From 9f1c86bff37468e516128838a7a29ea8a9c4e6ad Mon Sep 17 00:00:00 2001
From: porcuquine <porcuquine@users.noreply.github.com>
Date: Wed, 3 Jun 2020 12:29:22 -0700
Subject: [PATCH] Add DomainSeparationTag type.

---
 storage-proofs/core/src/crypto/mod.rs             | 12 ++++++++++--
 storage-proofs/core/src/drgraph.rs                |  4 ++--
 storage-proofs/porep/src/stacked/vanilla/graph.rs |  3 ++-
 3 files changed, 14 insertions(+), 5 deletions(-)

diff --git a/storage-proofs/core/src/crypto/mod.rs b/storage-proofs/core/src/crypto/mod.rs
index e9872f776b..87cd38f33b 100644
--- a/storage-proofs/core/src/crypto/mod.rs
+++ b/storage-proofs/core/src/crypto/mod.rs
@@ -5,9 +5,17 @@ pub mod pedersen;
 pub mod sloth;
 pub mod xor;
 
-pub fn derive_porep_domain_seed(domain_separation_tag: &str, porep_id: [u8; 32]) -> [u8; 32] {
+pub struct DomainSeparationTag(&'static str);
+
+pub const DRSAMPLE_DST: DomainSeparationTag = DomainSeparationTag("Filecoin_DRSample");
+pub const FEISTEL_DST: DomainSeparationTag = DomainSeparationTag("Filecoin_Feistel");
+
+pub fn derive_porep_domain_seed(
+    domain_separation_tag: DomainSeparationTag,
+    porep_id: [u8; 32],
+) -> [u8; 32] {
     Sha256::new()
-        .chain(domain_separation_tag)
+        .chain(domain_separation_tag.0)
         .chain(porep_id)
         .result()
         .into()
diff --git a/storage-proofs/core/src/drgraph.rs b/storage-proofs/core/src/drgraph.rs
index 056e02f758..e4770db73e 100644
--- a/storage-proofs/core/src/drgraph.rs
+++ b/storage-proofs/core/src/drgraph.rs
@@ -7,7 +7,7 @@ use rand::{rngs::OsRng, Rng, SeedableRng};
 use rand_chacha::ChaCha8Rng;
 use sha2::{Digest, Sha256};
 
-use crate::crypto::derive_porep_domain_seed;
+use crate::crypto::{derive_porep_domain_seed, DRSAMPLE_DST};
 use crate::error::*;
 use crate::fr32::bytes_into_fr_repr_safe;
 use crate::hasher::{Hasher, PoseidonArity};
@@ -218,7 +218,7 @@ impl<H: Hasher> Graph<H> for BucketGraph<H> {
         );
 
         let mut drg_seed = [0; 28];
-        let raw_seed = derive_porep_domain_seed("Filecoin_DRSample", porep_id);
+        let raw_seed = derive_porep_domain_seed(DRSAMPLE_DST, porep_id);
         drg_seed.copy_from_slice(&raw_seed[..28]);
 
         Ok(BucketGraph {
diff --git a/storage-proofs/porep/src/stacked/vanilla/graph.rs b/storage-proofs/porep/src/stacked/vanilla/graph.rs
index f8941fd853..06296291c3 100644
--- a/storage-proofs/porep/src/stacked/vanilla/graph.rs
+++ b/storage-proofs/porep/src/stacked/vanilla/graph.rs
@@ -15,6 +15,7 @@ use storage_proofs_core::{
     crypto::{
         derive_porep_domain_seed,
         feistel::{self, FeistelPrecomputed},
+        FEISTEL_DST,
     },
     drgraph::BASE_DEGREE,
     drgraph::{BucketGraph, Graph},
@@ -187,7 +188,7 @@ where
         let bg_id = base_graph.identifier();
 
         let mut feistel_keys = [0u64; 4];
-        let raw_seed = derive_porep_domain_seed("Filecoin_Feistel", porep_id);
+        let raw_seed = derive_porep_domain_seed(FEISTEL_DST, porep_id);
         feistel_keys[0] = u64::from_le_bytes(raw_seed[0..8].try_into().unwrap());
         feistel_keys[1] = u64::from_le_bytes(raw_seed[8..16].try_into().unwrap());
         feistel_keys[2] = u64::from_le_bytes(raw_seed[16..24].try_into().unwrap());