ic-ec — elliptic-curve cryptography

Curve25519 in two guises:

• [X25519] — RFC 7748 key agreement.
• [Ed25519] — RFC 8032 signatures.

Both are built on a shared constant-time field implementation ([field::Fe]) with 51-bit limbs.

use ic_ec::X25519;
use ic_core::traits::KeyAgreement;

let alice_sk = [0x11u8; 32];
let bob_sk = [0x22u8; 32];
let (mut alice_pk, mut bob_pk) = ([0u8; 32], [0u8; 32]);
X25519::public_key(&alice_sk, &mut alice_pk)?;
X25519::public_key(&bob_sk, &mut bob_pk)?;

let (mut s1, mut s2) = ([0u8; 32], [0u8; 32]);
X25519::agree(&alice_sk, &bob_pk, &mut s1)?;
X25519::agree(&bob_sk, &alice_pk, &mut s2)?;
assert_eq!(s1, s2);
# Ok::<(), ic_core::Error>(())

FIPS position

Curve25519 is not on the FIPS 186-5 / SP 800-186 approved list for signatures, and X25519 is not an approved SP 800-56A scheme. They are here because modern protocols require them, and the ontology marks them accordingly so ic-fips blocks them in approved mode. The approved curves (P-256/384/521, ECDSA, ECDH) and the post-quantum FIPS 203/204 schemes are registered in the ontology with implementation_status: Planned — an agent querying for an approved signature scheme gets an honest "not available here" rather than a silent substitution.