# All Questions

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### Messages exchanged between Bob Alice are encrypted safe?

Can you help me understand the following reasoning? If Alice sends Bob a message and that message is encrypted with two keys simultaneously: a symmetric key (Ks) and Bob's public key. The symmetric ...
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### Would it be possible to create a game where one would need to decrypt a simple encryption?

This might sound pretty weird, but I was thinking of a game a person could play alone with a pen and paper. I got this idea where the person would write a random four letter string on a paper, and ...
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### 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 ...
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Here is the protocol outline I am looking at (source: Foundations of Computer Security, Lecture 60: The Needham-Schroeder Protocol) $$\begin{array}{ccl} 1.& A \to S \colon& A,B,N_a \\ ... 2answers 102 views ### Game with symmetric key Alice and Bob are playing Rock-paper-scissors. Alice chooses a \leftarrow\{stone, paper, scissors\} and a nonce R_A used as symmetric key for encryption$$A → B : A, R_A(a) Bob chooses $b ... 2answers 103 views ### hill cipher encryption way 1x3 plaintext matrix Can someone help me with a Hill cipher? When do I have to use: 1x3 plain text matrix (p1, p2, p3) * 3x3 key matrix 3x3 key matrix * 3x1 plain text matrix Or they are both correct? I tried to ... 2answers 88 views ### Digital Signature using symmetric key cryptography Generally digital signature is a public key cryptography concept.But it needs high overhead. So is there any publication or link available where 'digital signature using symmetric key' has been ... 1answer 183 views ### Relation between key size and PRNG state size Some (supposedly) cryptographically secure PRNGs have an internal state of only 160 bits or less. When the algorithm is otherwise properly designed, that seems like enough to generate a 128 bit key ... 1answer 139 views ### How secure is this use of Ziv-Lempel encoding? I'm reading patent application US 20120278897 A1 — “System and method of sort-order preserving tokenization”. Near the bottom they describe their token generation algorithm, which basically involves ... 1answer 382 views ### Attacks on the RSA Cryptosystem I was reading some articles about attacks on RSA system and I wonder about some generalization of the following theorem. Theorem (Coppersmith). Let$N=pq$be an$n$-bit RSA modulus, where ... 1answer 33 views ### Private set intersection, using a semi-trusted server Alice has a set$S$of words. Bob has a set$T$of words. They want to compute the intersection$S \cap T$of their words, with the help of a semi-trusted third party Trent. Trent runs a central ... 1answer 256 views ### How do institutions like banks do RSA with big primes? When encrypting with RSA it is often infeasible to decrypt by just doing c^d mod n, because for example when using the primes$(p,q)=(12553,1233)$, which are small ... 1answer 145 views ### Calculating amount of time for brute forcing ciphertext depending on the size of the key I am a graphic design student and for my information graphic project I have chosen the topic of the history of encryption and how the security level developed over the centuries. It’s basically an ... 1answer 165 views ### AES-CTR with ephemeral keys vs IV Let's say that we have a key exchange of some sort, which leaves A and B sharing the long-term secret$S$. Then, A and B want to use AES-CTR for the communication, which leaves us with several ... 1answer 110 views ### Diffie-Hellman Key Exchange with Authentication: Man-in-the-Middle query I have been reading up on MiTM attacks, and the prevention of them using public key certificates. Recently I learnt about Diffie-Hellman Key Exchange with Authentication, and how it uses signed ... 1answer 41 views ### What is the best way to share a shared secret key over HTTPS to be used for HMAC authentication? I am writing an application in Java that will be using SHA-1 HMAC message authentication. From what I understand, a connection over HTTPS is considered secure enough to share a secret key in plain ... 1answer 34 views ### SHA-256 Partial Collision of initial 36 bits and more I was lucky enough to, by brute force, have found two different messages, whose SHA-256 hashes collide in the first 9 hexadecimal characters, which are 36 bits, ... 1answer 60 views ### Is script execution time a decent source of pseudorandom number generation? This is for a PHP script for password generation. Naturally there are other things being calculated before the password is generated. But I figure the time it takes for the script to initialize and ... 1answer 39 views ### Compared to GCM or XTS modes, how secure is H xor R1, E (R2, R1, Message) for confidentiality and integrity? Let R1 and R2 be (32 byte) random values, and let a H = Hash (R1, R2, Message) be of the same length as each R value. Provided E (R2, R1, Message) is operating in some chaining mode, are there any ... 1answer 44 views ### Is there a method to combine encryption and ring signing? There's the well-known question on whether to sign or encrypt first. However, if instead a message is to be ring-signed such that either recipient could be the actual signer, is there any scheme that ... 1answer 63 views ### Hash functions with or without secret key The classical definition of hash functions (found in books) are OK, but when studying a little more there is a lot of notions that seem ambiguous (contradictory) to me : Sometimes we have hash ... 1answer 73 views ### ElGamal with elliptic curves I It is very interesting to see @tylo's answer on ElGamal with elliptic curves. Instead of mapping the message to the elliptic curve point it just reduces an elliptic curve point to its$x$coodrinate. ... 