Packages (.PKG)

There are two kinds of PS VITA package files (.pkg):

1. PS VITA Game Packages (.pkg)

2. PS VITA Firmware Packages (.pkg)

Game Packages

Debug and Retail v1.0 (not the actual ones) PS VITA Game Package files (.pkg) can be decrypted & extracted using the "PS VITA .pkg xTractor"

A picture showing the unpacked game .pkg structure:

See also: System_File_Object_(SFO)_(PSF), Keys

Firmware Packages

PS VITA Firmware Package files (.pkg) are inside PS VITA Update Files (.pup).

Those packages can not be decrypted, yet.

PSN

Game Update

It is a bit upgraded but basicly the same as on PS3. Once a game tab is opened, the VITA downloads a PKG for this game tab. This includes update information, such as if an update if available. If thats the case, the game tab will show you a yellow arrow on the top of the screen which gives you information about the update available. This information is stored in XML's which are gathered via URL's like this example one:

 http://gs.ww.np.dl.playstation.net/ppkg/np/PCSG00001/PCSG00001_T1/0101/c653f481544f8b19/changeinfo.xml

this is the content:

<?xml version="1.0" encoding="UTF-8"?>
<changeinfo titleid="PCSG00001">
  <changes app_ver="01.01">
    <![CDATA[
オンライン仕様に関わる動作の安定性を向上しました
    ]]>
  </changes>
</changeinfo>

This is the original update PKG.

 http://gs.ww.np.dl.playstation.net/ppkg/np/PCSG00001/PCSG00001_T1/c653f481544f8b19/JP0700-PCSG00001_00-RIDGERACERPSVITA-A0101-V0100-fd9baf01343b2db6df0d434b17ef822a9699c6da-PE.pkg 

original link(SKFU BLOG)

the update is stored with the XML.

 http://gs.ww.np.dl.playstation.net/ppkg/np/[TITLE_ID]/[TITLE_ID]_T1/[Version]/[An HASH]/changeinfo.xml