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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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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34 views

OTR AKE protocol implementations security

While looking at the different versions of OTR protocol I discovered a strange thing: there is no trace of the patch for the weaknesses that were noted in “Finite-State Security Analysis of OTR ...
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123 views

Efficient way to confirm identity

I am working on a multiplayer game. I have a central server which handles all data transmission and coordinates all games. Clients which involved in a single session send requests to do actions to ...
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41 views

Is it possible and safe to use SAKKE for signing/verification, rather than for encryption?

Is it safe to use the Sakai–Kasahara key encryption algorithm (SAKKE) for signing/verification, rather than for encryption? (Example at bitbucket.org) In particular, I want many Bobs to be able to ...
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171 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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68 views

How to use a stream cipher to sign a message?

Are there known constructions which allow to sign a message M (let's say it will be sent as clear text) using a stream cipher C and a symmetric secret key K? So, we have M, C, K and we want to send M|...
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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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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. ...
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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 ...
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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 ...
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52 views

authentication protocol questions/security

Disclaimer: I am the only person that uses my software. This is just experimental fun. I previously wrote a server/client that used the secure remote password protocol authentication. I had an idea ...
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96 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. ...
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30 views

Authenticate encrypted seed for KEM + AEAD hybrid cryptosystem

Say I want to encrypt something using RSA / KEM and an authenticated cipher. I encrypt using the following scheme: generate random seed z using ...
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114 views

Avoiding known plaintext attacks with an additional XOR-Layer

Can a cipher that is vulnerable to an known plaintext attack be made secure by adding an additional XOR-encryption? That is: suppose I have an (w.l.o.g. symmetric) encryption algorithm E were the ...
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125 views

Lowest number challenge scheme

Suppose Alice knows a secret number $a$, and Bob knows a secret number $b$. Is there a simple way for Alice and Bob to know who has the lowest number, without Alice & Bob exchanging their numbers ...
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228 views

File Encryption (EFS method)

I'm implementing (for learning purposes) a file encryptor, which uses the following method (from http://en.wikipedia.org/wiki/Encrypting_File_System). I have 3 kind of keys: RSA public/private, AES ...
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144 views

Designing a protocol to record attendance to lectures

Scenario: a class that is not mandatory. The teacher wants a protocol that will satisfy the following requirements: It must record each student's attendance. A student X should not be able to say ...
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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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51 views

How to force an adversary to call a certain oracle?

Consider there is a protocol in real world, which uses a random oracle $\mathcal{H}$. In the ideal world, after the calling of $\mathcal{H}$ by some parties, intuitively I want the simulator gets some ...
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86 views

Why does encryption in STS protocol protect against identity attacks?

The basic STS protocol contains encryption of the signature as shown in Wikipedia. https://en.wikipedia.org/wiki/Station-to-Station_protocol If we would like to defend against MITM attack, this ...
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114 views

Standards/RFCs for non-Diffie-Hellman perfect forward secrecy?

Some time has passed since PFS introduction and we now have secure&proven asymmetric ciphers that can generate strong keys very efficiently (elliptic RSA variants and/or QD-Mceliece can generate ...
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369 views

Elliptic Curve based blind signature implementation

I want to use Elliptic Curve based blind signature scheme for my research. There is no proper implementation of ECC-based blind signatures. Can someone describe to me which things I need to follow ...
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56 views

Common pitfalls of session key activation?

Assume that initiator $I$ and responder $R$ of a key agreement protocol have agreed on new symmetric session keys $K'_{auth}$ and $K'_{enc}$, e.g. by way of Diffie-Hellman and key derivation, possibly ...
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95 views

Reliability of a single-pass deniable authentication protocol?

