Secure triple-DES encryption using a 112-bit key derived from the password
What? Triple-DES is secure? Do you know that NIST has deprecated 3DES in 2017?
Even looking at the bit length naively, anything below 128-bits hardly can be considered secure.
The app definitely can be upgraded to use AES 256-bit, the feature was implemented back in 2002 when 3DES was still fresh and new. The code hasn't ever been tested, so it's implementation might be as secure as a Lego safe. The question is whether it's worth it and if it isn't easier to write a proper cold wallet app for Palm OS instead.
You can program PalmOS at least in C , C++ and assembler, but I guess that any programming language is able to be used given enough work.
Also, libraries written in C and C++ already exist, so porting them to the Palm OS won't be a huge problem. There is MathLib.prc shared Palm OS math library ,which itself is based on the Sun Microsystems' libm:
https://github.com/fidian/MathLibMaybe we can take the existing code for generating secure cold wallets, including appropriate libraries and port them to Palm OS. The only hard work that remains is programming an user interface to allow usage of the program and additional security features such as locking access to the rest of the OS without explicit user's consent.
How about support for older processor architecture? For example, Palm TX uses Intel XScale PXA 270, where Intel XScale itself uses ARMv5.
At very least, you need to find compiler which support ARMv5 and manually convert assembly code.
The solution is simple: code in C/C++, so that it will both on ancient 68k and more modern ARM Palms alike. I don't have any advanced knowledge of Palm programming, but knowing that some apps from 68k era still work on ARM Palms, it should be feasible.