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Deduplicate Sapling key agreement logic

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This commit is contained in:
Jack Grigg 2019-03-23 17:51:30 +13:00
parent 247f3fb038
commit 2b1583d75f
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GPG Key ID: 9E8255172BBF9898
3 changed files with 37 additions and 17 deletions
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11
librustzcash/src/rustzcash.rs
View File

@ -58,7 +58,7 @@ use std::ffi::OsString;
use std::os::windows::ffi::OsStringExt;
use sapling_crypto::primitives::{ProofGenerationKey, ViewingKey};
use zcash_primitives::{sapling::spend_sig, JUBJUB};
use zcash_primitives::{note_encryption::sapling_ka_agree, sapling::spend_sig, JUBJUB};
use zcash_proofs::{
load_parameters,
sapling::{CommitmentTreeWitness, SaplingProvingContext, SaplingVerificationContext},
@ -536,15 +536,12 @@ pub extern "system" fn librustzcash_sapling_ka_agree(
Err(_) => return false,
};
// Multiply by 8
let p = p.mul_by_cofactor(&JUBJUB);
// Multiply by sk
let p = p.mul(sk, &JUBJUB);
// Compute key agreement
let ka = sapling_ka_agree(&sk, &p);
// Produce result
let result = unsafe { &mut *result };
p.write(&mut result[..]).expect("length is not 32 bytes");
result.copy_from_slice(&ka);
true
}

16
sapling-crypto/src/jubjub/edwards.rs
View File

@ -45,6 +45,14 @@ fn convert_subgroup<E: JubjubEngine, S1, S2>(from: &Point<E, S1>) -> Point<E, S2
}
}
impl<E: JubjubEngine> From<&Point<E, Unknown>> for Point<E, Unknown>
{
fn from(p: &Point<E, Unknown>) -> Point<E, Unknown>
{
p.clone()
}
}
impl<E: JubjubEngine> From<Point<E, PrimeOrder>> for Point<E, Unknown>
{
fn from(p: Point<E, PrimeOrder>) -> Point<E, Unknown>
@ -53,6 +61,14 @@ impl<E: JubjubEngine> From<Point<E, PrimeOrder>> for Point<E, Unknown>
}
}
impl<E: JubjubEngine> From<&Point<E, PrimeOrder>> for Point<E, Unknown>
{
fn from(p: &Point<E, PrimeOrder>) -> Point<E, Unknown>
{
convert_subgroup(p)
}
}
impl<E: JubjubEngine, Subgroup> Clone for Point<E, Subgroup>
{
fn clone(&self) -> Self {

27
zcash_primitives/src/note_encryption.rs
View File

@ -128,14 +128,21 @@ fn generate_esk() -> Fs {
Fs::to_uniform(&buffer[..])
}
fn sapling_ka_agree(esk: &Fs, pk_d: &edwards::Point<Bls12, PrimeOrder>) -> Vec<u8> {
let ka = pk_d
.mul(esk.into_repr(), &JUBJUB)
.double(&JUBJUB)
.double(&JUBJUB)
.double(&JUBJUB);
let mut result = Vec::with_capacity(32);
ka.write(&mut result).expect("length is not 32 bytes");
pub fn sapling_ka_agree<'a, P>(esk: &Fs, pk_d: &'a P) -> [u8; 32]
where
edwards::Point<Bls12, Unknown>: From<&'a P>,
{
let p: edwards::Point<Bls12, Unknown> = pk_d.into();
// Multiply by 8
let p = p.mul_by_cofactor(&JUBJUB);
// Multiply by esk
let p = p.mul(*esk, &JUBJUB);
// Produce result
let mut result = [0; 32];
p.write(&mut result[..]).expect("length is not 32 bytes");
result
}
@ -294,7 +301,7 @@ pub fn try_sapling_note_decryption(
cmu: &Fr,
enc_ciphertext: &[u8],
) -> Option<(Note<Bls12>, PaymentAddress<Bls12>, Memo)> {
let shared_secret = sapling_ka_agree(&ivk, &epk);
let shared_secret = sapling_ka_agree(ivk, epk);
let key = kdf_sapling(&shared_secret, &epk);
let mut plaintext = Vec::with_capacity(564);
@ -328,7 +335,7 @@ pub fn try_sapling_compact_note_decryption(
cmu: &Fr,
enc_ciphertext: &[u8],
) -> Option<(Note<Bls12>, PaymentAddress<Bls12>)> {
let shared_secret = sapling_ka_agree(&ivk, &epk);
let shared_secret = sapling_ka_agree(ivk, epk);
let key = kdf_sapling(&shared_secret, &epk);
let nonce = [0u8; 12];