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Questions tagged [protocol-design]

Design of cryptographic protocols, i.e. ways of using algorithms (primitives) to achieve one or more security goals like integrity, confidentiality, authenticity (maybe together with non-security-related goals). If you ask about a specific protocol, tag with its name instead (or additionally, if about its design).

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Can the encrypt-and-authenticate method result in secure authenticated encryption if the MAC scheme has unique tags(non-deterministic)?

If we use non-deterministic MACs in encrypt-and-authenticate approach, is it secure?
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Efficient interactive proof of existence of path in a graph

Suppose Alice wants to convince Bob that she has found a path of length $M$ between vertices $v$ and $w$ in a certain graph. Bob can verify this claim in $O(M)$ time by having Alice send the list of ...
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Digital Signature Password verification

I currently have this TOFU protocol: First connection: Client generates salt and inputs a password Client saves salt Client hashes password with argon2 and salt Client generates Ed25519 keys Client ...
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When Shamir secret sharing used in one time pad scheme

In the following, all operations are defined over a finite field of prime order. Please note that what I'm explaining below is a part of a bigger protocol, however, to keep things simple I just ...
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Acceptable points of failure when applying encryption in an application [on hold]

I am working an a Windows application that will encrypt and decrypt files using AES Encryption. The 32 byte key which is diversified and derived using a ATSHA204 unique serial number and some addition ...
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MPC protocols for high school kids

I was explaining MPC to a high school student. He was excited and asked me for some examples. The only ones that I could think of are by using garbled circuits. Are there some simple MPC protocols for ...
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Protocol Design for IoT devices having PSK using AES-GCM

Handshake: 1) Client To Server: "AES-GCM(Client_random_128bit,client_iv,psk),client_id,tag,client_iv" 2) Server To Client: "AES-GCM(Server_random_128bit,client_iv++,psk),tag ...
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cryptographically signed streaming data

On a high level the question is: how does one cryptographically sign streaming data? Here is the context: a number of people are continuously streaming data to me the data is public and does not ...
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Facebook app-scoped identifiers and similar - implementing stateless ID obfuscation

After certain privacy concerns Facebook rolled out a bunch of changes to their APIs, one being "scoping" user identifiers per app. In effect, this means that Alice's canonical facebook user ID is ...
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How to prevent reflection attack in Needham-Schroeder in ECB mode?

We know that Needham-Schroeder is vulnerable to a reflection attack as shown here. How can I make it secure using ECB and without using timestamps? I need to modify the protocol. Otwan-Rees is a ...
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Maximum key stream sequence per key/IV pair in communication protocols

In the paper "LIZARD – A Lightweight Stream Cipher for Power-constrained Devices", one of the design rational of Lizard cipher is key stream size per key/iv pair. A5/1 produces only 228 keystream ...
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Needham–Schroeder fix by adding opponent's identity to the first message

Recap: Needham–Schroeder is as follows: $A \rightarrow B : \{A, N_a\}_{pk_B}$ $B \rightarrow A : \{N_a, N_b\}_{pk_A}$ $A \rightarrow B : \{N_b\}_{pk_B}$ Then, there is a MITM attack by Lowe ...
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How to create an ultra-secure connection between two clients with xor? [closed]

At work, I was asked to create ultra-secure connection over lan between two computers. It will be some kind of messager. I have a bunch of same random data in them(near 100mb). Also I can start a ...
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Obfuscating functions that are mostly zero

Let $f_k(x)$ be a boolean function of two arguments with two properties: The function $f$ can be efficiently computed. The output is always 0 or 1, and for any fixed $k$, if we choose $x$ randomly, $\...
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62 views

Secure multi-party random number generation

This question is actually continuation of my previous one. Secure multi-party computation for digital signature to implement solution there, I have to generate random data for padding (I will use ...
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Signal protocol: when, and why, is X3DH run again between the same two users?

This question concerns the Signal protocol's X3DH key agreement protocol as documented here. Obviously, if Alice and Bob have never contacted each other before, they need to run X3DH at least once to ...
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How to encrypt numeric data on a ticket

I have a customer with an existing ticketing system that generates tickets for events like theaters, movies, football and so on. The information in each ticket is encoded in a 16 decimal digit ...
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Dynamic accumulator with only non-membership witness

Goal: Construct a dynamic accumulator which can add elements and provide non-membership witnesses. I wanted to know if my construction is correct. Consider a group $Z_p$ where $p$ is prime number. ...
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Proof of ignorance to prevent “double-spend”?

Suppose I have some knowledge that I want to transfer securely from Alice's computer to Bob's computer, and prove that future breaches to Alice's computer will not reveal that information to someone ...
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1answer
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Validating a shared secret between two parties, one bit at a time

What is the following protocol known as? Is it considered secure? Would it work? Background Alice and Bob each have a secret. They wish to determine if they both know the same secret. If they do ...
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1answer
151 views

Zero Knowledge range proof

I like the idea of a Zero Knowledge range proof. But I read that, to prove my age in a range, a commitment is required by a trusted party (TP) stating my age. How does that work? is the commitment a ...
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1answer
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Fairness in Multi party computation

Why for achieving the fairness, less than a half of the parties should be corrupted? ($t<m/2$, where $t$ is the number of corrupted parties and $m$ is the total number of the involved parties). How ...
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Simple but secure method to share secret (128 bit AES key) though an untrusted relay

I am creating an end-to-end encrypted group messenger, and am looking for a way for online members of the chat to a arrive at a shared secret that can be used as a cryptographic key. This will ...
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Is my reasoning sound in the included scenario?

There is a package that contains a device, the device is activated/deactivated over a short range radio signal - it's function is to detect any unauthorised tampering of the package during the time it ...
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Concept for a RSA “repeater”. Is it sensible?

