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sdk/note: ElGamal decrypt()

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parazyd
2023-03-08 11:27:20 +01:00
parent 0b5c2393e1
commit 5cc394ae21
1 changed files with 26 additions and 6 deletions
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32
src/sdk/src/crypto/note.rs
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@@ -19,7 +19,7 @@
use chacha20poly1305::{AeadInPlace, ChaCha20Poly1305, KeyInit};
use darkfi_serial::{Decodable, Encodable, SerialDecodable, SerialEncodable};
use halo2_proofs::arithmetic::Field;
use pasta_curves::{group::Group, pallas};
use pasta_curves::pallas;
use rand_core::{CryptoRng, RngCore};
use super::{diffie_hellman, poseidon_hash, util::mod_r_p, PublicKey, SecretKey};
@@ -82,6 +82,7 @@ impl AeadEncryptedNote {
/// An encrypted note using an ElGamal scheme verifiable in ZK
pub struct ElGamalEncryptedNote<const N: usize> {
pub encrypted_values: [pallas::Base; N],
pub ephem_public: PublicKey,
}
impl<const N: usize> ElGamalEncryptedNote<N> {
@@ -91,9 +92,11 @@ impl<const N: usize> ElGamalEncryptedNote<N> {
rng: &mut (impl CryptoRng + RngCore),
) -> Result<Self, ContractError> {
// Derive shared secret using DH
let ephem_secret = mod_r_p(pallas::Base::random(rng));
let (ephem_pub_x, ephem_pub_y) = PublicKey::from(public.inner() * ephem_secret).xy();
let shared_secret = poseidon_hash([ephem_pub_x, ephem_pub_y]);
let ephem_secret = pallas::Base::random(rng);
let (ss_x, ss_y) = PublicKey::from(public.inner() * mod_r_p(ephem_secret)).xy();
let shared_secret = poseidon_hash([ss_x, ss_y]);
let ephem_public = PublicKey::from_secret(SecretKey::from(ephem_secret));
let mut blinds = [pallas::Base::zero(); N];
for i in 0..N {
@@ -105,11 +108,24 @@ impl<const N: usize> ElGamalEncryptedNote<N> {
encrypted_values[i] = values[i] + blinds[i];
}
Ok(Self { encrypted_values })
Ok(Self { encrypted_values, ephem_public })
}
pub fn decrypt(&self) -> Result<[pallas::Base; N], ContractError> {
pub fn decrypt(&self, secret: &SecretKey) -> Result<[pallas::Base; N], ContractError> {
// Derive shared secret using DH
let (ss_x, ss_y) =
PublicKey::from(self.ephem_public.inner() * mod_r_p(secret.inner())).xy();
let shared_secret = poseidon_hash([ss_x, ss_y]);
let mut blinds = [pallas::Base::zero(); N];
for i in 0..N {
blinds[i] = poseidon_hash([shared_secret, pallas::Base::from(i as u64 + 1)]);
}
let mut decrypted_values = [pallas::Base::zero(); N];
for i in 0..N {
decrypted_values[i] = self.encrypted_values[i] - blinds[i];
}
Ok(decrypted_values)
}
@@ -144,5 +160,9 @@ mod tests {
let encrypted_note =
ElGamalEncryptedNote::encrypt(plain_values, &keypair.public, &mut OsRng).unwrap();
let decrypted_values = encrypted_note.decrypt(&keypair.secret).unwrap();
assert_eq!(plain_values, decrypted_values);
}
}