1  // Copyright (c) 2019-2025 Alpha-Delta Network Inc.
 2  // This file is part of the alphavm 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  use super::*;
17  
18  impl<E: Environment, const RATE: usize> HashToGroup for Poseidon<E, RATE> {
19      type Input = Field<E>;
20      type Output = Group<E>;
21  
22      /// Returns a group element from hashing the input.
23      #[inline]
24      fn hash_to_group(&self, input: &[Self::Input]) -> Result<Self::Output> {
25          // Ensure that the input is not empty.
26          ensure!(!input.is_empty(), "Input to hash to group cannot be empty");
27          // Compute the group element as `MapToGroup(HashMany(input)[0]) + MapToGroup(HashMany(input)[1])`.
28          match self.hash_many(input, 2).iter().map(Elligator2::<E>::encode).collect_tuple() {
29              Some((Ok((h0, _)), Ok((h1, _)))) => Ok(h0 + h1),
30              _ => bail!("Poseidon failed to compute hash to group on the given input"),
31          }
32      }
33  }
34  
35  #[cfg(test)]
36  mod tests {
37      use super::*;
38      use alphavm_console_types::environment::Console;
39  
40      type CurrentEnvironment = Console;
41  
42      const ITERATIONS: u64 = 1000;
43  
44      macro_rules! check_hash_to_group {
45          ($poseidon:ident) => {{
46              // Initialize Poseidon.
47              let poseidon = $poseidon::<CurrentEnvironment>::setup("HashToGroupTest")?;
48  
49              // Ensure an empty input fails.
50              assert!(poseidon.hash_to_group(&[]).is_err());
51  
52              let mut rng = TestRng::default();
53  
54              for _ in 0..ITERATIONS {
55                  for num_inputs in 1..8 {
56                      // Sample random field elements.
57                      let inputs = (0..num_inputs).map(|_| Uniform::rand(&mut rng)).collect::<Vec<_>>();
58  
59                      // Compute the hash to group.
60                      let candidate = poseidon.hash_to_group(&inputs)?;
61                      assert!((*candidate).to_affine().is_on_curve());
62                      assert!((*candidate).to_affine().is_in_correct_subgroup_assuming_on_curve());
63                      assert_ne!(Group::<CurrentEnvironment>::zero(), candidate);
64                      assert_ne!(Group::<CurrentEnvironment>::generator(), candidate);
65  
66                      let candidate_cofactor_inv = candidate.div_by_cofactor();
67                      assert_eq!(candidate, candidate_cofactor_inv.mul_by_cofactor());
68                  }
69              }
70              Ok(())
71          }};
72      }
73  
74      #[test]
75      fn test_poseidon2_hash_to_group() -> Result<()> {
76          check_hash_to_group!(Poseidon2)
77      }
78  
79      #[test]
80      fn test_poseidon4_hash_to_group() -> Result<()> {
81          check_hash_to_group!(Poseidon4)
82      }
83  
84      #[test]
85      fn test_poseidon8_hash_to_group() -> Result<()> {
86          check_hash_to_group!(Poseidon8)
87      }
88  }