ristretto255_pedersen - [devnet]

This module implements a Pedersen commitment API, over the Ristretto255 curve, that can be used with the Bulletproofs module.

A Pedersen commitment to a value v under commitment key (g, h) is v * g + r * h, for a random scalar r.

use 0x1::option;
use 0x1::ristretto255;

Constants

The default Pedersen randomness base h used in our underlying Bulletproofs library. This is obtained by hashing the compressed Ristretto255 basepoint using SHA3-512 (not SHA2-512).

const BULLETPROOF_DEFAULT_PEDERSEN_RAND_BASE: vector<u8> = [140, 146, 64, 180, 86, 169, 230, 220, 101, 195, 119, 161, 4, 141, 116, 95, 148, 160, 140, 219, 127, 68, 203, 205, 123, 70, 243, 64, 72, 135, 17, 52];

Structs

`Commitment`

A Pedersen commitment to some value with some randomness.

struct Commitment has drop

Fields

point: ristretto255::RistrettoPoint

Functions

`new_commitment_from_bytes`

Creates a new public key from a serialized Ristretto255 point.

public fun new_commitment_from_bytes(bytes: vector<u8>): option::Option<ristretto255_pedersen::Commitment>

Implementation

public fun new_commitment_from_bytes(bytes: vector<u8>): Option<Commitment> {
    let point = ristretto255::new_point_from_bytes(bytes);
    if (point.is_some()) {
        let comm = Commitment {
            point: point.extract()
        };
        std::option::some(comm)
    } else {
        std::option::none<Commitment>()
    }
}

`commitment_to_bytes`

Returns a commitment as a serialized byte array

public fun commitment_to_bytes(comm: &ristretto255_pedersen::Commitment): vector<u8>

Implementation

public fun commitment_to_bytes(comm: &Commitment): vector<u8> {
    ristretto255::point_to_bytes(&ristretto255::point_compress(&comm.point))
}

`commitment_from_point`

Moves a Ristretto point into a Pedersen commitment.

public fun commitment_from_point(point: ristretto255::RistrettoPoint): ristretto255_pedersen::Commitment

Implementation

public fun commitment_from_point(point: RistrettoPoint): Commitment {
    Commitment {
        point
    }
}

`commitment_from_compressed`

Deserializes a commitment from a compressed Ristretto point.

public fun commitment_from_compressed(point: &ristretto255::CompressedRistretto): ristretto255_pedersen::Commitment

Implementation

public fun commitment_from_compressed(point: &CompressedRistretto): Commitment {
    Commitment {
        point: ristretto255::point_decompress(point)
    }
}

`new_commitment`

Returns a commitment v * val_base + r * rand_base where (val_base, rand_base) is the commitment key.

public fun new_commitment(v: &ristretto255::Scalar, val_base: &ristretto255::RistrettoPoint, r: &ristretto255::Scalar, rand_base: &ristretto255::RistrettoPoint): ristretto255_pedersen::Commitment

Implementation

public fun new_commitment(v: &Scalar, val_base: &RistrettoPoint, r: &Scalar, rand_base: &RistrettoPoint): Commitment {
    Commitment {
        point: ristretto255::double_scalar_mul(v, val_base, r, rand_base)
    }
}

`new_commitment_with_basepoint`

Returns a commitment v * G + r * rand_base where G is the Ristretto255 basepoint.

public fun new_commitment_with_basepoint(v: &ristretto255::Scalar, r: &ristretto255::Scalar, rand_base: &ristretto255::RistrettoPoint): ristretto255_pedersen::Commitment

Implementation

public fun new_commitment_with_basepoint(v: &Scalar, r: &Scalar, rand_base: &RistrettoPoint): Commitment {
    Commitment {
        point: ristretto255::basepoint_double_mul(r, rand_base, v)
    }
}

`new_commitment_for_bulletproof`

Returns a commitment v * G + r * H where G is the Ristretto255 basepoint and H is the default randomness base used in the Bulletproofs library (i.e., BULLETPROOF_DEFAULT_PEDERSEN_RAND_BASE).

public fun new_commitment_for_bulletproof(v: &ristretto255::Scalar, r: &ristretto255::Scalar): ristretto255_pedersen::Commitment

Implementation

public fun new_commitment_for_bulletproof(v: &Scalar, r: &Scalar): Commitment {
    let rand_base = ristretto255::new_point_from_bytes(BULLETPROOF_DEFAULT_PEDERSEN_RAND_BASE);
    let rand_base = rand_base.extract();

    Commitment {
        point: ristretto255::basepoint_double_mul(r, &rand_base, v)
    }
}

