# All Questions

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### Proper Way to Encrypt Data with Two Keys?

I'm going to develop a system that will have two keys. One supplied and generated by the system that's specific to an individual user and one from the user. I plan on using AES. Does it make sense ...
125 views

### Computational indistinguishability and example of non polynomial algorithm

The wikipedia page on computational indistinguishability says that two ensembles are not distinguishable if "any non-uniform probabilistic polynomial time algorithm A" cannot tell them apart. To help ...
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### Cryptographic Symmetric Stream Cipher

Let me know a cryptographic symmetric stream cipher system with only two functions say S() and P() and it should satisfy the following conditions: There will be two independent computers say M1 and ...
503 views

### Common Modulus Attack in a Lucas Group

I'm trying to decrypt a message that is encrypted using a LUC encryption scheme and running into roadblocks. I know that with RSA if Alice and Bob use the same public modulus but different encryption ...
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### Which keys are necessary to decrypt Application data in a SSL connection?

I'm debugging an application which communicates between client and server using a SSL/TLS connection, and want to capture and analyze the sent data. Are the client write keys and server write keys ...
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### Sematically Secure McEliece

I am read the Lemma 2 (pp13) in the paper [1]. Here a make a question Why "for any $Hash_z$ and any $Gen$"? The author of paper reply The reason why "for any $Hash_z$ and any $Gen$" is that if ...
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### Chosen Plaintext Attacks

Assuming the ability to launch Chosen Plaintext Attacks (CPA), how many oracle calls an attacker needs to break the affine cipher? and how
130 views

### Fiat-Shamir signature

I have a question about Fiat-Shamir signature: A hash function is h(w)=w mod 2011 and w1=2623, w2=3269, w3=1938. What is h=? and how to determine k.t bits?
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### How does one find out ciphers/passwords without knowing what cryptographic algorithms are used?

If one does not reveal what cryptographic algorithms are used, how does a cracker find out a password/cipher that is used to communicate data? I heard that because there are methods to try cracking ...
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### Kryptos : K3. What is the accepted transposition for a solution?

I'm studying the Kryptos sculpture with its cryptographic puzzles K1 to K4. It's understood that K3 is solved via transposition, but I have seen several solutions. Which is the best/accepted one?
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How does padding in PMAC work? I have been told two stories: Firstly, I have been told that it works similar to CMAC padding, and secondly, I have been told that it does not need padding. I find the ...
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### Security of .net AES implementation and security of a hash MAC

Hello I wanted to ask if there is any review about the security of the AES implementation of the .net Framework? I found nothing concrete to that question, searching the Internet. And, but this is a ...
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### RSA and One Time Password (OTP) service

What is the expert cryptographic opinion on the following? Assume that there is a web server and a client on web page. User on the Client calls an OTP web service on the server which a) creates a ...
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### How compared encryption algorithm in terms of efficiency

I doing to compare two algorithm cryptography. first algorithm is RSA cryptography and second algorithm is El Gamal elliptic curve cryptography. now I want a way to compare between two algorithm by ...
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### elgamal based decryption mixnet

Can anybody help me to understand elgamal based decryption mixnet? Pure elgamal can be used in mixnet (re-encryption mixnet) and its very easy, and I have implemented decryption mixnet using RSA also. ...
178 views

### Cryptographic Protocol using NaCL

Why? I wanted to add some security and privacy to a chat-type server for playing various games (with a few things that are done on the server to limit cheating). Going by the "Don't implement ...
78 views

### Factorize RSA knowing several N and E

I did a CRT challenge yesterday and theres one problem I was unable to solve, probably due to my lack of understanding advanced crypto math. Its about RSA. There are ten given pairs of N and E ...
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### Is this a valid real-time authentication scheme?

The scenario in Alice/Bob/Cindy terms: Alice approaches someone she doesn't know, but thinks is Bob, and asks for some secret information. Bob doesn't know and doesn't trust Alice, but Alice says she ...
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### Timestamping services authorities, utilizing Linked, hybrid and other than PKI schemes

What are well respected Cryptographic Timestamping authorities utilizing more sophisticated than just PKI (RFC 3161) schemes, like Linked, Linked and signed, distributed hash trees (maybe P2P?), ...
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### What happens when you use Windows credentials to sign a message?

I'm trying to dig into the messages that are exchanged when you sign a message using Windows credentials. I've modified the default service that is provided when you create a WCF service to use the ...
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### Is this a secure multiparty protocol?

I am facing the following situation and i am trying to break down the problem into some specific cryptogrphic primitives. There is a function F that takes as input a bit string and produces a ...
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### can we do double encryption of a message without first key?

Lets assume $k_1$, $k_2$ are two keys and there can be any relation between them like $k2 = E(k1)$ that is key $k_2$ is encryption of $k_1$ using some other long term key or any other relation. ...
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### Attacks on a stream cipher

What attacks are there against stream ciphers? I found 2: Bit-flipping attack. Since every input bit mention exactly one output bit, it is possible to change ciphertext bits where the corresponding ...
I like know Why $Pr[\mathsf{PRIV_{EAV}}(\Pi,A,n)=1] = 1/2$, when $\Pi$ is a One Time Pad. I trying: Pr[\mathsf{PRIV_{EAV}}(\Pi,A,n)=1] = Pr[b'=0|b=0]Pr[b=0] + ...