The Cryptographic Doom Principle

Re:The Cryptographic Doom Principle by angry_octet on Tuesday April 14, 2015 @01:43PM (#9375968)

So wrong. Your custom cipher could be leaking key material in the encrypted output, almost certainly leaks the key via timing channels, could be leaking the known cipher key by timing channels and more (and this is assuming separate keys).

The CC decode stage will be subjected to every possible edge case to see if it will do something dumb, like the oracle attacks mentioned in the article. And it could also leak information about the KC decode via timing attacks.

If this was for offline file encryption, where you do the steps separately, maybe okay. But not for online encryption where chosen plaintext is possible.

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Re:The Cryptographic Doom Principle by madez on Tuesday April 14, 2015 @01:51PM (#9376034)

Read this thread.

CC is a bijective function on (blocksize of KC) bits.

CC knows nothing at all about KC.

Implementation can be done in another computer without security problem while you get obscurity.

Read this thread.

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Re:The Cryptographic Doom Principle by angry_octet on Tuesday April 14, 2015 @02:05PM (#9376143)

You don't mention separate computers until now. It's a big difference. I thought we were discussing implementing crypto, not some theoretical properties you achieve when conditions are just right.

I'm not saying trust the Windows implementation of AES, you can put it through some other cipher with a strong implementation as well, but don't just make up your own one.

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