iOS 11.3 (build 15E5211a) is an official Apple over-the-air update for the iPhone 5s (GSM), released on 2018-03-12T17:05:44Z. The update package is 219.75 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: e39f8d55d85487300f17be92c33212348769613b.zip.