randombytes
randombytes(sk,32);
void randombytes(unsigned char *ptr, size_t l);
void randombytes(unsigned char *ptr, size_t l);
void randombytes(unsigned char *ptr, size_t l);
randombytes(c, 4);
randombytes(sk, Small_bytes);
randombytes(sk+4, 3*n);
randombytes(sk+params->index_len, 3*n);