nm`
    pub g_vec: Vec<ProjectivePoint>,
    /// Will be used for the value commitment: `commitment = x*g + s*h_vec[0]`
    /// Dimension: `dim_nv+9`
    pub h_vec: Vec<ProjectivePoint>,

    /// Additional points to be used in WNLA.
    /// Dimension: `2^n - dim_nm`
    pub g_vec_: Vec<ProjectivePoint>,
    /// Dimension: `2^n - (dim_nv+9)`
    pub h_vec_: Vec<ProjectivePoint>,
}

impl ReciprocalRangeProofProtocol {
    /// Creates commitment for the private value and blinding: `commitment = x*g + s*h_vec[0]`
    pub fn commit_value(&self, x: &Scalar, s: &Scalar) -> ProjectivePoint {
        self.g.mul(x).add(&self.h_vec[0].mul(s))
    }

    /// Creates commitment for the reciprocals and blinding: `commitment = s*h_vec[0] + <r, h_vec[9:]>`
    pub fn commit_poles(&self, r: &[Scalar], s: &Scalar) -> ProjectivePoint {
        self.h_vec[0].mul(s).add(&vector_mul(&self.h_vec[9..], r))
    }

    /// Verifies zk-proof that committed value lies in [0..dim_np^dim_nd) range.
    pub fn verify(&self, commitment: &ProjectivePoint, proof: Proof, t: &mut Transcript) -> bool {
        transcript::app_point(b"reciprocal_commitment", commitment, t);
        let e = transcript::get_challenge(b"reciprocal_challenge", t);

        let circuit = self.make_circuit(e);

        let circuit_commitment = commitment.add(&proof.r);

        circuit.verify(&[circuit_commitment], t, proof.circuit_proof)
    }

    /// Creates zk-proof that committed value lies in [0..dim_np^dim_nd) range.
    pub fn prove<R>(&self, commitment: &ProjectivePoint, witness: Witness, t: &mut Transcript, rng: &mut R) -> Proof
        where
            R: RngCore + CryptoRng
    {
        transcript::app_point(b"reciprocal_commitment", commitment, t);
        let e = transcript::get_challenge(b"reciprocal_challenge", t);

        let r = (0..self.dim_nd).map(|i|
            witness.digits[i].add(&e).invert().unwrap()
        ).collect::<Vec<Scalar>>();

        let r_blind = Scalar::generate_biased(rng);
        let r_com = self.commit_poles(&r, &r_blind);

        let mut v = vec![witness.x];
        r.iter().for_each(|r_val| v.push(*r_val));

        let w_l = witness.digits;
        let w_r = r;
        let w_o = witness.m;

        let circuit = self.make_circuit(e);

        let circuit_witness = circuit::Witness {
            v: vec![v],
            s_v: vec![witness.s.add(r_blind)],
            w_l,
            w_r,
            w_o,
        };

        let circuit_commitment = circuit.commit(&circuit_witness.v[0], &circuit_witness.s_v[0]);
        Proof {
            circuit_proof: circuit.prove::<R>(&[circuit_commitment], circuit_witness, t, rng),
            r: r_com,
        }
    }

    /// Creates circuit parameters based on provided challenge. For the same challenge will generate same parameters.
    #[inline(always)]
    pub fn make_circuit(&self, e: Scalar) -> ArithmeticCircuit<impl Fn(PartitionType, usize) -> Option<usize> + '_>
    {
        let dim_nm = self.dim_nd;
        let dim_no = self.dim_np;

        let dim_nv = self.dim_nd + 1;
        let dim_nl = dim_nv;
        let dim_nw = self.dim_nd * 2 + self.dim_np;

        let a_m = vec![Scalar::ONE; dim_nm];

        let mut W_m = vec![vec![Scalar::ZERO; dim_nw]; dim_nm];
        (0..dim_nm).for_each(|i| W_m[i][i + dim_nm] = minus(&e));

        let a_l = vec![Scalar::ZERO; dim_nl];
        let base = Scalar::from(self.dim_np as u32);

        let mut W_l = vec![vec![Scalar::ZERO; dim_nw]; dim_nl];

        // fill for v-part in w vector
        (0..dim_nm).for_each(|i| W_l[0][i] = minus(&pow(&base, i)));

        // fill for r-part in w vector
        (0..dim_nm).for_each(|i|
            (0..dim_nm).for_each(|j| W_l[i + 1][j + dim_nm] = Scalar::ONE)
        );

        (0..dim_nm).for_each(|i| W_l[i + 1][i + dim_nm] = Scalar::ZERO);

        (0..dim_nm).for_each(|i|
            (0..dim_no).for_each(|j|
                W_l[i + 1][j + 2 * dim_nm] = minus(&(e.add(Scalar::from(j as u32)).invert_vartime().unwrap()))
            )
        );

        // partition function -> map all to ll
        let partition = |typ: PartitionType, index: usize| -> Option<usize>{
            if typ == PartitionType::LL && index < self.dim_np {
                Some(index)
            } else {
                None
            }
        };

        ArithmeticCircuit {
            dim_nm,
            dim_no,
            k: 1,
            dim_nl,
            dim_nv,
            dim_nw,
            g: self.g,
            g_vec: self.g_vec.clone(),
            h_vec: self.h_vec.clone(),
            W_m,
            W_l,
            a_m,
            a_l,
            f_l: true,
            f_m: false,
            g_vec_: self.g_vec_.clone(),
            h_vec_: self.h_vec_.clone(),
            partition,
        }
    }
}