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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1answer
101 views

Private set intersection, using a semi-trusted server

Alice has a set $S$ of words. Bob has a set $T$ of words. They want to compute the intersection $S \cap T$ of their words, with the help of a semi-trusted third party Trent. Trent runs a central ...
5
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2answers
443 views

NTRU crypto from unseen.is; myth busting help

I am always on the look out for privacy enhancing technologies. I stumbled upon the service from unseen.is. I had a look at their site (specifically here) and even though I lack knowledge there are a ...
1
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1answer
106 views

Which data to share in CTR mode?

Suppose I've got two clients $A$ and $B$. Client $A$ encrypts data in CTR (Counter) mode to get a ciphertext. What information will client $B$ have to receive from $A$ to decrypt the ciphertext? Just ...
2
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0answers
98 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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2answers
417 views

Tools for modelling and analysis of cryptographic protocols

I am designing some cryptographic protocols and I am new to it. Are there any well-known tools that can be used to model and design these protocols? And also verify or analyze their validity? If not ...
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125 views

Designing a secure IM protocol

I haven't been programming much lately, so I figured I would make an encrypted instant-messaging program (read: Skype clone) with groups to hone my skills. That's not important though, I can do that. ...
2
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0answers
897 views

Cryptographic Protocol using NaCl

Why? I wanted to add some security and privacy to a chat-type server for playing various games (with a few things that are done on the server to limit cheating). Going by the "Don't implement ...
4
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2answers
261 views

Perfect Forward Secrecy with Pre-shared Key

I've recently been looking at how to do perfect forward secrecy on a unidirectional connection (server can only push messages to client, client cannot respond). What I've come up with is the idea of ...
5
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2answers
394 views

Computationaly hard detokenization algorithm for credit card numbers

I am designing a vault that tokenizes credit card numbers (a plaintext that consists of 16 decimal digits), with the following requirements: Given some plaintext, the vault returns an index. If ...
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0answers
74 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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0answers
110 views

Going Blind, Group or Ring?

I have several problems approaching the following problem: Let's assume that we have Alice, Bob and Cathy. Alice wants to present a message to Cathy, showing her that someone else has signed it (Bob), ...
3
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3answers
200 views

Is the following authentication protocol insecure?

I am a student taking cryptography this semester. I was just wondering why can't we use this simple protocol? Alice → Open Connection → Bob Alice ← Cert$_b$ ← Bob Alice → {K$_{AB}$}$_{Bob}$ → Bob ...
2
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1answer
63 views

Can you explain the counter in the Key derivation function of PACE?

I try to understand the PACE-Protocol, especially the Key Derivation Function in ECDH on page 33. Can someone explain me, what the Counter is good for? Often there are iteration counters in KDF - but ...
2
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3answers
141 views

Combating traffic analysis over request-response protocols

Suppose I am to design a request-response protocol (similar HTTP). For the sake of simplicity let us assume that this is a "chat" protocol where the client can only perform two actions: Contribute a ...
3
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2answers
143 views

What was the problem in the SSL version 2.0?

What is the main reason (attacks) the appearance of the protocol SSL version 2.0 to replace version 3.0?
2
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1answer
183 views

Is this new server API authentication protocol secure?

I need a secure protocol to authenticate client side users with my server which has an API. I am devising something more secure particularly to resist active MITM attacks where an attacker may modify ...
6
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1answer
2k 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 ...
2
votes
1answer
97 views

What kind of Quantum cryptography technology(protocols) can be used for Mobile Ad hoc networks(MANETS)?

Typically ad hoc networks do not have a proper infrastructure and the routing is done only through the base stations which are connecting a wired and wireless network. Does quantum cryptography ...
10
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0answers
256 views

Shared secret: Generating Random Permutation

-- or: How to Play Poker Without a Dealer I know this question is long but it's a really interesting theoretical problem about shared secrets and multi-party computation. General Problem: "Shared ...
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1answer
295 views

What's wrong with my security model - or how can it be attacked?

