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bio website github.com/CodesInChaos
location Frankfurt, Germany
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visits member for 3 years, 3 months
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Oct
30
comment How to develop a public key cryptosystem based on a hard problem?
For asymmetric encryption or key-exchange your system needs lots of mathematical structure. Almost all one-way functions are not suitable. For example with diffie-hellman key-exchange you not only need the property that $A=G^a \mod p$ is hard to invert, you also have the property that $A^b=(G^a)^b = G^{ab} = (G^b)^a = B^a$ i.e. you are able to compute the same shared secret using $A$ and $b$ or $B$ and $a$. Where lowercase letters are private keys and upper case letters the corresponding public keys.
Oct
30
comment How to develop a public key cryptosystem based on a hard problem?
You only described a one-way function so far, something similar to a hash function. You didn't say where the asymmetric component comes in.
Oct
30
reviewed Approve suggested edit on Why does the new encryption scheme proposed by authors stop an adversary from guessing the subspace of the secret key?
Oct
30
comment How does the IV or initial counter increase internally for each block in AES CTR mode?
There isn't really a one true CTR mode. There are many different variants of CTR mode which differ by how they compute the per-block input from IV and counter.
Oct
29
comment Making ECDSA public keys one bit shorter
For a fixed generator there cannot be a significant subset of weak keypairs since you could use that to break all of them.
Oct
29
comment How good is using AES CTR mode with initial counter as 0?
One problem with constant IV is that it enables multi-target attacks. When using AES-128 an attacker you can break all messages encrypted with this scheme with $2^{128}$ work and break one random message cost only $2^{128}/t$ for $t$ known ciphertext. So I'd avoid constant IVs with 128 bit keys, but 256 bit keys it doesn't really matter.
Oct
29
comment Deterministic nonces in CTR mode
One problem with constant IV is that it enables multi-target attacks. When using AES-128 an attacker you can break all messages encrypted with this scheme with $2^{128}$ work and break one random message cost only $2^{128}/t$ for $t$ known ciphertext. So I'd avoid constant IVs with 128 bit keys, but 256 bit keys it doesn't really matter.
Oct
28
revised Hi Sec National algorithm
deleted 26 characters in body
Oct
28
reviewed Approve suggested edit on What is the limit of plaintext required to break the Vigenère encryption?
Oct
28
comment Definition of a CSPRNG
If an application wants to offer forward secrecy it needs a PRNG that can't be run backwards.
Oct
28
reviewed Approve suggested edit on The weak link is the password?
Oct
26
comment The weak link is the password?
For password based encryption the password is usually the weakest link. It's one of the reasons for avoiding passwords as much as possible.
Oct
26
comment Timing Attacks on ECDSA, ECDHE, AES and SHA2
I'd expect typical implementations of SHA-2 to resist timing attakcs, but naive implementations of all others should suffer from timing attacks. What's tricky is figuring out in which situations they're practical and in which they are not.
Oct
25
comment RSA with modulus product of many primes
A related question: Are there any standards of multi-prime RSA key generation? and AGL's blog post about how security and performance scale with the number of primes
Oct
25
comment RSA with modulus product of many primes
You can use multiple primes as long as they're large enough. It gives you less security for a given modulus size, but it can give you a better performance/security trade-off.
Oct
25
reviewed Approve suggested edit on Hypothetical unknown cipher - security in obscurity?
Oct
25
revised How do I prove that this PRNG is easily distinguished from a random sequence of numbers (modulo m)?
added 5 characters in body
Oct
24
comment Knowing pre-encryption data, can we find the private key CryptoLocker used?
No, if they implemented asymmetric encryption properly, such attacks are not possible.
Oct
24
answered How to design a cryptographically secure file hosting service
Oct
24
comment RSA decrypt long messages (javascript)
Please don't cross-post