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bio website github.com/CodesInChaos
location Frankfurt, Germany
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visits member for 3 years, 4 months
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Oct
22
comment Encrypt a file for random access but only after an initial read of the whole file
I wouldn't bother. Just focus on using a good password based KDF (such as scrypt). That way an attacker can verify the file with only a few bytes but they still incur the cost of the KDF for each password.
Oct
22
comment Encrypt a file for random access but only after an initial read of the whole file
@StephenTouset As far as I can tell it does. You first need to commit to a password and then process the whole file to learn the actual key and thus any information about the file.
Oct
21
comment Small Prime Difference in RSA
Where is the advantage of this over straight up trial division starting at $\sqrt{n}$?
Oct
21
comment Why do the elliptic curves recommended by NIST use 521 bits rather than 512?
Primes of this form $2^n-1$ are known as Mersenne primes.
Oct
21
comment Small Prime Difference in RSA
1) Compute the square root of the product. 2) Go to the next odd number. 3) Test if division works. 4) If not, add 2 and repeat from step 3.
Oct
20
comment Protection of Elliptic Curve Implementations against side-channel attacks
Some people care about software implementations and talk about the relevant performance and side channels, other people care about hardware implementations and talk about the relevant performance and side channels. The linked talk falls in the software category.
Oct
16
comment How do you test randomness?
Short answer: You can't test if it's good. You can only check if it's bad in specific ways.
Oct
14
comment Can Diffie-Hellman be scaled up or force-multiplied?
@AndrewHoffman That's the case, but I don't get your point. If establishing a connection needs a terabyte RSA key and hours of computation, that's not acceptable performance for me.
Oct
14
comment Can Diffie-Hellman be scaled up or force-multiplied?
When you're worried about quantum computers, don't use RSA or Diffie-Hellman. With these algorithms increasing sizes enough to avoid QCs implies unacceptable performance for the defender.
Oct
13
comment How can convert affine to Jacobian coordinates?
Note that the division in the Jacobian -> Affine transformation is based on the Modular multiplicative inverse. You can't just use the integer division operation offered by common programming languages.
Oct
10
comment How does MD5 process text which is shorter than 512 bits
Like all Merkle-Damgård hashes, MD5 is susceptible to length extension attacks even with padding. What proper padding prevents is trivially collisions between a message and a padded message. As an example of such trivial collisions, look at PBKDF-HMAC-x.
Oct
10
comment Is it possible to demonstrate that md5(x) != x for any x?
@Desthro The input to MD5 is variable length and supports 128 bit inputs. You're confusing the MD5 compression function, which has a 512 bit input, with the MD5 hash.
Oct
10
comment Block Cipher Modes
Concerning your (5) something like $E[k_1](m \oplus k_2) \oplus k_2$ might be a better example of a mode like algorithm increasing the brute force cost.
Oct
9
comment Is .NET DESCryptoServiceProvider secure in this case?
If you want to secure communication between two computers, you're better off with SSL/TLS than using low level crypto.
Oct
9
comment Is .NET DESCryptoServiceProvider secure in this case?
If you're a beginner, use jbtule's answer to Encrypt and decrypt a string. It's one of the few secure examples of symmetric encryption using C#.
Oct
9
comment Security analysis of Spritz?
@owlstead At least choosing constants is often done via computer optimization and it's not unusual to try variations of a algorithm and check which has the nicest properties.
Oct
9
comment Do Export Restrictions Still Apply To The Key Length of RC4?
There is still some export regulation, but it boils down to "fill out a certain form" to register your strong crypto export.
Oct
3
comment RSA given q, p and e?
Sounds like you're using doubles instead of big integers.
Oct
3
comment Alternative to NSA encryption algorithm
Quantum computers can efficiently compute discrete logarithms in groups, including finite fields and elliptic curves. So Diffie-Hellman is dead once QC's capable of running Shor's algorithm appear.
Oct
2
comment Hardness proof?
We can also show that AES-CBC is secure as unauthenticated encryption if AES itself is a secure block cipher.