# All Questions

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### Can we ensure the security of a crypto-algorithm and -implementaton against acoustic cryptanalysis?

Like people always say: “Attacks only get worse…” — which is why I'm asking early. I have been reading the paper “RSA Key Extraction via Low-Bandwidth Acoustic Cryptanalysis” published December 18, ...
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### Algebraic Normal Form Piccolo [closed]

I'm trying to verify the claim of paper Improved Algebraic Fault Analysis: A Case Study on Piccolo and with Applications to other Lightweight Block Ciphers about the numbers of equations in algebraic ...
741 views

### How exactly does key whitening manage to increase security?

Wikipedia states that key whitening increases security: In cryptography, key whitening is a technique intended to increase the security of an iterated block cipher. It consists of steps that ...
163 views

### A way around digital signatures?

Scenario: I have to protect the integrity of some files that will be exchanged between entities $A$, $B$, $C$. Entity $A$ creates the file (e.g. configuration) and sends it to $B$ and $C$. Entities ...
482 views

### What characters are valid in PGP encrypted and signed messages?

What characters may be present in a PGP encrypted message or a PGP signature? For example, do encrypted messages only use the Roman alphabet + some numbers and symbols? Can the character set be ...
311 views

### How can I control the output of a hash function to output to specific data according to similarity?

I do not know if the question lies exactly in that field but I'll give it a try unless rejection. I want to study methods of applying LSH functions to feet in a specific area of digest values. ...
195 views

### Regain 3DES ECB key, assuming I have both encrypted and decrypted text

Let's assume I've encrypted some text with some 24-byte key using 3DES in ECB mode. Is it possible to regain the key if I have both encrypted and decrypted text? (Excluding bruteforce.)
270 views

### What is Perceptual Encryption?

What is "Perceptual Encryption", and where do we use it? I came across it whilst reading a paper on ECC in a multimedia context, from which I quote: Hence, to achieve perceptual encryption, the ...
72 views

### 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 ...
728 views

### Does AES specify error messages when using the wrong password to decrypt?

I am writing a small program which uses AES. In testing it with wrong passwords, I get error prompts from Microsoft C# component saying "the padding is bad"; whereas I expect wrongly decoded texts. Do ...
112 views

### 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 ...
328 views

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 ...
887 views

### 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 ...
502 views

### PRF and hash functions

Is there a difference between PRF and a hash function? For example: Creation of a secret key is using PRF and creating a secret key is using hash function.
313 views

### Should HMAC or NMAC or plain Keccak be used for a secure MAC?

After some digging around in the HMAC spec I found this (paraphrased): Step 1: If the length of Key equals the block size of the hash function (512 bits/64 Bytes for SHA-256), set the key equal ...
138 views

### 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?
117 views

### Computing youngest person among 3 while keeping ages private

I already found a protocol to find out who is richer (older) between two parties, but Is there any protocol to find the youngest person among 3 parties, without revealing actual ages?
81 views

### Where can I find source code of a compiler that secures a circuit (or attemps to)? [closed]

In the paper “Multiparty Computation Secure Against Continual Memory Leakage”, on page 1239 under section “Using an LDS Compiler Instead of OCL Compiler”, the authors discuss why they decided to use ...
121 views

### 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 ...
891 views

### Can curve25519 keys be used with ed25519 keys?

Can curve25519 keys be used with ed25519? I'd prefer to use ed25519, but there isn't a fast java version. For my application, I'd like to use curve25519 until I can get a faster ed25519 for java. ...
334 views

### 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 ...
77 views

### 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 ...
60 views

### References and resources for learning to implement crypt. algorithms? [closed]

I wanted to learn about cryptography so they recommended me some of the books of Bruce Schneier. I'm now reading Cryptography Engineering and planning to follow with this one ...
67 views

### 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 ...
97 views

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 $a$?
3k views

### What is the difference between Scrypt and PBKDF2?

After reading these two resources I am wondering am I getting all the differences between Scrypt and PBKDF2. As far as I understood, the similarity is: both are password-based key derivation ...
59 views

