# All Questions

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### Increase number of rounds for SPN and Feistel ciphers

Read a post on Schneiers blog (and again 2011) about increasing the number of rounds for AES from to "AES-128 at 16 rounds, AES-192 at 20 rounds, and AES-256 at 28 rounds" to raise the security. ...
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### What is the period of a cipher?

For the following explanation of RC4: It is a variable key-size stream cipher with byte-oriented operations. The algorithm is based on the use of a random permutation. Analysis shows that the ...
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### Verifying multiplicative inverse on a prime field in NIST's ECDSA_Prime.pdf

I am trying to learn about the Elliptic Curve Digital Signature Algorithm (ECDSA) by verifying the results in some example calculations. I found a PDF of example ECDSA calculations from NIST here: ...
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### Is this an acceptable implementation of ARC4 encryption for my system?

I am building an open source hardware system that will be used to control things over the internet. The system consists of a Base Station and Modules which use wireless communication at 2.4GHz to ...
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### Is One Time Pad considered Chosen-Plaintext Attack Secure?

If we're considering Chosen-Plaintext Attack setting, then the adversary has access to the Encryption Oracle right, and we know that OTP is only considered secure if we use the key only once. How ...
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### One Time Pads and reuse of the decrypted message?

How is it insecure when Alice encrypts a message with a One-Time-Pad to Bob, and Bob then uses the decrypted message from Alice as the next One-Time-Pad? For example: Alice sends Bob a message ...
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### The security of an encrypt-and-MAC

I would like to know what is the security of an encrypt-and-MAC with different keys for each transaction For example: the one-time-pad with $k_1$ and the HMAC with $k_2$ C = M \oplus k_1\\ MAC = ...
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### How do RSA and ElGamal key sizes compare?

I have a rather silly question regarding the comparison of RSA with ElGamal over integers. If you want to compare their performance in the same level of security, does the modulus of both of them need ...
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### Using one-way hash functions as the encryption method

Suppose two parties want to communicate securely with each other (Bob and Alice) using a simple messaging system in English. There are approximately 180,000 currently used words in the English ...
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### Why not use CBC, not send IV, and assume first plaintext block is garbage? [duplicate]

Possible Duplicate: Using CBC with fixed IV Forgive me if this has been asked before, I looked but haven't seen any answers that suit. Is there any danger in using CBC, encrypting a message ...
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### Capacity of Advanced Encryption Standard in terms of File Encryption

what is the capacity of AES in terms of File Encryption? is it really good to encrypt a large files in AES? ex. I am encrypting a 8GB of File... is it still good to used AES? is it still good to used ...
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### Converting a pre-image resistant hash to second pre-image resistant

I am looking for some standard conversion from any hash function $f$, which has pre-image resistance, to another hash function with second preimage resistance. Is there such a standard conversion?
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Given $n=pq$ for $p,q$ known, I can calculate $\phi(n)$. $e$ is selected such that $\gcd (e,\phi(n)) = 1$. Using this, how do I calculate the RSA private key? Example: I have $n = 35$, with $(... 1answer 364 views ### How can CBC-MAC be secure when message length is fixed? I was doing some self-initiated knowledge gathering about digests, signatures and hmacs and I ran across the fact that you can use CBC as a MAC, but if the message size is not fixed; then it is not ... 3answers 2k views ### Which attacks can be avoided by the use of OFB instead of ECB? For a file encryption program, I was told to use Output Feedback mode (OFB) instead of ECB (Electronic code book) mode. Which attacks can I avoid by this choice? 2answers 883 views ### Quadratic residue problem on composite integers Its believed that the quadratic residue modulo$n=p·q$for large primes$p$and$q$is intractable, which forms the basis of some cryptosystems. However, it is solvable if the factors of$n$are know,... 1answer 108 views ### Setting up of polynomials for CP-ABE or KP-ABE Access Trees My question I guess is how the selection is done. A brief explanation with a simple access tree will be very helpful. 1answer 32 views ### Camellia Key Schedule Camellia is a widely used International standard now. Its Key Schedule seems to be too simple as compared other famous Ciphers like Twofish and CAST-256. What are the per-requisites for the key-... 1answer 192 views ### Finding public exponent e I'm trying to create an algorithm to find the public exponent e given a plain (non-CRT) private key that doesn't include the public exponent, i.e. I've only got$n$and$d$. A question has already ... 2answers 365 views ### Store hashed email and compare hash values I have a number of different systems sending me email addresses, but I don't actually need the underlying email, just a hash of the email address. I know I can compare hash values to find matches ... 3answers 852 views ### RSA Key generation: How is multiplicative inverse computed? As per Wikipedia, RSA keygen goes like this: Choose two distinct prime numbers p and q. Compute$n = pq$. Compute$\varphi(n) = (p − 1)(q − 1)$. Choose an integer e such that$1 < e < \varphi(...
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I have an embedded device. It produces larges files (200 MB). I want the device to encrypt the file before writing to disk, so I gave them all a 16-byte random key. How can I transform the large ...
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### ElGamal signatures systems

Let $p$ prime number $q/p-1$ prime and $g\in (Z/pZ)^*$ element of order $q$.Also $a\in \{1,...,q-1\}$ the private key and $y\equiv g^a\pmod p$ the correspoding public key.For each of the following ...
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I have an application that I use sha3-512 to hash my password with a randomly generated 64 characters salt for each password. Is it bad to use this method to store passwords? I know many people ...