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I like crypto. Need I say more?


1d
comment How can I solve this modular equation?
Compute the multiplicative inverse of 5 mod 13 (using extended euclidean algorithm). Then multiply 2 by that value. Viola, you have x.
1d
comment RSA with modulus n=p²q
@Thor, I don't think CGFoX is planning on making the primes smaller to achieve the same bit size. Especially since the question specifies that using $p^2q$ would allow operations on a bigger $\mathbb{Z}_n$. That said, if the only benefit is a larger group, I would just pick larger primes to get the larger group personally (as you suggest).
1d
comment Lowest number challenge scheme
@fkraiem remember though, you would have to always run the coin-flip (whether there was a tie or not), otherwise you leak whether or not there was a tie. My point is, things can get complicated.
Jul
19
comment Sectors of small data encryption
Pretty much every commonly used cipher today can meet your stated needs. Picking the best will require knowing your unstated needs. Who is the recipient? If it is someone other than yourself, do you have a secret key shared with them? Can you securely store a key?
Jul
18
comment Polynomial representation of the affine part of the AES S-box
Could you explain what l0-l8 are? I'm too lazy to read the paper right now.
Jul
18
comment Test PFS / EC-DHE authentication support
I noticed that you cross-posted on StackOverflow (here). Please know that cross-posting on multiple SE sites is against the rules. I'm going to check with moderators on a couple of other sites to see if there is a better place I can migrate this question to.
Jul
18
comment Storing encryption key
Is this a stand alone app, or a client server app?
Jul
17
comment Are there any reasons for using SSL over IPSec?
@CodesInChaos, you are right. I am pinging the mods.
Jul
17
comment Given $g$, $b$, $g^{ab}$, is finding $g^a$ a hard problem?
In what group is $b^{-1}$ computed?
Jul
17
comment Are there any reasons for using SSL over IPSec?
Well technically from the first country to your home the connection would be encrypted with IPSec and SSL. When it reaches your home country, IPSec is removed and only SSL remains.
Jul
17
comment Are there any reasons for using SSL over IPSec?
Sure. Say I am in a different country and don't want my internet traffic snooped on. I can use IPSec to tunnel the internet traffic back to a server in my home country. Once that traffic leaves that server in my home country it will no longer be encrypted. So I use SSL to connect to, for example, a web mail server.
Jul
15
comment Decrypting an encrypted text out of order
Use a stream cipher
Jul
15
comment Decryption issue with self-coded AES-128
Richie, you are right. I realized that after I typed my comment and just left it. Feel free to roll back if you want.
Jul
15
comment CBC-MAC length extension attack with IV simulation
Are you able to capture many messages or just one? If so, do some of them have your account and the amount 1000000? If you could post example messages, that would be helpful.
Jul
15
comment Ciphertext indistinguishability (IND-CPA) for symmetric cryptography
Not if the IV is changing. That is why the comment I linked to is so important. An encryption algorithm is just a primitive, how are you actually going to use it? That is what you have to define.
Jul
15
comment Ciphertext indistinguishability (IND-CPA) for symmetric cryptography
This comment as well as the answers, etc might interest you.
Jul
15
comment Ciphertext indistinguishability (IND-CPA) for symmetric cryptography
For the first part, the adversary can submit any two messages. So one (or both) could be repeated.
Jul
15
comment CBC-MAC length extension attack with IV simulation
Let me rephrase, when you say "capture a valid message from target user", is that message encrypted + you have the MAC or is it plaintext + you have the MAC?
Jul
15
comment A question about elliptic curves and finite fields in bilinear pairings
What pairing-free scheme are you looking at?
Jul
15
comment Decryption issue with self-coded AES-128
+1 This should be very helpful to the OP. I fixed one minor mistake in your key schedule.