x25519: use manual impls instead of zeroize_derive - #776
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The types involved are all simple 1-tuple newtypes where zeroization only involves calling `zeroize` on the inner type, making all of the involved impls relatively trivial. Avoiding custom derive arguably improves auditability as you don't need to expand a proc macro to see the resulting code. It decreases the number of required dependencies in order for the `zeroize` feature to work, where some of those dependencies are incredibly heavy (particularly `syn`).
tarcieri
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Jul 7, 2025
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| impl Drop for EphemeralSecret { | ||
| fn drop(&mut self) { | ||
| #[cfg(feature = "zeroize")] | ||
| self.zeroize(); | ||
| } | ||
| } |
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The reason for gating the inner zeroize invocation on the feature as opposed to the whole Drop impl is so enabling the zeroize feature doesn't change the Drop bounds / presence of drop glue. There are some weird edge cases around this approach avoids.
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Note: this is largely a workaround for the I think this upstream change should take care of the problem going forward, as well: RustCrypto/utils#1190 |
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The types involved are all simple 1-tuple newtypes where zeroization only involves calling
zeroizeon the inner type, making all of the involved impls relatively trivial.Avoiding custom derive arguably improves auditability as you don't need to expand a proc macro to see the resulting code. It decreases the number of required dependencies in order for the
zeroizefeature to work, where some of those dependencies are incredibly heavy (particularlysyn).