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Almost 4 1/2 ounces of gold went unclaimed as the 6-characters long key that protected a PDF document encrypted using our Polymorphic Medley Cipher (Version 2) was NOT broken. The passphrase was: P-07/1.
The 6 characters could have been any character a .. z, A .. Z, but as well the following characters were equally possible: >, <, |, ,, (comma), ., -, _, #, ', +, ~, *, ^, °, !, ", §, $, %, &, /, (, ),= ,?, {, }, [, ]
The password decrypts a PDF file that contains some text and an image.
The encrypted PDF file is available for download here.
Windows software (including full source code) that is capable to decrypt the PDF file is available for download here.
For each character there are 26 + 26 + 29 = 81 possibilities. 81^6 = 282,429,536,481, which is slightly higher than 2^38 = 2,748,877,906,944.
So it's a 38 bit challenge. The cipher that is to be broken is the Polymorphic Medley Cipher (Version 2) which uses the well-analyzed base ciphers AES, Twofish, Serpent, Cast-256, RC6, SEED, Camellia and Anubis in a cascade.
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Features of the Polymorphic Medley Cipher include:
- 128 .. 1024 bit variable key length (only depends on the length of the password => 128 bit in our case)
- 128 bit block length
- Long key setup time: selectable up to 50ms on an Intel Core i7 950 clocked at 3.06GHz
- 5 "base" hash functions that are used to compute the internal state from the key
- Set of base hash functions: SHA-256, Whirlpool, RIPEMD, Tiger and HAVAL-256
- 8 "base" ciphers executed in a cascade
- Set of base ciphers: AES, Twofish, Serpent, Cast-256, RC6, SEED, Camellia and Anubis
- The actual cipher being selected by the key from approx. 16 million equally probable combinations
- Built-in support for Cipher Block Chaining (CBC mode, which is used for this challenge)
- 16 MBytes of RAM used to hold Internal State
- Compatible with any 32- or 64 bit microprocessor or microcontroller
- Free and complete source code (Visual Studio 2010 C++ project available by clicking here)
- Royalty-free use for any legal civil application
The task to break the Polymorphic Medley Cipher is several orders of magnitude more difficult than breaking AES alone. This is why we are very confident that this 128 bit cipher protects valuable data reliably in this public challenge.
The challenge clearly had primarily an academic value rather than anything else. If the PDF file was encrypted with the standard AES Rijndael cipher, the first participants in this challenge would have claimed the price after no more than a single day.
Why?
Well, here's the maths: 6 characters, each character selected from a set of 81 characters: 81^6 = 282,429,536,481 (approx. 282 billion possible key combinations)
A brute force attack on AES 128 runs at approx. 4.6 million key combinations per second. In order to try all possible 282 billion key combinations it consequently takes 17 hours AT MAXIMUM.
Taking into account that more than four ounces of gold are quite expensive these days - why the heck are we nuts and give away a lot of money that easily?
The truth is that the challenge is pretty hard. Of course we are not so stupid to use AES with short keys.
Who could take part and what was needed to take part at the challenge?
- everybody can !
- it's free !
- you can even find the source code here
The challenge started on March 05, 2013. It ended on April 01,2013.
Good luck!
C.B. Roellgen |