# All Questions

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### Non-malleable file encryption using AES XTS 256?

I'm looking to do file encryption of a bunch of individual files, some small, some quite large. The files will be write-once/read-many, so I could use CBC, however, since the read-access needs to ...
247 views

### Using AES-CBC and providing the IV in file header -> security hole? [duplicate]

currently I audit some code I've written in the past to use KeePass 1.x databases. I stumbled over the following question: The database itself is decrypted with AES-CBC and inside the file header the ...
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### How is key rotation defined?

I'm aware that it's advisable to rotate cryptographic keys periodically. HKDF accepts high-entropy input (IKM - Input Key Material), and expands it to an arbitrary length. It also accepts a salt, ...
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### Hash function with values in a multiplicative group of prime order [closed]

I have to implement a cryptographic protocol which involves a cryptographic hash function $H: \{0,1\}^* \to G$. It is viewed as random oracle. $G$ is a multiplicative group of prime order. I want to ...
72 views

### Why is it impractical to generate a semiprime dictionary? [duplicate]

This might be a very simple question. However, I am just learning the concept, so just excuse me. I am wondering why there is not any attempt to generate all semiprime numbers? (as an dict. attack to ...
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I'm trying to reverse engineer key exchange protocol and faced with the following problem: Protocol is based on Diffie-Hellman key exchange method: g - generator m - modulus Alice: a - private key $A ... 0answers 71 views ### Will D-Wave's quantum computers ruin classical encryption? [duplicate] D-Wave has commercially available 512-qbit quantum computers now. A lot of big names are taking it seriously. Google, NASA, and USRA have joined forces to start a quantum AI lab. How far are we ... 0answers 146 views ### Complex Numbers on Elliptic Curves & Usage in Tate Pairing I'm working with understanding the internals of the Tate Pairing. I was going through an example of the curve$E: y^2 = x^3 + 3x$over$\mathbb{F_{11}}$. The author is showing the computation of ... 0answers 135 views ### More technical details on the ongoing (alleged) Chinese cyberattacks [closed] Recently, there has been quite a lot of news about the Chinese compromising various US weapons systems and stealing military designs through "cyberwarfare". I am reading the news sources about these ... 0answers 51 views ### Conditions for proving that a signcryption scheme is secure If I'm able to prove that any scheme satisfies confidentiality ad unforgeability conditions, will it be a valid signcryption scheme, without explicit signature and encryption parts ? 0answers 42 views ### calculating beta for elgamal elliptic curves [duplicate] Suppose we use elgamal elliptic curves for secure communication. Bob selects a prime$p$, an elliptic curve$E$, a point$\alpha$on$E \pmod p$, and a secret integer$f$. Suppose that Bob has ... 0answers 114 views ### Is OAEP reversible? Given nothing more than some integer$m =$OAEP($M$), is it possible to recover the original plaintext$M$? In other words, without being given the hash functions or the random string used for ... 0answers 109 views ### Algorithm digipass-like I'm pretty sure there are famous algorithms for my problem, but I don't have enough knowledge in this field, so I need your lights. Here si the problem : Alice sends key X to Bob. Bob has an ... 0answers 149 views ### Perfect secrecy and change of plaintext probability distributions How to prove that if a cryptosystem has perfect secrecy for a given plaintext probability distribution then it will have perfect secrecy for all other possible plaintext probability distributions? Do ... 0answers 471 views ### How do I generate decryption keys for the IDEA algorithm from the 128 bit key? I am trying to implement IDEA algorithm in C#, just to learn how it works. I have taken a 128 bit binary key and generated the 52 encryption keys using the following code: ... 0answers 153 views ### How fast can a wrong decryption key be detected using ECC? When can a decryption function detect that the ECC key I use for decryption is incorrect? Is it possible to do that during initialization, or does the complete message have to be decrypted to do that? ... 0answers 102 views ### Secure modulus length for Diffie-Hellman [duplicate] What is secure modulus length for modular exponentiation so that finding discrete log is computationaly impossible? 