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Feb
16
suggested approved edit on lfsr tag wiki excerpt
Feb
16
revised Berlekamp-Massey algorithm: case when sequence length is less than double the length of the LFSR
edited tags
Feb
16
comment AES encryption with shared IV
What are you using as integrity checks? A MAC every packet or every "message" (is there a difference? I suppose you are using TCP so is a "message" defined by your application?) and are the client and server authenticated upon handshake?
Feb
16
comment AES encryption with shared IV
Why do you need to send an IV with every packet to begin with? If you are trying to defend against replay attacks, there are better ways to go about that.
Feb
15
comment Low complexity implementation of a small blocksize cipher (< 64 bit)
@D.W. Thank you, that makes sense.
Feb
15
comment Low complexity implementation of a small blocksize cipher (< 64 bit)
I would consider the $2^{22}$ block limit as a deal breaker, to be honest. That means you can barely encrypt 20MB of data before having to change IV's. But of course it depends on usage. Also, isn't the probability of "problem" more like $1 - e^{- b^2 / 2^{45}}$? I'm thinking of the birthday paradox and probability of a collision, though that doesn't apply for all modes of operation.
Feb
14
comment Use of CBC-AES-256 to encrypt usernames
@amaterasu Doesn't that mean he can brute-force every username if you are reusing key+IV?
Feb
11
comment PBKDF2 for key diversification
How much entropy does your master key have? Whether or not you need a PBKDF depends on that.
Feb
9
answered brute force attack on KDF vs KEY
Feb
9
comment Name for identical operations for encryption and decryption
This is not worth an answer, but the closest mathematical term I can think of would be an involution. I am not sure if there is a cryptographic term for primitives which satisfy this property.
Feb
8
comment AES implementation in java that allows key of 320-bit length
Key derivation function.
Feb
7
reviewed Reject Are there two known strings which have the same MD5 hash value?
Feb
7
comment How to best obtain bit sequences from throwing normal dice?
@PaŭloEbermann To be fair the term "subcritical" is usually used in the context of probability distributions and not events, but I like to use it to highlight a particular asymptotic behaviour at probability 1.
Feb
6
comment How to best obtain bit sequences from throwing normal dice?
@PaŭloEbermann Yes, subcritical means less than 1. As long as the probability is less than 1 the algorithm will terminate and the expected number of rolls is finite (though it tends to infinity as the probability approaches 1)
Feb
6
comment How to check the strength of an encryption algorithm?
@Mok-KongShen And therefore, bitwise addition is a "primitive" as well. Where should the line be drawn? Obviously, where it matters, and that is always at protocol level (below that, we're talking more about "mathematical primitives" than anything else). Put differently, an S-Box provides no security properties on its own - it is merely a more or less nonlinear mapping - but does in the context of a cipher or a hash function - like DES - where its nonlinearity can be assessed with respect to criteria such as resistance to linear/differential cryptanalysis, etc...
Feb
6
comment How to check the strength of an encryption algorithm?
If you want to learn cryptography: break first, design later.
Feb
6
comment RSA primes vs. largest known primes
It is also possible to select an integer in such a way that deterministically proving its primality be efficient (general-purpose deterministic tests are kind of slow, but for instance knowing the factorization of $p - 1$ helps a lot) should you need that. Most cryptographic applications don't need to unconditionally guarantee the integer is prime (so they just pick at random) but sometimes a primality certificate may be desirable.
Feb
5
comment How to check the strength of an encryption algorithm?
If you have to ask, it's not secure at all.
Feb
4
comment Entropy in natural language texts
How is collecting a huge library of texts, and generating something that sort-of kind-of looks random from it, simpler and less awkward than generating 128-256 pseudorandom bits from a well-vetted and easily accessible source of entropy? Your scheme doesn't even let you measure the amount of entropy you're collecting to any degree of accuracy ("entropy" is a lot more than just "english text has 0.6 to 1.3 bits of entropy per character").
Feb
4
comment Entropy in natural language texts
Which is exactly what I said. What advantage does your scheme have over, say, using AES? And what advantages does AES have over yours? In your application, that is.