# All Questions

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$N=p·q$ ($p$ and $q$ are prime numbers), $m_1, ..., m_x$ are the messages, $e$ and $d$ are RSA encryption and decryption exponents, respectively. I am given $e, m_1, m_1^e, m_1^d, ..., m_x, m_x^e, ... 2answers 959 views ### phi(P*Q) = (P-1) * (Q-1) I was trying to understand RSA when I encountered the Euler Function. I do understand this:$\phi(P)$, where$P$is a prime is$P-1$. However it seems that for a number$N$such at$N=P\cdot Q$where ... 1answer 71 views ### Is there a big RSA Data Set Is there a big dataset containing RSA public$(n,e)$and private keys$d$and primes$p,q$where$n = p.q$? 5answers 2k views ### Galois fields in cryptography I don't really understand Galois fields, but I've noticed they're used a lot in crypto. I tried to read into them, but quickly got lost in the mess of heiroglyphs and alien terms. I understand they're ... 1answer 827 views ### Necessity for finite field arithmetic and the prime number p in Shamir's Secret Sharing Scheme Shamir's original paper (PDF, 197kb) describing a threshold secret sharing scheme states: To make this claim more precise, we use modular arithmetic instead of real arithmetic. The set of ... 1answer 304 views ### How do unkeyed hash functions (for MDCs) provide security? Unkeyed hash functions are, by definition, hash functions computed without a key. SHA-1 is an example. MDCs (message digest codes) are a subclass of unkeyed hash functions. How are unkeyed hash ... 1answer 975 views ### A single password manager vs password generator/hash I have been wondering about the options available for managing passwords. However, they all seem to fail if the master password is compromised (which isn't a big surprise). On one hand you have ... 2answers 112 views ### Polynomials and efficient computability In public key crypto, the popular definitions of security (CPA, CCA1,2) depend on PPT adversaries. I'm trying to understand why adversaries should be PPT. It's clear that adversaries should be at ... 1answer 134 views ### inverse element in Paillier cryptosystem As I know, in Paillier cryptosystem, the encryption$c$of a message$m$is calculated as$c=g^m r^n \bmod n^2$. Now, I am wondering if I can derive$g^m \bmod n^2$given that I know$c$,$r$, and ... 1answer 575 views ### What are the benefits of lattice based cryptography? Previously we visited the benefits of elliptic curves for cryptography. Lattice based cryptography is starting to become quite popular in academia. The primary benefit of lattice based crypto is the ... 2answers 1k views ### RSA blind signatures in practice Hi I have a problem with moving my blind signature implementation from educational (textbook RSA) to more practical (padded RSA) side. David Chaums paper gives a following figure:$r$- blinding ... 0answers 158 views ### Transforming simplest protocol into a Sigma-protocol I have some questions from previous years exams, I hope you could help me with them. :) Suppose that a protocol satisfies the properties of a$\Sigma$-protocol, except that it is only (plain) ... 1answer 188 views ### What is an oracle adversary? I'm trying to figure out block ciphers and this is the first time I've encountered the term "oracle adversary". It appears in the context of defining a PRP and a PRF. Can someone please explain what ... 1answer 209 views ### Why doesn't this replay attack work on ECDSA? I've just started working with elliptic curves and ECSDA in particular, so my understanding of the underlying math isn't great. The thing I'm currently stuck on is trying to understand why replay ... 2answers 136 views ### Practical implementations of Multiparty computations [closed] Are there any practical implementations and or software platforms to prototype applications based on MPC ? 3answers 281 views ### Can I use PGP to sign a message without providing cryptographic non-repudation? The difference between a digital signature and a MAC is non-repudiation. A message with a digital signature proves that only the sender could have signed the message, whereas a message with a MAC ... 1answer 145 views ### Need for Twin Elgamal encryption What is the need for two private/public keys in twin elgamal? I'm relatively new and would need some help. 1answer 565 views ### RC4 encryption -> AES encryption = more or less secure than RC4 or AES alone? Say I have ... 3answers 210 views ### Deterministic key generation In a situation where it is required to generate n number of keys deterministically from a single piece of seed information can we assume that b breached number of keys, no matter what the quantity ... 1answer 350 views ### using Post-quantum asymmetric ciphers instead of RSA We can't trust RSA to encrypt our Emails so what is best post-quantum cryptography system as alternative for RSA which provide good security and don't be breakable? because McEliece cryptosystem looks ... 1answer 308 views ### Are there any Implementations of Secure Indexes? [closed] There are several papers about Secure Indexes, for Example "Searchable Symmetric Encryption: Improved Definitions and Efficient Constructions" and "Secure Indexes". ... 1answer 255 views ### Why are protocols often proven secure under the random oracle model instead of a hash assumption? Is this true that whenever you design a protocol using a hash function, you must prove its security under the random oracle? I mean, is it possible to devise a protocol$P$using a function$H$, and ... 2answers 405 views ### Public key cryptography - public key encrypts and cannot decrypt? I understand the basics behind public key cryptography, in that each party has two keys - the public one encrypts, and the private one decrypts. What I cannot figure out is, How does the public key ... 2answers 886 views ### How can I break a Vigenère cipher with partial plain text? I have an exercise to do regarding Vigenère encryption. I've got the cipher text: WNZTNVIEEGTJYKRRWYUELWNZTNV and a partial plain text: ... 2answers 309 views ### Are really, really long passwords any securer than short ones? Just for fun, I want to encrypt a message that will take about 10 or so years to decrypt. My idea is to encrypt a message with AES-512 with a password one million decimal digits long. Knowing not ... 