})
	if err != nil {
		return nil, err
	}
	if len(metadata) > MaxMetadataSize {
		return nil, errors.New("config: encryption metadata is too large")
	}
	header[0] = Version
	binary.LittleEndian.PutUint32(header[1:], uint32(len(metadata)))
	buffer.Write(header[:])
	buffer.Write(metadata)

	return io.MultiReader(
		&buffer,
		stream.EncryptReader(plaintext, nonce, nil),
	), nil
}

	}
	return nil
}

// DerivePartKey derives an unique 256 bit key from an ObjectKey and the part index.
func (key ObjectKey) DerivePartKey(id uint32) (partKey [32]byte) {
	var bin [4]byte
	binary.LittleEndian.PutUint32(bin[:], id)

	mac := hmac.New(sha256.New, key[:])
	mac.Write(bin[:])
	mac.Sum(partKey[:0])
	return partKey
}

// SealETag seals the etag using the object key.

	if bts, err := c.MarshalMsg(metaDataPoolGet()); err == nil {
		crc ^= xxhash.Sum64(bts)
		metaDataPoolPut(bts)
	}

	// Combine upper and lower part
	var tmp [4]byte
	binary.LittleEndian.PutUint32(tmp[:], uint32(crc^(crc>>32)))
	return tmp
}

// XL metadata constants.
const (
	// XL meta version.
	xlMetaVersion101 = "1.0.1"

	// XL meta version.
	xlMetaVersion100 = "1.0.0"