There are a few versions of the EFI compress/decompress tools outside of the UEFI Shell commands, for OS-level usage. Here are two, there are others, I am not sure which is most up-to-date:
https://github.com/sstjohn/python-eficompressor
https://github.com/linearregression/python-eficompressor
Note there is an EfiCompress and EfiDecompress, as well as TianoCompress (but no TianoDecompress). Comparing to the Tianocore commands for freshness would be useful:
https://github.com/tianocore/edk2-ShellPkg/blob/master/Library/UefiShellDebug1CommandsLib/EfiCompress.c
https://github.com/tianocore/edk2-ShellPkg/blob/master/Library/UefiShellDebug1CommandsLib/EfiDecompress.c
https://github.com/tianocore/edk2-ShellPkg/blob/master/Library/UefiShellDebug1CommandsLib/Compress.c
https://github.com/tianocore/edk2-BaseTools/blob/master/Tests/TianoCompress.py
As well, the UEFI spec has an appendix with some source code on this topic. I have not checked if the source in the spec is in sync with the sources on Tianocore.
I’ve heard that EFI/UEFI has had 4 versions of compression algorithms, at least one of them is broken in a few ways, but I don’t have any specific details. I am not sure of the variatios of the compression algorithms used over time by EFI/UEFI in EDK1 and EDK2, and current UEFI spec. I wish I could find some specific test that verifies these errors. Teddy Reed’s UEFI-Firmware-Parser is also a current tool that deals with this compression issue. I also wonder if there are more recent compression algorithms that’d be better suited for current UEFI usage.
Firmware Security 