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Topic: Encrypted letter (Read 1059 times) |
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denis
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Encrypted letter
« on: May 10th, 2007, 8:48am » |
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A friend of mine sent me the text below and asked me if I know how to decrypt it. He is an english teacher and is dabling in encryption so I don't know how hard to crack. Blank lines have no bearing on the decryption. If it can help, the text is a letter. i.e. the first line is a date, then a greeting, then the main body of the letter.
I have no idea what the encoding was used nor the contents of the letter. But decryption is not my forte so I tought I'd run it through the forum.
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4W.)04Hbx:pTkMax
2cY#Ybqsz
GzUD)C””M),boc?e.1GWt7;VN
wJS HXD@VMDG;Na3Tgg8A0G9y
t$MtF-85dQ/L2eNH4W9fC2Imd
9 O”mGwSaEyRntt:0q v,8C31
‘ti1NP.Cskp6,X.1UqzaN6s0j
S3T$k/.go71r91wO5t)shL/oM
ZF42C:vC1Y9oqn@oHpVEDAFds
.fVNg,Jg-(axVsi ;N6tnh5Z-
Naf(p/OtnW$wWDWYaFM3b.2Pm
?aUtSn-8XSAA;sc@kY(pw MkP
Bb,’KdqWOi1w6/wDdtlk’a2cN
X9/k#?XlxE#9I/mKF7vlq?Atx
ZmW3ii8NG6Rq’;0zgtf#7J2/U
GuAPn”ApTCeqT?o@V0B2R(-qw
AhWJja0?D/O,Ezs;BLJD3Qefn
bO7,a(t’BH2eb8GY0a) A@uTX
@ZvOvNv3t0cJvHv’AFC3)V.u?
c9jat0s-tFBc’sA0”P(1EjmPq
#IzjYD#YB)d#W9n9H;NI6AmL,
cSNfuv26gv-mX6Z??’F/R0Zyz
F?5
TbBC@WmX$ YjB
217t,pupDkUPui:
s? QMpdFdW8UQJE4M4,
YOPlOl”Q/TEVkJ2@Mn-y
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towr
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Re: Encrypted letter
« Reply #1 on: May 10th, 2007, 1:59pm » |
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Well, considering the form of the letter is preserved, I'd say it's some form of substitution cypher. But more than just letters are shuffled around.
Do you have any regular (non-encrypted) letters from him? It'd be helpfull to know his usual style (qua dates, greetings, signature etc)
Without knowing the type of encryption, nor the author, just one cyphertext is not much to go on.
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denis
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Re: Encrypted letter
« Reply #2 on: May 10th, 2007, 2:45pm » |
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I don't have a standard letter format from him. I did a quick letter frequency analysis and there are more than 60 different characters used in the first half of the letter only! So the base character set is fairly large. Not sure how easy or if its worth going any further.
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| « Last Edit: May 10th, 2007, 2:45pm by denis » |
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Grimbal
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Re: Encrypted letter
« Reply #3 on: May 10th, 2007, 3:36pm » |
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I count 80 characters, including the space, the carriage-return and line-feed characters.
In short: ”#$’(),-.‘/0123456789:;?@ABC..Zabc..z
That's 78 "printable" characters. But it doesn't cover a whole range in ASCII. It uses @, ", #, $, but not !, %, &, *, +. It also doesn't use <=> between the digits and the uppercase, or [\] between uppercase and lowercase. So there is some choice of characters. It also looks quite uniform. I don't know how to tackle it.
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BNC
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Re: Encrypted letter
« Reply #4 on: May 11th, 2007, 7:25am » |
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Do you know the name of the person the letter was sent to?
We can assume the second line is "dear <name>", which may be helpful.
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How about supercalifragilisticexpialidociouspuzzler [Towr, 2007]
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SMQ
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Re: Encrypted letter
« Reply #5 on: May 11th, 2007, 8:09am » |
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on May 10th, 2007, 3:36pm, Grimbal wrote:| In short: ”#$’(),-.‘/0123456789:;?@ABC..Zabc..z |
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If the letter includes some sort of pricing information, that could be the set of characters used in the plaintext. Given that the ciphertext has 25 characters per line and is still formatted as a letter, I doubt line breaks are part of the cipher.
If the first line is really just a date, it's too long to have been in the last few months, so the letter is likely not current correspondence between denis and his friend, but something else. Knowing their real-life names or addresses (the most likely interpretation of the last three lines) is probably useless, then...
