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        riddles >> easy >> crypto challenge
        
(Message started by: towr on May 25^th, 2015, 1:49am)

Title: crypto challenge
Post by towr on May 25^th, 2015, 1:49am

On https://gist.github.com/tqbf/3132713 you'll find 327 lines of hex-encoded characters, one of the lines is a line of English text encoded by XOR-ing it with a single character, the rest of the characters are random.

What is the line of text?

[hide]Did you find the right line before trying to decode it?[/hide]

Title: Re: crypto challenge
Post by markr on May 26^th, 2015, 12:08am

[hide]"now that the party is jumping"[/hide]

It was the first line I decoded.

I can't get hide to work....

//added hide tags --towr

Title: Re: crypto challenge
Post by towr on May 26^th, 2015, 8:40am

To hide something you can put hide tags around it.
Like
[hide]<hidden text here>[/hide]

Some javascript on the forum is broken, so the buttons for adding tags or smileys may not work, but adding them manually still works.

Title: Re: crypto challenge
Post by rloginunix on May 26^th, 2015, 8:46am

Well done but your [hide]capitalization is a bit off[/hide].

For completeness:

The phrase is [hide]Now that the party is jumping[/hide]
The key is [hide]5, (53)₁₀, (35)₁₆[/hide]
The line number is [hide]one hundred seventy one[/hide]

on 05/26/15 at 00:08:42, markr wrote:

I can't get hide to work....

At the top of this page there is a "Help" link. Click it. On the left-hand side of the help page there is another link called "Posting" - basic tags usage is here.

To hide a chunk of text surround it with the "hide" and "/hide" tags each of which must be inside the square brackets [ and ], tight, no spaces. To hide a chunk of text in a rectangle (block) use "hideb" and "/hideb" tags in the same way. You may also click the corresponding buttons in the "Add YABBC tags" section.

[e]
sorry, towr - didn't see you on the forum at the time of this post, my bad.
[/e]

Title: Re: crypto challenge
Post by SMQ on May 26^th, 2015, 9:15am

For finding the right line, a simple trick is to [hide]check the high bit of each byte[/hide]. For ASCII text they'll all be the same, while for random data they'll (very) likely be different.

--SMQ

Title: Re: crypto challenge
Post by towr on May 26^th, 2015, 9:38am

I just looked for the line with [hide]the least number of distinct (encrypted) characters[/hide]
And then [hide]I guessed the most common character was "e", but of course it was <space>[/hide]