dst = msgp.AppendBytes(dst, ver.meta)
	}

	// Update size...
	binary.BigEndian.PutUint32(dst[dataOffset-4:dataOffset], uint32(len(dst)-dataOffset))

	// Add CRC of metadata as fixed size (5 bytes)
	// Prior to v1.3 this was variable sized.
	tmp = tmp[:5]
	tmp[0] = 0xce // muint32
	binary.BigEndian.PutUint32(tmp[1:], uint32(xxhash.Sum64(dst[dataOffset:])))
	dst = append(dst, tmp[:5]...)

	objectEncryptionKey                []byte
	partDecRelOffset, partEncRelOffset int64
}

func (d *DecryptBlocksReader) buildDecrypter(partID int) error {
	var partIDbin [4]byte
	binary.LittleEndian.PutUint32(partIDbin[:], uint32(partID)) // marshal part ID

	mac := hmac.New(sha256.New, d.objectEncryptionKey) // derive part encryption key from part ID and object key
	mac.Write(partIDbin[:])
	partEncryptionKey := mac.Sum(nil)