iOS 6.1.3 (build 10B329) is an official Apple over-the-air update for the iPhone 4 (CDMA). The update package is 75.14 MB. This is a delta (partial) update that requires 6.0 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: 30749e14c76d63e75c6c5f45375fc4998dd99d8e.zip.