code: public static byte[] sha1(@NotNull String input, @Nullable byte[] salt, int iterations) {
  		return digest(input.getBytes(Charsets.UTF_8), get(SHA_1_DIGEST), salt, iterations);
  	}
docs: 对输入字符串进行sha1散列，带salt而且迭代达到更高更高的安全性.
  
  @see #generateSalt(int)