pub struct DiscreteLogTable<G: Group> { /* private fields */ }
Expand description

Lookup table for discrete logarithms.

For Ciphertexts 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§

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impl<G: Group> DiscreteLogTable<G>

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pub fn new(values: impl IntoIterator<Item = u64>) -> Self

Creates a lookup table for the specified values.

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pub fn get(&self, decrypted_element: &G::Element) -> Option<u64>

Gets the discrete log of decrypted_element, or None if it is not present among values stored in this table.

Trait Implementations§

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impl<G: Clone + Group> Clone for DiscreteLogTable<G>

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fn clone(&self) -> DiscreteLogTable<G>

Returns a copy of the value. Read more
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fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source. Read more
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impl<G: Debug + Group> Debug for DiscreteLogTable<G>

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fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter. Read more

Auto Trait Implementations§

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impl<G> Freeze for DiscreteLogTable<G>

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impl<G> RefUnwindSafe for DiscreteLogTable<G>
where G: RefUnwindSafe,

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impl<G> Send for DiscreteLogTable<G>
where G: Send,

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impl<G> Sync for DiscreteLogTable<G>
where G: Sync,

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impl<G> Unpin for DiscreteLogTable<G>
where G: Unpin,

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impl<G> UnwindSafe for DiscreteLogTable<G>
where G: UnwindSafe,

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impl<T> Any for T
where T: 'static + ?Sized,

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fn type_id(&self) -> TypeId

Gets the TypeId of self. Read more
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impl<T> Borrow<T> for T
where T: ?Sized,

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fn borrow(&self) -> &T

Immutably borrows from an owned value. Read more
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impl<T> BorrowMut<T> for T
where T: ?Sized,

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fn borrow_mut(&mut self) -> &mut T

Mutably borrows from an owned value. Read more
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impl<T> From<T> for T

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fn from(t: T) -> T

Returns the argument unchanged.

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impl<T, U> Into<U> for T
where U: From<T>,

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fn into(self) -> U

Calls U::from(self).

That is, this conversion is whatever the implementation of From<T> for U chooses to do.

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impl<T> Same for T

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type Output = T

Should always be Self
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impl<T> ToOwned for T
where T: Clone,

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type Owned = T

The resulting type after obtaining ownership.
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fn to_owned(&self) -> T

Creates owned data from borrowed data, usually by cloning. Read more
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fn clone_into(&self, target: &mut T)

Uses borrowed data to replace owned data, usually by cloning. Read more
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impl<T, U> TryFrom<U> for T
where U: Into<T>,

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type Error = Infallible

The type returned in the event of a conversion error.
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fn try_from(value: U) -> Result<T, <T as TryFrom<U>>::Error>

Performs the conversion.
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impl<T, U> TryInto<U> for T
where U: TryFrom<T>,

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type Error = <U as TryFrom<T>>::Error

The type returned in the event of a conversion error.
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fn try_into(self) -> Result<U, <U as TryFrom<T>>::Error>

Performs the conversion.
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impl<V, T> VZip<V> for T
where V: MultiLane<T>,

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fn vzip(self) -> V