iOS 11.3 (build 15E5178f) is an official Apple over-the-air update for the iPhone 5s (GSM), released on 2018-02-06T18:21:25Z. The update package is 295.29 MB. This is a delta (partial) update that requires 11.3 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: 524c261772ab7d5a56f9c90c34c98e13f6cad2a5.zip.