Struct zerocaf::ristretto::RistrettoPoint

pub struct RistrettoPoint(pub EdwardsPoint);

Methods

impl RistrettoPoint

pub fn compress(&self) -> CompressedRistretto

Encode a Ristretto point represented by the point (X:Y:Z:T) in extended coordinates.

pub fn elligator_ristretto_flavor(r_0: &FieldElement) -> RistrettoPoint

Computes the Ristretto Elligator map. This gets a RistrettoPoint from a given `FieldElement´.

pub fn from_uniform_bytes(bytes: &[u8; 64]) -> RistrettoPoint

Construct a RistrettoPoint from 64 bytes of data.

If the input bytes are uniformly distributed, the resulting point will be uniformly distributed over the group, and its discrete log with respect to other points should be unknown.

Implementation

This function splits the input array into two 32-byte halves, takes the low 255 bits of each half mod p, applies the Ristretto-flavored Elligator map to each, and adds the results.

This function is taken from the Ristretto255 implementation found in curve25519-dalek

pub fn new_random_point<T: Rng + CryptoRng>(rand: &mut T) -> RistrettoPoint

Generate a random RistrettoPoint from a 64-byte array generated with user-provided rng.

The provided rng has to implement: Rng + CryptoRng.

This function uses the elligator hash map twice, once for [0..31] & another for [32..64] giving a uniformly distributed random value.

This implementation follows the idea pointed on the random point generation used in curve25519-dalek.

Trait Implementations

impl<'a, 'b> Add<&'a RistrettoPoint> for &'b RistrettoPoint

type Output = RistrettoPoint

The resulting type after applying the + operator.

fn add(self, other: &'a RistrettoPoint) -> RistrettoPoint

Performs the addition of two RistrettoPoints following the Twisted Edwards Extended Coordinates formulae.

This implementation is specific for curves with a = -1 as the isomorphic twist is for Doppio.

[Source: 2008 Hisil–Wong–Carter–Dawson], (http://eprint.iacr.org/2008/522), Section 3.1.

impl Add<RistrettoPoint> for RistrettoPoint

type Output = RistrettoPoint

The resulting type after applying the + operator.

fn add(self, other: RistrettoPoint) -> RistrettoPoint

Performs the addition of two RistrettoPoints following the Twisted Edwards Extended Coordinates formulae.

This implementation is specific for curves with a = -1 as the isomorphic twist is for Doppio.

[Source: 2008 Hisil–Wong–Carter–Dawson], (http://eprint.iacr.org/2008/522), Section 3.1.

impl Clone for RistrettoPoint

fn clone(&self) -> RistrettoPoint

Returns a copy of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl ConstantTimeEq for RistrettoPoint

fn ct_eq(&self, other: &RistrettoPoint) -> Choice

As specified on the Ristretto protocol docs: https://ristretto.group/formulas/equality.html and we are on the twisted case, we compare X1*Y2 == Y1*X2 | X1*X2 == Y1*Y2.

impl Copy for RistrettoPoint

impl Debug for RistrettoPoint

fn fmt(&self, f: &mut Formatter) -> Result

Formats the value using the given formatter.

impl Default for RistrettoPoint

fn default() -> RistrettoPoint

Gives back the Identity point for the Extended Edwards Coordinates which is endoded as a RistrettoPoint with coordinates: (X, Y, Z, T) = (0, 1, 1, 0).

impl<'a> Double for &'a RistrettoPoint

type Output = RistrettoPoint

fn double(self) -> RistrettoPoint

Performs the point doubling operation ie. 2*P over the Twisted Edwards Extended Coordinates.

This implementation is specific for curves with a = -1 as the isomorphic twist is. Source: 2008 Hisil–Wong–Carter–Dawson, http://eprint.iacr.org/2008/522, Section 3.1. Cost: 4M+ 4S+ 1D

impl Eq for RistrettoPoint

impl Identity for RistrettoPoint

fn identity() -> RistrettoPoint

Gives back the Identity point for the Extended Edwards Coordinates which is endoded as a RistrettoPoint with coordinates: (X, Y, Z, T) = (0, 1, 1, 0).

impl<'a, 'b> Mul<&'b RistrettoPoint> for &'a Scalar

type Output = RistrettoPoint

The resulting type after applying the * operator.

fn mul(self, point: &'b RistrettoPoint) -> RistrettoPoint

Scalar multiplication: compute self * Scalar. This implementation uses the algorithm: add_and_doubling which is the standard one for this operations and also adds less constraints on R1CS.

