iOS 6.1.3 (build 10B329) is an official Apple over-the-air update for the iPhone 4 (CDMA). The update package is 17.15 MB. This is a delta (partial) update that requires 6.1.2 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: 678f66d0fc83382b0a5e3adf2be41fb526156058.zip.