# All Questions

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### Homogenous and heterogeneous Unbalanced Feistel Networks

Unbalanced Feistel networks can be homogenous (F-function identical in each round), or they can be heterogeneous (F-function not always identical in each round). The advantage of heterogeneous UFNs ...
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### How to only encrypt a subset of the plaintext

I was wondering if there is a smart way for a user to only encrypt a subset of a plaintext. I'll try to be more specific. Let's suppose the user U wants to use a special cipher such that given a ...
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### ECDSA with SHA256 and sepc192r1 curve: Impossible, or how to calculate $e$?

I need to use ECDSA as the signing algorithm and SHA256 for hashing the message. I'm running into troubles verifying the signature calculated on two different platform (one is BouncyCastle, another ...
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### Interleaving bytes to make an effectively larger block size

Will applying a 16 byte bit block cipher such as AES over a 256 byte block to in the following way result in a much stronger cipher:- Apply block cipher with first key digest to each 16 byte group. ...
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### How does Truecrypt change password without the need for a complete re-encryption of volume

From what I understand: TrueCrypt takes the password as message Add salt calculates a digest use digest for encryption From what I understand. A good hash function has Second pre-image ...
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### Skein or Keccak stream cipher construction

I am wondering if using Skein or the Keccak hash algorithm in this construction (as a stream cipher) is secure: $H$ = Keccak or Skein hash with a 256 bit output $K$ = The main 256 bit random key, ...
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### Size of Fresh Ciphertext's Noise in FHE over the integers

I'm studying FHE over the Integer which is https://eprint.iacr.org/2009/616.pdf In the remark 3.4, it says that the fresh ciphertexts have noise at most $2^{\rho'+2}$. I don't know why that ...
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### Revealing random bit permutation

I am new in cryptography. I want to determine the complexity of revealing a random bit permutation which is used as block cipher for plaintexts (bitstrings of length n). An adversary catches different ...
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### Secure MultiParty Computation with secret inputs for secret outputs

I want to know if it’s possible to use a SMPC (Secure Multi-Party Computation) to have $N$ entities compute the outcome of a known mathematical operation with two or more secret inputs, where each ...
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### where to keep the AES keystream?

I am trying to implement an AES encryption on my messages in my app and I want to have a different keystream for each "message group". Therefore, currently I am holding the keystreams in the database ...
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### Constant data as input to hash

I want to use hash function on some data, and part of this data, might be constant for a certain period. The output of the hash function is used as authentication data (MAC). I want to know if there ...
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I am working on AES. Can we expand $s(a \oplus b)$ in terms of $s(a)$ and $s(b)$ where $a$ and $b$ are two eight bit inputs and $s(a)$ is the S-box value of $a$?
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I have thought of a system for generating passwords which works as follows: Take the following items: A password, such as williamwallace. A secret 1000 digit ...
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### Public key in fully homomorphic encryption over the integers

I'm reading “Fully Homomorphic Encryption over the Integers” by van Dijk et al. I wonder why $x_0$, which is a component of the public key, should be an odd number?
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### Point addition equation in projective co ordinates

How can I get point addition equation for elliptic curves in projective co ordinate system? Can I get it by changing $$x = X/Z$$ and $$y =Y/Z$$ in the equation for affine co ordinates' group law? ...
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### Test Vectors for ciphers

While implementing ciphers (/hash functions, ...), I often face this problem: Where to find test vectors for it; so that I can guarantee my program is correct. It is generally a tedious job to find ...
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### Public key Issue - same key pair as existing one? [duplicate]

My question is a bit naive, but what if someone generates the same RSA key pair as someone else? This person would have the same private key and so would be able to decrypt messages not intended to ...
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### ECDH anonymous key exchange to avoid PKI

I want to use TLS to encrypt the communication between peers in a P2P network. Each peer has a well known 256bit peer identifier (the public key of a 256bit elliptic curve keypair). Both peers need ...
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### OTT service using FPE

Would it be possible to create an Over-The-Top communication utility that will encrypt voice using format preserving encryption (voice clear-text to audio encrypted stream) and send that over an ...
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### Implementing CD serial key system

I am trying to create a system where to unlock the application one needs to enter a serial code. I have read many articles on the theme but there are two problems bugging me. One is, If I have a ...
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### True Random Number Generator by milliseconds per keystroke (TRNG-Kms)

The simplest way to generate truly random numbers for OTP keys is to measure the time in milliseconds between each keystroke on a keyboard. The randomness depends on the user typing in various speeds. ...
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### Should I calculate two CMACs over two different strings that share common bytes?

I am trying to secure my RF communication in which one RF package consists of two separate segments. I need to make sure that one segment of one packet is not replaced with a valid segment of some ...
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### Reversing DJB2 Hashes

I have some spare time, and a few hundred DJB2-hashed values sitting around. I thought I'd try to do something "useful" and invert DJB2, such that I could calculate the plaintext of the hashes (which ...