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 ...

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Salary Negotiation Problem

Imagine Alice is applying for a new job. Alice has an idea of the minimum salary that she is willing to accept—let's call this value A. Bob, the hiring manager for ...
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25 views

Secure Communication Protocol Design using oblivious transfer?

I have a problem I need to solve with the following scenario and I hope someone can help me find an approach or direction to start tackling it. Consider Alice as a sender who has $n$ strings which ...
195
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11answers
48k views

Should we MAC-then-encrypt or encrypt-then-MAC?

Most of the time, when some data must be encrypted, it must also be protected with a MAC, because encryption protects only against passive attackers. There are some nifty encryption modes which ...
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0answers
308 views

What is the original SKID3 protocol?

While searching for a mutual authentication protocol I often stumbled upon SKID3. However I encountered different variations of it. The basic structure is the following: (1) $A \rightarrow B: r_A$ (...
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1answer
53 views

What is a simple information authentication protocol for constrained devices?

Background: I have an application where devices will poll information from some source on the network. These devices are very basic and have modest processing and memory capabilities. Hashing (and ...
3
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3answers
109 views

DIY message level security?

This might be in danger of being too elementary a question for this community but I'm hoping for expert help: Assuming that TLS is not enough to protect messages transmitted between a client and a ...
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2answers
200 views

Is there a way to optimize a linear scan while preserving anonymity?

I've been wrestling with a problem, and I was hoping if someone else had a bright idea. Here's the problem: I have two sides, Alice and Bob. Alice has a single high entropy string $A$, and Bob has a ...
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1answer
53 views

Encoding an element in $r=r'||h(r')$ way

We consider a finite field $\mathbb{F}_p$, where $p$ is a large prime e.g. 256-bit. We have $b$ a fixed element of the field. We encode it as $b'=b||h(b)$, where $h(.)$ is a cryptographic hash ...
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1answer
121 views

Authentication protocol which detects client impersonation from another machine

Consider following authentication protocol. Client ClientA knows some initial secret KeyA shared with server. Client also knows IP of legitimate server. Now when client wants to establish connection ...
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2answers
3k views

Signal vs Telegram in terms of protocols?

Some time ago, the question was asked in chat, why MTProto (Telegram's protocol) is supposedly worse than Axolotl (Signal's protocol) as both protocols have been the inventions of their respective ...
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0answers
70 views

Who invented the $1^n$ notation? [duplicate]

I am always wondering about the seemingly odd syntax $1^n$ which designates the security strength of a cryptographic algorithm. Who invented this (odd) syntax and what was the reason for inventing ...
16
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2answers
280 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,...
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0answers
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How much bandwidth is used in a typical IKE/ISAKMP initialization?

How much bandwidth is used in a typical IKE/ISAKMP initialization? How many UDP packets are sent in each direction, and what is their typical size? I'm referring to initialization of IPsec via IKE/...
3
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1answer
62 views

Does encryption of data/information take place in peer to peer networks like Gnutella, Bittorrent?

Do peer to peer networks like Gnutella, Bittorrent have any encryption system to secure the users privacy or encrypt the file/data being shared? Elaborate please.
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0answers
86 views

Encrypted comms between devices on LAN

I'm trying to encrypt a protocol that shares data between devices on a local area network (i.e.no connection to the internet). I don't want to use predefined keys because they're too easy to read from ...
4
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0answers
173 views

Yaos Millionaire Problem: Why distance >= 2?

I'm currently reading about Yao' Millionaire Problem: http://research.cs.wisc.edu/areas/sec/yao1982-ocr.pdf Alice and Bob want to know which of them is richer. Let $j \in \{1, \cdots 10\}$ be Bobs ...
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0answers
61 views

Simultaneous 2 way exchange without trusted third party

Stakeholders: Alice - has a message, M containing a secret, SA that Bob wants, where H(SA) is a hash which may be used by Bob to redeem some Bitcoin time-locked transaction sent previously by Alice. ...
3
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0answers
97 views

What is the lightweight key exchange protocol of choice?

Assume I have to implement a secure channel protocol by myself. Assume further that for some obscure reasons (library restrictions?) I can't use any of the pre-made libraries for SSH, TLS and such. ...
8
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1answer
187 views

Santa Claus' secret permutation

This December, $N$ friends play secret santa: they select a random permutation $\sigma$ of $N$ (without fixed point). For Santa Claus, everyone has to bring a gift to the next person in the ...
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0answers
111 views

Efficient proof of knowledge using Wegman-Carter hash

A verifier wants to ensure, with only little exchange of data with other systems, that a large block of data $M$ that the verifier holds is also available to some other system(s). It is not an ...
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0answers
39 views

Key Distribution Center Key Protocol Analysis

As shown in the image, why is Circle 1 to be B and Circle 2 to be A? Why is not the opposite, that is, Circle 1 to be A and Circle 2 to be B? like this picture From my understanding, Notation B in ...
21
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4answers
3k views

Why is plain-hash-then-encrypt not a secure MAC?

It seems that even in MAC-then-encrypt systems like SSL, something like HMAC is used rather than a plain hash. Why? Suppose we use some stream cipher; then why can't we use $Encrypt(m | H(m))$ as ...
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0answers
33 views

cumulative secrets

Imagine a server with an authentication scheme that utilizes an element of randomness in new sessions (i.e. one that uses the secure remote password protocol). At the end of a successful ...
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8answers
8k views

Guarding against cryptanalytic breakthroughs: combining multiple hash functions

Assume I want to design a protocol (or data format or similar) including some cryptographic hash, and want it to be as future-proof as possible, i.e. I want to avoid that breakthroughs in cryptography ...
2
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0answers
81 views

Designing a secure protocol to avoid MITM?

