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bio website github.com/CodesInChaos
location Frankfurt, Germany
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visits member for 3 years, 6 months
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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 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 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 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 Can cryptography be used to hide routing information from the router?
Jun
17
reviewed Approve Anonymity in end-to-end encryption
Jun
15
comment Security of authenticated encryption modes gcm & ccm
If robustness is more important than performance, then I prefer HMAC+encryption in a encrypt-then-MAC scheme over GCM and the like.
Jun
15
reviewed Approve How do I decrypt ciphertext with this cipher?
Jun
15
comment Can cryptography be used to hide routing information from the router?
It's not obvious to me that homomorphic encryption helps here
Jun
14
reviewed Approve Why is H(message||secret_key) not vulnerable to length-extension attack?
Jun
14
revised Why is H(message||secret_key) not vulnerable to length-extension attack?
added 64 characters in body
Jun
14
reviewed Approve understanding a length extension attack