Crypto MUST NOT become part of the Rust standard library, because Rust's compatibility guarantees would have to be broken when any underlying cryptographic prim

Crypto MUST NOT become part of the Rust standard library, because Rust's compatibility guarantees would have to be broken when any underlying cryptographic primitive or protocol is broken (or worryingly weakened) and needs to be removed. While that could be done with the "unsoundness fix" escape hatch, it's better to minimize such changes. I'd like to see an "extension" library managed like the standard library (and shipped with Rust, included in the prelude, etc) but with SemVer, so that breaking changes could be made more easily.