ctutils: remove (Partial)Eq impls for Choice#1315
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These were added in #1266 to simplify a migration from `subtle::Choice` with a TODO to eventually remove them. They're used in tests, including it seems, the ones for `ctutils`. They're problematic because the goal of `Choice` is to be an opaque boolean-alternative for use in constant-time code, but especially a derived `Partial(Eq)` can peek inside them and bypass the encapsulation they're trying to provide in a way that's easy to branch on. Now that `crypto-bigint` has actually been migrated to `ctutils`, we can followup on removing these as part of some final breaking changes.
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These were added in #1266 to simplify a migration from
subtle::Choicewith a TODO to eventually remove them. They're used in tests, including it seems, the ones forctutils.They're problematic because the goal of
Choiceis to be an opaque boolean-alternative for use in constant-time code, but especially a derivedPartial(Eq)can peek inside them and bypass the encapsulation they're trying to provide in a way that's easy to branch on.Now that
crypto-biginthas actually been migrated toctutils, we can followup on removing these as part of some final breaking changes.