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Sep
8
comment Variable length variable output encryption with out any padding?
Look for format preserving encryption. But if you can afford it, you should use an IV and a MAC, even if they cost a couple of bytes.
Sep
7
comment How To prove Any Change to $v=a\cdot y+b$ maks $y=(a)^{−1}\cdot (v−b)$ Uni. random value
Please do not ask nearly identical questions on multiple sites of the stackexchange network. How To prove Any Change to v=a⋅y+b maks y=(a)−1(v−b) Uni. random value on math.se should suffice.
Sep
6
reviewed Approve OpenPGP Public-Key algorithm
Sep
6
comment Calculation of time needed to crack DES with my CPU
A playstation 3 seems to be able to test about a 850 million DES keys per second.
Sep
6
revised Calculation of time needed to crack DES with my CPU
edited tags
Sep
6
comment Calculation of time needed to crack DES with my CPU
5000 CPU cycles per block sounds quite slow to me.
Aug
22
awarded  Enlightened
Aug
22
awarded  Nice Answer
Aug
20
comment Shuffleless PRNG function with non-repeating values?
search for format preserving encryption and ffx mode.
Aug
20
comment Shuffleless PRNG function with non-repeating values?
Skip32 and ipcrypt have 32 bit blocks.
Aug
19
comment File encryption with AES CTR mode
Reused kev/iv pairs amount to a many-time-pad. For many kinds of data, such as txt or html files this leaks a lot of information seeing 2 versions and nearly perfect recovery seeing 3 versions. We have several questions about that, just search a bit.
Aug
16
comment How to verify the integrity of RSA encrypted messages?
@t0b0 That an attacker can replace the key and message is always the case for asymmetric encryption. You need to add some kind of sender authentication, such as a signature or DH+MAC if you want to prevent that. The concept vlp describes is known as hybrid-encryption and sound, as long as you take the pitfalls otus mentioned into account.
Aug
14
comment Chopping off SHA256 entropy?
The only reason to prefer SipHash over truncated SHA2 is performance. SipHash isn't even designed to be collision resistant.
Aug
12
comment Security impact of signing small data using RSA
Consider using HTTPS/SSL/TLS to secure the connection in addition to your signature scheme.
Aug
12
comment Security impact of signing small data using RSA
Are you using proper padding, like PSS?
Aug
10
comment How can I compare two hash algorithms?
The best way we know for determining the security of primitives is having experts trying to break it for years. It's unlikely that they'll bother to do so with your algorithm.
Aug
10
comment Is it possible to validate a Public Key in RSA?
There are efficient algorithms with which the owner of the key can prove that e and phi(n) are co-prime.
Aug
5
reviewed No Action Needed Attribute-based encryption for cloud storage
Aug
4
comment Why do crypto libs use table lookups when they're vulnerable to timing attacks?
@user54609 bitslicing is only efficient for parallelizable modes.
Aug
2
comment Is modular Barrett reduction usable for Ed25519?
The order is still pretty close to a power-of-two, so you can use a variant of the approach described at: What are the computational benefits of primes close to the power of 2?