split method

List<SecureKey> split(Sodium sodium, List<int> lengths)

Creates multiple secure keys of different lengths from a single key. It is especially useful for using pwHash to generate enough bytes for multiple keys.

The returned keys are independent copies of portions of the original key, with the same kind of memory protection. The copying is done on secure, native memory controlled by sodium, without exposing the data to dart when using the dart VM.

Implementation

List<SecureKey> split(Sodium sodium, List<int> lengths) => runUnlockedSync(
      (originalKeyData) {
        var sum = 0;
        final originalLength = originalKeyData.length;
        RangeError.checkValueInInterval(lengths.length, 1, originalLength);
        for (final length in lengths) {
          RangeError.checkValueInInterval(length, 1, originalLength);
          RangeError.checkValidRange(sum, sum + length, originalLength);
          sum += length;
        }

        final keys = <SecureKey>[];
        try {
          var start = 0;
          for (final length in lengths) {
            final splitKey = SecureKey(sodium, length)
              ..runUnlockedSync(
                (splitKeyData) => splitKeyData.setRange(
                  0,
                  length,
                  originalKeyData,
                  start,
                ),
                writable: true,
              );
            keys.add(splitKey);
            start += length;
          }
        } catch (e) {
          for (final key in keys) {
            key.dispose();
          }
          rethrow;
        }

        return keys;
      },
    );