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bio website github.com/CodesInChaos
location Frankfurt, Germany
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visits member for 3 years, 4 months
seen 51 mins ago

Sep
28
comment Is there any implementation of scrypt that allows a specific limit on memory?
@RickyDemer If you run multiple computations in parallel, the memory multiplies with the number of those instances, but if you run them sequentially it does not. You should set the memory parameter so that your total RAM can support all your CPU cores. Once you increase the parallelism parameter beyond your CPU cores, only the runtime increases.
Sep
28
comment How to perform benchmark of block/stream ciphers?
eBACs is a popular benchmarking suite which includes stream ciphers. You should be able to include your own ciphers into it.
Sep
28
revised Why is AES not a Feistel cipher?
deleted 3 characters in body; edited tags; edited title
Sep
27
comment Pre-image resistant but not 2nd pre-image resistant?
There are some hashes with use more rounds for finalization than between consuming inputs. For those it's pretty likely that first pre-images are much harder to find than second pre-images.
Sep
27
comment Why does second pre-image resistance imply pre-image resistance
Their definition of first pre-image resistance seems to be that it's hard for most inputs to find the original input. My pathological example only works for a few inputs.
Sep
27
revised Why does second pre-image resistance imply pre-image resistance
added 436 characters in body
Sep
27
comment Why does second pre-image resistance imply pre-image resistance
hmm I can't think of a way that gives an n bit hashfunction n bit second pre-image resistance without giving it n bit first pre-image resistance. Perhaps their definition has some additional constraints.
Sep
27
comment Why does second pre-image resistance imply pre-image resistance
For example consider the pathological 512 hashfunction that concatenates the first 256 bits of the input with the output of a a secure 256 bit hashfunction. This isn't first pre-image resistant, but has 256 bits of second pre-image resistance.
Sep
27
comment Why does second pre-image resistance imply pre-image resistance
It doesn't. So where did you find that claim?
Sep
27
comment Shamir's Secret Share
A computer can't represent real numbers
Sep
26
comment Is modern encryption needlessly complicated?
You seem to have a weird definition of "full understanding". IMO even its designers don't come anywhere close to fully understanding it. For example for basic understanding AES s-boxes, you need to understand binary finite fields. You need to understand how differential works, why there are no simple formulas that can solve AES for the key,... Even basic understanding of AES requires a lot of study. As a practical example consider the NSA tweak to DES. Cryptographers needed decades to understand that simple tweak. If you don't understand the consequences of that tweak, you don't understand DES
Sep
26
comment Using Whirlpool hashing function to encrypt data
Or you could simple undo the feed-forward. That way you directly get a block-cipher. No need for a Feistel network.
Sep
26
awarded  Civic Duty
Sep
25
comment Algorithm for sharing secret information with redundant keys
A common choice is Shamir's Secret Sharing
Sep
25
comment Is there a developer's resource that ties encryption methods and strengths to the appropriate usage scenarios?
For the password part, see How to securely hash passwords? on security.SE
Sep
24
comment Could completely public passphrase hashes ever be reliably secure?
For good passwords yes, for bad passwords no. Unfortunately typical passwords are bad.
Sep
24
comment Achieving 256-bit encryption strength with PBKDF2 - HMAC-SHA1
For the "compute part of the output cheaply" issue I recommend using HKDF-Expand as second step, that way one can produce arbitrarily sized output at little cost.
Sep
24
comment Why is RSA encryption significantly faster than decryption?
Encryption and signature verification are much faster than decryption and signing when using RSA. The public exponent e is small (typically 17 bits) and the private exponent d (~1024 bits) is large leading to a cheaper calculation for $m^e$.
Sep
24
comment Achieving 256-bit encryption strength with PBKDF2 - HMAC-SHA1
Are you expecting passwords with ~240 bits of entropy? You only get that much entropy with an epic passpoem.
Sep
23
comment What is the security loss from reducing Rijndael to 128 bits block size from 256 bits?
@owlstead It certainly seems attractive to use it for disk encryption, it's a natural tweakable blockcipher with large blocks. XTS mode is a bit ugly, and 128 bit blocks are a bit narrow, so AES-XTS doesn't look so good to me.