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I'm an engineer with experience in applied cryptography, in particular in Smart Card systems.


Mar
21
comment Coding of unsigned int to prevent guessing next ID
Indeed. Or any block cipher with a small block, as common in Format-Preserving Encryption. I have re-tagged the question accordingly. Following that tag will lead to many related questions with good answers.
Mar
20
revised Information-theoretic bound on leakage by timing measurement
Polish rationale
Mar
20
comment Information-theoretic bound on leakage by timing measurement
@Maarten Bodewes: following your comment I added a rationale.
Mar
20
revised Information-theoretic bound on leakage by timing measurement
Added rationale
Mar
20
asked Information-theoretic bound on leakage by timing measurement
Mar
20
revised Do asymmetric signatures require constant-time verification?
Expand on message leakage
Mar
19
revised Do asymmetric signatures require constant-time verification?
Expand
Mar
19
revised Do asymmetric signatures require constant-time verification?
Expand
Mar
19
comment Do asymmetric signatures require constant-time verification?
@SylarMorgan: you are very right to mention the secrecy of the message! The first version of my answer had forgotten about that, shame on me, time to go to bed!
Mar
19
revised Do asymmetric signatures require constant-time verification?
Oups, forgot about message leak
Mar
19
revised Do asymmetric signatures require constant-time verification?
The hypothetical leak would likely be only partial
Mar
19
answered Do asymmetric signatures require constant-time verification?
Mar
19
comment Deterministically generate a RSA public/private key pair from a passphrase (with sufficient entropy)?
@Maarten Bodewes: I agree wholeheartedly, and thinking more about it find this very drawback has serious consequences.
Mar
19
revised Deterministically generate a RSA public/private key pair from a passphrase (with sufficient entropy)?
Expand on the major drawback identified and kindly added by Maarten Bodewes
Mar
19
revised Deterministically generate a RSA public/private key pair from a passphrase (with sufficient entropy)?
Some proofreading
Mar
19
revised Deterministically generate a RSA public/private key pair from a passphrase (with sufficient entropy)?
Expand to qualify for extra credit :-)
Mar
19
revised Deterministically generate a RSA public/private key pair from a passphrase (with sufficient entropy)?
Expand to qualify for extra credit :-)
Mar
19
answered Deterministically generate a RSA public/private key pair from a passphrase (with sufficient entropy)?
Mar
19
comment What happens when a RC4 stream gets corrupted?
If RC4 was secure in a related-key setup, you could "append the blocknumber to the key", run a separate RC4 for each block, and that would be safe as long as a block is not modified (which amounts to keystream reuse). Problem is, RC4 key scheduling is insecure when used in this way. $\;$ We are wandering far away from the original question when we deal with security issues in unspecified variants of RC4, and with your performance issue; you should ask a separate question. Be careful to state your requirements/constraints, including if you have to use RC4 (or just consider this).
Mar
19
comment What happens when a RC4 stream gets corrupted?
In any case, you MUST NOT "reset the keystate" to the same state for every block, which would be the equivalent of re-using a pad in the One Time Pad. $\;$ If the file is read and written sequentially, it is best to use RC4 as designed, that is without resetting it. If you must access the blocks in random order, you need a carefully thought RC4 variant, perhaps where the key and block number are somewhat combined to "reset the keystate".