# All Questions

598 views

### A block cipher with independent keys for each round

I want to modify a standard block cipher in the following way. I replace each round key by a key picked at random. Is this block cipher as secure as the original one ? Thank you. EDIT Some missing ...
147 views

Let : $G_{0}$ and $G_{1}$ be two multiplicative cyclic groups of prime order $p$. $g$ is a generator of $G_{0}$ and $e$ is a bilinear map, $e : G0 × G0 → G1.$ $𝐶_{1} = 𝑔^{𝛽𝑠_{1}}$, $𝐶_{2} = ... 1answer 86 views ### Key Confirmation Attack [Key Distribution Center (KDC)] Okay this is how I understood it according to this: Alice$A$establishes a connection to$KDC$and prepares for session key Exchange$k_{ses}A$encrypts the request with her key$k_A(A, B)$... 1answer 1k views ### Why do crypto libs use table lookups when they're vulnerable to timing attacks? AESEngine.java, from BouncyCastle, uses table lookups as does aes_x86core.c, in OpenSSL. But per Cache-timing attacks on AES table lookups like what OpenSSL and BouncyCastle are doing are vulnerable ... 2answers 187 views ### Cryptosystems used to generate public key certificate Where can we find the cryptosystems used to generate public key certificate? Are the cryptosystems under the signature algorithm and signature hash algorithm? Do I need to analyze the packets ... 3answers 357 views ### Is signing a hash instead of the full data considered secure? I reference object in some of my code in hashes. The signature is itself is another object separate from the one I am signing (for obvious reason). I consider simpler to simply sign the reference to ... 0answers 28 views ### FFX Encryption over alphabet of arbitrary radix I understand how standard numeric FPE using a halved string in cycled Feistel networks is constructed and operates. I then read the paper regarding FFX encryption which should allow for any non-binary ... 1answer 56 views ### Can string lookups be vulnerable to timing attacks like array lookups are? Per “Can non-assembly crypto libraries truly be secure against timing attacks?”, array lookups are vulnerable to timing attacks. Like, if you do cresult[map[i]] and ... 1answer 42 views ### RSA problem - how to find$d$[duplicate] For example, let$p = 3$and$q= 11$, choose$e = 3$. What computation I have to apply in order to find the corresponding$d$? I know it's 7, but I want to know the exact process to be applied to find ... 2answers 8k views ### Definition of Textbook RSA What is the definition of Textbook RSA? What are some of the properties of textbook RSA? How does it differ from other RSAs? 1answer 66 views ### One time pad ciphers in emails In order to achieve very high security for privacy, would it be cryptographically secure to use one time pad ciphers in emails? The distribution of the keyword would pose no problems since I would ... 2answers 171 views ### Customizable Crypto Algorithms in Hardware Several companies offer customized cryptographic algorithms, for example Crypto AG (www.crypto.ch/en/company): The individually created customer algorithms are unknown to anyone else and are not ... 2answers 75 views ### Is Checksum to file back decoding possible? So, I was having this weird thought. If the checksums(MD5 or SHA...) are unique to any file and are modified if any part of the file is edited, why cant the checksums be decoded back to get the ... 1answer 115 views ### Can non-assembly crypto libraries truly be secure against timing attacks? http://cr.yp.to/antiforgery/cachetiming-20050414.pdf states the following: So what went wrong? Answer: NIST failed to recognize that table lookups do not take constant time. “Table lookup: not ... 0answers 39 views ### RSA Encryption: What happens if n is a factor of the message M? [duplicate] From what I have learned about RSA encryption, the message M and the modulo n must be coprime because Euler's theorem only holds for coprime numbers? for example, what happens if I choose p = 3, q = ... 1answer 35 views ### Key exchange resilience to DoS attack I am designing a user registration protocol for a system where I control both clients and servers. The aim is to establish a symmetric key for subsequent authentication, while minimizing the work ... 0answers 29 views ### Public SRP verifiers or public hash chain “public keys” when secret is low entropy password I want to set up the following: An untrusted server should host user sessions and authenticate users without knowing their passwords or being capable of creating a fake user session in the user's ... 1answer 37 views ### ssh-keygen DH Primality Testing I'm pretty familiar with using ssh-keygen to create groups that go in the /etc/ssh/moduli file for the Diffie-Hellman Group Exchange in openssh. Reading over the man page, it says "By default, each ... 1answer 52 views ### Extend OTP on random data? If Alice and Bob both start with a shared OTP$P_0$, which is 256-bytes long, and Alice wants to send a 512-byte message, would it be secure to send the first 256 bytes with standard OTP (... 3answers 99 views ### Why not put MAC in fixed position and cover padding for MAC-then-encrypt? The biggest problem with using MtE with a mode where it's known to be secure (CBC) is with the padding, where you can't retrieve the authentication until you know where it is by looking at the padding ... 1answer 36 views ### can cramer-shoup public key have two difefrent private key? since I am new to Cramer Shoup algorithm I want to know is it possible to have 2 different private key for a public key due the key pair generation algorithm that Cramer Shoup use? I know that in ... 1answer 86 views ### Is the GOST block cipher broken? Is the GOST cipher broken or known to be weak and insecure? Please try to simplify your answer since I am a programmer and not a cryptographer and please consider this web page and tell me if the ... 1answer 41 views ### Signature Verification: High level I'm trying to understand how certificate signing and verification works conceptually. I know the classic example with asymmetric cryptography- the sender encrypts data with public key of receiver, ... 2answers 121 views ### Implementing CBC Encryption Using Decryption I've implemented this algorithm, which, working from the end of the message backwards, creates a valid CBC ciphertext from any plaintext, using the block cipher's decryption operation instead of the ... 1answer 73 views ### The encryption scheme is secure? I have a scheme and I don't know that this scheme is semantic security or not. -Secret keys$\{s_1,s_2, x_1,x_2\}$and public parameter$p$(large prime number) -Encryption E(m):$C_1 = s_1m + x_1k ...
64 views

