Ed25519 Curve Operations in bellperson

bellperson gadget for ed22519 curve operations (point addition, scalar multiplication). It is inspired by the approach taken by circom-ecdsa.

Experimental code, do not use in production

Scalar multiplication with a 4-bit lookup gives the minimum number of constraints (about 1.3 million).

$ cargo t -r window_m -- --nocapture

running 1 test
lookup 3, Num constraints = 1347012
lookup 4, Num constraints = 1294624
lookup 5, Num constraints = 1307404
lookup 6, Num constraints = 1406882
test nonnative::circuit::tests::alloc_affine_scalar_multiplication_window_m ... ok

Repo Organization

• The scratch directory contains prototyping code and notes
• The src directory has the Rust code
  • The src/field.rs and src/curve.rs modules have the non-circuit and non-limbed versions of the ed25519 base field and curve.
  • The src/nonnative/vanilla.rs module has the non-circuit limbed version of the ed25519 base field. Not all the functions here are used in the gadget. Some are the result of prototyping limbed arithmetic and will be removed in the future.
  • The src/nonnative/circuit.rs module has the circuits

License

Licensed under MIT license as the field module is based on an earlier version of the MIT-licensed crypto/dalek-ff-group crate of Serai.