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Topic: Breaking o t p (Read 4090 times) |
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A
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Breaking o t p
« on: Mar 21st, 2012, 4:43am » |
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Hi
I do have 11 strings XOR encrypted with same key.
Why i can break them ? at least one of them. appreciate any input
Logic:
For each of the possible string i and j find mssg_i xor mssg_j store in xors
go a grid look up to identify possible candidates for space
I'm damn new to python and below is the work so far. (uses a ^ ' ' = A , B ^ ' ' =
b etc ) (Sorry just couldnt get them indented properly)
Code:
for i in range(11):
xors.append([])
for j in range(11):
msg_i_xor_msg_j = strxor(msgs[i].decode('hex'),msgs[j].decode('hex'))
xors[i].append(msg_i_xor_msg_j)
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Code:
for i in range(11):
print "==="
for j in range(11):
#for msg in xors:
out = ""
for char in xors[i][j]:
#if ord(char) >=32 and 126>=ord(char):
if (ord(char) >=65 and 90>=ord(char)) or (ord(char)>=97 and 122>= ord(char)):
out += char
else:
out += "_"
print out
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Grimbal
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Re: Breaking o t p
« Reply #1 on: Mar 21st, 2012, 5:35am » |
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Suppose
msg[i] are the crypted messages you have,
key is the key,
clear[i] are the clear messages: msg[i] = clear[i] xor key.
Then (msg[i] xor msg[j]) = (clear[i] xor clear[j]). You get rid of the key, but it is still the xor of 2 words. It gives nothing readable.
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A
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Perder todas as esperanças é liberdade!
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Posts: 236
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Re: Breaking o t p
« Reply #2 on: Mar 22nd, 2012, 11:30am » |
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Here is what i am doing
=> I am assuming all 11 msg[i]'s are [a-zA-Z] or ' '(space)
=> observation 'A' XOR ' ' = 'a' and 'a' XOR ' ' = 'A'
=>if msg[1] XOR msg[2] is a character at position k then either msg[1] or msg[2] has a space at position k
if all or most of msg[1] ^ msg[j] has space at position k then it is safe enough to conclude msg[1] has space at position k .
Find all spaces to get key
http://en.wikipedia.org/wiki/Venona_project
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| « Last Edit: Mar 22nd, 2012, 11:32am by A » |
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SMQ
wu::riddles Moderator
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Re: Breaking o t p
« Reply #3 on: Mar 28th, 2012, 5:17am » |
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on Mar 21st, 2012, 4:43am, R0B1N wrote:Hi
I do have 11 strings XOR encrypted with same key.
Why i can break them ? at least one of them. appreciate any input
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Posting assignments from Stanford's online cryptography class, are we?  I'd suggest the class discussion forums are a more appropriate venue...
--SMQ
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| « Last Edit: Mar 28th, 2012, 5:18am by SMQ » |
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--SMQ
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A
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Perder todas as esperanças é liberdade!
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Posts: 236
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Re: Breaking o t p
« Reply #4 on: May 1st, 2012, 4:41am » |
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on Mar 28th, 2012, 5:17am, SMQ wrote:
Posting assignments from Stanford's online cryptography class, are we? I'd suggest the class discussion forums are a more appropriate venue...
--SMQ |
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Yes It is from coursera.
It was hard to discuss anything in the coursera forum without spoiling the fun for others
I didn't want search engines to find it out before the deadline . Hence did not mention it 
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Barukh
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Re: Breaking o t p
« Reply #5 on: May 7th, 2012, 10:18pm » |
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on Mar 28th, 2012, 5:17am, SMQ wrote:
Posting assignments from Stanford's online cryptography class, are we? |
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I am attending this class, and find it very interesting. The lecturer is excellent, albeit problems are a bit too easy, in my opinion.
Anybody else enrolled? Impression?
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