`commitment_add`

Homomorphically combines two commitments lhs and rhs as lhs + rhs. Useful for re-randomizing the commitment or updating the committed value.

public fun commitment_add(lhs: &ristretto255_pedersen::Commitment, rhs: &ristretto255_pedersen::Commitment): ristretto255_pedersen::Commitment

Implementation

public fun commitment_add(lhs: &Commitment, rhs: &Commitment): Commitment {
    Commitment {
        point: ristretto255::point_add(&lhs.point, &rhs.point)
    }
}

`commitment_add_assign`

Like commitment_add but assigns lhs = lhs + rhs.

public fun commitment_add_assign(lhs: &mut ristretto255_pedersen::Commitment, rhs: &ristretto255_pedersen::Commitment)

Implementation

public fun commitment_add_assign(lhs: &mut Commitment, rhs: &Commitment) {
    ristretto255::point_add_assign(&mut lhs.point, &rhs.point);
}

`commitment_sub`

Homomorphically combines two commitments lhs and rhs as lhs - rhs. Useful for re-randomizing the commitment or updating the committed value.

public fun commitment_sub(lhs: &ristretto255_pedersen::Commitment, rhs: &ristretto255_pedersen::Commitment): ristretto255_pedersen::Commitment

Implementation

public fun commitment_sub(lhs: &Commitment, rhs: &Commitment): Commitment {
    Commitment {
        point: ristretto255::point_sub(&lhs.point, &rhs.point)
    }
}

`commitment_sub_assign`

Like commitment_add but assigns lhs = lhs - rhs.

public fun commitment_sub_assign(lhs: &mut ristretto255_pedersen::Commitment, rhs: &ristretto255_pedersen::Commitment)

Implementation

public fun commitment_sub_assign(lhs: &mut Commitment, rhs: &Commitment) {
    ristretto255::point_sub_assign(&mut lhs.point, &rhs.point);
}

`commitment_clone`

Creates a copy of this commitment.

public fun commitment_clone(c: &ristretto255_pedersen::Commitment): ristretto255_pedersen::Commitment

Implementation

public fun commitment_clone(c: &Commitment): Commitment {
    Commitment {
        point: ristretto255::point_clone(&c.point)
    }
}

`commitment_equals`

Returns true if the two commitments are identical: i.e., same value and same randomness.

public fun commitment_equals(lhs: &ristretto255_pedersen::Commitment, rhs: &ristretto255_pedersen::Commitment): bool

Implementation

public fun commitment_equals(lhs: &Commitment, rhs: &Commitment): bool {
    ristretto255::point_equals(&lhs.point, &rhs.point)
}

`commitment_as_point`

Returns the underlying elliptic curve point representing the commitment as an in-memory RistrettoPoint.

public fun commitment_as_point(c: &ristretto255_pedersen::Commitment): &ristretto255::RistrettoPoint

Implementation

public fun commitment_as_point(c: &Commitment): &RistrettoPoint {
    &c.point
}

`commitment_as_compressed_point`

Returns the Pedersen commitment as a CompressedRistretto point.

public fun commitment_as_compressed_point(c: &ristretto255_pedersen::Commitment): ristretto255::CompressedRistretto

Implementation

public fun commitment_as_compressed_point(c: &Commitment): CompressedRistretto {
    point_compress(&c.point)
}

`commitment_into_point`

Moves the Commitment into a CompressedRistretto point.

public fun commitment_into_point(c: ristretto255_pedersen::Commitment): ristretto255::RistrettoPoint

Implementation

public fun commitment_into_point(c: Commitment): RistrettoPoint {
    let Commitment { point } = c;
    point
}

`commitment_into_compressed_point`

Moves the Commitment into a CompressedRistretto point.

public fun commitment_into_compressed_point(c: ristretto255_pedersen::Commitment): ristretto255::CompressedRistretto

Implementation

public fun commitment_into_compressed_point(c: Commitment): CompressedRistretto {
    point_compress(&c.point)
}

`randomness_base_for_bulletproof`

Returns the randomness base compatible with the Bulletproofs module.

Recal that a Bulletproof range proof attests, in zero-knowledge, that a value v inside a Pedersen commitment v * g + r * h is sufficiently “small” (e.g., is 32-bits wide). Here, h is referred to as the “randomness base” of the commitment scheme.

Bulletproof has a default choice for g and h and this function returns the default h as used in the Bulletproofs Move module.

public fun randomness_base_for_bulletproof(): ristretto255::RistrettoPoint

Implementation

public fun randomness_base_for_bulletproof(): RistrettoPoint {
    ristretto255::new_point_from_bytes(BULLETPROOF_DEFAULT_PEDERSEN_RAND_BASE).extract()
}