1//! This module defines various traits required by the users of the library to implement.
  2use bellperson::{gadgets::num::AllocatedNum, ConstraintSystem, SynthesisError};
  3use core::{
  4  borrow::Borrow,
  5  fmt::Debug,
  6  ops::{Add, AddAssign, Mul, MulAssign, Sub, SubAssign},
  7};
  8use ff::PrimeField;
  9use merlin::Transcript;
 10use rug::Integer;
 11
 12/// Represents an element of a group
 13pub trait Group:
 14  Clone
 15  + Copy
 16  + Debug
 17  + Eq
 18  + Sized
 19  + GroupOps
 20  + GroupOpsOwned
 21  + ScalarMul<<Self as Group>::Scalar>
 22  + ScalarMulOwned<<Self as Group>::Scalar>
 23{
 24  /// A type representing an element of the base field of the group
 25  type Base: PrimeField;
 26
 27  /// A type representing an element of the scalar field of the group
 28  type Scalar: PrimeField + ChallengeTrait;
 29
 30  /// A type representing the compressed version of the group element
 31  type CompressedGroupElement: CompressedGroup<GroupElement = Self>;
 32
 33  /// A method to compute a multiexponentation
 34  fn vartime_multiscalar_mul<I, J>(scalars: I, points: J) -> Self
 35  where
 36    I: IntoIterator,
 37    I::Item: Borrow<Self::Scalar>,
 38    J: IntoIterator,
 39    J::Item: Borrow<Self>,
 40    Self: Clone;
 41
 42  /// Compresses the group element
 43  fn compress(&self) -> Self::CompressedGroupElement;
 44
 45  /// Attempts to create a group element from a sequence of bytes,
 46  /// failing with a `None` if the supplied bytes do not encode the group element
 47  fn from_uniform_bytes(bytes: &[u8]) -> Option<Self>;
 48
 49  /// Returns the affine coordinates (x, y, infinty) for the point
 50  fn to_coordinates(&self) -> (Self::Base, Self::Base, bool);
 51
 52  /// Returns the order of the group as a big integer
 53  fn get_order() -> Integer;
 54}
 55
 56/// Represents a compressed version of a group element
 57pub trait CompressedGroup: Clone + Copy + Debug + Eq + Sized + Send + Sync + 'static {
 58  /// A type that holds the decompressed version of the compressed group element
 59  type GroupElement: Group;
 60
 61  /// Decompresses the compressed group element
 62  fn decompress(&self) -> Option<Self::GroupElement>;
 63
 64  /// Returns a byte array representing the compressed group element
 65  fn as_bytes(&self) -> &[u8];
 66}
 67
 68/// A helper trait to generate challenges using a transcript object
 69pub trait ChallengeTrait {
 70  /// Returns a Scalar representing the challenge using the transcript
 71  fn challenge(label: &'static [u8], transcript: &mut Transcript) -> Self;
 72}
 73
 74/// A helper trait for types with a group operation.
 75pub trait GroupOps<Rhs = Self, Output = Self>:
 76  Add<Rhs, Output = Output> + Sub<Rhs, Output = Output> + AddAssign<Rhs> + SubAssign<Rhs>
 77{
 78}
 79
 80impl<T, Rhs, Output> GroupOps<Rhs, Output> for T where
 81  T: Add<Rhs, Output = Output> + Sub<Rhs, Output = Output> + AddAssign<Rhs> + SubAssign<Rhs>
 82{
 83}
 84
 85/// A helper trait for references with a group operation.
 86pub trait GroupOpsOwned<Rhs = Self, Output = Self>: for<'r> GroupOps<&'r Rhs, Output> {}
 87impl<T, Rhs, Output> GroupOpsOwned<Rhs, Output> for T where T: for<'r> GroupOps<&'r Rhs, Output> {}
 88
 89/// A helper trait for types implementing group scalar multiplication.
 90pub trait ScalarMul<Rhs, Output = Self>: Mul<Rhs, Output = Output> + MulAssign<Rhs> {}
 91
 92impl<T, Rhs, Output> ScalarMul<Rhs, Output> for T where T: Mul<Rhs, Output = Output> + MulAssign<Rhs>
 93{}
 94
 95/// A helper trait for references implementing group scalar multiplication.
 96pub trait ScalarMulOwned<Rhs, Output = Self>: for<'r> ScalarMul<&'r Rhs, Output> {}
 97impl<T, Rhs, Output> ScalarMulOwned<Rhs, Output> for T where T: for<'r> ScalarMul<&'r Rhs, Output> {}
 98
 99/// A helper trait for a step of the incremental computation (i.e., circuit for F)
100pub trait StepCircuit<F: PrimeField> {
101  /// Sythesize the circuit for a computation step and return variable
102  /// that corresponds to the output of the step z_{i+1}
103  fn synthesize<CS: ConstraintSystem<F>>(
104    &self,
105    cs: &mut CS,
106    z: AllocatedNum<F>,
107  ) -> Result<AllocatedNum<F>, SynthesisError>;
108}