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  #1  
Old 04-07-2018, 22:36
eychei eychei is offline
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known-plaintext attack

Hi,

its me again.

I do have a encrypted file and also do have the plaintext. How can I find out the encryption algo and how can i get the key?
They both have the same length. Thats all i know

Ciphertext hex is:

29 6E 0D 7D F1 37 48 C4 FC 80 46 C2 50 54 40 BB 4F AE A0 08 D3 BD 38 7D AF 56 2C E9 27 3E 50 6A 30 45 AC AC 13 7C 4A DC A7 0F A5 56 4E 5C C0 13 2D 07 C8 78 1F 4F 52 E8

Plaintext hex is:

52 75 6E 53 63 72 69 70 74 31 3D 4D 6F 64 65 73 4D 61 6E 61 67 65 72 2E 4C 6F 61 64 53 65 6C 65 63 74 65 64 4D 61 74 65 72 69 61 6C 73 28 22 44 65 66 61 75 6C 74 22 29


thanks for all the help here.

-e
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  #2  
Old 04-08-2018, 00:38
Kerlingen Kerlingen is offline
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With that information it's impossible to find algorithm or key. The algorithm is never kept secret, the security comes from the key.

All one-time-pads are a guaranteed solution for example and you can create an infinite number of custom encryption algorithms which all decrypt that exact ciphertext to that exact plaintext using whatever key you like.
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Old 04-08-2018, 01:26
eychei eychei is offline
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I do have more files in ciphertext and plaintext. Would it be possible with more data?

-e
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Old 04-08-2018, 02:36
Kerlingen Kerlingen is offline
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Reducing an infinite number by a finite number still results in an infinite number.
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Old 04-08-2018, 05:07
eychei eychei is offline
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Ok. Thx.

How about checking the executable which is decrypting/encrypting the files.
I do have that but could not find the encryption scheme.

-e
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Old 04-08-2018, 05:57
Kerlingen Kerlingen is offline
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Yes, that's the normal way to go. Unless something really strange is going on, this executable will contain the decryption algorithm and (depending on what the encrypted data is used for) might also contain the key or something equivalent.
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Old 04-08-2018, 06:03
eychei eychei is offline
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ok. I will look more into that.
If I do not find anything, i will post here.

-e
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