Imagine that you are designing an online game, the framework consists of a player A, a game host H and a trusted central server S. The player A has a symmetric key KAS and id A that is known to ...
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0answers
46 views

Election communication protocol

I'm not a cryptography expert, but this seems like it falls into this area. Imagine I want to design an election system (senate race for example) where I send the exact same ballot of 100 candidates ...
7
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1answer
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Is the “New Hope” Lattice Key Exchange vulnerable to a lattice analog of the Bernstein BADA55 Attack?

In the paper, "Post Quantum Key Exhange - A New Hope," the authors present a lattice-based key exchange based on the work of Chris Peikert. In this "New Hope" key exchange the authors try to gain ...
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0answers
61 views

How to normalize data of a generic HTTP request for the purpose of signing

I am working on PowerAuth 2.0, a solution for counter-based signing of HTTP requests (for the purpose of mobile banking). One of the tasks that I solved somehow but I am still not happy with the ...
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0answers
134 views

Simulation-Based Proof: When a Secret Key is Involved

Assume we have a protocol in which a party receives an encrypted random polynomial. The polynomial is encrypted using his public key. We want to construct a simulator for this party (so this party ...
4
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2answers
580 views

Verilog simulation & synthesis of Diffie-Hellman key exchange

Is there any freely available verilog implementaion of Diffie-Hellman key exchange? I couldn't find anything using google. So, assuming its not there I started implementing on my own. The code is ...
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1answer
62 views

A question about fully homomorphic encryption (FHE)

Hypothesis: We define the messages on a field $\mathtt{F}_p$, where $p$ is a large prime number. I am considering a dynamic outsourced private data scenario. Assume we have 3 messages: $m_1=2, ...
23
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6answers
3k 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 ...
0
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1answer
59 views

Creating a message authentication scheme

I have such situation. I have a device like dongle. But it has certain limitations. For example, it can only have implemented encryption and decryption functionality. The availability of ciphers ...
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1answer
82 views

Can we use merely permutation to hide a message?

This question is related to this: When all shares of a secret are given to adversary as a permuted matrix I think the below question is a simplified version of that. Assume we have a 40-bit ...
4
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2answers
77 views

How to implement 1-out-of-n OT from 1-out-of-2 OT?

How can I implement a 1-out-of-$n$ oblivious transfer protocol from 1-out-of-2 OT protocol which is resistant against passive corruption? Assume we can access 1-out-of-2 OT $n$ times.
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1answer
217 views

Two-party equality computation

Alice and Bob each secretly chooses an integer between 1 and 10, a and b. They want to know (with high probability) whether or ...
12
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2answers
4k views

Is TrueCrypt's multiple/cascading encryption safe?

Is TrueCrypt use of cascading encryption safe? Is it useful? TrueCrypt is arguably one of the most popular and widely used encryption applications in use today, yet it seems to use a very ...
4
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1answer
92 views

What is the recommended format/notation for crypto design?

Is there a recommended format or formal notation for documenting the combination of symmetric and asymmetric encryption, key derivation and other algorithms (and their inputs and outputs) that I think ...
3
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1answer
64 views

Have I made any glaring mistakes in my use of Yao's garbled circuits?

I would like to use garbled circuits to provide a service that allows people to vote where they do not need to reveal their votes to my server or to anyone else. Let's assume that I have secure ways ...
3
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1answer
38 views

Is this session start protocol secure?

I am working on a password manager application that saves the user's passwords in a remote server. I need to use AES in CTR mode to encrypt the passwords before sending them to the server. The client ...
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1answer
50 views

Why does Apple create a certificate for my push notification key [closed]

Brief rundown of how Apple Push Notifications (APN) work: Generate a keypair, generate a CSR for it Upload the latter to your Apple Developer account and associate it with your mobile app In the ...
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0answers
29 views

Publishing only items your subscriber previously subscribed to, without you knowing which those items are

Let's say you were given a dump from a security breach. You want to share the email addresses affected by the breach with a separate company who pays you for this service so that they can protect ...
3
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1answer
323 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. ...
4
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5answers
232 views

Is it possible to ensure security with zero pre-shared information?

Is it possible to secure a communications channel against both passive (sniffing) and active (injecting / MitM) attackers without either legitimate party knowing any pre-shared information? I know ...
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0answers
45 views

Security of a lightweight heartbeat protocol

I am implementing a heartbeat protocol so that a server can send notifications to clients. The notifications are not occurring so often, so I don't want to keep an open TCP+TLS session for each client,...
3
votes
1answer
77 views

How can I formally verify fuzzy commitment scheme based security protocol?

I am currently working on designing a security protocol which involves usage of fuzzy commitment schemes, for. eg Reed-Solomon codes which allows us to tolerate a certain level of error. I was ...
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3answers
144 views

List of post quantum cryptography protocols [closed]

What are the post quantum cryptography protocols that have been proposed until now? I know about McEliece cryptosystem, and LWE scheme. What are the others? Can you provide me a list or a website ...
1
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1answer
81 views

When we turn Random shuffle to Pseudorandom Shuffle

It's well known that a simple but efficient random shuffle algorithm can permute a vector of $n$ elements in $O(n)$ time. In the algorithm, we need to pick a value $U$ uniformly at random where $0\...
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2answers
3k views

Zero knowledge proof protocol example?

Alice is color blind. She never knows if her gloves are matched. Her brother Bob always teases her saying her gloves are mismatched and she should go change them. Alice wants to know if Bob ...