you should add vita, psm, and psp packages support

these are pretty much identical to the ps3 format, their just encrypted with different keys

example code for this can be found here in SnowPME;
https://github.com/OpenPSS/SnowPME/tree/main/subprojects/LibShared/Package
specifically: https://github.com/OpenPSS/SnowPME/blob/62d41cc4937f51089ebf820a4906043bbf7646cb/subprojects/LibShared/Package/PackageExtractor.cpp#L92

or if you prefer in C, you can look here https://silica.codes/Li/real-package-installer/src/branch/main/app/pkg.c
or here .. https://github.com/st4rk/PkgDecrypt/blob/master/pkg_dec.c

another thing to note; in the case of PSP, actually some pkgs (mainly, MINIs and PSX games) have files encrypted with PS3 keys, and others are encrypted with the PSP keys; the key used is determined by the 'flags' set on PKG_ITEM_RECORD;
none of these examples handle this case other than maybe skipping it-

basically the condition is ((flags >> 0x1C)&7) == 1 if thats true, you use the PSP key to decrypt this item;
otherwise, you use the PS3 key.

the only thing i know that actually handles this properly is pkg2zip; see. https://github.com/mmozeiko/pkg2zip/blob/9222c4e00235dfe7914e9db0cc352da07e63d9f9/pkg2zip.c#L693 .. although i will be the first to admit its code is not the nicest.

Start by comparing the existing PS3 package support with the referenced implementations: subprojects/LibShared/Package/PackageExtractor.cpp, app/pkg.c, pkg_dec.c, and pkg2zip.c. Trace how package keys and item flags are handled, especially the PSP mixed-key condition. Done means Vita, PSM, and PSP packages extract correctly, including PSP items that require either PSP or PS3 keys.