iOS 10.3 (build 14E277) is an official Apple over-the-air update for the iPhone 5s (GSM), released on 2017-03-27T16:57:54Z. The update package is 572.77 MB. This is a delta (partial) update that requires 10.2 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: 381346450fdc3d8dc7ff45ed2b0204a34406e2b6.zip.