CodesInChaos

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bio website github.com/CodesInChaos
location Munich, Germany
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visits member for 1 year, 9 months
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May
11
 comment Disk Erasing Security - Odd Number of Writes
Number of passes is irrelevant. If you actually overwrite the data once it's enough. Multiple overwrites were only necessary decades ago. The real problem is that it's hard to ensure that the data is overwritten at least once. Things like wear-leveling, defect sectors, shadow copies etc. can lead to copies of the data remaining even after you tried to overwrite them.
May
11
 comment How can I punish a hacker?
@ClickUpvote Everybody makes mistakes occasionally. If somebody makes enough of them and the police puts in the effort to dig through all that data you might catch someone. Often they catch one in a group and then use him as a mole to catch the rest.
May
10
 comment I found that the company I work for is putting a backdoor into mobile phones
It's easily possible to write backdoors that can't be used by anybody else.
May
8
 comment Is there any particular reason to use Diffie-Hellman over RSA for key exchange?
There is one significant difference between DH and RSA-encryption: DH implicitly authenticates both sender and receiver, whereas RSA only authenticates the receiver. If you want to authenticate the sender in a non interactive scheme, RSA can't easily replace DH.
May
8
 comment Generic defense againt SQL injection
ASP.net has similar "protection" by default.
May
8
 revised Is there any particular reason to use Diffie-Hellman over RSA for key exchange?
added 266 characters in body
May
8
 answered Is there any particular reason to use Diffie-Hellman over RSA for key exchange?
May
6
 comment Filtering In Iran
Tor with Obfsproxy might still work.
May
2
 comment Why is RSA using fixed point type numbers?
RSA uses integers, not fixed point. (Unless you see integers as special case of fixed point, but that's not an enlightening view in this context).
May
2
 comment Encrypting using AES 256, do I need IV?
1) In two-way communication I'd use a different key for each direction. Use HKDF to derive them from a master key. 2) If you use CBC mode you need to communicate a new IV per message (like TLS 1.1+ does it) or in theory you could derive it from the message number. Look up the BEAST attack for why you need a new random IV per message. 3) Consider using SSL/TLS. Learning to do crypto correctly takes quite a bit of time and it's still error prone. If you just need two-way communication use the standard solution.
May
2
 comment Encrypting using AES 256, do I need IV?
Side-note: Don't write symmetric crypto before you learn what authenticated encryption is and why you should use it.
May
2
 answered Encrypting using AES 256, do I need IV?
Apr
28
 comment What are the practical uses of large asymmetric keys?
I'd rather use ECC than huge RSA. A 256 bit curve is about as strong as 3000 bit RSA and the advantage of ECC increases the higher the desired security level.
Apr
28
 comment Asymmetric encryption algorithms
@Matthew That's why you should use hybrid encryption. Choose a random key, encrypt the actual message with symmetric crypto (for example AES-GCM) and then encrypt that key with RSA (don't forget proper padding i.e. OAEP).
Apr
28
 comment Should cookies that contain non sensitive information be encrypted?
typically a session ID is a random 128 bit value that the server looks up in some database/file to figure out which user it matches. On logout the server deletes the token from that database.
Apr
28
 comment How are large tech sites such as LivingSocial, Zappos, LinkedIn and Evernote hacked?
If a single missing mysql_real_escape_string can compromise your site, then your main mistake was using a bad API, not the forgotten escape. There are very few places where one wouldn't use parameterized statements.
Apr
28
 comment Should cookies that contain non sensitive information be encrypted?
The username can't be the only information in the cookie when tracking a logged in user. You clearly need some form of unguessable token, such as a session ID as well. Once you have that, you don't need to store the username in the cookie at all.
Apr
27
 comment Prevent DOS against RSA authentication
These ECDH numbers are still pretty low. For example a portable c implementation of Curve25519 can do 4.5k exchanges per second per core on a slightly faster computer.
Apr
26
 comment Prevent DOS against RSA authentication
You could use elliptic curve diffie hellman instead of RSA. That way a dedicated server should be able to do 5000+ keyexchanges per core and second.
Apr
25
 comment Authenticating a ciphertext
With MACs you still have quite a bit of deniability. Especially if you leak the MAC secret after it was used, like OTR does. But since courts are often happy to accept plaintext logs, this might be rather academic.
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