# All Questions

133 views

### Automated testing of cipher security for import/export compliance [closed]

What do we know about systems that automatically test and grade cipher security. The application in mind would be for checking for compliance with import/export regulations. I imagine a system that ...
555 views

### Is there a kind of OS entropy pool on Windows systems? [closed]

I am wondering if Windows provides an equivalent of /dev/urandom from linux ? Or any kind of system entropy pool ?
211 views

### Hash which can be used to verify one of multiple inputs?

Is there a hash function H1 which, when given inputs a, b, etc., produces output ...
79 views

### Committing Bilinear equation in Groth-Sahai framework

Groth-Sahai framework enables us to commit to QE, MSME, PP equations. Now, is the equation below committable in GS framework? A bilinear map $e: G_1 \times G_2 \rightarrow G_T$. $g_1 \in G_1$ and ...
165 views

### Two questions on EMSA-PKCS1-v1_5

If I implement EMSA-PKCS1-v1_5 in the following two non-standard ways, what kind of things could go wrong? The padding structure will be referred as (00|01|PS|00|DER(Digest Algo)|Digest), where | is ...
124 views

### Why should I use X.509 Authentication over PKC based Authentication?

So I have two examples and I don't understand why one would be chosen over the other. Example 1. A sends EPUb[r1] to B (asks B to prove knowledge of ...
128 views

### RSA signing security

I'm curious about the security of RSA signing with the same public private key pair when the same message is sent multiple times. It's my understanding that once you generate the hash of the message ...
85 views

### Exploration of Blum Micali Security By Seed Size

I'm new to cryptography and am most intrigued by mathematically based pseudo random number generators. With reference to the Blum Micali algorithm: $X_{i+1} = G^{X_i} \bmod P$ can security be ...
158 views

### Updating the secret key used for HMAC

I am designing a distributed system, composed by a set of physically distributed embedded devices (8 bit cores with less than 1 KB of RAM). The devices need to be able to authenticate the originator ...
66 views

### Verifying identity using a sha-1 hash

I was reading http://blog.zorinaq.com/?e=74 which is about a Windows kernel developer. The developer proves that he is an actual developer by posting the SHA1 hash of a particular revision of a file. ...
99 views

### Performing HMAC with random key before MAC comparison

In Laravel (a PHP framework) I can see that they calculate a HMAC with a random key over the final HMAC before comparison. This additional HMAC calculation is of course performed for both the ...
211 views

### open source whitebox-crypto implementation

I am trying to code a simple WBC situation to help my understanding about white-box cryptography. Details: I have 2 programs, a "server" and a "client", the server utilises caesar cipher (key = 2) ...
143 views

### What are the current limitations (and capabilities) of Functional Encryption used for access control?

I'm trying to make my way in Functional Encryption used for access control. I read a lot of papers such as "How to Run Turing Machines on Encrypted Data", "Functional Encryption: New Perspectives and ...
279 views

### Comparison among algorithm based on key length

Some months ago I found in some paper that we cannot compare symmetric algorithm with asymmetric algorithm based on the key length and more important we cannot compare asymmetric algorithm using only ...
65 views

### Pollard's Rho - Restricting the random function to the exponents

Pollard's Rho is usually constructed using a function $f:G \rightarrow G$ which behaves 'random enough' in order to detect a collision with Floyd's cycle detection trick. It is easy enough to observe, ...
161 views

### Abstracting primitives and modes of operation

I am developing a symmetric crypto library and have reached a roadblock. Looking at block ciphers, it is quite obvious that all block ciphers are trivially abstractable as a simple primitive ...
134 views

coded text: ij gj hnev xudmyx hn igim umif obaxidyw kxzq si the key is JULIET, but i cannot figure out how it is used. Any help would be awesome!
327 views

### Help converting sha256 to 32-bit stream

I need some help with hash value calculation. I am a bit confused by this statement that I found on w3 website on calculation of a DigestValue for xmldsig ( ...
107 views

### Is ASCON cipher broken?

http://eprint.iacr.org/2015/030 present several attacks of ASCON but does not have a conclusion section. I'm having troubles estimating what are the consequences on the use of ASCON. What's your ...
216 views

### What cryptanalysis is possible against two independent keystreams XORed against plaintext?

If a wise person was unsure about which commercial cryptography standards are truly secure from the fascist powers that be, it would seem the obvious option for companies and individuals is to now use ...
103 views

### Formal security of recycled random blinding in a Paillier scheme

This question is a follow-up/variant on a previous question. Supposing that we are trying to generate a large number of (indistinguishable) ciphertexts of a given plaintext and want to avoid the ...
128 views

### What kind of attack does the current brokenness of SHA-1 allow?

I understand that the following is becoming feasible, or already is: Find any 2 data (d1 and d2), for which SHA1(d1) = SHA1(d2) However, it is not entirely clear ...
98 views

### Possible to use an accumulator to “license” or restrict the qty of certificates being used?

Suppose in a future version of x509 PKI, it is possible to limit the quantity of certificates being used, what would that look like? Here is a concept that won't work in the real world, but ...
208 views

### Nonces being used in SSL and MAC to prevent replay attacks

I'm a bit confused in the way nonces are used in these processes to prevent replay attacks. Heres How I think it works during SSL: Nonces are exchanged during stage one of the handshake protocol. ...
558 views

