anchor.diff:  -spec strong_rand_bytes(non_neg_integer()) -> binary().
   -spec rand_seed() -> rand:state().
   -spec rand_seed_s() -> rand:state().
  +-spec rand_seed_alg(Alg :: atom()) -> rand:state().
  +-spec rand_seed_alg_s(Alg :: atom()) -> rand:state().
   -spec rand_uniform(crypto_integer(), crypto_integer()) ->
   			  crypto_integer().
   
  
positive.code: 
  
  -spec rand_seed(binary()) -> ok.
  rand_seed(Seed) ->
      rand_seed_nif(Seed).
  
  rand_seed_nif(_Seed) -> ?nif_stub.
  
negative.code: -export([hmac/3, hmac/4, hmac_init/2, hmac_update/2, hmac_final/1, hmac_final_n/2]).
  -export([cmac/3, cmac/4]).
  -export([exor/2, strong_rand_bytes/1, mod_pow/3]).
  -export([rand_seed/0, rand_seed_alg/1]).
  -export([rand_seed_s/0, rand_seed_alg_s/1]).
  -export([rand_plugin_next/1]).
  -export([rand_plugin_uniform/1]).
  -export([rand_plugin_uniform/2]).
  -export([rand_cache_plugin_next/1]).
  -export([rand_uniform/2]).
  -export([block_encrypt/3, block_decrypt/3, block_encrypt/4, block_decrypt/4]).
  -export([next_iv/2, next_iv/3]).
  