nano-ecc

A very small ECDH and ECDSA implementation for 8-bit microcontrollers.

Based on kmackay's micro-ecc, a small ECDH and ECDSA implementation for 32-bit microcontrollers. For more information see https://github.com/kmackay/micro-ecc

Features

• Resistant to known side-channel attacks.
• Written in C, with optional inline assembly forthcoming
• Small code size: ECDH in as little as 6KB, ECDH + ECDSA in as little as 7KB
• No dynamic memory allocation.
• Reasonably fast: on an ATmega328P at 16MHz (AVR, 2-cycle 8x8 bit multiply), 192-bit ECDH shared secret calculation takes about 4034ms
• Support for 4 standard curves: secp128r1, secp192r1, secp256r1, and secp384r1
• BSD 2-clause license.

Usage Notes

Integer Representation

To reduce code size, all large integers are represented using little-endian bytes - so the least significant bytes is first. For example, the standard representation of the prime modulus for the curve secp128r1 is FFFFFFFD FFFFFFFF FFFFFFFF FFFFFFFF; in nano-ecc, this would be represented as uint8_t p[16] = {0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff 0xff, 0xff, 0xff, 0xff 0xff, 0xfd, 0xff, 0xff, 0xff};.

You can use the ecc_bytes2native() and ecc_native2bytes() functions to convert between the native byte representation and the standardized octet representation.

Generating Keys

You can use the makekeys program in the apps directory to generate keys (on Linux or OS X). You can run make in that directory to build for your native platform. To generate a single public/private key pair, run makekeys. It will print out the public and private keys in a representation suitable to be copied into your source code. You can generate multiple key pairs at once using makekeys <n> to generate n keys.

Using the Code

I recommend just copying (or symlink) ecc.h and ecc.c into your project. Then just #include "ecc.h" to use the nano-ecc functions.

See ecc.h for documentation for each function.

Speed and Size

Available optimizations are:

• ECC_ENABLE_DSA - Set to 0 to avoid including any DSA-related code.
• ECC_SQUARE_FUNC - Use a separate function for squaring.
• ECC_ASM - Choose the type of inline assembly to use. Currently only ecc_asm_none is available. In the near future we plan to provide ecc_asm_avr and ecc_asm_8051.

Comprehensive code size and performance analysis are forthcoming.