117 lines
4.0 KiB
Markdown
117 lines
4.0 KiB
Markdown
Ed25519
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-------
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This is a portable implementation of [Ed25519](http://ed25519.cr.yp.to/) based
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on the SUPERCOP "ref10" implementation. All code is in the public domain.
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All code is pure ANSI C without any dependencies, except for the random seed
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generation which uses standard OS cryptography APIs. If you wish to be entirely
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portable define `ED25519_NO_SEED`. This disables the `ed25519_create_seed`
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function, so if your application requires key generation you must supply your
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own seeding function (simply a 32 byte random number generator).
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Performance
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-----------
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On a machine with an Intel Pentium B970 @ 2.3GHz I got the following speeds (running
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on only one a single core):
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Seed + key generation: 345us
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Message signing (short message): 256us
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Message verifying (short message): 777us
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The speeds on other machines may vary. Sign/verify times will be higher with
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longer messages.
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Usage
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-----
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Simply add all .c and .h files in the `src/` folder to your project and include
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`ed25519.h` in any file you want to use the API. If you prefer to use a shared
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library, only copy `ed25519.h` and define `ED25519_DLL` before importing. A
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windows DLL is pre-built.
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There are no defined types for seeds, private keys, public keys or signatures.
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Instead simple `unsigned char` buffers are used with the following sizes:
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```c
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unsigned char seed[32];
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unsigned char signature[64];
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unsigned char public_key[32];
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unsigned char private_key[64];
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```
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API
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---
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```c
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int ed25519_create_seed(unsigned char *seed);
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```
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Creates a 32 byte random seed in `seed` for key generation. `seed` must be a
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writable 32 byte buffer. Returns 0 on success, and nonzero on failure.
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```c
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void ed25519_create_keypair(unsigned char *public_key, unsigned char *private_key, const unsigned char *seed);
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```
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Creates a new key pair from the given seed. `public_key` must be a writable 32
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byte buffer, `private_key` must be a writable 64 byte buffer and `seed` must be
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a 32 byte buffer.
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```c
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void ed25519_sign(unsigned char *signature,
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const unsigned char *message, size_t message_len,
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const unsigned char *public_key, const unsigned char *private_key);
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```
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Creates a signature of the given message with the keypair `(public_key,
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private_key)`. `signature` must be a writable 64 byte buffer. `message` must
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have at least `message_len` bytes to be read. The given keypair must be a
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keypair generated by `ed25519_create_keypair`.
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```c
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int ed25519_verify(const unsigned char *signature,
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const unsigned char *message, size_t message_len,
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const unsigned char *public_key);
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```
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Verifies the signature on the given message using `public_key`. `signature`
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must be a readable 64 byte buffer. `message` must have at least `message_len`
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bytes to be read. `public_key` must be a 32 byte public key generated by
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`ed25519_create_keypair`. Returns 1 if the signature matches, 0 otherwise.
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```c
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void ed25519_add_scalar(unsigned char *public_key, unsigned char *private_key,
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const unsigned char *scalar);
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```
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Adds `scalar` to the given keypair where scalar is a 32 byte buffer (possibly generated with `ed25519_create_seed`), generating a new keypair. You can calculate the public key sum without knowing the private key and vice versa by passing in NULL. This is useful for enforcing randomness on a keypair while only knowing the public key, among other things.
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Example
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-------
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```c
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unsigned char seed[32], public_key[32], private_key[64], signature[64];
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const unsigned char message[] = "TEST MESSAGE";
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/* create a random seed, and a keypair out of that seed */
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if (ed25519_create_seed(seed)) {
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printf("error while generating seed\n");
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exit(1);
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}
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ed25519_create_keypair(public_key, private_key, seed);
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/* create signature on the message with the keypair */
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ed25519_sign(signature, message, strlen(message), public_key, private_key);
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/* verify the signature */
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if (ed25519_verify(signature, message, strlen(message), public_key)) {
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printf("valid signature\n");
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} else {
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printf("invalid signature\n");
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}
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```
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