I have been using RSA signed/encrypted mailing a lot recently. Naturally, I wanted to use RSA mailing also on my phone, not only on my computer. However, I feel uneasy having my private key on my ...
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Is it necessary to transmit two or three points of an elliptic curve?

Are there cryptographic protocols, where a party should transmit by communication channel simultaneously two or three $\mathbb{F}_q$-points of an elliptic curve over a finite field $\mathbb{F}_q$? ...
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Does Off-The-Record protocol provide future (backward) secrecy?

I know Signal provides future (backward) secrecy, and that it is based on Off-The-Record protocol. However, does OTR by itself also provide future secrecy?
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Extending the Socialist millionaire problem to three parties

The usual solution of socialist millionaire problem allows to authenticate whether TWO parties have the same secret information. Are there any natural solution of the same problem for THREE parties?
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How to use proof of lack of knowledge?

This is a purely hypothetical example but is provable ignorance useful in cryptography? For example, let's say I have a trapdoor collision resistant function. I know the trapdoor and therefore some $...
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In a TLS 1.3 connection, how do the client and server choose a mutual cipher suite?

According to KeyCDN, TLSv1.3 connections are established in a single round trip: While TLS 1.2 requires two round-trips to complete the TLS handshake, 1.3 gets the job done in just one trip If ...
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1answer
47 views

rolling key with two keyfobs

Hy i just saw this Question: How does a rolling code work? And I just wondered how it is possible that my Vehicle (A 2013 Mazda 6) has two key fobs? As i understand this shuld not be possible. ...
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1answer
104 views

Detect MITM with hashed session-key — Is my protocol secure?

I have the following setup: An app ("client") wants to communicate securely with a device I created ("server"). The client has the public key of the server (and a hashed password) preinstalled. I use ...
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Authentication protocol for communication with Arduino Uno

I am using an ECDH key exchange to establish a shared secret between an Arduino Uno and an Android device. For this purpose I am using this library and more specifically Curve25519. This is the ...
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What's wrong with this digital signature scheme?

With regards to user authentication... The server sends Alice a randomly chosen number. Alice signs the number and sends the signature back to the server. The server checks the signature using Alice'...
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What conditions does a provable secure cryptosystem satisfy?

A cryptosystem can be entirely dependent on its underlying problem or it can have a reduction to other known problems. Solvability can be affordable if there exists a reduction of the base problem to ...
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1answer
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Computing/using RSA modulus without knowing its factors

There are some protocols, e.g. this, that require parties to compute/use RSA modulus: $N$ without knowing it's factors or $\phi(N)$. One way of doing it is to use a trusted party. Question: Is ...
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Instead of sending a set of random values, send a key for a PRF

Some Protocols require one party to send $n$ random challenges (or random values) to another party. For communication efficiency purpose, one can pick a random key for a pseudorandom function, and ...
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Economically Rational as a security proof

Is it possible to prove the security of a cryptocurrency payment protocol by saying that the actors will seek to maximize their profits. Would I need to set this up as a game and prove it that way or ...
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Time-release Protocol Implementation

“How to Build Time-Lock Encryption” by Jager “Time-release Protocol from Bitcoin and Witness Encryption for SAT” by Liu, Garcia, and Ryan I looked through the references, googled, searched GitHub ...
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How can process algebra help to design security protocols?

Would you please tell me how process algebra could help me to design security protocols? More specifically, can I use it for proving the security of protocols? Is process algebra used for any ...
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Which of these deductions are true about the simulator and the adversary?

Which of these deductions make sense? The simulator is actually being run by the adversary. It makes sense that the adversary initializes the simulator (which is just a program) with the input that ...
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Is function Deterministic or Probabilistic in the malicious security definition?

As you see, according to the attached definitions from "Efficient Secure Two-Party Protocols", the definition of the security in the semi-honest world has two cases for $f=(f_1,f_2)$.(deterministic ...
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A problem exists with the security proof in the secure AND example in the malicious model [closed]

Imagine that the malicious adversary in the real world uses $Y = 0$ as its input, therefore he computes the output as ($X$ && $y=0$) = $0$. We can conclude that the real view in the real world ...
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Reason for 3 rounds ChaCha in ChaCha20Poly1305@openssh

OpenSSH uses a slightly different ChaCha20Poly1305 AEAD construct then the one proposed by A. Langley and others for TLS. The TLS version The openSSH version (and here) The openSSH version uses two ...
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1answer
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How to use Real-Ideal model in a specific scenario (two party with cloud)

I have designed a two-party protocol where two parties outsource their input to the cloud. For example, Alice and Bob have inputs $X$ and $Y$, respectively, after which Alice and Bob encrypt their ...
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1answer
40 views

Using the security definition in the malicious model to prove security in the semi honest model

Can I use the security definition in the malicious model in order to prove the security of a two-party protocol which is in the semi-honest model? (I am using IDEAL/REAL Model paradigm) Would you ...
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2answers
108 views

Zero-Knowledge Bingo

Bingo is the game of chance where each player matches the numbers on their card with the numbers that the caller draws at random. When the first player has collected enough called numbers on their ...
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1answer
223 views

Getting a Keeloq manufacturer key

I have seen a lot of articles and research papers about breaking the Keeloq algorithm. My understanding is that the hardest part is getting the 64 bit manufacturer key. Some methods use crypto-...
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How do mix networks work with server downtime?

I am looking for an analysis of practical mix networks with server downtime. For example, if a message is supposed to go from A -> B -> C -> D, what happens if B wants to send the message but C is ...
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Should I use failed decryptings to handle multiple session keys?

I feel like this question is specific enough to stand on its own. Say I have a set of clients each with a unique ID and already established pair of session keys for each client. When a client ...