0answers 81 views ### Can a LIRA system work with cjdns or other decentralized meshnets? LIRA (Lightweight Incentivized Routing for Anonymity) is a scheme to incentivize participants in Tor to contribute resources, in particular bandwidth. The paper talks about it being used for Tor. Can ... 0answers 262 views ### Method and explanation for calculating difference in speed between DES and RSA Our assignment asks us to convert an RSA speed in bytes per second to a DES speed in bytes per second. Our professor's treatment of this ("RSA is 100 times slower than DES") seems insufficient. Could ... 0answers 287 views ### computing inverses in truncated polynomial rings manually for NTRU encryption [duplicate] Can someone explain how to find inverses in truncated polynomial rings manually (i.e. on pen and paper)? As an example from the tutorial: Example. Take$N=7$,$q=11$,$a=3+2X^2-3X^4+X^6$. The ... 0answers 88 views ### Strong RSA problem in$\mathbb Z^*_{n^2}$Comparing to this question, assume$C, M \in \mathbb Z^*_{n^2}$,$e \ge 3$, is it hard to compute$M$that satisfies$C=M^e \mod n^2$when$C$and$(n, e)$are given? 0answers 50 views ### Is there a way to analyse xxHash and tell, either by human analysis, or with an automated tool, that this hash function is or is not cryptographic? [duplicate] After reading some excellent papers on SipHash, I understood that good non-cryptographic hashes such as MurmurHash and CityHash are not secure for Internet usage, due to a certain type of DDos attack ... 1answer 200 views ### MD5 implementation As a personal project, I want to implement MD5 on an FPGA, but I have some doubts about the specifics of the implementation. My first source of how the algorithm is implemented was the RFC 1321, where ... 0answers 150 views ### Security of .net AES implementation and security of a hash MAC My question rather splits into two sections: Is AES correctly and security implemented in the .net Framework? Are there any reviews of implementation mistakes that would weaken the security of AES ... 0answers 43 views ### School exercise on untrusted channel comunication [duplicate] Possible Duplicate: Why is H(k||x) not a secure MAC construction? I've the following problem: two parties, A and B, share a secret key Kab. M is a plaintext message, H an unkeyed hash ... 0answers 422 views ### RSA and One Time Password (OTP) service What is the expert cryptographic opinion on the following? Assume that there is a web server and a client on web page. User on the Client calls an OTP web service on the server which: creates a RSA ... 0answers 543 views ### How compared encryption algorithm in terms of efficiency I want to compare two cryptographic algorithms. The first algorithm is RSA, and second algorithm is ElGamal elliptic curve cryptography. Now, I’m looking for a way to compare the speed of the two ... 0answers 162 views ### elgamal based decryption mixnet Can anybody help me to understand elgamal based decryption mixnet? Pure elgamal can be used in mixnet (re-encryption mixnet) and its very easy, and I have implemented decryption mixnet using RSA also. ... 0answers 57 views ### Generating Polynomials for the MPQS I'm going to try and eventually factor RSA-100, but my current QS needs a lot of improvement, so I'm going to try and switch over to the MPQS. I'm a bit confused as to how the MPQS works, which is ... 0answers 191 views ### Differential Cryptanalysis of FEAL-4 I'm currently carrying out a differential attack on the FEAL-4 algorithm, however I have hit a bit of a wall. Basically I attacked the final round first ($K3$) using the differential characteristic ... 0answers 187 views ### Sigma-protocol for 3SAT problem I have some questions from previous years exams, I hope you could help me with them. :) Let$g,h$denote generators of a group$G$of large prime order$n$such that$\log_g h$is unknown to anyone. ... 0answers 131 views ### Quadratic Sieve Bottleneck, Multiple Polynomials an option? After my failed attempt at trying to implement the ECM, I started working on the quadratic sieve. It works, but the bottleneck is finding smooth values over the factor base. The way I implemented it ... 0answers 89 views ### Why do we always append padding bits in SHA-512? [duplicate] Possible Duplicate: In the SHA hash algorithm, why is the message always padded? I'm reading the book Network Security Essentials written by William Stallings. To create a message digest ... 0answers 57 views ### IND-CPA security scheme [duplicate] Possible Duplicate: CPA Secure Chosen plaintext scheme The example for IND-CPA secure schemes given is generally: for a random r,$Enc_k(m) =(r|| E_k(r)XORm)$where$E$is a$PRF$... 