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  fmt::Debug,
  5  ops::{Add, AddAssign, Mul, MulAssign, Sub, SubAssign},
  6};
  7use ff::{PrimeField, PrimeFieldBits};
  8use merlin::Transcript;
  9use rug::Integer;
 10
 11/// Represents an element of a group
 12pub trait Group:
 13  Clone
 14  + Copy
 15  + Debug
 16  + Eq
 17  + Sized
 18  + GroupOps
 19  + GroupOpsOwned
 20  + ScalarMul<<Self as Group>::Scalar>
 21  + ScalarMulOwned<<Self as Group>::Scalar>
 22{
 23  /// A type representing an element of the base field of the group
 24  type Base: PrimeField + PrimeFieldBits;
 25
 26  /// A type representing an element of the scalar field of the group
 27  type Scalar: PrimeField + PrimeFieldBits + ChallengeTrait;
 28
 29  /// A type representing the compressed version of the group element
 30  type CompressedGroupElement: CompressedGroup<GroupElement = Self>;
 31
 32  /// A type representing preprocessed group element
 33  type PreprocessedGroupElement;
 34
 35  /// A type that represents a hash function that consumes elements
 36  /// from the base field and squeezes out elements of the scalar field
 37  type HashFunc: HashFuncTrait<Self::Base, Self::Scalar>;
 38
 39  /// A method to compute a multiexponentation
 40  fn vartime_multiscalar_mul(
 41    scalars: &[Self::Scalar],
 42    bases: &[Self::PreprocessedGroupElement],
 43  ) -> Self;
 44
 45  /// Compresses the group element
 46  fn compress(&self) -> Self::CompressedGroupElement;
 47
 48  /// Attempts to create a group element from a sequence of bytes,
 49  /// failing with a `None` if the supplied bytes do not encode the group element
 50  fn from_uniform_bytes(bytes: &[u8]) -> Option<Self::PreprocessedGroupElement>;
 51
 52  /// Returns the affine coordinates (x, y, infinty) for the point
 53  fn to_coordinates(&self) -> (Self::Base, Self::Base, bool);
 54
 55  /// Returns the order of the group as a big integer
 56  fn get_order() -> Integer;
 57}
 58
 59/// Represents a compressed version of a group element
 60pub trait CompressedGroup: Clone + Copy + Debug + Eq + Sized + Send + Sync + 'static {
 61  /// A type that holds the decompressed version of the compressed group element
 62  type GroupElement: Group;
 63
 64  /// Decompresses the compressed group element
 65  fn decompress(&self) -> Option<Self::GroupElement>;
 66
 67  /// Returns a byte array representing the compressed group element
 68  fn as_bytes(&self) -> &[u8];
 69}
 70
 71/// A helper trait to append different types to the transcript
 72pub trait AppendToTranscriptTrait {
 73  /// appends the value to the transcript under the provided label
 74  fn append_to_transcript(&self, label: &'static [u8], transcript: &mut Transcript);
 75}
 76
 77/// A helper trait to absorb different objects in RO
 78pub trait AbsorbInROTrait<G: Group> {
 79  /// Absorbs the value in the provided RO
 80  fn absorb_in_ro(&self, ro: &mut G::HashFunc);
 81}
 82
 83/// A helper trait to generate challenges using a transcript object
 84pub trait ChallengeTrait {
 85  /// Returns a Scalar representing the challenge using the transcript
 86  fn challenge(label: &'static [u8], transcript: &mut Transcript) -> Self;
 87}
 88
 89/// A helper trait that defines the behavior of a hash function that we use as an RO
 90pub trait HashFuncTrait<Base, Scalar> {
 91  /// A type representing constants/parameters associated with the hash function
 92  type Constants: HashFuncConstantsTrait<Base>;
 93
 94  /// Initializes the hash function
 95  fn new(constants: Self::Constants) -> Self;
 96
 97  /// Adds a scalar to the internal state
 98  fn absorb(&mut self, e: Base);
 99
100  /// Returns a random challenge by hashing the internal state
101  fn get_challenge(&self) -> Scalar;
102
103  /// Returns a hash of the internal state
104  fn get_hash(&self) -> Scalar;
105}
106
107/// A helper trait that defines the constants associated with a hash function
108pub trait HashFuncConstantsTrait<Base> {
109  /// produces constants/parameters associated with the hash function
110  fn new() -> Self;
111}
112
113/// A helper trait for types with a group operation.
114pub trait GroupOps<Rhs = Self, Output = Self>:
115  Add<Rhs, Output = Output> + Sub<Rhs, Output = Output> + AddAssign<Rhs> + SubAssign<Rhs>
116{
117}
118
119impl<T, Rhs, Output> GroupOps<Rhs, Output> for T where
120  T: Add<Rhs, Output = Output> + Sub<Rhs, Output = Output> + AddAssign<Rhs> + SubAssign<Rhs>
121{
122}
123
124/// A helper trait for references with a group operation.
125pub trait GroupOpsOwned<Rhs = Self, Output = Self>: for<'r> GroupOps<&'r Rhs, Output> {}
126impl<T, Rhs, Output> GroupOpsOwned<Rhs, Output> for T where T: for<'r> GroupOps<&'r Rhs, Output> {}
127
128/// A helper trait for types implementing group scalar multiplication.
129pub trait ScalarMul<Rhs, Output = Self>: Mul<Rhs, Output = Output> + MulAssign<Rhs> {}
130
131impl<T, Rhs, Output> ScalarMul<Rhs, Output> for T where T: Mul<Rhs, Output = Output> + MulAssign<Rhs>
132{}
133
134/// A helper trait for references implementing group scalar multiplication.
135pub trait ScalarMulOwned<Rhs, Output = Self>: for<'r> ScalarMul<&'r Rhs, Output> {}
136impl<T, Rhs, Output> ScalarMulOwned<Rhs, Output> for T where T: for<'r> ScalarMul<&'r Rhs, Output> {}
137
138/// A helper trait for a step of the incremental computation (i.e., circuit for F)
139pub trait StepCircuit<F: PrimeField> {
140  /// Sythesize the circuit for a computation step and return variable
141  /// that corresponds to the output of the step z_{i+1}
142  fn synthesize<CS: ConstraintSystem<F>>(
143    &self,
144    cs: &mut CS,
145    z: AllocatedNum<F>,
146  ) -> Result<AllocatedNum<F>, SynthesisError>;
147}
148
149impl<F: PrimeField> AppendToTranscriptTrait for F {
150  fn append_to_transcript(&self, label: &'static [u8], transcript: &mut Transcript) {
151    transcript.append_message(label, self.to_repr().as_ref());
152  }
153}
154
155impl<F: PrimeField> AppendToTranscriptTrait for [F] {
156  fn append_to_transcript(&self, label: &'static [u8], transcript: &mut Transcript) {
157    for s in self {
158      s.append_to_transcript(label, transcript);
159    }
160  }
161}