I look for one-pass deniable authentication protocol with a short message payload for my project and find a solution: ...
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158 views

Obfuscating point-like functions

There are standard schemes for obfuscating a point function; I'm wondering if we know how to obfuscate a slight generalization of a point function. I'll elaborate more precisely. Definition 1. A ...
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148 views

encrypted file sharing protocol

I am trying to design a file exchange protocol for learning purposes, inspired by PGP, but fixing some of its shortcomings. Assuming the machine where the creation and decryption of the file happens ...
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153 views

Should layered use of crypto always have a cryptographic binding between the layers?

Reading the latest TLS weakness, it seems that multiple weaknesses have been found over the years caused by not ensuring that messages are sent over the same channel, and in general a lack of ...
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84 views

Why do authors execute a leakage resilient election protocol inside a leak-free phase?

In the paper "Multiparty Computation Secure Against Continual Memory Leakage", on page 1241 (that's page 7 of the PDF) under section 2.3, the authors discuss "The Election Protocol" that they use to ...
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96 views

Relaxed trust criterion for mental poker server?

I've read a lot about protocols for mental poker without a trusted server, but I'm interested in the possibility of a faster, more practical protocol that relaxes that criterion a bit and "trusts" a ...
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220 views

Transforming simplest protocol into a Sigma-protocol

I have some questions from previous years exams, I hope you could help me with them. :) Suppose that a protocol satisfies the properties of a $\Sigma$-protocol, except that it is only (plain) ...
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127 views

Computer appliance protocol

I build the computer appliance system that consist of software server and multiple controllers. The system I want to build must be pluggable in the sense that when I connect a controller C to the ...
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196 views

Setting protocol parameters to achieve concrete security

Background One issue with modern security proofs is that they are usually asymptotic. In other words, such proofs are usually formulated as follows: For any polynomial-time adversary $\mathcal A$, we ...
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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 ...
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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 ...
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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 ...
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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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132 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 ...
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44 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,...
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When we use one time pad TWICE in two different ways

Assumption and Notations: All the values defined over the field $\mathbb{F}_p$, where $p$ is a large prime number. We denote multiplicative inverse of value $v$ by $v^{-1}$. All values are non-zero ...
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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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40 views

Is this ECC based messaging method secure?

I developing an encrypted messaging for ZeroNet (aP2P file-based network, website: zeronet.io) and would like to have some guidelines if any of this could work. My first idea: In ZeroNet every user ...
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113 views

Simplest way for strong cryptography in chat

I am a beginner in cryptography and I am interested for several weeks on this for my chat application. Basically, it is a centralized model. All messages are stored and potentially visible by ...
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56 views

Encryption with a known plaintext

I'm building an application where users can be a part of groups, and can obtain and distribute URLs from the group page that allow anyone who clicks on them to join said group. Groups should not ...
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64 views

Obliviously computing the Least common multiple of two poylnomials

Consider I have two polynomials $f_1$ and $f_2$ of the same degree. I want to secure them (using any kind of encryption except FHE) and outsource them to an untrusted server. I want him to compute the ...
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45 views

Hybrid fair exchange protocol

A gradual fair exchange (layman term) is a form of fair exchange protocol where Alice will transfer 1 bit to Bob then Bob will transfer 1 bit to Alice. The flaw with this protocol is that the party ...
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132 views

ECC cryptography with shorter signature when not needing high security?

I am new here and fairly new to cryptography, so if I say something wrong, let me know. I am trying to set up a system where a user can receive a temporary license key over the phone, put it into ...
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92 views

A question or few about Mental Poker

I have spent some time studying the "Mental Poker" protocol (sometimes called SRA), initially proposed by Shamir, Rivest, and Adleman -- http://people.csail.mit.edu/~rivest/ShamirRivestAdleman-...
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65 views

Is container format relevant to security of encrypted message inside?

Still trying to design a fully binary cryptography container format for my mobile app, I am here asking if container is ever relevant. Thanks to Apple, I cannot use GPG directly because I can neither ...
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189 views

What would make it impossible to deny that decryption of a package has taken place?

I'm part of a team designing a system where a user have to be able to read a certain package, if he has preformed an action or series of actions that makes it legal for him to do so. The tricky part ...