dunno if my math is right, but in hex a byte can be between 00 and FF, going through the characters 0123456789ABCDEF. 0xFF is 255 in decimal. including 00, that's 256 possible characters for a single byte.
if the key were two bytes, that means it can be between 00 00 and FF FF. 256 possible combinations for each byte. 256 * 256 = 65536, so 65536 possible combinations for the two-byte key.
if we take a 16 byte key like the 3DS and Wii U, that would be 256 * 256 * 256 * 256 * 256 * 256 * 256 * 256 * 256 * 256 * 256 * 256 * 256 * 256 * 256 * 256 (or 256 ^ 16). that would make it 340,282,366,920,938,463,463,374,607,431,768,211,456 or basically 340 undecillion possible combinations. that's 39 decimal digits. (I had to use Wolfram Alpha for this due to the large number.)
you could probably bring it down if you only count characters you can type normally on a keyboard (like letters, digits, etc.), but it's still going to be pretty big.
I'm sorry, I'm kinda bored, so I did this. but encryption's fun, isn't it?
...with that said, I checked my console and re-added tubehax to it. I removed it once to use youtube but forgot to re-add it I guess. I'm not going to make the same mistake with 5.3.2/5.4.0. I think I remember hearing 5.5.0 didn't patch anything, and then turns out it did.