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19h
comment Prime factorization
@tylo GNFS depends on the size of the number. But some other algorithms like ECM depend on the size of the smallest factor. If your factors are small enough so that ECM is faster, then the cost will depend on the size of the factors. If all the factors are big enough so that GNFS is faster, the size of the factors doesn't matter.
19h
comment Prime factorization
Since factoring a 512 bit semiprime costs about $100, it's clearly more than a standard computer can do in a few hours. Your number has 392 bits, so factoring would be relatively cheap, but I don't know if it'd fall below your limit. If the number has small factors, ECM should be faster than GNFS.
1d
comment Security aspects of using a global values as nonce and additional data for AES?
Strictly speaking, you must never reuse a (key, nonce) pair.
1d
comment How are onetimepads distributed?
Both parties could meet in person and exchange a disk containing the pad. Or perhaps you send a diplomatic courier with the key material in a sealed bag. The annoying key-distribution is one of the reasons why one-time-pads aren't very popular.
2d
comment Can Grover's algorithm be parallized?
@mikeazo I think I was asking the wrong question. I've changed it a bit, to be closer to what matters for attacks on cryptography.
2d
comment What is the “compression function” in Merkle-Damgård?
Yes. MD is a domain extender which turns a fixed input size hash into a variable input size hash.
2d
comment Is it possible to break enigma code with a todays laptop
When you say "rollers", you mean the "rotors", right?
2d
comment side channel attacks against TDES (compared to AES)
Concerning [3des] vs [tdes], we've now added [tdes] as a synonym for [3des].
2d
comment Super-simple encryption of short strings
1) Why use encryption at all? I'd rather use a lookup table/tokenization. 2) If you want to use crypto, why use format-preserving-encryption? 2) Anonymizing data sets is hard. It's often possible to correlate data from different sources to deanonymize such data.
2d
comment side channel attacks against TDES (compared to AES)
So it wasn't just a timing attack, but a power analysis attack? In that case you're pretty much doomed with any general purpose CPU. If you want to prevent attacks where the attacker has physical access to the device, you should use special purpose hardware designed to make these attacks harder. The choice of cipher matters far less compared to how much effort the hardware designer put into preventing those attacks.
2d
comment side channel attacks against TDES (compared to AES)
I don't think the AES side-channels are as big as you think. If you're referring to DJB's paper, he used a very precise timer on the server to attack AES.
2d
comment Encrypt music loops for reading but not copying
This is abour DRM, not about achievable security objectives.
Apr
21
comment AES encryption only taking 32 bits
This is a programming problem, not a crypto problem.
Apr
20
comment what are the NTRU keysize and application in industry ?
NTRU is patented, which has hampered adoption.
Apr
20
comment DHKE choice of private keys
You can apply the same logic to any particular private key. The attacker guessing correctly that your private key is 1 is just as unlikely as the attacker correctly guessing it's another value. 1 isn't special.
Apr
20
comment DHKE choice of private keys
Doesn't a 128 bit exponent result in a 64 bit security level? A 256 bit exponent might be wiser.
Apr
20
comment DHKE choice of private keys
Obviously the shared secret would be the same as the public key if the private key is 1. But I don't see how that's a problem. A good stream cipher occasionally outputs zero bytes as well, in which case the ciphertext byte will equal the plaintext byte.
Apr
20
comment DHKE choice of private keys
I wonder why $1$ is missing in your examples, it looks like a perfectly fine private key to me. I'd choose the private key $x$ to fulfill $0<x<q$ where $q$ is the order of the generator (typically $(p-1)/2$).
Apr
20
comment DHKE choice of private keys
If you forbid $p-1$, shouldn't you also forbid $(p-1)/2$?
Apr
20
comment Is it ever unsafe to compress an EC point?
@poncho Curve25519 has $p \equiv 5 \pmod 8$. P-224 has $p \equiv 1 \pmod 4$. But there are efficient algorithms for computer square-roots in both of those fields.