### 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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First of all, I apologize if this is a stupid question, but I don't have any background in cryptography. I'm looking for a secure hash algorithm $H$ with the property $H(K_1+n)\oplus ... 2answers 482 views ### Quantum key distribution simulation I'm looking for a simulation of the Quantum Key Distribution protocol. Does anyone here have one that they could recommend? 2answers 571 views ### Is perfect-forward secrecy achieved with RSA? I am new to cryptography and am going through the book Understanding Cryptography by Paar and Pelzl. From what I understand Symmetric key distribution systems like Kerberos do not provide PFS ... 1answer 736 views ### Correctly generating cryptographically secure pseudorandom numbers (in C)? I am learning about cryptography, purely for my own interest. As part of that, I am implementing a simple one-time-pad toolset in C. Naturally, I need to generate random numbers to create the pad, ... 1answer 817 views ### Theoretical attack on RSA The high security of RSA is granted, because it is very hard to factorize $$N = p * q$$ Nevertheless, there is actually no need of factorizing$N$, in order to generate the$PrivateKey$, but the ... 1answer 1k views ### How is the MD2 hash function S-table constructed from Pi? For fun, I'm learning more about cryptography and hashing. I'm implementing the MD2 hash function following RFC 1319 (http://tools.ietf.org/html/rfc1319). I'll preface by saying I know there are ... 1answer 326 views ### Relation between attack and attack model for signatures I would like to know: What is the relationship between an attack and an attack model. For example, let$\Pi$be the Lamport signature scheme. This signature has it's security based on the one-way ... 1answer 2k views ### How to break an arbitrary XOR and Rotation based encryption? I heard encryption based purely on XOR and Rotation is inherently weak. The paper Rotational Cryptanalysis of ARX says: It is also easy to prove that omitting addition or rotation is devastating, ... 1answer 76 views ### run length testing [closed] Looking for guidance/references with/about calculations: I am designing a widget that creates N-bit binary sequences. My customers target spec for the sequence's minimum entropy is X bits/bit. I plan ... 1answer 199 views ### Simple proof of work example? Can anyone show me a simple proof of work algorithm that I can use to stop spammers? I've looked at hashcat, but i think there's a bit too much specialized hardware for bitcoin mining. That is, the ... 1answer 77 views ### Composing and Inverting Symmetric Encryption Keys Using a symmetric encryption algorithm$E$on a message$M$, users usually send$E(M)$to the recipient and then the recipient will compute$E^{-1}(E(M))=M$to retrieve the message. For what symmetric ... 2answers 2k views ### Why is CBC with predictable IV considered insecure against CPA I just learned that using CBC encryption with an IV which is predictable is not secure. From what I understand, using certain plain texts, and then guessing the IV that is uses, the attacker can ... 1answer 2k views ### How many RSA keys before a collision? I was wondering how many possible private/public keys exist? If a million people – for whatever reason – would try to generate 5 keys each in the same minute (on the same date and time) is there a ... 1answer 216 views ### Using Lattice-based cryptography for TLS\SSL Given the general benefits of Lattice-based cryptography, such as: Post quantum Security Security from worst case scenario Efficiency What could the outlook of shifting from RSA \ ECC-based ... 1answer 67 views ### Symmetric-key login protocol I'm trying to analyze a login protocol based on symmetric key cryptography. I'm just starting out, so this may very likely be a very bad idea, but nonetheless I'd like to hear your thoughts on it. ... 0answers 140 views ### Given a 'good' basis for a lattice, how can we solve the CVP? I'm doing a little bit of reading about lattices. I read that if we can find a 'short' basis for our given lattice, we can solve CVP and SVP very efficiently. However, the paper didn't describe an ... 0answers 747 views ### Reasons for Chinese SM2 Digital Signature Algorithm In the IETF RFC draft named "SM2 Digital Signature Algorithm" a signature algorithm is specified. The RFC does however not mention why this signature algorithm has been defined. Nor does it specify ... 1answer 115 views ### Is this an acceptable All-or-Nothing Transform? I was thinking about AONTs, and designed the one below, I call it CHANT for Chained-Hash All-or-Nothing Transform; it's my very first shot at something of the sort, and was hoping I could get your ... 3answers 565 views ### Rainbow table for DES with all-zero plaintext? Consider the function$F$from$\{0,1\}^{56}$to$\{0,1\}^{64}\$, mapping the operative bits of a DES key to the ciphertext for all-zero plaintext. How could we organize a rainbow table to invert that ...
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I'm looking to do some research into how RSA is used in the wild. I've read through a few papers and it seems other researchers have had no trouble collecting millions of keys to perform analysis on. ...
239 views

### Encrypting or HMACing password digests

Assuming I'm using bcrypt to digest passwords, is any additional security gained by either encrypting or HMACing the resulting digests? By requiring a key to compare password hashes, I would expect ...