**Problem**: Although rand has the declaration ``` impl<R: BlockRngCore + CryptoRng> CryptoRng for BlockRng<R> {} ``` there's no equivalent for `BlockRng64<R>`, so a `BlockRng64` can't pass any compile-time check for a `CryptoRng` even when the core does.
Problem: Although rand has the declaration
there's no equivalent for
BlockRng64<R>, so aBlockRng64can't pass any compile-time check for aCryptoRngeven when the core does.