Random cipher from a friend

Question

Below is what I have. I know that X is padding, and I've tried ROT1-25. I assume it's substitution, but I don't see it.

TUAUC IHCRN OSELL CDXNE AHEX

Answer 1

The message is very short, but a cursory frequency analysis tells you that ...

... the letter distribution isn't far from the distribution in English texts: E is the most frequent letter, along with C. There are some Ls, some Hs to go with the Cs, and so on. This is more likely a transposition cipher than a substitution cipher.

The first letter is T and ...

... if you look at the second letter of the second block and the third letter of the third block, they are H and E, which conventiently spells THE. Rearrange the letters in a rectangle of width 6:

T U A U C I
H C R N O S
E L L C D X
N E A H E X

You can now read the message column-wise from top to bottom.

The message reads:

The nuclear launch code is XX.

Use it wisely. :)