9
votes
2answers
935 views

Can any MAC be used as a KDF?

First, let me clarify what I mean with a Key Derivation Function (KDF). I'm interested in KDFs that take an $n$-bit symmetric master key and some diversification data of arbitrary length as input and ...
2
votes
3answers
62 views

Is there a method/protocol to validate a self-signed certificate by comparing a shortened hash?

I'm working on a solution where an iPad should connect to a server software running on a laptop using TLS with a self-signed certificate that was automatically generated on the laptop during the ...
34
votes
5answers
6k views

In RSA, how does the CPU deal with this huge modulus (8192 bits)?

Whilst I understand how the RSA algorithm works, I don't understand how the CPU operates when it needs to use the mod function with a huge number $n$, for example. ...
0
votes
0answers
52 views

Why is RSA still being used? [duplicate]

In hybrid encrytion, I still see that some site's use RSA in their https connection, so now I wonder, why do they not use ECC instead of RSA, ECC requires less computational power and encrypt's and ...
2
votes
1answer
529 views

Decrypting a blowfish cipher with three keys

Disclaimer: I'm pretty new to cryptography and I don't have a strong mathematical background. I apologize in advance if I missed something blatantly obvious. I participated in a security CTF this ...
-3
votes
0answers
68 views

Public-key Cryptography: I need a technical answer [on hold]

So, I already understand the point of Public-key cryptography, and how it's supposed to work. I understand the basics, and I've seen way to many diagrams. What I haven't seen enough of, however, is ...
3
votes
1answer
75 views

tripartite diffie hellman with Weil pairing

I try to understand how the tripartite Diffie-Hellman key exchange works. I read Joux's paper for this: https://www.semanticscholar.org/paper/A-One-Round-Protocol-for-Tripartite-Diffie-Hellman-Joux/...
2
votes
1answer
140 views

Difference left-or-right CPA security, IND-CPA security

I am trying to understand the notion of left-or-right-CPA (LOR-CPA) security for private-key encryption schemes introduced in my lecture. If I understood it correctly so far, the only difference to ...
3
votes
1answer
111 views

Is the use of AES in LoRaWAN correct?

I'm reading about LoRaWAN (specification). This network protocol has a particular way to encrypt data, detailed in the part 4.3.3.1. Here is a recap of how the encryption work, as I understood it. ...
1
vote
1answer
39 views

Crypto lib that use files instead of passphrase [on hold]

I would like to program an application to allow people to encrypt files without using a password or pass-phrase but an arbitrary long file. I'm searching for a library that allows me to safely create ...
5
votes
1answer
46 views

Binary format of encrypted PGP private key?

Short Version of the Question: I would like to remove any predictable information from an encrypted private keys binary representation. Does anyone have a hint where the binary format for encrypted ...
1
vote
2answers
186 views

Verifying Without Knowing Key

Say user Bob sends an encrypted message to a server. People can download the message from this server and later get the key directly from Bob. Is it possible for the server to somehow verify that ...
0
votes
1answer
63 views

Given a prime exponent e and a prime number n, find b, where b^e = 1 mod n

Can anyone help me with the following problem. Given a prime exponent $e$ and a prime number $n$, find $b$, where $b^e \equiv 1 \bmod n \land b > 1$. For example, $b^5 \equiv 1 \bmod 11$ how to ...
3
votes
1answer
43 views

On the security definition of password-authenticated key exchange

I found in all PAKE papers, the security is defined as something like this: Let $Succ(A)$ be the probability that an attacker $A$ successfully distinguished the session key from a random string. Then ...
1
vote
1answer
24 views

Conditional probability with Vigenere Cipher given specific plaintexts and key sizes

Apologies if this should be in the Mathematics stack exchange, I just ask it here because the context is cryptography. Here is the question that I seemingly cannot get correct: Consider the ...
2
votes
1answer
81 views

