code: function getKeyVersion(key, _skipCache) {
      if (typeof VERSION_CACHE[key] !== 'string') {
        let sign = thorin.util.sha2(key + thorin.util.sha1(key));
        sign = sign.substr(0, SIGNATURE_LENGTH);
        if (_skipCache === true) return sign;
        VERSION_CACHE[key] = sign;
        AVAILABLE_KEYS[sign] = key;
      }
      return VERSION_CACHE[key];
    }
docs: /*
  Versions the given key returning a SIGNATURE_LENGTH string.
  This allows us to version encrypted content