How to break a 32 bit block cipher without key? From what I know Skip32 is the only 32 bit block cipher and I heard its not secure. What do I do or which tool do I use to break a 32-bit block cipher?
I did search for this but all I find is attacks for DES(64 bit) and AES(128 bit) but none for Skip32.
The block size does not directly determine the security of a block cipher. Even with a 32 bit block cipher the number of possible permutations is 2^32!, a stupendously big number.

Small block sizes are however cumbersome to use in secure modes of operation as the input is limited. For instance, it would be easy to have repeating counters in counter mode encryption.

So attacks generally rely on low key sizes or - of course - the construction of the algorithm itself. Now for Skipjack there don't seem to be any known attacks. The key size is not very large, but brute forcing it seems still (just) out of reach.

Skip32 seems to use the same key size. It seems to use largely the same structures and 24 out of the original 32 rounds. Skipjack has only been attacked successfully for 16 rounds. So it is very possible that it is secure. The problem is that this cipher doesn't seem to have any paper or design document assigned to it. Basically there is just code and comments. This is a likely reason that no crypto-analysis can be found.

So basically: there is no generic attack against 32 bit block ciphers. Skip32 could well be secure, but as it hasn't been analyzed, nobody knows for sure. AES and DES on the other hand are well used and analyzed (and survived pretty well under those circumstances).

If you want to attack it, it might be best to check if the the way it is used is secure or not, because the 32 bit block size will certainly influence that.



If you just want to encrypt 32 bit values you should also have a look at Format Preserving Encryption (FPE). Those modes of operation can use standardized ciphers while achieving the same goal (although possibly at the cost of efficiency).