Update digest requirement from 0.7 to 0.8 (#141)

* Update `digest` and `blake2` requirement from 0.7 to 0.8

Updates the requirements on [digest](https://github.com/RustCrypto/traits) to permit the latest version.
- [Release notes](https://github.com/RustCrypto/traits/releases)
- [Commits](https://github.com/RustCrypto/traits/compare/digest_v0.7.2...digest-v0.8.1)

Co-authored-by: dependabot-preview[bot] <27856297+dependabot-preview[bot]@users.noreply.github.com>
Co-authored-by: Pratyush Mishra <pratyushmishra@berkeley.edu>

crypto-primitives/src/prf/blake2s/constraints.rs

@@ -530,12 +530,11 @@ impl<ConstraintF: PrimeField> PRFGadget<Blake2s, ConstraintF> for Blake2sGadget
 #[cfg(test)]
 mod test {
     use algebra::jubjub::Fq as Fr;
-    use digest::{FixedOutput, Input};
     use rand::{Rng, SeedableRng};
     use rand_xorshift::XorShiftRng;
 
     use crate::prf::blake2s::{constraints::blake2s_gadget, Blake2s as B2SPRF};
-    use blake2::Blake2s;
+    use blake2::VarBlake2s;
     use r1cs_core::ConstraintSystem;
 
     use super::Blake2sGadget;
@@ -634,13 +633,15 @@ mod test {
         let mut rng = XorShiftRng::seed_from_u64(1231275789u64);
 
         for input_len in (0..32).chain((32..256).filter(|a| a % 8 == 0)) {
-            let mut h = Blake2s::new_keyed(&[], 32);
+            use digest::*;
+            let mut h = VarBlake2s::new_keyed(&[], 32);
 
             let data: Vec<u8> = (0..input_len).map(|_| rng.gen()).collect();
 
-            h.process(&data);
+            h.input(&data);
 
-            let hash_result = h.fixed_result();
+            let mut hash_result = Vec::with_capacity(h.output_size());
+            h.variable_result(|res| hash_result.extend_from_slice(res));
 
             let mut cs = TestConstraintSystem::<Fr>::new();
 
@@ -663,7 +664,6 @@ mod test {
             assert!(cs.is_satisfied());
 
             let mut s = hash_result
-                .as_ref()
                 .iter()
                 .flat_map(|&byte| (0..8).map(move |i| (byte >> i) & 1u8 == 1u8));
 

crypto-primitives/src/prf/blake2s/mod.rs

@@ -1,5 +1,5 @@
 use alloc::vec::Vec;
-use blake2::Blake2s as b2s;
+use blake2::{Blake2s as B2s, VarBlake2s};
 use digest::Digest;
 
 use super::PRF;
@@ -18,7 +18,7 @@ impl PRF for Blake2s {
 
     fn evaluate(seed: &Self::Seed, input: &Self::Input) -> Result<Self::Output, CryptoError> {
         let eval_time = start_timer!(|| "Blake2s::Eval");
-        let mut h = b2s::new();
+        let mut h = B2s::new();
         h.input(seed.as_ref());
         h.input(input.as_ref());
         let mut result = [0u8; 32];
@@ -80,10 +80,13 @@ impl Blake2sWithParameterBlock {
     }
 
     pub fn evaluate(&self, input: &[u8]) -> Vec<u8> {
+        use digest::*;
         let eval_time = start_timer!(|| "Blake2sWithParameterBlock::Eval");
-        let mut h = b2s::with_parameter_block(&self.parameters());
+        let mut h = VarBlake2s::with_parameter_block(&self.parameters());
         h.input(input.as_ref());
         end_timer!(eval_time);
-        h.result().to_vec()
+        let mut buf = Vec::with_capacity(h.output_size());
+        h.variable_result(|res| buf.extend_from_slice(res));
+        buf
     }
 }