Programming Challenges - Page 3

Village Idiot · 09-28-2009, 06:34 PM

Quote:

Originally Posted by ioan1k

Everyone give up on posting a challenge?

Here is a new one ...

Decrypt the following string

Code:

dc:f5:16:77:f2:b6:99:7b
:e4:fc:88:e2:c0:80:44:e8
:6d:26:3e:b5:d2:8e:1f:f5
:3e:f5:44:cf:6a:bd:f0:9e
:44:d0:6a:a0:24:3e:f4:d7

Hint ... the result is 32 bytes long

This is composed of a encrypting Hybrid algorithm using various encryption methods, I doubt that this is crackable (but that is the challenge)

Challenge Level: Advanced

Can you give us a example of a different string and what it looks like when encrypted?

Salathe · 09-28-2009, 06:35 PM

Challenge 7 Solution

Quote:

Originally Posted by Village Idiot

Are you sure you encoded it right? It comes out as gibberish when converted to ascii or anything else.

Absolutely sure that it was encoded right. The hint (Base64) should've given a clue but I guess the string was not particularly clear once you had used base64_decode on it.

Here's a step-by-step that I just took because I had actually forgotten the original encoding method.

1. base64_decode the string. This gives the message Q-: 7 rtaryynup gnro V
Now here's the crunch, that initial set of three characters looks kind of like a smiley face (which usually comes at the end of a phrase) and the only capital letter (not in the smiley) is at the end of the message (yet capitals usually come at the beginning). So, reverse the message!
2. Use strrev to see what the message says in reverse, giving V orng punyyratr 7 :-Q. Ok, well if that's a sentence then it is gobbledygook (nonsense)! So it has a structure like a sentence but the letters are all messed up (but the non-letter smiley characters are ok, and 7 is the number of this challenge). So what mixes up letters yet leaves other characters intact... str_rot13!
3. Use str_rot13 on the message, to give I beat challenge 7 :-D
Aha, the message in all it's glory!

So the solution, would be very simply (though obviously arriving at that solution wasn't simple!):

PHP Code:


			
function challenge7($message) {
    return str_rot13(strrev(base64_decode($message)));
}

ob_start('challenge7'); 
// Hint: Base 64
echo '
  ============
  US 06ID cgcn
  R hcnl5bn Vw
  IGdu cm8 gVg
  ============
';
ob_end_flush();

Phew

Village Idiot · 09-28-2009, 06:38 PM

Quote:

Originally Posted by Salathe

Challenge 7 Solution

Absolutely sure that it was encoded right. The hint (Base64) should've given a clue but I guess the string was not particularly clear once you had used base64_decode on it.

Here's a step-by-step that I just took because I had actually forgotten the original encoding method.

1. base64_decode the string. This gives the message Q-: 7 rtaryynup gnro V
Now here's the crunch, that initial set of three characters looks kind of like a smiley face (which usually comes at the end of a phrase) and the only capital letter (not in the smiley) is at the end of the message (yet capitals usually come at the beginning). So, reverse the message!
2. Use strrev to see what the message says in reverse, giving V orng punyyratr 7 :-Q. Ok, well if that's a sentence then it is gobbledygook (nonsense)! So it has a structure like a sentence but the letters are all messed up (but the non-letter smiley characters are ok, and 7 is the number of this challenge). So what mixes up letters yet leaves other characters intact... str_rot13!
3. Use str_rot13 on the message, to give I beat challenge 7
Aha, the message in all it's glory!

So the solution, would be very simply (though obviously arriving at that solution wasn't simple!):

PHP Code:


			
function challenge7($message) {
    return str_rot13(strrev(base64_decode($message)));
}

ob_start('challenge7'); 
// Hint: Base 64
echo '
  ============
  US 06ID cgcn
  R hcnl5bn Vw
  IGdu cm8 gVg
  ============
';
ob_end_flush();

Phew

It all makes sense now

ioan1k · 09-28-2009, 06:59 PM

Quote:

Originally Posted by Village Idiot

Can you give us a example of a different string and what it looks like when encrypted?

Yes I can :)

The original string is a Sha1 hash .... as should the first be, The hash is the hashed version of the key to a 1024 bit key used for a DH Secret Key

Encrypted String:

Code:

5b:37:91:43:ee:e6:22:7f
:ed:ed:c6:84:72:87:b6:55
:bb:32:b7:84:ca:ce:54:c8
:1d:4e:37:87:39:72:10:42
:2a:70:3c:02:b5:2f:91:26

Original

Code:

b3fa38c7c3cff8d2b0bc1fcd9a9e8b1a

Hint:

Hex
DES
48 Bytes

Good Luck :)

Update:

Added some hints... have fun 8)