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location Netherlands
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visits member for 2 years, 11 months
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Java and security expert with over 10 years of experience with the language and with the practical application of cryptographic protocols - including the design of protocols within international standardization bodies. Creator of a heavily used common criteria certified product. Over 30 years of experience with computers. Likes kids, cats, reading, movies and several sports.


5h
comment How to guess the encoding of a string?
Oh, toons in PNG format. Hint: first concatenate all the stings, then split on =. Then decode and save. There is an additional header that you may want to cut away. And it could be that there is no = delimiter. In that case you may get multiple files after each other. Good luck.
6h
comment Rijndael performance
@otus I think it means operations, but that does not make much sense over operations per second. So I'll leave it to the user to explain.
1d
comment The security of an encrypt-and-MAC
A few remarks: the ciphertext itself is not protected, so this scheme could be vulnerable to padding oracle attacks - they are not prevented by this protocol in itself. Furthermore, having a HMAC over just the plaintext is a bit dangerous, usually you want to at least include the IV in the MAC calculation - if it is used and send with the ciphertext. If other protocol information and the IV is included in the MAC calculation then I guess you can alleviate the requirement to separate keys per transaction.
2d
comment Verify signed file using GPG by passing in signature hosted online rather than stored locally (i.e. in keyring)?
What about wget or a similar cli utility?
2d
comment Protection of Elliptic Curve Implementations against side-channel attacks
@CodesInChaos You are probably right, but does it invalidate the question enough to close it?
Oct
20
comment Cryptography system that limits the length of the encypted message
Thank you for telling me all that, Tianren Lu, I never would have guessed.
Oct
19
comment Cryptography system that limits the length of the encypted message
Sorry, but a one time pad is basically a theoretical construct. Using it for a practical application such as SMS encryption is not a good idea. Using a stream cipher could work, but you would make sure that both sides stay in sync somehow.
Oct
19
comment Implementation of garbled circuits using RSA
@ThomasM.DuBuisson Maybe change that into an answer? Negative answers are answers just as well.
Oct
19
comment problem with “one time pad”
This is pretty well explained by - for instance - Boneh, isn't it? The idea of such practice is that you learn to do this yourself.
Oct
19
comment SHA-1 collision resistance
Anything missing from the given answer, dear new user? It's been a while.
Oct
17
comment Elliptic curve parameters
I don't think you can validate outputs efficiently by hand. If you have a well described question for a specific implementation you could post on StackOverflow.
Oct
16
comment Encrypting twice with different modes?
How much more difficult than AES-256 in CTR mode? If the CTR is well applied, that question doesn't make much sense. Assumed that they could brute force 128/256 bit AES keys? You might as well assume that the attacker already has the keys, that would be a much more believable scenario.
Oct
16
comment HMAC_DRBG Generate Process: requesting N bytes at once different from requesting N bytes in total?
Or maybe I'm just too used to the properties of KBKDFs :)
Oct
16
comment Does NSS fully implement PKCS 11?
OK, but I don't see anything in your question that assumes that this is about using the PKCS#11 interface from NSS. Especially the title seems contradictory. And I think that your comment about the PKCS#11 functions supported by NSS basically answers your own question :)
Oct
16
comment Comparing Files: Is it better to use multiple hash algorithms or just one?
OK, I see now. Sorry about that, you can just run until you find an inequality, and only test further if you don't find any. Slightly different use case as within most schemes.
Oct
15
comment AES: Guess Password using the unencrypted text?
Well, the lazy was a bit tongue in cheek. PGP makes a lot of sense here and you can encrypt without providing a password at all.
Oct
15
comment Comparing Files: Is it better to use multiple hash algorithms or just one?
@Gutblender True, makes much less sense for small files. Although hashes of course are really small, 32 bytes at most. And you could create a hash tree and check a complete folder at once as well.
Oct
15
comment Comparing Files: Is it better to use multiple hash algorithms or just one?
I understand that, but are you only going to copy files with no obvious inequalities? So, if there is no obvious inequality, you leave it? Wouldn't that cause corruption?
Oct
15
comment Comparing Files: Is it better to use multiple hash algorithms or just one?
How can you be prepared for collisions? If you see the same hash value, you will skip (and your result will be incorrect). If you don't you are back to square one.
Oct
15
comment How would I write my own asymmetric encryption algorithm (not RSA, DES etc)?
1. Define a one way trapdoor function, 2. fall through it :)