--SMQ
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--SMQ
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denis
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Re: Encrypted letter
« Reply #6 on: May 13th, 2007, 9:33pm » |
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The person's name is Hany, so that the 2cY#Ybqsz part could quite conceivebaly be "Dear Hany"
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Grimbal
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Re: Encrypted letter
« Reply #7 on: May 14th, 2007, 1:48am » |
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Then it is not a simple substitution cypher.
It doesn't seem to be, anyway.
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Sameer
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Re: Encrypted letter
« Reply #8 on: May 14th, 2007, 12:34pm » |
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Did somebody make a chart? I mean the frequency of most used letters might give clues to vowels or certain other things...
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denis
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Re: Encrypted letter
« Reply #10 on: May 15th, 2007, 8:24am » |
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From looking at the encrytped date string "4W.)04Hbx:pTkMax", one would conclude that if 2007 were encrypted somewhere in there, a straight substitution crypt yould yield a double character but it does not. This could indicate a encryption that uses a key of a certain length. So it would seem a more complex cypher was used in this case.
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| « Last Edit: May 15th, 2007, 9:29am by denis » |
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Random Lack of Squiggily Lines
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Re: Encrypted letter
« Reply #11 on: Jun 8th, 2007, 9:08am » |
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+╟εε§ 13
deos it use any ALT + _____
?
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You can only believe i what you can prove, and since you have nothing proven to cmpare to, you can believe in nothing.
I have ~50 posts to hack a "R" into a "D". Which one?
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fiziwig
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Re: Encrypted letter
« Reply #12 on: Jun 13th, 2007, 6:01pm » |
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Is there a problem with the server? I tried to post a reply and ogt:
Bad Request
Your browser sent a request that this server could not understand.
Apache/2.0.59 (Unix) mod_ssl/2.0.59 OpenSSL/0.9.8e Server at www.ocf.berkeley.edu Port 80
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fiziwig
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Re: Encrypted letter
« Reply #13 on: Jun 13th, 2007, 6:08pm » |
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FYI the string double-quote percent-sign r double quote causes the server to crash when I click "post". I had to change that string in the examples below to something else to get this post to be accepted.
Some possibilities:
1. A one-to-many mapping so that, for example "E" might become any one of "nv,8C" (pick one at random while encoding).
2. A base 80 (or base 78) equivalent of the text (similar to the base 64 used to encode images into email).
3. A polyalphabetic cipher where the various alphabets use different collections of characters from the 80 seen in the text. If it has a repeating key then coincidence analysis would reveal the key length.
4. Are spaces and punctuation omitted or enciphered? Probably enciphered given alphabet size and the fact that line lengths are all uniform, implying that linefeed is meaningless.
5. A block substitution where each pair of letters enciphers to a pair of cipher text letters. E.g. "th" becomes "Qr" but "te" becomes "vM", so that individual letters lose their identities depending on their neighbors. (Also might be letter triples, but less likely) However, pair frequency analysis argues against this possibility.
6. Pairwise character sums, for example, "the" becomes (t+h), (h+e), (e+space)", etc, where the sums are binary, or alternatively come out of an arbitrary addition table (or set of keyed addition tables).
7. One-time pad, or long key text.
There are dozens of other possibilities but these are just a few off the top of my head.
What I would try first would be base 78 or base 80. I would start by translating the whole thing into either of those two bases and start looking for repetitions and regularities.
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towr
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Re: Encrypted letter
« Reply #14 on: Jun 14th, 2007, 1:47am » |
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on Jun 13th, 2007, 6:08pm, fiziwig wrote:| FYI the string double-quote percent-sign r double quote causes the server to crash when I click "post". |
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I seem to get the same problem with just a percent sign
Which is pretty odd, because I'm sure I've used it on the board a few times.
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Grimbal
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Re: Encrypted letter
« Reply #15 on: Jun 14th, 2007, 3:04am » |
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%20
Maybe it is filtering for some special characters and thinks it needs to unescape the percent-encoded characters, as if it were in an URL.
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denis
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Re: Encrypted letter
« Reply #16 on: Jun 14th, 2007, 1:05pm » |
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My guess is the most likely candidate is a one to many mapping looking at the background of the person who encoded it. I know him from way back and high school math was not his strength. He is is not really computer literate as well. I expect a "home grown" type of encryption in this case. So base 78 or base 80 (similar to base 64 encoding) is unlikely.
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