input

Key to OPKG is your flag. An archive containing some files.
HINT:- Misc300 I’m not soft, I’m not hard but Firm I am

output

$ file *
misc300.elf: ELF 32-bit LSB executable, MIPS, MIPS32 rel2 version 1 (SYSV), statically linked, stripped
$ chmod +x misc300.elf
$ ./misc300.elf
qemu: uncaught target signal 4 (Illegal instruction) - core dumped
Instruction non permise (core dumped)

After some research on the net, this link was useful.

$ qemu-system-mipsel -kernel misc300.elf -nographic -m 256

Wait for the booting stuff.
And go to OPKG file:

The flag is flag{RWSvIveoiFjI6WS/h3J8Us0wUEjA53cQLuHJEwOD/sT5JsGvguZjlKmU}