code: protected String hash(String key) throws VictimsException {
          try {
              MessageDigest mda = MessageDigest
                      .getInstance(MessageDigestAlgorithms.SHA_256);
              return Hex.encodeHexString(mda.digest(key.getBytes()));
          } catch (NoSuchAlgorithmException e) {
              throw new VictimsException(String.format("Could not hash key: %s",
                      key), e);
          }
      }
docs: The hashing function used by the Cache.
  
  @param key
  @return
  @throws VictimsException