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The audit recommends checking failure cases for from_bytes, from_bytes_unechecked, and from_repr. This isn't feasible. from_bytes is allowed to have non-canonical values. [0xff; 32] may accordingly be a valid point for non-SEC1-encoded curves. from_bytes_unchecked doesn't have a defined failure mode, and by name, unchecked, shouldn't necessarily fail. The audit acknowledges the tests should test for whatever result is 'appropriate', yet any result which isn't a failure on a valid element is appropriate. from_repr must be canonical, yet for a binary field of 2^n where n % 8 == 0, a [0xff; n / 8] repr would be valid.
35 lines
1.3 KiB
Markdown
35 lines
1.3 KiB
Markdown
# Ciphersuite
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Ciphersuites for elliptic curves premised on ff/group.
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### Secp256k1/P-256
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Secp256k1 and P-256 are offered via [k256](https://crates.io/crates/k256) and
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[p256](https://crates.io/crates/p256), two libraries maintained by
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[RustCrypto](https://github.com/RustCrypto).
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Their `hash_to_F` is the
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[IETF's hash to curve](https://www.ietf.org/archive/id/draft-irtf-cfrg-hash-to-curve-16.html),
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yet applied to their scalar field.
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### Ed25519/Ristretto
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Ed25519/Ristretto are offered via
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[dalek-ff-group](https://crates.io/crates/dalek-ff-group), an ff/group wrapper
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around [curve25519-dalek](https://crates.io/crates/curve25519-dalek).
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Their `hash_to_F` is the wide reduction of SHA2-512, as used in
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[RFC-8032](https://www.rfc-editor.org/rfc/rfc8032). This is also compliant with
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the draft
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[RFC-RISTRETTO](https://www.ietf.org/archive/id/draft-irtf-cfrg-ristretto255-decaf448-05.html).
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The domain-separation tag is naively prefixed to the message.
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### Ed448
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Ed448 is offered via [minimal-ed448](https://crates.io/crates/minimal-ed448), an
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explicitly not recommended, unaudited, incomplete Ed448 implementation, limited
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to its prime-order subgroup.
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Its `hash_to_F` is the wide reduction of SHAKE256, with a 114-byte output, as
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used in [RFC-8032](https://www.rfc-editor.org/rfc/rfc8032). The
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domain-separation tag is naively prefixed to the message.
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