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I was challenged by a friend to decrypt a piece of text that was somehow encrypted. The encrypted text is the following:

LY3IoH5HWSnp9-efCfOH3jqmoGaXdURF4YAKgIh2KotjHLyFbLBgXr0uzPu1-K0sEGUogoTduKF1_eklAVzOlEfziqIvqtlhZeJPF8H2ER0jLc25jPC8_AOPlAvTHKdA8BVPFPwu1Ldaul4IPBVWJSJc5fhTGJAjfSL2Rum-pW8VCSJwnB3LZR1ACVR0KN0HCv7hIKJ88TNUc4hHk5g4sstPxdeQqUIu7GjY1C8M3jl4EMo9yqHoo1Mj7Q4vxPWGUM_OhMR46s772EpqNXk62pldQomWovdvB2pYh_srTFYM0u5MMQd5Z1nUUCwA--QiQX5cJmSxw7U8lVo78K6Qm4oGirfFJVlYIzPClCNziLewhEXvaKv1KmDtnUi03lAXQMuHjQqfMzMLJibXrw

How would one go about solving this type of puzzle?

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    I guess I would ask for help on Security.SE. Oh wait...
    – executifs
    Jun 23, 2014 at 11:01
  • at that lenght, sure it's not an OTP? Does somehow encrypted mean that the principle is that there is a key, a message and a algorithm? Jun 23, 2014 at 11:11
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    Also, did you try searching for parts of it yet? google.nl/search?q=LY3IoH5HWSnp9 Could very well be your friend just used a string found somewhere (perhaps a GUID) to pull your leg.
    – SQB
    Jun 23, 2014 at 13:04
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    @SQB - it is too long to be a GUID. It is not a good question for SE or Crypto. It is too broad to discuss general decryption of an unknown algorithm and is off topic on either site. It does appear that it is an identifying token rather than an encrypted message though from those search results. Jun 23, 2014 at 13:26
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    @SQB - If it wasn't too broad, it would probably be on topic there. But this question is an entire field of study, not a Q/A topic. "How do I break generic encryption?" takes multiple text books and college classes, not a several paragraph answer. Jun 23, 2014 at 13:29

2 Answers 2

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Maybe frequency analysis could be a first step. But it will only help you with simple substitution ciphers.

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Short answer : you don't.

One of the main rules about encryption is that the security mustn't rely on the algorithm staying secret. This is because this information can always leak in some way : reverse-engineering, people talking too much... However, in this case "security through obscurity" happens to be pretty solid.

With great knowledge about cryptography, and more likely if the encryption used is weak, you might be able to notice some pattern or other information that narrows down the potential encryption algorithms. But decoding this string without any other information seems pretty difficult.

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