1answer 121 views ### WebcryptoAPI - secure or not [closed] This is about the new W3 WebcryptoAPI draft standard. Here is a post by one of it's authors https://plus.google.com/u/0/105761279104103278252/posts/CSwVZ1RUijo It says its in part trying to change ... 0answers 429 views ### Stream Cipher : Never use stream cipher key more than once [duplicate] Possible Duplicate: Taking advantage of one-time pad key reuse? How does one attack a two-time pad (i.e. one time pad with key reuse)? Denote C is cipher text, m is message, and PRG(k) is ... 0answers 134 views ### Timestamping services authorities, utilizing Linked, hybrid and other than PKI schemes What are well respected Cryptographic Timestamping authorities utilizing more sophisticated than just PKI (RFC 3161) schemes, like Linked, Linked and signed, distributed hash trees (maybe P2P?), ... 0answers 229 views ### Is TOTP or a timestamp encryption a better timestamp-based authentication token system? Are there advantages to using TOTP over encrypting a timestamp with a shared secret, in cases where the readability or ease of typing the token are not important? 0answers 215 views ### Proper formatting of symmetric algorithm secret key Given this description from RFC 4880 sec 5.1: The value "m" in the above formulas is derived from the session key as follows. First, the session key is prefixed with a one-octet algorithm ... 0answers 79 views ### Applying multiple hash functions to improve security? [duplicate] Possible Duplicate: Guarding against cryptanalytic breakthroughs: combining multiple hash functions I'm a total newb to cryptography but after reading what I've read about it, I had a ... 1answer 216 views ### NTRUEncrypt - Choose the initial random polynomial I'm trying to implement NTRUEncrypt but encounter some problems. I've finished all the basic functions that are needed for the scheme base on this Document, but I can't find an algorithm to check the ... 0answers 61 views ### cipher text only attack - how to know when to stop when brute-force attack? [duplicate] Possible Duplicate: How can I do a brute force (ciphertext only) attack on an CBC-encrypted message? My question is about a cipher text only attack - I have as input only the initialization ... 0answers 228 views ### Most frequently used digital signature schemes in the recent years I am looking to understand if there are any hard figures on which digital signature schemes are most commonly in use today. I'm only really interested in what is employed recently (ie. last couple ... 0answers 76 views ### Is it possible to build an unfair noisy channel from 1 out of 2 oblivious transfer [closed] For a fair channel, sender sends a bit b and receiver gets it with probability 1/2 and gets b's flipped value with probability 1/2. It is trivial to build a fair noisy channel from 1 out of 2 ... 0answers 358 views ### Diffie hellman key exchange on elliptic curve over an extension field [closed] I am attempting to do a final semester project where I implement Diffie-Hellman key exchange on an elliptic curve over an extension field (2^256). Can anybody help me to generate the extension field ... 1answer 290 views ### ZKIP for Paillier public key correctness I'm using the Paillier cryptosystem in a protocol similar to mental poker. In the beginning of the protocol, each player generates a Paillier public key$(n,g)$. Later in the protocol, a player may ... 0answers 82 views ### Two untrusted party want to exchange data: how to ensure each one gets the data it needs? [duplicate] Possible Duplicate: Two untrusted party want to exchange data: how to insure each one gets the data it needs? I am trying to come up with what could maybe be a novel algorithm for an ... 1answer 133 views ### Collision attacks on digital signatures After reading this document about MD5 collision attacks, I still don't understand how collisions can make digital signatures insecure. In the paper, the researchers created two files with the same ... 1answer 100 views ### Standard serialization format for libsodium-based messages Does anyone know of a standardized serialization format which can be (or already is) widely used for encrypted messages? For a variety of reasons (mostly complexity, age and poor support across a lot ... 1answer 83 views ### RSA Key composition I'm trying to figure out how it is composed the RSA key. Follow what I know : For a RSA 2048, 2048 is the bit length of the module. The public key is composed by$(e,M)$when$e\$ is the public ...

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