Module k256

Koblitz secp256k1 Elliptic Curve Primitives

This module implements the secp256k1 elliptic curve operations in constant time. The curve equation is y² = x³ + 7 over the prime field F_p where:

• p = 2^256 - 2^32 - 977
• The curve order n = 0xFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFEBAAEDCE6AF48A03BBFD25E8CD0364141

All operations are implemented to be constant-time to prevent timing attacks.

Structs

FieldElement

secp256k1 field element representing values in F_p

Point

A point on the secp256k1 elliptic curve in affine coordinates

Scalar

secp256k1 scalar value for use in elliptic curve operations

Enums

PointFormat

Format of a serialized elliptic curve point

Constants

K256_FIELD_ELEMENT_SIZE

Size of a secp256k1 field element in bytes (32 bytes = 256 bits)

K256_KEM_SHARED_SECRET_KDF_OUTPUT_SIZE

Size of the KDF output for secp256k1 ECDH-KEM shared secret derivation

K256_POINT_COMPRESSED_SIZE

Size of a compressed secp256k1 point in bytes: format byte (0x02/0x03) + x-coordinate

K256_POINT_UNCOMPRESSED_SIZE

Size of an uncompressed secp256k1 point in bytes: format byte (0x04) + x-coordinate + y-coordinate

K256_SCALAR_SIZE

Size of a secp256k1 scalar in bytes (32 bytes = 256 bits)

Functions

base_point_g

Get the standard base point G of the secp256k1 curve

generate_keypair

Generate a cryptographically secure ECDH keypair

kdf_hkdf_sha256_for_ecdh_kem

Key derivation function for ECDH shared secret using HKDF-SHA256

scalar_mult

General scalar multiplication: compute scalar * point

scalar_mult_base_g

Scalar multiplication with the base point: scalar * G