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bio website github.com/CodesInChaos
location Frankfurt, Germany
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visits member for 3 years, 4 months
seen 8 hours ago

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.
Sep
23
comment Extracting only the entropy
If you manage to estimate entropy, then you can still simply truncate the hash to the estimated entropy. Entropy estimation and extraction are mostly independent.
Sep
23
comment Using Whirlpool hashing function to encrypt data
But of course HMAC causes another factor 2 slowdown of an already slow construction.
Sep
23
comment Using Whirlpool hashing function to encrypt data
Your operation can't be decrypted in the first place. So it's not even encryption.
Sep
23
comment Using Whirlpool hashing function to encrypt data
Your specific mode looks crazy. At best it's similar to ECB, which is a very weak block cipher mode. Your construction is actually fatally broken for some hashfunctions, since the DataBlock XOR hash step might interfere with their feed-forward operation.
Sep
23
comment Where is the S-Box generated in Rijandel/AES?
When using AES-NI instructions it's not even hardcoded in software, it's hardcoded in hardware :)
Sep
23
comment Where is the S-Box generated in Rijandel/AES?
I didn't listen to the talk, but perhaps you're confusing round-keys and s-boxes. Round-keys can be computed on the fly or precomputed. In the latter case, they're computed during key setup.