1answer 182 views ### RSA Key generation Public exponent too big I'm currently writing a paper about RSA (a self-chosen subject). I'm writing about the key-generation in RSA, and I have problem finding the public exponent e. I have chosen p = 61 and q = 53. Then ... 4answers 355 views ### Is there a secret sharing scheme which allows delegation/re-sharing without reconstructing the original secret? EDIT: Ilmari Karonen's answer below well not exactly what I want, gives a very good idea of what I am trying to accomplish. Are there any known secret sharing schemes that allow new parties to be ... 0answers 110 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 ... 1answer 422 views ### Diffie-Hellman is Post-quantum secured? If Alice and bob have a secure channel for key-exchange and mallory don't man-in-the-middle attack them but in the future eavesdrop connection and see the key exchanged, can mallory break it like RSA ... 2answers 293 views ### The security proof for Key Policy Attribute Based Encryption My question relates to the original KP-ABE paper: http://research.microsoft.com/en-us/um/people/vipul/abe.pdf I'm having trouble understanding the proof (pages 10–13) that the scheme is secure in ... 1answer 234 views ### RSA Without Padding? I've been looking at the weakness with plain/textbook RSA, where the same message is encrypted and sent to multiple destinations. In this case, it is possible to recover the message. Given that an ... 4answers 315 views ### How to prove membership of a list without disclosing the list members? I'm designing a messaging system where the sender A sends a message m with a signature s to n Receivers. A Receiver Ri should then be able to prove to a Verifier V that he is one of the receivers of ... 2answers 436 views ### AES key expansion vs. a hash Is there something special about the AES key expansion algorithm that makes it secure, or it is a compromise between security and speed? For example, say with a key I expand it by taking pbkdf2(key) ... 1answer 202 views ### Does RSA-OEAP have integrity and authenticity properties? RSA-OAEP is IND-CCA2 secure (indistinguishable under an adaptive chosen ciphertext attack). Does it also have the INT-CTXT (integrity of ciphertext) and INT-PTXT (integrity of plaintext) properties? ... 2answers 237 views ### Speeding up partially known plaintext preimage recovery attack on MD5 Suppose there are three messages A, B and C of different length, that are 16 DWORDs in ... 2answers 646 views ### decrypt AES without whole key Is there a way to decrypt a AES cipher Text which was encrypted twice with some key, when having a part of this key? (the last 3 bytes of the key are missing) 1answer 3k views ### Compare Blockmode CBC (with diffuser) against XTS I have some problems in understanding the "advantage" of AES-XTS compared to CBC with diffuser. I read something about FileVault, in this paper they mention the two modes of operations XTS and CBC ... 2answers 405 views ### How can I add more rounds to AES? I'd like to understand a bit more about the AES key schedule if anyone would mind explaining that. For instance, why is the way the schedule generated (with recursive xors and occasional ... 1answer 837 views ### Get RSA PlainText without Knowing Private Key If I have an algorithm,RSA-Crack(), that, for a given RSA public key (n,e), is able to decrypt 1% of the messages encrypted with that key (without knowledge of the corresponding private key).Can there ... 2answers 268 views ### Non-Interactive Zero-Knowledge-Proof for discret Logarithm? In a Non-Interactive$Zero-Knowledge-Proof$, the challenge is chosen by the Prover. I am trying to find a Non-Interactive Zero-Knowledge-Proof based on the following problem: DISCRETE LOGARITHM ... 1answer 358 views ### AES Secure key generation and storage I have a client-server application, which is transferring data between its components in a secure way. I currently use AES algorithm with CBC mode to transfer data and file. This is the scenario: ... 1answer 165 views ### Comparing plaintext to contents of ciphertext Given an authenticated mode of encryption, when comparing a plaintext string against the contents of a ciphertext, which approach is typically considered safer? Encrypt the plaintext and compare ... 4answers 332 views ### How is it possible to parallelize a hashing function to crack an iteratively hashed password? Suppose I have an algorithm that relies on multiple iterations of a hash function like SHA1 to slow down an attacker trying to bruteforce a hash. ... 2answers 532 views ### AES key padding Is the initial AES key (expanded to the key schedule) byte padded if less than e.g. 16 bytes? Is there a safe way of determining if decryption was successful (i.e. used the correct key)? 1answer 507 views ### In RSA encryption, does the value of e need to be random? I am a novice programmer and am just finishing up an RSA encryption program that I am writing for practice. Currently I have the program generate a relatively small random value for the public key e. ... 2answers 268 views ### AES encrypting multiple files So if I want to encrypt all the files in a folder with AES (same password) I take each file and generate the key schedule using PBKDF2. As the PBKDF2 algorithm takes in a salt then this salt should ... 0answers 144 views ### Sigma-protocol for 3SAT problem I have some questions from previous years exams, I hope you could help me with them. :) Let$g,h$denote generators of a group$G$of large prime order$n$such that$\log_g h$is unknown to anyone. ... 1answer 723 views ### RSA-OAEP Input Parameters When creating padding for RSA using OAEP, a message is prepared as follows: Hash(Input Parameter) || Zeros || 1 || Message My question is, what should the Input ... 2answers 212 views ### Is there any research on the problem of making a number more memorable to humans? Authentication protocols often rely on humans dealing with large numbers correctly. For example, when a user logs into a remote machine using SSH for the first time, she is prompted to confirm that ... 1answer 570 views ### Weakness in using only one RSA key pair for two-way communication? In Alice/Bob/Cindy terms (EDIT: and with a little more detail): Alice and Bob have each securely obtained one key of an RSA keypair from a trusted third party. Alice has one key ($e$and$n\$), Bob ...

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