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Currently I am having a doubt, while making a "DES PCBC" encryption on an image I observe a bit of the silhouette of the image (Probably because of the XOR between plaintext blocks and ciphertext ones on the algorithm). That happens if I set IV and Key to 0.

However, if I change just the key (key in HEX values), the silhouette disappears. It doesn't happen when I leave the key at 0 and only change the IV.

Currently, I'm a bit lost. Apparently I'm seeing the ciphertext "prevailing" over the plaintext on key change, but I'm seeing plaintext "prevailing" with ciphertext if I don't change the key.

Can someone explain why that happens?

EDIT

If I leave IV and Key at 0 in PCBC I see a dim image silouette (I am using DES because I'm making a mode analysis). I also see the dim image silhouette if I increase the IV (with the key at 0), but if you increase the key (and keep IV at 0), the silouette is no longer visible.

I want to know if in the XOR and a big key the Ciphertext prevails over plaintext, because in that case I would have solved a problem in my PCBC analysis.

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I'm confused. What exactly are you seeing in the image? –  pg1989 Oct 9 '13 at 23:04
2  
I'm confused. Why are you using DES? –  nightcracker Oct 9 '13 at 23:07
    
If I leave IV and Key in zeros in PCBC I see a dim image silouette (I am using DES because I'm making a mode analysis) that happens also if you increase the IV (key in zeros), but if you increase the key (IV in zeros), the silouette is no longer visible, I want to know if in the XOR and a big key the Ciphertext prevails over plaintext, in that case I would have solved a problem in my PCBC analysis –  user2863147 Oct 10 '13 at 13:49
    
What you describe reminds me of the images at en.wikipedia.org/wiki/Block_cipher_modes_of_operation where they use them to show that ECB sometimes badly fails at hiding data patterns. –  e-sushi Oct 10 '13 at 15:17
    
This may be a problem with the key schedule. I would consider posting a link to examples to compare –  Richie Frame Oct 10 '13 at 18:44
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