1  // Copyright (c) 2019-2025 Alpha-Delta Network Inc.
  2  // This file is part of the deltavm library.
  3  
  4  // Licensed under the Apache License, Version 2.0 (the "License");
  5  // you may not use this file except in compliance with the License.
  6  // You may obtain a copy of the License at:
  7  
  8  // http://www.apache.org/licenses/LICENSE-2.0
  9  
 10  // Unless required by applicable law or agreed to in writing, software
 11  // distributed under the License is distributed on an "AS IS" BASIS,
 12  // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 13  // See the License for the specific language governing permissions and
 14  // limitations under the License.
 15  
 16  pub mod hasher;
 17  use hasher::BHPHasher;
 18  
 19  mod commit;
 20  mod commit_uncompressed;
 21  mod hash;
 22  mod hash_uncompressed;
 23  
 24  use deltavm_console_types::prelude::*;
 25  
 26  use serde::{Deserialize, Serialize};
 27  use std::sync::Arc;
 28  
 29  const BHP_CHUNK_SIZE: usize = 3;
 30  
 31  /// BHP256 is a collision-resistant hash function that processes 256-bit chunks.
 32  pub type BHP256<E> = BHP<E, 3, 57>; // Supports inputs up to 261 bits (1 u8 + 1 Fq).
 33  /// BHP512 is a collision-resistant hash function that processes inputs in 512-bit chunks.
 34  pub type BHP512<E> = BHP<E, 6, 43>; // Supports inputs up to 522 bits (2 u8 + 2 Fq).
 35  /// BHP768 is a collision-resistant hash function that processes inputs in 768-bit chunks.
 36  pub type BHP768<E> = BHP<E, 15, 23>; // Supports inputs up to 783 bits (3 u8 + 3 Fq).
 37  /// BHP1024 is a collision-resistant hash function that processes inputs in 1024-bit chunks.
 38  pub type BHP1024<E> = BHP<E, 8, 54>; // Supports inputs up to 1044 bits (4 u8 + 4 Fq).
 39  
 40  /// BHP is a collision-resistant hash function that takes a variable-length input.
 41  /// The BHP hash function does *not* behave like a random oracle, see Poseidon for one.
 42  ///
 43  /// ## Design
 44  /// The BHP hash function splits the given input into blocks, and processes them iteratively.
 45  ///
 46  /// The first iteration is initialized as follows:
 47  /// ```text
 48  /// DIGEST_0 = BHP([ 0...0 || DOMAIN || LENGTH(INPUT) || INPUT[0..BLOCK_SIZE] ]);
 49  /// ```
 50  /// Each subsequent iteration is initialized as follows:
 51  /// ```text
 52  /// DIGEST_N+1 = BHP([ DIGEST_N[0..DATA_BITS] || INPUT[(N+1)*BLOCK_SIZE..(N+2)*BLOCK_SIZE] ]);
 53  /// ```
 54  #[derive(Clone, Debug, PartialEq, Deserialize, Serialize)]
 55  #[serde(bound = "E: Serialize + DeserializeOwned")]
 56  pub struct BHP<E: Environment, const NUM_WINDOWS: u8, const WINDOW_SIZE: u8> {
 57      /// The domain separator for the BHP hash function.
 58      domain: Vec<bool>,
 59      /// The internal BHP hasher used to process one iteration.
 60      hasher: BHPHasher<E, NUM_WINDOWS, WINDOW_SIZE>,
 61  }
 62  
 63  impl<E: Environment, const NUM_WINDOWS: u8, const WINDOW_SIZE: u8> BHP<E, NUM_WINDOWS, WINDOW_SIZE> {
 64      /// Initializes a new instance of BHP with the given domain.
 65      pub fn setup(domain: &str) -> Result<Self> {
 66          // Ensure the given domain is within the allowed size in bits.
 67          let num_bits = domain.len().saturating_mul(8);
 68          let max_bits = Field::<E>::size_in_data_bits() - 64; // 64 bits encode the length.
 69          ensure!(num_bits <= max_bits, "Domain cannot exceed {max_bits} bits, found {num_bits} bits");
 70  
 71          // Initialize the BHP hasher.
 72          let hasher = BHPHasher::<E, NUM_WINDOWS, WINDOW_SIZE>::setup(domain)?;
 73  
 74          // Convert the domain into a boolean vector.
 75          let mut domain = domain.as_bytes().to_bits_le();
 76          // Pad the domain with zeros up to the maximum size in bits.
 77          domain.resize(max_bits, false);
 78          // Reverse the domain so that it is: [ 0...0 || DOMAIN ].
 79          // (For advanced users): This optimizes the initial costs during hashing.
 80          domain.reverse();
 81  
 82          Ok(Self { domain, hasher })
 83      }
 84  
 85      /// Returns the domain separator for the BHP hash function.
 86      pub fn domain(&self) -> &[bool] {
 87          &self.domain
 88      }
 89  
 90      /// Returns the bases.
 91      pub fn bases(&self) -> &Arc<Vec<Vec<Group<E>>>> {
 92          self.hasher.bases()
 93      }
 94  
 95      /// Returns the random base window.
 96      pub fn random_base(&self) -> &Arc<Vec<Group<E>>> {
 97          self.hasher.random_base()
 98      }
 99  
100      /// Returns the number of windows.
101      pub fn num_windows(&self) -> u8 {
102          NUM_WINDOWS
103      }
104  
105      /// Returns the window size.
106      pub fn window_size(&self) -> u8 {
107          WINDOW_SIZE
108      }
109  }