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Add prf_expand() and use that in sapling key derivation

This commit is contained in:
Deirdre Connolly 2020-04-02 21:34:18 -04:00 committed by Deirdre Connolly
parent b3db623e29
commit 13f2c229d9
1 changed files with 22 additions and 24 deletions
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46
zebra-chain/src/keys/sapling.rs
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@ -17,6 +17,21 @@ use rand_core::{CryptoRng, RngCore};
#[cfg(test)]
use proptest::{arbitrary::Arbitrary, array, prelude::*};
/// Invokes Blake2b-512 as PRF^expand with parameter t, to derive a
/// SpendAuthorizingKey and ProofAuthorizingKey from SpendingKey.
///
/// https://zips.z.cash/protocol/protocol.pdf#concreteprfs
fn prf_expand(sk: [u8; 32], t: u8) -> [u8; 64] {
let hash = blake2b_simd::Params::new()
.hash_length(64)
.personal(b"Zcash_ExpandSeed")
.to_state()
.update(&sk[..])
.update(&[t])
.finalize();
return *hash.as_array();
}
// TODO: replace with reference to redjubjub or jubjub when merged and
// exported.
type Scalar = jubjub::Fr;
@ -66,15 +81,9 @@ impl From<SpendingKey> for SpendAuthorizationKey {
/// https://zips.z.cash/protocol/protocol.pdf#saplingkeycomponents
/// https://zips.z.cash/protocol/protocol.pdf#concreteprfs
fn from(spending_key: SpendingKey) -> SpendAuthorizationKey {
let hash = blake2b_simd::Params::new()
.hash_length(64)
.personal(b"Zcash_ExpandSeed")
.to_state()
.update(&spending_key.0[..])
.update(&[0])
.finalize();
let hash_bytes = prf_expand(spending_key.0, 0);
Self(Scalar::from_bytes_wide(hash.as_array()))
Self(Scalar::from_bytes_wide(&hash_bytes))
}
}
@ -103,15 +112,9 @@ impl From<SpendingKey> for ProofAuthorizingKey {
/// https://zips.z.cash/protocol/protocol.pdf#saplingkeycomponents
/// https://zips.z.cash/protocol/protocol.pdf#concreteprfs
fn from(spending_key: SpendingKey) -> ProofAuthorizingKey {
let hash = blake2b_simd::Params::new()
.hash_length(64)
.personal(b"Zcash_ExpandSeed")
.to_state()
.update(&spending_key.0[..])
.update(&[1])
.finalize();
let hash_bytes = prf_expand(spending_key.0, 1);
Self(Scalar::from_bytes_wide(hash.as_array()))
Self(Scalar::from_bytes_wide(&hash_bytes))
}
}
@ -133,16 +136,11 @@ impl From<SpendingKey> for OutgoingViewingKey {
/// https://zips.z.cash/protocol/protocol.pdf#saplingkeycomponents
/// https://zips.z.cash/protocol/protocol.pdf#concreteprfs
fn from(spending_key: SpendingKey) -> OutgoingViewingKey {
let hash = blake2b_simd::Params::new()
.hash_length(64)
.personal(b"Zcash_ExpandSeed")
.to_state()
.update(&spending_key.0[..])
.update(&[2])
.finalize();
let hash_bytes = prf_expand(spending_key.0, 2);
let mut bytes = [0u8; 32];
bytes[..].copy_from_slice(hash.as_bytes());
bytes[..].copy_from_slice(&hash_bytes);
Self(bytes)
}
}