Add ANSI-X9.63-KDF support: adjust comments on hashmaxlen and remove …

…unnecessary overflow check

ansi-x963-kdf/src/lib.rs

@@ -69,17 +69,16 @@ where
  return Err(Error::NoOutput);
  }
 
- // 1. Check if |Z| + |SharedInfo| + 4 >= hashmaxlen
+ // 1. Check that |Z| + |SharedInfo| + 4 < hashmaxlen
+ // where "hashmaxlen denote the maximum length in octets of messages that can be hashed using Hash".
+ // N.B.: `D::OutputSize::U64 * (u32::MAX as u64)`` is currently used as an approximation of hashmaxlen.
  if secret.len() as u64 + shared_info.len() as u64 + 4 >= D::OutputSize::U64 * (u32::MAX as u64)
  {
  return Err(Error::InputOverflow);
  }
 
- // Counter overflow is possible only on architectures with usize bigger than 4 bytes.
- const OVERFLOW_IS_POSSIBLE: bool = core::mem::size_of::<usize>() > 4;
-
  // 2. Check that keydatalen < hashlen × (2^32 − 1)
- if OVERFLOW_IS_POSSIBLE && (key.len() as u64 >= D::OutputSize::U64 * (u32::MAX as u64)) {
+ if key.len() as u64 >= D::OutputSize::U64 * (u32::MAX as u64) {
  return Err(Error::CounterOverflow);
  }