Help Needed Getting Started

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Help Needed Getting Started
Topic Started: Sep 25 2006, 02:35 PM (380 Views)
namelessguy	Sep 25 2006, 02:35 PM Post #1
Just registered Posts: 3 Group: New Members Member #68 Joined: September 25, 2006	Hi, I've a crypto problem I need to crack. The thing is I have no idea about how to do it or to even start going about it. This is the first line of the cipher text: Quote: &:Y<Ł]RP(]?&>>&G<:~&Ł]?R%~^]:P5P&P%>^%R[Y4E_9 To make it clear this is from college and I want to do this myself I just need help starting off. The problem is supposed to be encrypted using a classical cipher. Any help offered will be much appreciated, Many thanks, Leigh.



rot13	Sep 25 2006, 02:46 PM Post #2
Elite member Posts: 306 Group: Trusted Member Member #14 Joined: September 29, 2005	namelessguy Sep 25 2006, 02:35 PM Hi, I've a crypto problem I need to crack. The thing is I have no idea about how to do it or to even start going about it. This is the first line of the cipher text: Quote: &:Y<Ł]RP(]?&>>&G<:~&Ł]?R%~^]:P5P&P%>^%R[Y4E_9 To make it clear this is from college and I want to do this myself I just need help starting off. The problem is supposed to be encrypted using a classical cipher. Any help offered will be much appreciated, Many thanks, Leigh. Have you tried counting letter frequencies? Does it have more than 26 unique characters? If not, are the frequencies close to the expected distribution for English? If not, have you tried doing a Kasiski test or using Index of Coincidence to see if it might be a polyalphabetic cipher with a discernable key length?



Revelation	Sep 25 2006, 02:49 PM Post #3
Administrator Posts: 386 Group: Admin Member #1 Joined: August 23, 2005	Actually, the more text you give us, the easier it will be for us to say something about the cipher. My guess is that it is a simple substitution cipher. So what you need to do is associate an encrypted letter with a letter from the alphabet using letter freqencies. There are some articels about that on this forum. I suggest you look here. Good luck!
	RRRREJMEEEEEPVKLWENFNVJKEEEEEAOLKAFKLXCFZAASDJXZTTTTTTTLSIOWJXMOKLAFJNNKFNXN RAGRBAQEMHIGDJVDSEOXVIYCELFHWLELJFIENXLRATALSJFSLCYTKLASJDKMHGOVOKAJDNMNUITN RRRRLJVEEEEECLYVYHNVPFTAEEEEEMWLMEIRNGLARWJAKJDFLWNTIERJMIPQWOTZEOCXKNUBNXCN RJIRPOWEANFUSNCZVDVZNMSFEKLOEPZLDKDJWSAAAAAAAOERHJCTNCKFRIMVKSOFOMKMANREWNBN RZUDRGXEEEEENFQIDVLQNCKNEEEEEDGLLLLLLAWIOSNCDARLODMTOEJXMILDFJROTKJSDNLVCZNN


Donald	Sep 25 2006, 03:32 PM Post #4
Elite member Posts: 454 Group: Trusted Member Member #8 Joined: September 2, 2005	Look through the decryption tutorials, as Revolution advised, and check frequencies as Rot13 suggested. In all likelyhood you have a mono-substitution cipher here, but quite possibly with an alphabet that includes punctuation and spacing. Make some stabs at it, and when you get stuck, come back here for more specific hints!



PulsarSL	Sep 26 2006, 12:55 AM Post #5
Super member Posts: 157 Group: Members Member #7 Joined: September 1, 2005	insecure's program from this topic here (direct link to source code: here) coupled with a good dictionary is very helpful in cracking monosubs. I don't think it can handle characters other than a-z, but you should keep it in mind for the future. Pulsar



insecure	Sep 26 2006, 06:45 AM Post #6
Elite member Posts: 381 Group: Trusted Member Member #10 Joined: September 9, 2005	It retains non-alphabetic characters as punctuators, but yes, it was designed to be used for solving simple cryptograms, so it only helps with A-Z. I should think it would be easy enough to modify, though.



namelessguy	Sep 28 2006, 10:54 AM Post #7
Just registered Posts: 3 Group: New Members Member #68 Joined: September 25, 2006	Thanks for all the replies. I haven't tried any methods to crack the ciphertext at the moment. The lecturer wants us to write programs to break them so he deliberately made them much to big to do by hand. I'm currently trying to code up some programs to do that.



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