micro-ecc-integration

micro-ecc Integration

Overview

Use this skill to integrate micro-ecc (kmackay/micro-ecc, header uECC.h) by treating randomness, key storage, curve choice, and test vectors as security-critical. ECC that compiles but never called uECC_set_rng() or uses mismatched key byte formats is not working. The core key generation, signing, verification, and ECDH functions return 1 on success and 0 on failure (uECC_verify returns 1 only for a valid signature); the size-query helpers instead return a byte count, and uECC_compress/uECC_decompress return void.

When To Use

Use this skill when:

• The user wants ECDH (uECC_shared_secret), ECDSA (uECC_sign/uECC_verify), or key generation (uECC_make_key) on an MCU using micro-ecc.
• The issue involves uECC_make_key/uECC_sign returning 0, bad signatures, key mismatch, RNG, curve selection, endian/format mismatch, or slow scalar multiplication.
• The project uses uECC.h, uECC.c, a uECC_Curve, or uECC_set_rng.

Do not use this skill for full TLS stacks. Use mbedtls-integration for TLS. For AES/SHA/HMAC primitives, use tinycrypt-integration.

First Questions

Ask for:

• Curve and operation: uECC_secp160r1, uECC_secp192r1, uECC_secp224r1, uECC_secp256r1, or uECC_secp256k1; and ECDH vs ECDSA.
• Target MCU, compiler, and whether a hardware TRNG/crypto peripheral exists.
• The RNG source wired into uECC_set_rng() and the key storage policy.
• Public/private key byte format and endian expectations of the peer (uECC_VLI_NATIVE_LITTLE_ENDIAN setting, compressed vs uncompressed).
• Test vector, signature, or verification failure details, and the return code seen.

Integration Checklist

1. Choose curve deliberately. Pick a uECC_Curve via uECC_secp256r1() (or the peer's curve) and enable it with the matching uECC_SUPPORTS_secp256r1 macro. Disable unused curves to save flash.

2. Provide a real RNG first. Register uECC_set_rng(uECC_RNG_Function fn) where fn has signature int fn(uint8_t *dest, unsigned size) and returns 1 when dest is filled with good entropy, 0 otherwise. Without a valid RNG, both uECC_make_key and uECC_sign return 0. Only uECC_sign_deterministic (RFC 6979-style deterministic nonce, needs a uECC_HashContext) works without an RNG.