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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Is this protocol secure?

Before anyone freaks out, this is purely speculative and I am not developing a cryptosystem! I can't see anything wrong with this protocol, but my knowledge of cryptography is rather superficial: ...
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Is it safe to say that a XOR with an unknown input provides a random output?

I am wondering if you have an input $x_{1}$ and you XOR it with an unknown random second input $x_{2}$, is it safe to say that the resulting $x_{1}\oplus x_{2}$ will be random ? The final idea would ...
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Failure of parallel composition

Is there a simple example of a cryptographic protocol that is secure when used on its own (with only one instance active at a time) but becomes insecure in a concurrent setting, i.e., a failure of ...
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what motivated the design decisions of RFC 8291 (“Message Encryption for Web Push”)?

Related question here. I'm reading RFC 8291, which describes a protocol to protect web push messages sent between an application server and a user agent (typically a mobile browser or other mobile ...
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How can a recipient recognize which encrypted messages are intended for them?

Let's say there's a decentralized email service where parties' public keys are known. A sender sends a message to a recipient by encrypting via RSA with the recipient's public key and posting the ...
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Given ciphertexts C1, C2 of different messages P1 and P2; how can we prove that both C1 and C2 were encrypted using public keys of the same pair?

I vaguely recall reading about a scheme that accomplished this but am not able to figure out which one it was. For the sake of brevity I'm gonna omit any nonces. Let's say we have an asymmetric ...
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Combining ECC And RSA for a Web Based Chat system

I'm a building a Web application chat message system(Over TLS) and i would like to know if the following theory is correct. Sender I'm generating keyPairs using RSA and another KeyPairs using ECC. By ...
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In group key agreement/exchange protocols, does key independence implies forward and backward secrecy?

Kim et al. [here] define Foward and Backward secrecy as follows: Forward Secrecy (not perfect foward secrecy): the inability for a passive attacker to obtain past group keys from a subset of new ...
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What is the main difference between anonymous authentication and using an anonymous credential?

What is the main difference between anonymous authentication and the use of an anonymous credential? And when we should use them?
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Signature algorithm for constrained environment, curve25512 already present for ECDH

I'm working in a very constrained (in code size/memory) microcontroller environment where I'll need public key signature verification. The algorithm to be used can be chosen, and there's no ...
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Unilateral authentication with implicit key authentication

Is it possible to design a cryptography protocol with achieving unilateral authentication of one party A by party B using implicit key authentication? Key authentication is the property whereby one ...
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Is this a reasonable design for encrypting records in a key/value database?

A while back I designed a protocol for en encrypted key/value service. My main goal was to minimize the value of a breached database by using cryptographic algorithms where a brute-force cracking ...
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What are different types of signature properties?

I am reading about digital signatures these days. I read about blind signatures, group signatures and ring signatures. Are there other type of signatures as well?
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Anonymizing a group chat

I wonder if it's possible to have a peer-to-peer group chat protocol, where anybody is free to join the chat and broadcast with a chosen username to all others who have joined it, but with a strong ...
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Using crypto_sign then crypto_box_seal for anonymous messages

If you have a message M and you want the sender (alice) to be anonymous to everyone but the recipient (bob), is it ok to do? ...
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How to formally define the security of Random Oblivious Transfer

Assume that there is a protocol $(A,B)$ such that receives no input and satisfies: $A$ - outputs two random bits $x_0, x_1 \in \{0,1\}$ $B$ - outputs a random bit $b \in \{0,1\}$ and also outputs $x_b$...
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Securing communication between limited embedded systems

I am currently trying to harden communication over a limited physical communication channel on an embedded system. The Scenario I think the system is rather typical for small embedded applications: ...
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Construct an Oblivious Transfer protocol using a secure protocol that outputs random bits between two sides

Assume that there is a protocol $(A,B)$ such that receives no input and satisfies: $A$ - outputs two random bits $x_0, x_1 \in \{0,1\}$ $B$ - outputs a random bit $b \in \{0,1\}$ and also outputs $x_b$...
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How to attack Oblivious Transfer from a malicious sender that can deviate from the protocol

I am looking at at the $1–2 \space \text{oblivious transfer}$ that is described here: https://en.wikipedia.org/wiki/Oblivious_transfer#:~:text=In%20cryptography%2C%20an%20oblivious%20transfer,Rabin. I ...
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MAC-then-encrypt in SIGMA protocol for authenticated key exchange

The SIGMA protocol proposed in 2003 and used in TLS 1.3 and IKE stands for "SIGn-and-MAc" and can optionally protect identity using encryption. The SIGMA-I variant illustrated below ...
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How to securely deal cards?

Thanks to a certain pandemic going around I was wondering whether there is any cryptographic way to remotely deal cards without the dealer being able to know them and without requiring to trust a ...
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Are there any mutual-distance bounding protocols in RFID context?

Distance-bounding algorithms are a classical solution for the Relay Attack, wherein a verifier can determine an upper bound on its distance from the prover. However, recent literature is discussing ...
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Designing a simple challenge-response symmetric mutual authentication protocol

I am designing a protocol that 2 devices will use to mutually authenticate over an unreliable, unsecure channel. The system must be fast and low-power, so symmetric cryptography is a requirement. I ...
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2answers
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Prove that you have the data when hash is public

I am designing an online service where users can upload files (3d models) for processing. I want to speed up things when the same file is uploaded by many different users by allowing them to post a ...
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Is establishing a secret key possible given this characteristic primitive?

I am wondering if there are any readily available solutions for the following problem: I have a ring-topology network with several devices connected to it, some malicious, some legitimate. I want to ...
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How to securely share AES key between two remote devices (client and server) through UDP protocol?

