elliptic-curve: bump crypto-bigint to v0.7.0-rc.8 (#2025)

This notably enables the `subtle` feature of `hybrid-array`. This
apparently broke `digest` where previously the unsized coercion was
working until an explicit impl was available. So this PR also includes a
small fix to `digest`.

Author: tarcieri

Cargo.lock

@@ -133,7 +133,7 @@ impl<T: Update + FixedOutput + MacMarker> Mac for T {
         if n != Self::OutputSize::USIZE {
             return Err(MacError);
         }
-        let choice = self.finalize_fixed().ct_eq(tag);
+        let choice = self.finalize_fixed().as_slice().ct_eq(tag);
         if choice.into() { Ok(()) } else { Err(MacError) }
     }
 
@@ -146,7 +146,7 @@ impl<T: Update + FixedOutput + MacMarker> Mac for T {
         if n != Self::OutputSize::USIZE {
             return Err(MacError);
         }
-        let choice = self.finalize_fixed_reset().ct_eq(tag);
+        let choice = self.finalize_fixed_reset().as_slice().ct_eq(tag);
         if choice.into() { Ok(()) } else { Err(MacError) }
     }
 

digest/src/mac.rs

@@ -18,7 +18,7 @@ and public/secret keys composed thereof.
 
 [dependencies]
 base16ct = "0.3"
-crypto-bigint = { version = "0.7.0-rc.6", default-features = false, features = ["rand_core", "hybrid-array", "zeroize"] }
+crypto-bigint = { version = "0.7.0-rc.8", default-features = false, features = ["rand_core", "hybrid-array", "zeroize"] }
 hybrid-array = { version = "0.4", default-features = false, features = ["zeroize"] }
 rand_core = { version = "0.9.0", default-features = false }
 subtle = { version = "2.6", default-features = false }