Struct elastic_elgamal::DiscreteLogTable
source · pub struct DiscreteLogTable<G: Group> { /* private fields */ }
Expand description
Lookup table for discrete logarithms.
For Ciphertext
s to be partially homomorphic, the encrypted values must be
group scalars linearly mapped to group elements: x -> [x]G
, where G
is the group
generator. After decryption it is necessary to map the decrypted group element back to a scalar
(i.e., get its discrete logarithm with base G
). Because of discrete logarithm assumption,
this task is computationally infeasible in the general case; however, if the possible range
of encrypted values is small, it is possible to “cheat” by precomputing mapping [x]G -> x
for all allowed x
ahead of time. This is exactly what DiscreteLogTable
does.
§Examples
let mut rng = thread_rng();
let receiver = Keypair::<Ristretto>::generate(&mut rng);
let ciphertexts = (0_u64..16)
.map(|i| receiver.public().encrypt(i, &mut rng));
// Assume that we know that the plaintext is in range 0..16,
// e.g., via a zero-knowledge proof.
let lookup_table = DiscreteLogTable::new(0..16);
// Then, we can use the lookup table to decrypt values.
// A single table may be shared for multiple decryption operations
// (i.e., it may be constructed ahead of time).
for (i, enc) in ciphertexts.enumerate() {
assert_eq!(
receiver.secret().decrypt(enc, &lookup_table),
Some(i as u64)
);
}
Implementations§
source§impl<G: Group> DiscreteLogTable<G>
impl<G: Group> DiscreteLogTable<G>
Trait Implementations§
Auto Trait Implementations§
impl<G> Freeze for DiscreteLogTable<G>
impl<G> RefUnwindSafe for DiscreteLogTable<G>where
G: RefUnwindSafe,
impl<G> Send for DiscreteLogTable<G>where
G: Send,
impl<G> Sync for DiscreteLogTable<G>where
G: Sync,
impl<G> Unpin for DiscreteLogTable<G>where
G: Unpin,
impl<G> UnwindSafe for DiscreteLogTable<G>where
G: UnwindSafe,
Blanket Implementations§
source§impl<T> BorrowMut<T> for Twhere
T: ?Sized,
impl<T> BorrowMut<T> for Twhere
T: ?Sized,
source§fn borrow_mut(&mut self) -> &mut T
fn borrow_mut(&mut self) -> &mut T
Mutably borrows from an owned value. Read more