mirror of https://github.com/zcash/orchard.git
76 lines
2.4 KiB
Rust
76 lines
2.4 KiB
Rust
use blake2b_simd::Params;
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const PRF_EXPAND_PERSONALIZATION: &[u8; 16] = b"Zcash_ExpandSeed";
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/// The set of domains in which $PRF^\mathsf{expand}$ is defined.
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pub(crate) enum PrfExpand {
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Esk,
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Rcm,
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OrchardAsk,
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OrchardNk,
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OrchardRivk,
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Psi,
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OrchardZip32Child,
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OrchardDkOvk,
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OrchardRivkInternal,
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}
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impl PrfExpand {
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fn domain_separator(&self) -> u8 {
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match self {
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Self::Esk => 0x04,
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Self::Rcm => 0x05,
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Self::OrchardAsk => 0x06,
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Self::OrchardNk => 0x07,
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Self::OrchardRivk => 0x08,
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Self::Psi => 0x09,
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Self::OrchardZip32Child => 0x81,
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Self::OrchardDkOvk => 0x82,
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Self::OrchardRivkInternal => 0x83,
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}
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}
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/// Expands the given secret key in this domain, with no additional data.
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///
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/// $PRF^\mathsf{expand}(sk, dst) := BLAKE2b-512("Zcash_ExpandSeed", sk || dst)$
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///
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/// Defined in [Zcash Protocol Spec § 5.4.2: Pseudo Random Functions][concreteprfs].
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///
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/// [concreteprfs]: https://zips.z.cash/protocol/nu5.pdf#concreteprfs
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pub(crate) fn expand(self, sk: &[u8]) -> [u8; 64] {
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self.with_ad_slices(sk, &[])
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}
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/// Expands the given secret key in this domain, with the given additional data.
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///
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/// $PRF^\mathsf{expand}(sk, dst, t) := BLAKE2b-512("Zcash_ExpandSeed", sk || dst || t)$
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///
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/// Defined in [Zcash Protocol Spec § 5.4.2: Pseudo Random Functions][concreteprfs].
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///
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/// [concreteprfs]: https://zips.z.cash/protocol/nu5.pdf#concreteprfs
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pub(crate) fn with_ad(self, sk: &[u8], t: &[u8]) -> [u8; 64] {
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self.with_ad_slices(sk, &[t])
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}
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/// Expands the given secret key in this domain, with additional data concatenated
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/// from the given slices.
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///
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/// $PRF^\mathsf{expand}(sk, dst, a, b, ...) := BLAKE2b-512("Zcash_ExpandSeed", sk || dst || a || b || ...)$
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///
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/// Defined in [Zcash Protocol Spec § 5.4.2: Pseudo Random Functions][concreteprfs].
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///
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/// [concreteprfs]: https://zips.z.cash/protocol/nu5.pdf#concreteprfs
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pub(crate) fn with_ad_slices(self, sk: &[u8], ts: &[&[u8]]) -> [u8; 64] {
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let mut h = Params::new()
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.hash_length(64)
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.personal(PRF_EXPAND_PERSONALIZATION)
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.to_state();
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h.update(sk);
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h.update(&[self.domain_separator()]);
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for t in ts {
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h.update(t);
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}
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*h.finalize().as_array()
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}
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}
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