---
name: "lib1305"
section: "3"
platform: "linux"
package: "lib1305-dev"
version: "0~20250415-1"
release: "Debian 13 (Trixie)"
platforms: ["linux"]
url: "https://new.carta.tech/lib1305"
---

# lib1305(3)

### NAME

lib1305 - C API for the lib1305 implementation of the Poly1305 one-time authenticator

### SYNOPSIS

Using lib1305:

-

  ```
  #include <lib1305.h>
  ```

Link with -l1305.

Authenticating a message:

-

  ```
  unsigned char a[poly1305_BYTES];
  const unsigned char m[mlen];
  const unsigned char k[poly1305_KEYBYTES];
  poly1305(a,m,mlen,k);
  ```

Verifying an authenticator:

-

  ```
  const unsigned char a[poly1305_BYTES];
  const unsigned char m[mlen];
  const unsigned char k[poly1305_KEYBYTES];
  int result;
  result = poly1305_verify(a,m,mlen,k);
  ```

### DESCRIPTION

lib1305 is an implementation of the Poly1305 one-time authenticator. The lib1305 functions follow the SUPERCOP onetimeauth API except that

- •

  the function names are lib1305-specific instead of crypto\_onetimeauth\_\*,

- •

  message lengths are long long instead of unsigned long long, and

- •

  the poly1305 function returns void instead of int.

The poly1305 function generates an authenticator a\[0\], a\[1\], ..., a\[poly1305\_BYTES-1\] given a message m\[0\], m\[1\], ..., m\[mlen-1\] and a secret key k\[0\], k\[1\], ..., k\[poly1305\_KEYBYTES-1\]. “One-time” means that the secret key must not be reused to generate an authenticator of another message.

The poly1305\_verify function verifies an authenticator a\[0\], a\[1\], ..., a\[poly1305\_BYTES-1\] given a message m\[0\], m\[1\], ..., m\[mlen-1\] and a secret key k\[0\], k\[1\], ..., k\[poly1305\_KEYBYTES-1\]. It returns 0 if the authenticator is valid, otherwise nonzero.

### SEE ALSO

[**randombytes**(3)](/randombytes/3.md)