iOS 11.3 (build 15E216) is an official Apple over-the-air update for the iPhone 5s (GSM), released on 2018-03-29T17:11:45Z. The update package is 718.01 MB. This is a delta (partial) update that requires 11.1.2 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: 09e865239fa0b4b9fb719a74ac9832cd54c1f277.zip.