Calculating Polynomial Inverse with extended euclid in java

I'm trying to understand the NTRU-PKCS and therefor I wanted to code a naive Version of it. Now my Problem: I tried to calculate the inverse of a Polynomial with an extended Version of euclids ...
-2
votes
1answer
46 views

In Shamir's (t, n) secret sharing scheme why don't use infinite field? [duplicate]

Well, we use finite fields to select shares. What happened if we use infinite fields.then will the scheme be vulnerable? Easy to break? Or share generation and reconstruction will be difficult? ...
1
vote
1answer
35 views

Given C is a code of length n. Containing M code-words with a distance d

I'm studying for my exam and came across this question below. I don't understand how to get $d$. I get $C$ is a code of length $n$. Containing $M$ code-words with a distance $d$. $(n,M,d)$ But how ...
3
votes
1answer
677 views

CBC-MAC length extension attack with IV simulation

I'm doing the Cryptopals challenges (formerly the Matasano challenges) and struggling with second part of the 49th problem where I'm asked to do the length extension attack with CBC-MAC without IV ...
2
votes
1answer
120 views

How does DH work when combined with ECC or RSA?

I know that Diffie-Hellman is used to create keys in a secure way over an insecure channel. But there is one thing which I cannot understand: I see that a lot of sites use ECC or RSA alongside DH. ...
2
votes
0answers
58 views

Are analog quantum computers a threat to RSA and DLP?

We already know that D-WAVE's "quantum computers" can't really run the Shor's algorithm, because the way they're built doesn't qualify them as universal quantum computers. Now researchers actually ...
9
votes
1answer
72 views

What's the reasoning behind the design of the TLS 1.2 PRF?

TLS 1.2 defines a PRF-like construction $P_{hash} : \{0,1\}^* \times \{0,1\}^* \rightarrow \{0,1\}^l$ for key derivation, etc. To quote the spec: We define a data expansion function, ...
3
votes
1answer
64 views

proof of correctness Ring-LWE cryptosystem

I've been studying Ring-LWE based crytposystems such as the one in this paper, but I can't seem to find/come up with a proof of correctness for this particular scheme. The encryption goes as follows: ...
0
votes
0answers
27 views

Password manager that uses a mix of long and short key derivation functions

I was reading "A Convenient Method for Securely Managing Passwords, Halderman et al., 2005". In short, the authors say to do the following: ...
3
votes
0answers
32 views

Quantum complexity of LWE

As per my understanding LWE is quantum secure because there is no known quantum algorithm to solve LWE in polynomial time. Due to the reductions given by Regev et al. If there is any algorithm that ...
5
votes
1answer
65 views

What is the most efficient attack on NTRU?

So, I got how finding the private key is equivalent to resolving the SVP. I also understood that the LLL algorithm can only be used in small dimensions. Now, I wonder what is the most efficient attack ...
-1
votes
0answers
26 views

Identify a hash which was already seen? [on hold]

I have a question. In our group we are processing a large number of datasets. Each one is identified by its hash (pseudo-random ASCII string). We are currently looking for a way to tell if we already ...
3
votes
1answer
83 views

Salting Hash stored on RFID tag?

In my application, I am trying to prevent counterfeit widgets from being used on our gadgets; think HP ink-cartridges. I will be doing such with UHF RFID tags embedded in the widgets. Unfortunately, ...
1
vote
3answers
3k views

How to check the strength of an encryption algorithm?

I asking for advice on how to check strength of an encryption algorithm.
0
votes
0answers
53 views

Security Proof in Fuzzy Identity Based Encryption?

Been having a great deal of difficulty understanding the use of simulators to prove security of ABE schemes so I though I would start from the first ABE paper (Fuzzy Identity Based Encryption) to try ...
1
vote
0answers
12 views

how to create and use sub keys with PGP? [migrated]

let's say i wish to have forward secrecy with PGP, that requires me to create multiple sub keys to be used and destroyed accordingly, how should i do it?
4
votes
3answers
211 views

After a diffie hellman key exchange, what is the common secret used for?

