doc: add and unify return statements in crypto.md

Conform return statements to the style guide and tool parsers.

Also bring back a description fragment
that seems to be erroneously deleted in
1e07acd

Backport-PR-URL: #22870
PR-URL: #19853
Reviewed-By: James M Snell <[email protected]>
Reviewed-By: Rich Trott <[email protected]>
Reviewed-By: Luigi Pinca <[email protected]>
Reviewed-By: Gibson Fahnestock <[email protected]>
Reviewed-By: Trivikram Kamat <[email protected]>
Reviewed-By: Ruben Bridgewater <[email protected]>
Reviewed-By: Tobias Nießen <[email protected]>