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Clarify wording on the nightly feature and CT

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Closes #147
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Henry de Valence 2018-07-16 14:30:14 -07:00
parent ca8c46220b
commit 8d46eacd2c
1 changed files with 11 additions and 4 deletions
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README.md
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@ -102,13 +102,19 @@ group.
All operations are implemented using constant-time logic (no
secret-dependent branches, no secret-dependent memory accesses),
unless specifically marked as being variable-time code.
When using the `nightly` feature, we also insert an optimization
barrier before every conditional move or assignment.
We believe that our constant-time logic is lowered to constant-time
assembly, at least on `x86_64` targets.
As an additional guard against possible future compiler optimizations, the
`nightly` feature places an optimization barrier before every
conditional move or assignment. More details can be found in [the
documentation for the `subtle` crate][subtle_doc]. This is
recommended, but not required.
Some functionality (e.g., multiscalar multiplication or batch
inversion) requires heap allocation for temporary buffers. **All
inversion) requires heap allocation for temporary buffers. All
heap-allocated buffers of potentially secret data are explicitly
zeroed before release**.
zeroed before release.
However, we do not attempt to zero stack data, for two reasons.
First, it's not possible to do so correctly: we don't have control
@ -186,3 +192,4 @@ contributions.
[docs-internal]: https://doc-internal.dalek.rs/curve25519_dalek/
[criterion]: https://github.com/japaric/criterion.rs
[parallel_doc]: https://doc-internal.dalek.rs/curve25519_dalek/backend/avx2/index.html
[subtle_doc]: https://doc.dalek.rs/subtle/