### Is double hashing collision resistant?

Double hashing can surely provide more security than only one layer of hashing but does that necessarily mean it is more collision resistant? This question in a more mathematical form: If $H$ is a ...
609 views

### Is RSA with SHA1 broken?

I am using CryptSignMessage to sign a string/file. Is using RSASha1 insecure? I know Sha1 is broken as a hashing algorithm, but does that also mean that using it for signing with RSA is broken?
71 views

### Confused with the role of AES round keys

AES works when each plaintext block is arranged in a 4x4 array of bytes called states. State goes through 10 rounds of encryption consisting of 4 operations: bytesub, shiftrow, mix columns and add ...
402 views

### What cryptography is suitable to motivate High School students to learn math?

A High School math teacher in the Bronx asked me if I knew of any way to use cryptography in a way that motivates students (15 to 18 years old) to learn math. I do know that many of them want to ...
57 views

### TimeStamp in Cache-time attacks on AES [closed]

I have recently read about AES cache timing attacks. More specifically, I read Daniel Bernstein paper Cache-timing attacks on AES. I have a question about the code in Appendix A: ...
4k views

### Specification of the Megamos crypto algorithm

It has recently emerged that a paper that was scheduled to appear at Usenix Security 2013, titled "Dismantling Megamos Crypto: Wirelessly Lockpicking a Vehicle Immobiliser", has been censored ...
83 views

### PKI Infrastructure

I've got a very simple but for me a difficult question. I analyzed the public key cryptography and understand the process. But I didn't understand why is only the receiver able to decrypt to message. ...
277 views

### Programming language for modular arithmetic over large numbers [closed]

I'am trying to implement algorithms on integer factorization.This involves dealing with integers of 200-500 digits and doing modular arithmetic over them.Which programming language has inbuilt support ...
89 views

### How bad would it be to reuse the random blinding factor in a scheme like Paillier?

A secure and somewhat fast way to "re-encrypt" (refresh? anonymise?) a Paillier ciphertext, $c$, is to multiply it by an exponentiated random value: $c \gets c \cdot r^n \mod n^2$ (with \$r \in ...
383 views

### Implementing a web app where the server cannot decrypt its own data?

I'm a cryptography novice, but I think that the world needs to move towards an "encrypt everything" mentality as much as possible. As a result, I've been thinking a lot about ways to build a web app ...
269 views

### Factors of RSA modulus

In the article A Method for Obtaining Digital Signatures and Public-Key Cryptosystems, the original RSA article, it is mentioned that Miller has shown that n (the modulus) can be factored using any ...
144 views

### Private Information Retrieval--Is it still theoretical?

Are there any real world products in which private information retrieval techniques are used?(a data hosting server oblivious of which data item was fetched from it?)If not what are the major barriers ...
128 views

### Key Recovery Smart-Vercauteren SWHE

In the article (https://eprint.iacr.org/2009/571.pdf, pag 8) of Smart and Vercauteren, it is mentioned that the recovery of the private key is an instance of the small principal ideal problem. But I ...
117 views

### white-box cryptography and its applications [closed]

I am a programmer who is doing research into whitebox cryptography. What I hope to do is to use WBC for an DRM application however as some of us may know, WBC is theoretically impossible therefore I ...
245 views

### Difference between Pseudorandom Function vs randomly chosen function

I am currently going through a course in cryptography. In this, I stumbled upon Pseudorandom Functions. I got a little idea of Pseudorandom Generators which map an input string (key) to an extended ...
28 views

### How to find the factors of the modulus? [duplicate]

In the article "A Method for Obtaining Digital Signatures and Public-Key Cryptosystems", the original RSA article, it is mentioned that Miller has shown that n (the modulus) can be factored using any ...
323 views

### ASN.1 encoding off RSASSA-PSS default parameters

I am not totally sure the question belongs to crypto and not stackoverflow but nevertheless... The problem is the encoding of the RSASSA-PSS default algorithm identifier parameters in an X509 ...
158 views

### private keys for multiple devices [closed]

I have an architecture where: a user can have multiple devices (phones) the server needs to broadcast the payload to all devices through the same channel (basically, all devices listen and receive ...
1k views

### Difference between Hash function and Random Oracle

Going through the blog post, I was under the impression that any cryptographic scheme which makes use of hash function is said to be using random oracle. But, I have come across one construction of ...
46 views

### Can one deduce the symmetric key size used to encrypt a given a piece of ciphertext?

Assume an attacker captures a piece of ciphertext encrypted with a symmetric key. He knows all the details of the algorithm used to encrypt except for the size of the key used in this case. Can he ...
166 views

### Key management protocol for end-to-end security on Advanced Metering Infrastructure

I am currently working on a research on end-to-end security implementation for Advanced Metering Infrastructure (AMI). Pardon me if I a bit off topic or not asking the right question as I am ...
90 views

### Integrity protection in wireless sensor networks [closed]

I have done a lab about wireless sensor nodes and got in touch with encryption for the very first time. There are some questions on my sheet, especially on integrity protection (the attacker wants to ...
249 views

### Problem with implementing DES in python

i'm implementing DES in python and i've stumbled upon a problem i can't really find the problem, after debugging it i narrowed it down to this function, can anyone tell me if i'm implementing the DES ...
89 views

### Unique assignment of X.509 certificate to each client

I'm trying to implement a short scale electronic voting application in a domain comprised of no more than 100 clients. System administrator is able to create new election instances and each client is ...