c := Checksum{Type: t, Encoded: base64.StdEncoding.EncodeToString(raw), Raw: raw}
	if !c.Valid() {
		return nil
	}
	return &c
}

// ReadCheckSums will read checksums from b and return them.
// Returns whether this is (part of) a multipart checksum.
func ReadCheckSums(b []byte, part int) (cs map[string]string, isMP bool) {
	res := make(map[string]string, 1)
	for len(b) > 0 {
		t, n := binary.Uvarint(b)
		if n < 0 {