How do I generate random keys for tiny-ECDH-c?

You need to use an external source of randomness, like /dev/urandom on Unix or a hardware RNG, to fill the private key buffer before calling ecdh_generate_keys(). The library itself does not handle random number generation, as noted in the README.

What elliptic curves does tiny-ECDH-c support?

It supports 10 standard NIST curves, including 5 pseudo-random and 5 Koblitz curves, with symmetric security levels from 80 to 256 bits. Specific curves are defined in ecdh.h, as mentioned in the README.

Is tiny-ECDH-c secure for production use in IoT devices?

While it implements standard ECDH, the library lacks advanced security features like side-channel resistance. It's best for resource-constrained environments where code size is critical, but a security audit is recommended for production.

How does tiny-ECDH-c compare to mbed TLS for embedded systems?

Tiny-ECDH-c is much smaller and focuses only on ECDH, whereas mbed TLS offers a full cryptographic suite with more features. Choose based on whether you need minimal footprint or comprehensive functionality.

How to integrate tiny-ECDH-c into an ARM GCC project?

Include ecdh.c and ecdh.h, compile with optimization flags like -Os, and provide random data for keys. The README shows an example compilation command for ARM GCC to achieve the small footprint.

Does tiny-ECDH-c support ECDSA signing?

No, ECDSA is not implemented; it's listed as a TODO in the README. If you need signing, you must use another library or implement it separately.

What are the memory requirements for using different curves?

A keypair requires between 72 and 216 bytes of RAM depending on the curve size, as mentioned in the README. ROM usage is minimal, typically 2.1K for ARM.

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tiny-ECDH-c

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A minimal, portable C implementation of Elliptic-Curve Diffie-Hellman for secure key exchange.

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What is tiny-ECDH-c?

Tiny-ECDH-c is a minimal, portable C implementation of the Elliptic-Curve Diffie-Hellman key agreement algorithm. It allows two parties to establish a shared cryptographic secret over insecure channels using elliptic-curve cryptography, with a focus on small code size and no external dependencies.

Target Audience

Embedded systems developers, IoT engineers, and anyone needing lightweight cryptographic key exchange in resource-constrained C environments.

Value Proposition

It offers the smallest known ECC implementation in C, is public domain, supports multiple standard curves, and requires zero internal memory allocation—making it ideal for systems where code size and portability are critical.

Overview

Small portable Elliptic-Curve Diffie-Hellman in C

Use Cases

Best For

Adding ECDH key exchange to embedded firmware
Implementing secure communication in IoT devices with limited resources
Educational projects learning about elliptic-curve cryptography
Prototyping cryptographic protocols in C without heavy libraries
Systems requiring public-domain cryptographic code
Applications where minimal ROM/RAM usage is a priority

Not Ideal For

Projects requiring ECDSA digital signatures for authentication
Applications that need built-in random number generation for key creation
Systems where a comprehensive, audited cryptographic library is mandatory for compliance
Teams looking for active community support and frequent feature updates

Pros & Cons

Pros

Extremely Small Footprint

Compiles to only 2.1K ROM for ARM with zero internal RAM allocation, as demonstrated in the README's size report for embedded systems.

Portable and Dependency-Free

Written in standard C with no external dependencies, making it easy to integrate into various projects, including resource-constrained environments.

Multiple Standard Curves

Supports 10 NIST curves offering 80 to 256 bits of security, providing flexibility for different security needs, as listed in ecdh.h.

Simple and Clear API

Exposes just two functions—ecdh_generate_keys() and ecdh_shared_secret()—simplifying implementation, with examples in ecdh_example.c.

Public Domain Licensing

All material is in the public domain, allowing unrestricted use in any project without legal concerns, as stated in the README.

Cons

Limited Cryptographic Features

Only implements ECDH; ECDSA for signing is listed as a TODO, making it unsuitable for applications requiring digital signatures.

Manual Randomness Management

Users must provide their own random data for private keys, which can be error-prone and requires secure external random number generation.

Basic Security Protections

No built-in protection against out-of-bounds memory access from malicious input, as the README warns, limiting its use in high-security contexts.

Sparse Documentation

Beyond basic examples, the README lacks detailed tutorials or best practices for secure integration, which could hinder adoption.

Frequently Asked Questions

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