nParts, err := strconv.Atoi(valSplit[1])
		if err != nil {
			return nil
		}
		alg |= ChecksumMultipart
		wantParts = nParts
	}
	bvalue, err := base64.StdEncoding.DecodeString(value)
	if err != nil {
		return nil
	}
	c := Checksum{Type: alg, Encoded: value, Raw: bvalue, WantParts: wantParts}
	if !c.Valid() {
		return nil
	}
	return &c
}