CodesInChaos

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bio website github.com/CodesInChaos
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Sep
7
 comment S-box design criteria and random sboxes
At least in the case of DES, the s-boxes were stronger than random boxes, since the NSA modified them to make them more resistant to differential cryptoanalysis.
Sep
6
 reviewed Approve suggested edit on Encrypting small values with RSA private key
Sep
6
 comment Password crackers in CUDA
hashcat
Sep
6
 comment Is it possible to pick your Ed25519 public key?
I believe the root question is: "Can an attacker impersonate a known public key by creating a keypair with a similar looking public key, for which he can execute private key operations such as signing or diffie-hellman." The actual representation of the private key is irrelevant.
Sep
6
 comment Is it possible to pick your Ed25519 public key?
Your talking about "multiplicate inverse" is still weird. AFAIK there is no operation that multiplies two points on a curve. There is only an operation that multiplies a scalar with a curve point. If you look at the analogous operation in a finite field $B^{a'}=A'$, you can't find an inverse element for $B$ either.
Sep
5
 comment verify contents, but not order
You need to also verify that the contents are in a certain subset of values, e.g. 0 to 51. Else some ciphertexts might not represent valid values.
Sep
5
 comment Randomized stream cipher using multivariant quadratic equations
1) Most proofs are asymptotic and don't tell you anything about concrete sizes of the problem. BBS has concrete proofs too, and those require much bigger modulus sizes than most people expect. 2) You need a proof that a problem choses in the manner you do is hard too. I believe some knapsack based cryptosystems fell to this.
Sep
4
 comment implications of SSH server key compromission when authenticating users against a public key
One interesting question is, if a MitM who knows the server's private key can he execute a downgrade attack to the RSA key exchange?
Sep
3
 awarded  Nice Answer
Sep
3
 comment implications of SSH server key compromission when authenticating users against a public key
If SSH doesn't suck, the only thing he should be able to do is impersonate the server.
Sep
2
 reviewed Approve suggested edit on Is TOTP or a timestamp encryption a better timestamp-based authentication token system?
Sep
2
 comment How will Cryptography be changed by Quantum Computing?
This question about how quantum computers can be used to break crypto. And not about those useless quantum-crypto schemes. To quote your article: "Note that this is totally separate from quantum computing, which also has implications for cryptography."
Sep
2
 comment How to encrypt data and know it will be secure for at least a few decades?
It helps against crypto-analysis, and brute-force is irrelevant for ciphers with 256 bit keys. But a cryptographic system is only as strong as its weakest part. It's unlikely that the actual cipher is the weakest part in your system.
Sep
2
 comment How to encrypt data and know it will be secure for at least a few decades?
But where does your user keep the key? Does he print it? Does he memorize 1000 bits?
Sep
2
 comment How to encrypt data and know it will be secure for at least a few decades?
The main issue is, From where do you get the keys? Do you expect the user to enter 1000 key bits manually? If you use a normal password, that is most likely the weakpoint in your scheme. And you didn't specify a chaining mode, or if you're suing a MAC.
Aug
31
 comment verify contents, but not order
If Maeher is right, search for "Mental Poker"
Aug
31
 comment verify contents, but not order
Your question is a bit underspecified. Please add some detail. Perhaps you can simply sort the parts before hashing, perhaps you need some sort of homomorphic encryption, and perhaps it's impossible.
Aug
31
 comment HRNG for One Time Pad
hm? If you burn 64 bytes or so(half for the initialziation, half for the masking of the final value), you push the chance of acceptance to beyond $2^{-200}$ for realistic message sizes. That should work for pretty much any universal hash, such as Poly1305 or what GCM uses.
Aug
31
 comment How to submit a new method of encryption?
Don't be too hopeful. It's very likely that your method is badly broken.
Aug
31
 comment HRNG for One Time Pad
@SimonJohnson Pretty much any universal hash works fine in that way. If done correctly, an attacker has a certain chance that his forged message gets accepted, and no matter how big is computational power, he can't increase that chance. The chance increases with the message length, but you can easily choose your parameters so that it's still extremely low.
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