What is the common secret that is established used for? What types of interactions are now possible?
4
votes
1answer
72 views

Enhance security by combining bits of 4 different hashes

Assuming that performances do not matter, is there any real benefit in terms of security (in general) in combine hashes in this way: hash functions: ...
3
votes
1answer
31 views

Conditions for Perfect Secrecy with the Vigenere Cipher

Please forgive my ignorance here as I'm far from a math major and I've never looked into cryptography before so if this seems stupid - it probably is. There is a question in a quiz I'm attempting that ...
7
votes
3answers
552 views

Did non-military cryptography appear in 50's and 60's only due to NSA leaks?

I'm not talking about scytale, but encryption like RSA, DES, etc... How did exactly civil cryptography evolve after World War II?
-1
votes
0answers
20 views

How do we compare two hash functions / cryptographic functions [closed]

I know what hash functions are but as my research project I am comparing two cryptographic algorithms so I am a bit confused about on what bases should I compare the two algorithms as these are ...
0
votes
1answer
57 views

Questions about length key of RSA 2048 bit

I use putty gen to generate RSA key, I choose length of key is 2048 bit, it generate public key: ...
-1
votes
0answers
23 views

Counter-Mode Message Authentication Code [duplicate]

Excuse my naivety,I don't know much about crypto. But I've been wondering, couldn't counter-mode be used for MAC just like CBC in CBC-MAC, assuming nonce for the counter is not repeated? Am I missing ...
5
votes
1answer
64 views

Are there any high level memory-hard PBKDF constructions?

The PBKDF2 construction from PKCS #5 v2 has the convenient feature that it can be implemented using only standard interchangeable cryptographic primitives. Specifically, it only requires the ...
-1
votes
0answers
14 views

.cyt file extension, don't know what software to use to open this file type [closed]

I encrypted some zip files in 2010 and found them recently on my hard drive, but I have no idea what software I used to encrypt them so now I cannot open the files, which is very annoying. The files ...
16
votes
2answers
261 views

Is it possible for Alice and Bob to both sign a message “simultaneously”?

Let's say that there is a message which is considered valid if signed by both Alice and Bob. Alice could sign the message and then give it to Bob, so that he can sign it and give it back to her. But,...
1
vote
1answer
27 views

Can I use the Sequence Number as the (implicit) IV in AES-GCM IPsec?

The RFC https://tools.ietf.org/html/rfc4106#page-5 states that, under AES-GCM IPsec, each packet is expanded by 8 bytes for the IV and up to 16 bytes for the ICV. Why? Since we already have a ...
0
votes
0answers
21 views

Diffie-Hellman combined with DSA/RSA

we have learned Diffie-Hellman, RSA and DSA (Digital Signature Algorithm) in university. Because DH is vulnerable of Man-in-the-Middle we had the task to program the DH combined with RSA to protect ...
-1
votes
0answers
55 views

NSA Suite B revoked [closed]

NSA Suite B was formerly documented in CNSSP-15 "National Information Assurance Policy on the Use of Public Standards for the Secure Sharing of Information Among National Security Systems". NSA has ...
3
votes
1answer
98 views

Change initial hash value of SHA512/t

Fips 180-4 defines under 5.3.6 how to calculate initial hash values for SHA512/t for a given value t. Can someone explain me how the t actually affects the outcome of the procedure (which, as far as I ...
4
votes
1answer
662 views

What does this notation stand for when describing a code?

This code has appeared in some online course material. I understand the $(5, 4, 3)$ refers to (length, num codewords, distance) but no explanation of the $Z_2^5$ notation is given: One $(5,4,3)$ ...
45
votes
5answers
31k views

Can you help me understand what a cryptographic “salt” is?

I'm a beginner to cryptography and looking to understand in very simple terms what a cryptographic "salt" is, when I might need to use it, and why I should or should not use it. Can anyone offer me a ...

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