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I like crypto. Need I say more?


Nov
14
comment Why have 4th and 5th steps in Needham-Schroeder Protocol?
B could do that, but that is application specific. There are tons of applications out there were all we need is authentication with no further encrypted communications (e.g., electronic system where I prove to you who I am and you open a door for me). $N_b-1$ is the number $N_b$ minus one. If the random nonce $N_b$ is chosen to be $5$, A would encrypt and send $4$. If A can't decrypt, A can't get $N_b$ so A can't send $N_b-1$.
Nov
14
revised Scalar Multiplication on Elliptic Curves
added 11 characters in body
Nov
14
answered Scalar Multiplication on Elliptic Curves
Nov
14
revised Scalar Multiplication on Elliptic Curves
added 1 characters in body
Nov
14
revised Why have 4th and 5th steps in Needham-Schroeder Protocol?
deleted 79 characters in body
Nov
14
answered Why do the outputs of parties in an MPC protocol have to be indistinguishable from the ideal / real world (as opposed to inputs)?
Nov
14
answered Why have 4th and 5th steps in Needham-Schroeder Protocol?
Nov
14
revised Why have 4th and 5th steps in Needham-Schroeder Protocol?
added 208 characters in body
Nov
13
comment Why have 4th and 5th steps in Needham-Schroeder Protocol?
Can you tell us what protocol diagram you are looking at so we can all be on the same page?
Nov
12
answered How do I cryptanalyze a password field?
Nov
12
revised How do I cryptanalyze a password field?
added 45 characters in body
Nov
12
answered MD5 theoretical question
Nov
12
comment Does RSA work for any message M?
I agree. That said, just wanted to make you aware that SE does not notify downvoters when you edit. I'm assuming that is the reason why some have not changed their vote. Could be a nice feature though.
Nov
12
revised How do I cryptanalyze a password field?
edited tags
Nov
12
comment How do I cryptanalyze a password field?
Continued: is there an obvious block length? In other words, do the sizes of all ciphertexts have some common multiple (like 40 bits or 80 bits). If you can access many, many ciphertexts, what is the entropy? If the entropy isn't high, it might be an encoding scheme instead of encryption.
Nov
12
comment How do I cryptanalyze a password field?
Since you know one plaintext/ciphertext pair, here are a few questions that if I were trying to figure it out I would want to know. Is the ciphertext deterministic for a single user? Is it deterministic across multiple users? You say the lengths are not the same. Do same length passwords have same length corresponding "ciphertexts"?
Nov
12
comment How do I cryptanalyze a password field?
The question was not closed because of my suggestion. It was closed because requests to analyze or decrypt data are off topic. See the FAQ. The stackoverflow folks warned you this might happen if you go back there and read the comments. I'd suggest you look at the FAQ for what is on topic and edit the question to make it on topic, then we might be able to help.
Nov
11
comment How do I cryptanalyze a password field?
From the information you have given, I think the best advice you can give your customer is to switch applications. It is highly likely given the details you've provided that the password storage is not very secure. Makes you wonder what other mistakes the developers made.
Nov
10
awarded  Nice Answer
Nov
5
comment Is multiplicative secret sharing secure?
I assumed that $\mathbb{Z}_n^*$ was, by definition, elements that are co-prime to $n$. Either way, I appreciate the answer.