1answer 140 views ### Insecurity in Needham and Schroeder protocol? I've been studying specifically the authentication algorithm Needham and Shroeder, and understand the idea in general of the message exchange. But, researching on the subject, I found a question that ... 1answer 79 views ### Reusing PGP key when generating SSL Certificate Authority? Does it make sense to reuse some of the keys from my PGP (gnupg, gpg) keyblock when generating my own SSL Certificate Authority (a toy one for myself and a few web services of mine)? In an ideal ... 1answer 67 views ### Breaking Double Encryption I am trying to understand how an attacker knows when he has successfully decrypted a ciphertext for an assignment. As such, some pointers/hints for the following questions would be greatly ... 1answer 65 views ### Non-interactive Zero-knowledge proof signature validation without public key I'm looking for a method for a scenario with following requirements: At least 3 people (A,B,C,...) are in a Network where they can broadcast messages to everyone but not communicate with a specific ... 1answer 41 views ### Modular protocol design What does modular protocol design mean? Why does TLS not have modular protocol design? What protocols have modular design? (IPSec, SSH) 1answer 57 views ### Attacking both authenticity and secrecy in authenticated encryption modes looks like NIST only approved GCM mode for authenticated encryption and other modes don't have any approval or a good implementation available. Is that possible a weakness in$GHASH$compromise ... 1answer 66 views ### Advise key management protocol Assume that sender and recipient both already have each others public keys(certificates). Sender needs to generate session key to encrypt some data and sends encrypted data to recipient. All offline - ... 1answer 74 views ### Sematically Secure McEliece I am read the Lemma 2 (pp13) in the paper "Kazukuni Kobara and Hideki Imai: Semantically Secure McEliece Public-Key Cryptosystems –Conversions for McEliece PKC– (PKC 2001)". Related to the question ... 0answers 118 views ### PGP encryption options I recently began using PGP desktop and found several options for my encryption capabilities. Which of these (AES, Cast, Triple DES, TwoFish, IDEA) is the most recent, firstly, secondly may the NSA not ... 0answers 57 views ### Use of Different keys with PCBC Currently I am having a doubt, while making a "DES PCBC" encryption on an image I observe a bit of the silhouette of the image (Probably because of the XOR between plaintext blocks and ciphertext ones ... 0answers 98 views ### How many messages needs to be send to server to get AES key in Cache-timing Attack I'm trying to evaluate the correlation between key length and the number of messages that needs to be send to server during Cache timing Attack. I read both D. Bernstein, “Cache-timing attacks on ... 0answers 129 views ### How do multiple parties agree on a target block to hash for? Bitcoin style blockchain… I have party(node) A, B, C and algorithm X. Algorithm X generates the first half of a target hash input - the "solution" to the problem. I want A, B and C to sign their ... 0answers 128 views ### High throughput and efficient data encryption/description? (other than AES) What are some of the high throughput and efficient ciphers? I know AES has generally good performance, but is there anything more efficient that it now? I would like to perform small performance test ... 0answers 322 views ### How is the initial permutation of DES created? I am creating a program in C language with DES (Data Encryption Standard) functionality, but don't know how to apply the initial permutation. Is it achieved by swapping the values? If "yes", then ... 0answers 50 views ### How many blocks can we change if know MAC and key I stumbled across a question while studying about MAC, I was thinking if the attacker knows the key and the MAC and he wants to change the message to send to the victim, then how many blocks can he ... 0answers 217 views ### Keepass Twofish plugin security Keepass is a well known open-source password manager program, with plugin support. One of the offered plugin is a twofish encryption mode of operation in lieu of the build-in AES algorithm ... 0answers 46 views ### Identifying a PKI cert uniquely A Web Application wants the user to digitally sign a transaction using a PKI certificate. All users are pre-registered with the web-application. Pre-registeration includes uploading the Public part of ... 0answers 143 views ### How to safely sign a 6 characters String? I have to decide, whether a document, which I am given, was correctly signed by a private key. my Ideas is to sign the document id using RSA with the private key and to print the following onto the ... 0answers 49 views ### Are there any bi-bidirectionally indistinguishable Asymmetric Encryption Algorithms I have been using Asymmetric Encryption for a while, and I have come across an interesting concept, and it would be cool if it could be done. Are there any Asymmetric Encryption Algorithms where the ... 0answers 75 views ### can permutation matrix be found in parallel processing technique? Let us say there exists a permutation matrix$n \times n$for some large$n$. Then, there are$n!$possible permutations. If one to use brute-force to find the secret permutation among$n!$... 0answers 131 views ### Sigma-protocol for 3SAT problem I have some questions from previous years exams, I hope you could help me with them. :) Let$g,h$denote generators of a group$G$of large prime order$n$such that$\log_g h\$ is unknown to anyone. ...
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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. ...