What is the advantage of AEAD ciphers? Why is the TLS working group pushing for them? I thought modern cipher suites require SHA256 for authentication. What advantage is there to including Poly1305? ...
28 views

### Is modular Barrett reduction usable for Ed25519?

I currently try to implement Ed25519 following this draft. I have implemented every field operation except the reduction by the group order $q$ (in chapter 5). I looked for a reduction algorithm and ...
34 views

### Is constructing IND-CCA2 public key encryption schemes particularly easy with the KEM/DEM approach?

After the introduction of McBits, I was interested what security notions are neccessary for IND-CCA2 security of integrated encryption schemes (IES, following the key encapsulation mechanism / data ...
7 views

### How to correctly convert TAG value to the right format so that to Verify HMAC? [migrated]

I'm working on HMAC generation and verifying to check data integrity. I can correctly generate the MAC value but when sending it through socket to another program for verification, I faced with ...
77 views

### How is the MAC or HMAC secret shared with the other party for verification?

I've seen people everywhere say to use a MAC or HMAC with block ciphers. I think I understand the basics, but I'm still not sure how the HMAC secret is distributed so the other party can verify that ...
22k views

One runtime platform provides an API that supplies PKCS#5 padding for block cipher modes such as ECB and CBC. These modes have been defined for the triple DES, AES and Blowfish block ciphers. The ...
7k views

### What is the difference between MAC and HMAC?

In reference to this question, what are the "stronger security properties" that HMAC provides over MAC. I got that MAC requires an IV whereas HMAC doesn't. I also understood that MAC may reveal ...
45 views

### Encryption algorithms larger than 256 Bit for “big data” encryption?

I'm somewhat new to encryption. When looking at encryption programs for big data, I frequently see a maximum of 256 bits. Why do we generally restrict our (symmetric) keys to 256 bits? Can more ...
2k views

### Why should I make my cipher public?

As I understand it, the less people know about the internals of my protocol or cipher, the more secure the protocol is. However Kerckhoffs's principle states that A cryptosystem should be secure ...
13 views

### Are there any paper/human strong crypto systems? [duplicate]

Are there any paper/human executed crypto systems that have reasonable strength? I am aware of a few candidates so far Solitare from Cryptonomicon https://en.wikipedia.org/wiki/Solitaire_(cipher) ...
266 views

### What are the practical implications of ciphertext distinguishability?

Commonly there are four ways to "break" a secrecy-focused cryptosystem: Recover the secret key Recover the message Distinguish an encryption from random noise Distinguish the encryption of two ...