Remove "as", except for floats as needed

Also updates Bulletproofs from C to not be length prefixed, yet rather 
have Rust calculate their length.

Corrects an error in key_gen where self was blamed, instead of the 
faulty participant.

crypto/frost/src/key_gen.rs

@@ -200,7 +200,7 @@ fn complete_r2<R: RngCore + CryptoRng, C: Curve>(
   // Step 2. Verify each share
   let mut shares = HashMap::new();
   for (l, share) in serialized {
-    shares.insert(l, C::F_from_slice(&share).map_err(|_| FrostError::InvalidShare(params.i()))?);
+    shares.insert(l, C::F_from_slice(&share).map_err(|_| FrostError::InvalidShare(l))?);
   }
 
   // Calculate the exponent for a given participant and apply it to a series of commitments
@@ -240,6 +240,7 @@ fn complete_r2<R: RngCore + CryptoRng, C: Curve>(
   // Stripe commitments per t and sum them in advance. Calculating verification shares relies on
   // these sums so preprocessing them is a massive speedup
   // If these weren't just sums, yet the tables used in multiexp, this would be further optimized
+  // As of right now, each multiexp will regenerate them
   let mut stripes = Vec::with_capacity(usize::from(params.t()));
   for t in 0 .. usize::from(params.t()) {
     stripes.push(commitments.values().map(|commitments| commitments[t]).sum());

crypto/frost/src/sign.rs

@@ -143,7 +143,7 @@ fn sign_with_share<C: Curve, A: Algorithm<C>>(
 
       let commitments = commitments.remove(l).unwrap();
       let mut read_commitment = |c, label| {
-        let commitment = &commitments[c .. c + C::G_len()];
+        let commitment = &commitments[c .. (c + C::G_len())];
         transcript.append_message(label, commitment);
         C::G_from_slice(commitment).map_err(|_| FrostError::InvalidCommitment(*l))
       };

crypto/frost/src/tests/literal/secp256k1.rs

@@ -27,7 +27,7 @@ impl Curve for Secp256k1 {
   }
 
   fn id_len() -> u8 {
-    Self::id().len() as u8
+    u8::try_from(Self::id().len()).unwrap()
   }
 
   fn generator() -> Self::G {

crypto/multiexp/src/lib.rs

@@ -55,7 +55,7 @@ pub fn multiexp<
     }
 
     for s in 0 .. tables.len() {
-      res += tables[s][nibbles[s][b] as usize];
+      res += tables[s][usize::from(nibbles[s][b])];
     }
   }
   res
@@ -75,7 +75,7 @@ pub fn multiexp_vartime<
 
     for s in 0 .. tables.len() {
       if nibbles[s][b] != 0 {
-        res += tables[s][nibbles[s][b] as usize];
+        res += tables[s][usize::from(nibbles[s][b])];
       }
     }
   }