iOS 12.1.3 (build 16D5032a) is an official Apple over-the-air update for the iPhone 5s (GSM), released on 2018-12-19T18:07:00Z. The update package is 222.68 MB. This is a delta (partial) update that requires 12.1.1 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: 2e6c668c34ecbea6d40d030008074509d09d6368.zip.