Decrypt challenge

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mrminecrafttnt
Posts: 131
Joined: Feb 11, 2013 12:23

Decrypt challenge

Post by mrminecrafttnt »

Your mission is to decrypt this message!
This can complete be done in Freebasic, its not too hard.. :)

Code: Select all

dim as string message = "Vq/yNcZe45Tp0PjgEitdOelz4F6NhexKxCeO"
adeyblue
Posts: 299
Joined: Nov 07, 2019 20:08

Re: Decrypt challenge

Post by adeyblue »

Oof, that's a bit strong. You better hope he doesn't figure it out
deltarho[1859]
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Re: Decrypt challenge

Post by deltarho[1859] »

My first port of call was to brute force XOR. That didn't work.

My next port of call was a monoalphabetic cipher such as Caesar's cipher. With a ciphertext of 36 characters we should have at least three or four spaces. We have four times 'e' but I did not like the look of the last 'e' in the ciphertext. I tried a brute force using all possible rotations, but that failed as well.

The next port of call would be a polyalphabetic cipher such as Vigenére's cipher. The question there would be key length - 3, 4, 5 or whatever. However, mrminecrafttnt wrote "its not too hard" and a brute force code would take a few lines and the computation would take quite a while as well. I figured a less complex cipher was used.

I reckon then a simple substitution cipher is being used but which one? Of course, my coding may be at fault. We could be lucky and strike it early, but we could be at it for days.

Of course, I could be being too clever for my own good and something elementary is being used. Decryption is not easy, and the security services would use applications with banks of ciphers. They would simply drop in the ciphertext and let them get on with it.

For the moment I am beaten and well done adeyblue. "You better hope he doesn't figure it out" got me looking at the '45' in the ciphertext, but that didn't help.
deltarho[1859]
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Re: Decrypt challenge

Post by deltarho[1859] »

Of course a cipher may not be employed and what we are looking at is Base64 encoding and the plaintext is 27 characters long.

I don't have any Base64 decoding to hand and I have other things to do and cannot get bogged down on this. I might come back to this but just not now.

A Base64 character map plus a cipher would be good. Come to think of it, Plaintext > Base64 > Enigma machine might have taken Bletchley Park a bit longer.

Added: I have just tried an online Base64 decoder and no luck. Maybe a simple substitution cipher is being used as well. If so, are we still in the "its not too hard" domain?
mrminecrafttnt
Posts: 131
Joined: Feb 11, 2013 12:23

Re: Decrypt challenge

Post by mrminecrafttnt »

Yep it is Base64 encoded, but after this you need to decrypt it..
Hint: use randomize, xor, rnd and brain.. :)
deltarho[1859]
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Re: Decrypt challenge

Post by deltarho[1859] »

mrminecrafttnt wrote:and brain.. :)
Oh, really? I must make a note of that for future reference.

You have just breached forum policy.

Tread careful.
jj2007
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Re: Decrypt challenge

Post by jj2007 »

mrminecrafttnt wrote:its not too hard
The word "its" is a possessive pronoun like "mine" and "your". What you mean is "it's", which is a contraction of "it is". No problem, you are still young ;-)

Thanks for pointing us to a simple truth: If you don't know which method was used for encryption, it can be pretty hard to decrypt a string.
deltarho[1859]
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Re: Decrypt challenge

Post by deltarho[1859] »

Image
c-sanchez
Posts: 145
Joined: Dec 06, 2012 0:38

Re: Decrypt challenge

Post by c-sanchez »

deltarho[1859] wrote:
mrminecrafttnt wrote:and brain.. :)
You have just breached forum policy.

Tread careful.
hahahaha how "use your brain" breach the forum policy?
After all, it is a forum where programmers gather, and certainly, programming requires using your brain.

I don't know much about the subject, let's say I'm ignorant, but I don't think someone can decrypt that without using their... "mind"?
deltarho[1859]
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Re: Decrypt challenge

Post by deltarho[1859] »

In the thread 'encryption in zip or xor?' there are three versions of 'Sub EncDec'; the last one being on Oct 17. On Oct 22, we get a decrypt challenge from someone who rarely posts; 0.08 posts per day. The encryption method employed appears to be 'EncDec' like with Base64 thrown in.

I am not drawing any conclusions here — merely making an observation.

I am given a hint, including using my brain. That is an insult and against forum policy. That should be blatantly obvious to anyone.

Not relevant here, but my posts per day are 1.86; second only to fxm.
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