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seen Apr 16 at 16:00

Jul
14
comment Encrypted counter as IV in CBC mode encryption using same key
If the IV was encrypted using a separate key then taking advantage of this scheme would be equivalent to somehow predict the values of an AES-CTR based PRNG. Since you're using the same key the reasoning doesn t apply but is there a reason why you can t derive 2 keys from your initial key and then go about your buisness ?
Jul
13
comment Is OpenPGP vulnerable to the “crypto doom principle”?
Actually Sign-Then-Encrypt is worse than its Symmetric counter : in the public key setting, you can forward messages to make them appear having come from the original signer
Jul
10
comment Selecting bijective functions for permutations
I would also suggest taking a look at the permutation inside Keccak, it doesn't use any S-Boxes either...
Jul
5
comment Is this ECC encryption key sharing method okay?
The key being used here is always the same which means that you're basically doing ECDH followed by regular symmetric encryption. Thus you need to be careful as to how much data you're going to encrypt with your key.
Jun
26
answered How do you find the inverse degree of a hash function?
Jun
13
comment Is it possible to cryptographically prove when was the last time a ciphertext was decrypted/encrypted?
Given that you can make multiple copies of the same document I don't really see how you can be assure that a document wasn't encrypted/decrypted.
Jun
6
answered Composition of block ciphers and 3DES
Apr
29
comment Custom crypto library in C
I don't understand how the sleep function can help you prevent timing attacks : how do you know how much time you need to sleep ? Also if your using the worst case running time as a reference you need to know what it is precisely on the platform your library is running which requires fine tuning after every install which. May I ask why you're not using and existing library (NaCl, openssl ect) ?
Apr
10
answered EC equivalent for RSA-OAEP
Apr
9
answered Signature schemes for underpowered devices (8bit microcontroller)
Mar
14
revised Is this encryption algorithm build from MD5 secure?
added reference to Hash CFB
Mar
6
comment Is this encryption algorithm build from MD5 secure?
Look at the effect of flipping a bit in the last ciphertext block, if I understood the algorithm correctly this only flips the corresponding bit in the last plaintext block which might be useful if you know the format of the message even if you don't know the content
Mar
6
answered Is this encryption algorithm build from MD5 secure?
Feb
23
comment Why nobody considers counter re-keying as a standard Block Cipher Mode?
Interestingly those approaches are looked at carefully in the context of side channel attacks : this prevents differential power analysis (since we cannot get traces on the same key) and the counter measures for SPA are well understood
Feb
19
answered Could use an explanation of the notation for an oracle adversary
Feb
15
comment Encrypting a key with the same key
Practically speaking it's so unlikely that it cannot be called "insecure". Theoritically speaking, if you take a look at the insides of aes you'll see that the first operation is xoring the plaintext with the key, effectively cancelling the state whatever the key. From then on the only difference between $AES_K(K)$ and $AES_{K'}(K')$ will come from the difference in the key scheduling of both keys. Hope it helps
Feb
9
comment Name for identical operations for encryption and decryption
What you consider a weakness can also become a strenght in some contexts. For example, embedded designs have very strict space requirements : having a encryption algorithm that is its own inverse is then something really valuable. Even in software it can be thought of as a good idea : less code means easier maintainability. Anyways I would say that while you're not wrong, if you can avoid it, do not give an encryption oracle to your adversary in the first place !
Jan
23
comment Initialize a PRNG with a password
I think I understand but generating with weak randomness isn't worth the fact that you don't have to store your keys. If I could store 256 bytes I rather seed my DPRNG with actual randomness then use [tools.ietf.org/html/rfc2898#section-6.2] to protect the key ?
Dec
19
comment AES vs Blowfish taking key-length into account
When considering the margin of security one should not forget that AES is THE target for more than 10 years now while the cryptanalitic effort on blowfish is not as strong nowadays
Dec
18
comment Good enough deterministic PRNG based on hashes
Good point, I forgot about the key reduction step