Ed25519

This is a portable implementation of Ed25519. All code is in the public domain.

All code is pure ANSI C without any dependencies, except for the random seed generation which uses standard OS cryptography APIs. If you wish to be entirely portable define ED25519_NO_SEED. This does disable the ed25519_create_seed function however (you can use your own seeding function if you wish.)

Usage

Simply add all .c and .h files in the src/ folder to your project and include ed25519.h in any file you want to use the API. If you prefer to use a shared library, only copy ed25519.h and define ED25519_DLL before importing. A windows DLL is pre-built.

There are no defined types for seeds, signing keys, verifying keys or signatures. Instead simple unsigned char buffers are used with the following sizes:

unsigned char seed[32]
unsigned char signature[64]
unsigned char verify_key[32]
unsigned char signing_key[64]

API

int ed25519_create_seed(unsigned char *seed);

Creates a 32 byte random seed in seed for key generation. seed must be a writable 32 byte buffer. Returns 0 on success, and nonzero on failure.

int ed25519_create_keypair(unsigned char *verify_key, unsigned char *sign_key, const unsigned char *seed);

Creates a new key pair from the given seed. verify_key must be a writable 32 byte buffer, sign_key must be a writable 64 byte buffer and seed must be a 32 byte buffer. Returns 0 on success, and nonzero on failure.

int ed25519_sign(unsigned char *signature,
                 const unsigned char *message, size_t message_len,
                 const unsigned char *sign_key);

Creates a signature of the given message with sign_key. signature must be a writable 64 byte buffer. message must have at least message_len bytes to be read. sign_key must be a 64 byte signing key generated by ed25519_create_keypair. Returns 0 on success, and nonzero on failure.

int ed25519_verify(const unsigned char *signature,
                   const unsigned char *message, size_t message_len,
                   const unsigned char *verify_key);

Verifies the signature on the given message using verify_key. signature must be a readable 64 byte buffer. message must have at least message_len bytes to be read. sign_key must be a 32 byte verifying key generated by ed25519_create_keypair. Returns 0 if the signature matches, 1 otherwise.

Example

unsigned char seed[32], sign_key[64], verify_key[32], signature[64];
const unsigned char message[] = "TEST MESSAGE";

/* create a random seed, and a keypair out of that seed */
ed25519_create_seed(seed);
ed25519_create_keypair(verify_key, sign_key, seed);

/* create signature on the message with the sign key */
ed25519_sign(signature, message, strlen(message), sign_key);

/* verify the signature */
if (ed25519_verify(signature, message, strlen(message), verify_key)) {
    printf("invalid signature\n");
} else {
    printf("valid signature\n");
}