I have two separate system (client) and (server). I am having a problem which is to encrypt a message from the client and decrypt at the server. In order to do that, I am required to transmit my key ...
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Is there an interactive proof protocol for proving that a preimage in a map $g: Z_{q}^{n} → G_{T}$ is mapped to a given public value, say y?

There already exist interactive proof protocols with logarithmic communication for proving that a secret multi-exponent $x ∈ Z^{n}_{q}$ for a public multi-exponentiation $P = \textbf{g}^{\textbf{x}} ∈ ...
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Use of nonces in the SIGMA protocol and not in C(2e, 2s) of NIST SP800-56a?

While reading the paper on the SIGMA: the ‘SIGn-and-MAc’ Approach to Authenticated Diffie-Hellman and its Use in the IKE Protocols (Krawczyk,2003), I noticed that in the "full-fledge" ...
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Is it easy to crack a hashed phone number?

I want to SHA256 hash phone numbers in order to hide them. Is this a good idea? Are there any other ways I could make this safe?
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Can two traitors safely reveal themselves to each other?

Suppose Alice is a traitor and suspects Bob might also be a traitor. If Bob is a traitor, she would like to conspire with him together, if not she doesn't want to reveal that she is a traitor. Is ...
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Corona Contact Tracing message exchange

For a university project, I have to design a contact tracing protocol. In my approach, a blockchain is used. Every participant has to generate 3 nonces for every contact. They are hashed in multiple ...
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Question of proving the opening of Pedersen Commitment

Given an opening $(m, r)$ of a Pedersen commitment $c = g^m h^r$, where $g, h$ are the generators of a group $G$ with prime order $q$ (public), a PPT prover wants to prove to a verifier the opening of ...
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Computational Binding of Pedersen Commitment

Let us assume that Alice and Bob are playing a game. Alice first commits her value chosen from $\{0,1\}$ via Pedersen commitment scheme and sends the commitment to Bob. Then Bob sends his value chosen ...
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Why do 5G, 4G, etc., use non-conventional algorithms?

Looking up information about 5G and the previous 3GPP standards, why have they been incorporating non-conventional algorithms into the standards? For example, AES has been considered secure for ages ...
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Diffie-Hellman Key Exchange - Key Derivation before Execution

I am dealing with protocol design regarding the Diffie-Hellman Key Exchange (DHKE). The DHKE is performed by the Key Master and some Slave Component. Afterwards, a session key is transmitted using the ...
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How are initialization vectors used in TLS 1.1?

From my understanding, TLS 1.0 can use CBC to encrypt data. To do so, it creates one initialization vector (IV), and then uses the previous ciphertext block as the IV for the next record. I made this ...
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Can two anonymous parties determine whether they interacted before, without being able to link encounters?

Assume an anonymous communication system in which anonymous parties randomly meet in pairs to exchange information. How could two anonymous parties determine whether they have interacted before, ...
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How does one ensure that a handshake protocol is secure assuming all underlying cryptography used are secure

Suppose one have to design handshake protocol using known secure cryptographic algorithm. The designer of implementer can assume that crypotography is secure but how would they ensure protocol itself ...
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How modern messengers encryption keys can't be hacked [closed]

I dont know is this question more like reverse-engineering or cryptographic. Why governments are hunting for encryptions keys? Aren't they delievering by the network the same as the encypted messages? ...
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Importance of Backward and forward secrecy

Which security feature is more important in security protocols being used in different applications? Forward Secrecy or Backward Secrecy
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Why isn't Kerberos using temporary keys to avoid dictionary attacks?

In the Kerberos protocol, the user sends his ID, the server (Or ticket granting server) ID and a nonce value. The Key Distribution Center uses a key (I assume symmetrical) derived from the client's ...
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How to design a secure challange-response authentication protocol?

I am implementing a custom challenge-response protocol to authenticate a client to a server. Mutual authentication is not required, i.e. the server doesn't need to be authenticated to the client. The ...
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Crypto AG (Switzerland) - Which algorithms were used and how did the backdoors work?

Backstory Crypto AG was a company located in Switzerland that specialized in communication security. They produced a number of encryption machines (some similar to the infamous Enigma) used for ...
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Conditioning access to private key?

I would like to provide a public/private keypair to a user, but require that the user obtain an authorizing key before being allowed to use the private key. I don't want the authorizing party to have ...
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Secure equivalent for giving an unknown card, applied to magician's card tricks

I suspect that this is already something trivial, but I can't find the answer, probably because I don't know how to search the cryptographic primitive that refers to my problem. Imagine the typical ...
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1answer
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Secret community forming based on zero-knowledge proof (IOT)

I want to discuss a simplistic scheme that comes to my mind, after I read about zero-knowledge proof and some fermentation time. I should mention that this is not born out of a business need or ...
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How to play Mental Skull

"Skull" or "Skull and Roses" is a table top game. The rules can be found here. I was thinking of how I could play this game P2P. At first it seemed easy: Each time I had to place a card face down I ...
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A modified question of Hazay & Lindell's Efficient Secure Two-Party protocols Book

Based on the question proposed on page 27, we propose a modified question as follows: Suppose the protocol is based on Paillier cryptosystem and $P_2$ has generated related public and private keys ($...
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Simulation-based proof in a particular scenario

Suppose we have a two-party protocol in the semi-honest model, which is based on an additive homomorphic cryptosystem like Paillier.(P2 will generate the public and private key and publish the public ...
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Simulator in semi-honest model in real/model paradigm

Does a simulator in the semi-honest model in IDEAL/REAL model paradigm necessarily make use of the corrupted party's input? For example, suppose a simulator given an input named $I$ and an output ...

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