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bio website github.com/CodesInChaos
location Frankfurt, Germany
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visits member for 3 years, 3 months
seen 9 hours ago

Jun
4
comment If RSA is limited to 117-200 bytes or so, is that a very limited use case?
Some people call RSA a block cipher, but that is not a useful way of viewing it. RSA certainly doesn't fulfill the security requirements of a block cipher, and it can't be used in typical modes of operation.
Jun
4
comment If RSA is limited to 117-200 bytes or so, is that a very limited use case?
@RobertHarvey An RSA modulus is typically between 1024 and 4096 bits, minus padding this allows you to put a few hundred bytes in it. In theory it's possible to split the message into multiple RSA blocks to overcome the limit, but there are no standard ways of doing this because it's a really dumb idea.
Jun
4
comment ECC Point Multiplication of Product
What are you using for n? The order of the curve? Or the modulus of the prime field? Scalars need to be reduced modulo the order.
Jun
4
comment ECC Point Multiplication of Product
Are you using bigintegers? With double you'll get loss of precision, with small integers you get overflows.
Jun
3
comment How insecure in practice?
For DES the answer is that it can definitely be decrypted using brute-force. A 56 bit key is far too small.
Jun
2
comment Can i modify data “protected” by a CRC16?
@John Both. Brute-force is cheap at only 16 bits. It's also possible to compute it directly, but I don't remember details. I used that to fix the CRC32 of files to an arbitrary value by modifying 4 consecutive bytes in one of my projects.
Jun
1
comment Can i modify data “protected” by a CRC16?
If you can control at least 2 of the first 50 bytes you can fix the CRC.
May
30
comment How well analyzed are giant block length ciphers?
The website you linked is certainly full of bullshit. A 256 bit block and 256 bit key is certainly enough for almost everything.
May
30
comment How well analyzed are giant block length ciphers?
It's easy to construct a large block blockcipher from a normal block cipher with a factor 2 performance hit. So I see little reason to use dedicated large block blockciphers.
May
25
comment What security authorities and standards reject $e=3$ in RSA, when, and with what rationale?
You don't need random padding to avoid the $e$ recipients vulnerability. You could make the padding depend on the recipient's public key e.g. hash(e||n).
May
25
comment Is Base64(SHA1(GUID)) still unique like the original GUID?
The length of a GUID is 16 bytes. You can encode these bytes as a 32 byte hex string.
May
25
comment How random are commercial TRNGS
There is one important pitfall about "injecting 160 bits is enough". You need to inject them all at once, without the attacker being able to observe the output of the PRNG in between.
May
25
comment How random are commercial TRNGS
@user1028028 Why does it matter if a PRNG is periodic? The universe will be barren and cold long before any computer finishes a whole period.
May
24
comment What is the fastest elliptic curve operation f(P) in affine coordinates such that f^n(P)=P only if n is large?
Can you describe what problem you actually want to solve?
May
22
reviewed Approve suggested edit on srp tag wiki
May
22
reviewed Approve suggested edit on srp tag wiki excerpt
May
22
comment How much data can I encrypt with AES before I need to change the key in CBC mode?
Another part of risk management is assessing how big the damage is. For an IV collision with AES-CBC it's typically not very big.
May
20
comment Is Wikipedia's table about SHA-2 collisions correct?
The :24 is probably referring to a version reduced to 24 rounds.
May
15
comment calculating beta for elgamal elliptic curves
I'd use an existing ECC library which offers a scalar multiplication function. But if you implement it yourself you can look at the Explicit-Formulas Database which as addition/doubling formulas for many curve forms.
May
15
comment calculating beta for elgamal elliptic curves
@BobbDizzles You need to look up the point addition and doubling formulas for your curve form.