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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 All operations are implemented using constant-time logic (no
secret-dependent branches, no secret-dependent memory accesses), secret-dependent branches, no secret-dependent memory accesses),
unless specifically marked as being variable-time code. unless specifically marked as being variable-time code.
When using the `nightly` feature, we also insert an optimization We believe that our constant-time logic is lowered to constant-time
barrier before every conditional move or assignment. 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 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 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. 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 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/ [docs-internal]: https://doc-internal.dalek.rs/curve25519_dalek/
[criterion]: https://github.com/japaric/criterion.rs [criterion]: https://github.com/japaric/criterion.rs
[parallel_doc]: https://doc-internal.dalek.rs/curve25519_dalek/backend/avx2/index.html [parallel_doc]: https://doc-internal.dalek.rs/curve25519_dalek/backend/avx2/index.html
[subtle_doc]: https://doc.dalek.rs/subtle/