Commits on Feb 1, 2023

1. elliptic-curve: consolidate AffineCoordinates trait …

   See RustCrypto/elliptic-curves#50 for some historic context.
   
   After being able to get by on `AffineXCoordinate` for generic ECDH and
   ECDSA, #1199 added an `AffineYIsOdd` trait which was needed to enable
   the generic ECDSA implementation in the `ecdsa` crate to compute the
   "recovery ID" for signatures (which is effectively point compression for
   the `R` curve point).
   
   This commit consolidates `AffineXCoordinate` and `AffineYIsOdd` into
   an `AffineCoordinates` trait.
   
   Some observations since prior discussion in
   RustCrypto/elliptic-curves#50:
   
   - Access to coordinates is through bytes, namely `FieldBytes`. This is
     so as to avoid exposing a crate's field element type. This approach
     isn't type safe (base field elements and scalar field elements share
     the same serialization) but does make ECDSA's weird reduction of a
     base field element into the scalar field straightforward in generic
     code.
   - Prior to this attempts were made to extract ECDSA-specific bits into a
     trait to handle these conversions, but it complicates both writing
     generic code and optimizing performance. While this still might be
     worth exploring, so far those explorations have largely failed.
   - Generally there have been a lot of requests for coordinate access
     specifically for things like point serialization formats. We ended up
     adding "compaction" support upstream but we have had requests for
     several other formats (e.g. Elligator Squared) where direct coordinate
     access would be useful.
   
   This trait can hopefully be replaced by a coordinate access API provided
   by the `group` crate in the future. See zkcrypto/group#30

   

   tarcieri committed Feb 1, 2023
   Configuration menu

   • View commit details
   • Copy full SHA for a7332bc
   • Browse repository at this point

   Copy the full SHA

   a7332bc View commit details

   Browse the repository at this point in the history