tari-project / tari-crypto / 6335787182

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feat!: differentiate scalar parsing from byte arrays (#194)

Currently, creating a scalar `RistrettoSecretKey` [from a byte
array](https://github.com/tari-project/tari-crypto/blob/053119f21/src/ristretto/ristretto_keys.rs#L90-L100)
performs modular reduction on 32 bytes. For cases where the input is
intended to be canonical, this is suboptimal. For cases where the input
is produced from a hashing operation, wide reduction should be used to
mitigate bias.

This work renames `SecretKey::from_bytes` to
`SecretKey::from_canonical_bytes` to support an underlying `ByteArray`
trait update. In the case of `RistrettoSecretKey`, it uses the curve
library's canonical parser and returns an error if the provided byte
slice is not a canonical scalar encoding.

It also adds a new `SecretKey::from_uniform_bytes` function that uses
wide reduction. For constructions like signatures and KDFs that use
hashing operations to produce scalar values, this function is used and
the underlying hashers are updated to produce 64-byte output in the case
of `RistrettoSecretKey`.

It updates the Schnorr signature API to support raw signing and
verification using challenge byte slices that are either canonical
encodings or uniform. It renames several existing functions for clarity.

It corrects a few typos that were discovered along the way.

Closes #189.

BREAKING CHANGE: This changes the way that scalars are produced from
byte arrays, modifies the `SecretKey` trait and corresponding
`RistrettoSecretKey` implementation, and updates the Schnorr signature
API.

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