Hankerson, Darrel; Vanstone, Scott; Menezes, Alfred (2004). Guide to Elliptic Curve Cryptography. Springer Professional Computing. New York: Springer-Verlag.

impl<'a, 'b> Mul<&'b Scalar> for &'a RistrettoPoint

type Output = RistrettoPoint

The resulting type after applying the * operator.

fn mul(self, scalar: &'b Scalar) -> RistrettoPoint

Scalar multiplication: compute self * Scalar. This implementation uses the algorithm: add_and_doubling which is the standard one for this operations and also adds less constraints on R1CS.

Hankerson, Darrel; Vanstone, Scott; Menezes, Alfred (2004). Guide to Elliptic Curve Cryptography. Springer Professional Computing. New York: Springer-Verlag.

impl Mul<RistrettoPoint> for Scalar

type Output = RistrettoPoint

The resulting type after applying the * operator.

fn mul(self, point: RistrettoPoint) -> RistrettoPoint

Scalar multiplication: compute self * Scalar. This implementation uses the algorithm: add_and_doubling which is the standard one for this operations and also adds less constraints on R1CS.

Hankerson, Darrel; Vanstone, Scott; Menezes, Alfred (2004). Guide to Elliptic Curve Cryptography. Springer Professional Computing. New York: Springer-Verlag.

impl Mul<Scalar> for RistrettoPoint

type Output = RistrettoPoint

The resulting type after applying the * operator.

fn mul(self, scalar: Scalar) -> RistrettoPoint

Scalar multiplication: compute self * Scalar. This implementation uses the algorithm: add_and_doubling which is the standard one for this operations and also adds less constraints on R1CS.

Hankerson, Darrel; Vanstone, Scott; Menezes, Alfred (2004). Guide to Elliptic Curve Cryptography. Springer Professional Computing. New York: Springer-Verlag.

impl<'a> Neg for &'a RistrettoPoint

type Output = RistrettoPoint

The resulting type after applying the - operator.

fn neg(self) -> RistrettoPoint

Negates a RistrettoPoint giving it's negated representation as a result.

Since the negative of a point is (-X:Y:Z:-T), it gives as a result: (-X:Y:Z:-T).

impl Neg for RistrettoPoint

type Output = RistrettoPoint

The resulting type after applying the - operator.

fn neg(self) -> RistrettoPoint

Negates a RistrettoPoint giving it's negated representation as a result.

Since the negative of a point is (-X:Y:Z:-T), it gives as a result: (-X:Y:Z:-T).

impl PartialEq<RistrettoPoint> for RistrettoPoint

fn eq(&self, other: &RistrettoPoint) -> bool

This method tests for self and other values to be equal, and is used by ==.

#[must_use] fn ne(&self, other: &Rhs) -> bool

This method tests for !=.

impl<'a, 'b> Sub<&'a RistrettoPoint> for &'b RistrettoPoint

type Output = RistrettoPoint

The resulting type after applying the - operator.

fn sub(self, other: &'a RistrettoPoint) -> RistrettoPoint

Performs the subtraction of two RistrettoPoints following the Twisted Edwards Extended Coordinates formulae.

Note that Subtraction is basically the addition of the first point by the second negated.

This implementation is specific for curves with a = -1 as the isomorphic twist is for Doppio.

[Source: 2008 Hisil–Wong–Carter–Dawson], (http://eprint.iacr.org/2008/522), Section 3.1.

impl Sub<RistrettoPoint> for RistrettoPoint

type Output = RistrettoPoint

The resulting type after applying the - operator.

fn sub(self, other: RistrettoPoint) -> RistrettoPoint

Performs the subtraction of two RistrettoPoints following the Twisted Edwards Extended Coordinates formulae.

Note that Subtraction is basically the addition of the first point by the second negated.

This implementation is specific for curves with a = -1 as the isomorphic twist is for Doppio.

[Source: 2008 Hisil–Wong–Carter–Dawson], (http://eprint.iacr.org/2008/522), Section 3.1.

impl ValidityCheck for RistrettoPoint

fn is_valid(&self) -> Choice

A valid RistrettoPoint should have exactly order L (Scalar Field Order) and also verify the curve equation.

This trait is mostly implemented for debugging purposes.

Returns

• `Choice(1) if the point has order L (not 2L, 4L or 8L) & satisfies the curve equation.
• `Choice(0) if the point does not satisfy one of the conditions mentioned avobe.