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
//! Defines a `TranscriptProtocol` trait for using a Merlin transcript.

use curve25519_dalek::ristretto::CompressedRistretto;
use curve25519_dalek::scalar::Scalar;
use merlin::Transcript;

use errors::ProofError;

pub trait TranscriptProtocol {
    /// Append a domain separator for an `n`-bit, `m`-party range proof.
    fn rangeproof_domain_sep(&mut self, n: u64, m: u64);

    /// Append a domain separator for a length-`n` inner product proof.
    fn innerproduct_domain_sep(&mut self, n: u64);

    /// Append a domain separator for a constraint system.
    fn r1cs_domain_sep(&mut self);

    /// Append a `scalar` with the given `label`.
    fn append_scalar(&mut self, label: &'static [u8], scalar: &Scalar);

    /// Append a `point` with the given `label`.
    fn append_point(&mut self, label: &'static [u8], point: &CompressedRistretto);

    /// Check that a point is not the identity, then append it to the
    /// transcript.  Otherwise, return an error.
    fn validate_and_append_point(
        &mut self,
        label: &'static [u8],
        point: &CompressedRistretto,
    ) -> Result<(), ProofError>;

    /// Compute a `label`ed challenge variable.
    fn challenge_scalar(&mut self, label: &'static [u8]) -> Scalar;
}

impl TranscriptProtocol for Transcript {
    fn rangeproof_domain_sep(&mut self, n: u64, m: u64) {
        self.append_message(b"dom-sep", b"rangeproof v1");
        self.append_u64(b"n", n);
        self.append_u64(b"m", m);
    }

    fn innerproduct_domain_sep(&mut self, n: u64) {
        self.append_message(b"dom-sep", b"ipp v1");
        self.append_u64(b"n", n);
    }

    fn r1cs_domain_sep(&mut self) {
        self.append_message(b"dom-sep", b"r1cs v1");
    }

    fn append_scalar(&mut self, label: &'static [u8], scalar: &Scalar) {
        self.append_message(label, scalar.as_bytes());
    }

    fn append_point(&mut self, label: &'static [u8], point: &CompressedRistretto) {
        self.append_message(label, point.as_bytes());
    }

    fn validate_and_append_point(
        &mut self,
        label: &'static [u8],
        point: &CompressedRistretto,
    ) -> Result<(), ProofError> {
        use curve25519_dalek::traits::IsIdentity;

        if point.is_identity() {
            Err(ProofError::VerificationError)
        } else {
            Ok(self.append_message(label, point.as_bytes()))
        }
    }

    fn challenge_scalar(&mut self, label: &'static [u8]) -> Scalar {
        let mut buf = [0u8; 64];
        self.challenge_bytes(label, &mut buf);

        Scalar::from_bytes_mod_order_wide(&buf)
    }
}