Stuff to do while you wait (with a message from Harry added)
The Empty Vault › Forums › Bureau of Security and Signals Intelligence Forum › Stuff to do while you wait (with a message from Harry added)
- This topic has 58 replies, 12 voices, and was last updated 4 months, 1 week ago by The-Letter-Wriggler.
23rd August 2022 at 9:10 am #69213madnessParticipant
[A message from Harry: This topic typically contains some tougher challenges set by experienced competitors for one another. Don’t be surprised or alarmed if you don’t know how to break them, they are not part of the competition! Have fun, Harry].
Is it too soon to post ciphers for fun?
I recently found an interesting challenge involving a nicer version of the Alberti cipher. The details of the cipher are in this PDF:
Just for you, I made a warm-up ciphertext. It’s longer, therefore easier. But be warned: some tricks you develop to
crack it might not work for the shorter ciphertexts. Let’s call this one “ciphertext 0”.
Here are the ciphertexts from the PDF:
So you can check your solution, here are the MD5 checksums for the plaintexts (all uppercase, no spaces or punctuation):
If you can solve #0, then you are doing great. If you can solve #1 you are very good. If you can solve #2, then
you are highly skilled. If you can do #3, #4, and #5, then you are obviously cheating. Have fun!18th September 2022 at 9:41 am #83837PuttPutt86Participant
[Editred by Harry: Thanks PuttPutt, the usual rules still apply. If anything in a message is encrypted we need to check it first, so do repost with he info as you suggest below. Great to have you back, Harry]
@Harry, @Jodie & @Elves: The above message is encrypted using the cipher that madness used for his ciphertext #0 above. If you want me to send you the plaintext and key before you approve this message for the forum, just let me know. Looking forward to another great challenge with you all. Many thanks, PuttPutt18th September 2022 at 9:41 am #83840PuttPutt86Participant
#1 is making me quite ‘hot’ under the collar
But I don’t even know where to start on #2!18th September 2022 at 9:49 am #83616madnessParticipant
This one has two parts. For the first part, the key is
3,15,23,25,17;9,2,7,4,2. You get the pleasure of figuring out
plaintext MD5: 5fd9888b7ef0d5fe53be01443bd3a103
The second part is encrypted with the same cipher, but you don’t
get the key.
plaintext MD5: 4c74283157456dc3cdc08e5a1ad0dadc18th September 2022 at 12:34 pm #83854PuttPutt86Participant
@Harry: No problem, please see below.
[Decrypt and cipher info removed by the Elves]20th September 2022 at 12:09 am #83859madnessParticipant
@PuttPutt86, thanks for the kind message. Nice to see you, too.
2 through 5 are not easy unless you figure out how to cheat. Ha ha ha ha20th September 2022 at 12:09 am #83889BreakTheCipherParticipant
I’ve tried my best to make a brute force script for this. It’s so close but it seems to be missing just a few bits in the final decrypt. Not sure if it’s a bug in my decrypt function or if it needs better optimisation, but hopefully it will work for most Alberti cipher texts once I fix this.29th September 2022 at 7:48 pm #84766BreakTheCipherParticipant
Ah! I’ve finally figured out how to ‘cheat’! There was an extra loop I had to incorporate in my hill climbing script… Thanks for the cipher madness, it was good practice.30th September 2022 at 3:25 pm #84777madnessParticipant
Curious to hear more about that loop. So no one else can read it, encrypt it with the same key as #3.
p.s. There are two more awesome ciphers “awaiting moderation.” ahem30th September 2022 at 3:25 pm #84869HarryKeymaster
Sorry madness, holding several back door later when people are more settled in.3rd October 2022 at 9:42 am #84976BreakTheCipherParticipant
It seems I called victory too early. The script stops working at cipher text #2, which is unfortunate. I had an idea for a dictionary-based attack, but it is proving to be difficult to find the key for a given cipher text that encrypts into a given plaintext. I think if I had a script to do this, I might have a chance at solving this once and for all.3rd October 2022 at 6:15 pm #85037madnessParticipant
@BreakTheCipher, there is some randomness in encrypting, so no such script can exist.
Now tell us about that loop.
To solve them all, you must cheat harder.4th October 2022 at 10:20 am #85081BreakTheCipherParticipant
Yes well the loop was just looping through the indicator letter to find which one it was. The only other information I can find to use against it is the odd IOC which is affected when values are swapped, but I couldn’t find a way to use it in a meaningful way.6th October 2022 at 5:15 pm #85591person_314Participant
I think which indicator letter you use doesn’t actually matter, I started with trying that as well but you get equally good results by just using the same letter and looping 26 times. I think you will just get a reordering of the inner wheel for each choice of indicator letter. Although like you I am also stuck after #1. Perhaps the cheat is guessing parts of the plain text? Or maybe there is some clever way to factor the cipher that I haven’t thought of?6th October 2022 at 10:46 pm #85758BreakTheCipherParticipant
Yeah the ‘guessing’ part is where I was going with the dictionary attack, but it might not work with a cipher like this I think. Perhaps if you just tried to work out each section of the cipher text individually and then try to work out what the whole thing means.
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