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bio website github.com/CodesInChaos
location Frankfurt, Germany
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visits member for 3 years, 1 month
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Jun
25
reviewed No Action Needed Non-malleable file encryption using AES XTS 256?
Jun
25
reviewed No Action Needed Finding a keylength in a repeating key XOR cipher
Jun
25
comment Best Asymmetric Encryption Standard for Communications?
I'd look at OTR and CurveCP. Not necessarily because they're what you want to implement, but because they're interesting to study. CurveCP has similar goals as SSL/TLS but is much easier to understand. OTR is interesting because it offers strong forward secrecy and deniability.
Jun
24
revised md5: is reverse length-extension attack possible?
edited tags
Jun
24
comment Is it possible to derive the midstate of a sha256 hash?
related: md5: is reverse length-extension attack possible?
Jun
24
comment Map Bytes to Number
There are several very similar question on stackoverflow. For example my own enerating uniform random integers with a certain maximum
Jun
24
comment If we can find prime numbers larger than 17 milion digits, why can't we find all 1024bit primes?
You are able to tell me a 100 digit number. So why can't you tell me all 9 digit numbers?
Jun
23
comment How is key rotation defined?
The question here is what you want to achieve with key rotation. Key rotation by itself doesn't do anything useful. One you decide on the desired security properties you can figure out what measures you want to take to achieve them, possibly including key rotation.
Jun
23
comment How to pad messages with large amount of padding
@StephenTouset If you apply say 2% padding, that's usually enough to hide which video you encrypted and not just that you encrypted some video. So even if you only apply a moderate amount of padding the gain is pretty big. The current version of Tahoe-LAFS doesn't apply padding, which I consider a pretty big flaw.
Jun
22
comment How to pad messages with large amount of padding
@StephenTouset For email like systems timing isn't that big a concern, but if you care about timing I'd worry more about higher level systems working on the plaintext rather than about the padding stripping code. Since this padding is protected by the MAC a timing difference doesn't allow forgery or anything really bad beyond losing a bit of length hiding.
Jun
21
awarded  Pundit
Jun
20
revised Verify Signature Failed
deleted 1 characters in body
Jun
19
reviewed Approve suggested edit on Difference between “one-way function” and “cryptographic hash function”
Jun
19
comment Is using EAX mode with a 64-bit block cipher a bad idea?
A 64 bit authentication tag isn't a big problem. Authentiation tags are not subject to offline attacks. With an ideal 64 bit MAC each forgery has a $2^{-64}$ chance of being accepted. Thus HMAC-SHA256 with a 128 bit key truncated to 64 bits would give okay security. But I don't know how close EAX is to an ideal MAC. Many AEAD schemes decay as message length increases or as more messages are observed. I'm too lazy to investigate how EAX fares. There is also the concern of birthday problem related attacks with $2^{32}$ cost.
Jun
19
reviewed Reject suggested edit on prime-numbers tag wiki
Jun
19
comment Is there a hash function which has no collisions?
There are collision free one way functions. For example $y = g^x \mod p$. But I'm pretty sure that SHA-512 would be a better choice, despite the collisions.
Jun
18
comment Can two cipher letters per plaintext letter easily defeat character frequency analysis?
Sounds like a homophonic substitution cipher.
Jun
18
reviewed Approve suggested edit on Hash function with values in a multiplicative group of prime order
Jun
17
comment Hash function with values in a multiplicative group of prime order
which group are you using?
Jun
17
reviewed Approve suggested edit on Can cryptography be used to hide routing information from the router?