in a code of encryption if y=mod(x,256); is used. how can i apply the same statement in decryption process to get x back if i have only y and 256 know..

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tania
tania 2016-1-2
评论： tania 2016-2-11
encryption scheme i used was bit level permutation

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Jan
Jan 2016-1-2
编辑：Jan 2016-1-2
You can't. If x is smaller than 256, the modulo operation replies x without changes. If x is larger than 256, this operation replies the remainder of the division, and the other information is lost. So if you do not store the value of floor(x / 256) anywhere, this "encryption" is not reversable in a unique manner.
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Walter Roberson
Walter Roberson 2016-2-9
That paper has an incorrect algorithm unless there is a non-standard notation that is explained earlier in the paper or unless there is a typesetting mistake in the formula. I would need a printed copy of the paper (based upon the original manuscript, not an image of it), and a magnifying glass to be certain, but with the image you have given the algorithm certainly appears to be wrong.

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