partStart = i
			break
		}
		cumulativeSum += size
		encPartSize, _ := sio.EncryptedSize(uint64(size))
		encCumulativeSum += int64(encPartSize)
	}
	// partStart is always found in the loop above,
	// because off is validated.

	sseDAREEncPackageBlockSize := int64(SSEDAREPackageBlockSize + SSEDAREPackageMetaSize)
	startPkgNum := (off - cumulativeSum) / SSEDAREPackageBlockSize