Ida: Pro Keys

Hex-Rays offers a free (limited to x86/x64, no decompiler) and an older IDA Demo (time-limited, saves disabled). These are not "keys" per se, but they are legal alternatives for learning.

By keeping your hands on the keyboard and utilizing these IDA Pro keys, you can focus on the logic of the malware or firmware you're analyzing, rather than the interface itself. ida pro keys