I'm working on a little personal project where security is very important, and I've thought for a while about the best way to do this. Now I am looking for a little outside help on good practices. The ...
4
votes
1answer
182 views

EC ElGamal versus static+ephemeral ECDH

A client application needs to encrypt a UDP datagram for a server with known EC public key $P$. Performing a full ECDH key exchange would defeat the benefit of using UDP as a connectionless protocol. ...
4
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1answer
134 views

Private Messaging

Suppose Alice and Bob wants to send messages through Sue without revealing to Eve that the exchange took place. Slightly more formally, I don't want Eve to have any advantage telling if Alice is ...
3
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1answer
311 views

Should new applications still use RSA? Is it worth going down the ECDH route for protocols?

I am currently designing an application for communication between two and more users. At the moment I am trying to figure out what methods to use for the asymmetric cryptology. With the recent ...
2
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1answer
112 views

Bit commitment with 1-out-of-2 oblivious transfer

I know a protocol for bit commitment using regular OT (Bob has 1/2 chance of learning the bit Alice transferred to him) which goes like this: COMMITMENT PHASE Alice chooses a bit $b$ For ...
8
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2answers
293 views

What current authenticated key exchange standards exist?

If neither of the 'big two' of TLS Handshake and IKE are appropriate in a given situation, what alternative Authenticated Key Exchange (AKE) standards exist and are recommended? Many protocols have ...
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0answers
34 views

Correlated or biased coin protocols?

There are a number of papers in the literature describing secure/fair coin flipping protocols. Unfortunately in my case, I am looking for coins that are epsilon-biased or epsilon-correlated. I am ...
2
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1answer
121 views

What does this step in this protocol for the Yao's Millionaire Problem mean?

I was reading “An Efficient Protocol for Yao’s Millionaires’ Problem” (Ioannidis and Grama 2003). In the proposed protocol in section three, it is written: (Step 4) For every $i$, $1 \le i \le d$, ...
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0answers
174 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 ...
4
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2answers
203 views

Is the following symmetric design secure?

Assume: $O$ be a reversible random permutation oracle on a finite set and $O^{-1}$ the inverse permutation (pretty much equivalent to a random permutation: What is the difference between a bijective ...
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1answer
129 views

Secure function evaluation

Consider 3 parties, Alice, Bob and Charlie. Suppose each party has a bit as input, i.e. Alice, Bob and Charlie hold $a, b, c \in \{0, 1\}$ respectively. Show how construct a scheme with which ...
6
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1answer
1k views

Is a known plaintext, ciphertext, and public-key a viable attack on RSA?

Assume Alice and Bob are using RSA to create a common session key and Cindy is listening, attempting to obtain the session key. Alice and Bob each have their public- and private-key pairs ...
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0answers
87 views

Could MITM securely identify identity?

Consider protocol like QUIC or MinimaLT which are essentially layer4 replacement for TCP/UDP (riding on top of UDP currently because of fear of random firewalls dropping new L4 protocol). From crypto ...
22
votes
3answers
1k views

Is this password migration strategy secure?

I want to upgrade the security of some existing databases of users' authentication tokens strictly for the purpose of making sure that if the database is stolen, attackers will not be able to guess ...
7
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1answer
201 views

Are there any differences in operation between existing Diffie-Hellman specifications?

Are there any differences in operation between existing Diffie-Hellman specifications, especially those within the RSA PKCS#3, ANSI X9.42 and RFC 2631 standards?
3
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1answer
120 views

How can two (or more) parties share and agree upon a common random seed?

I really don't know how to call this simple problem: Two (or more) parties need to establish a common (non-secret) value to be used as a seed for a deterministic RNG. The only requirement is that each ...
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1answer
200 views

Security of RSA-substitution-RSA

Following on from here, I am unconvinced that encrypting twice with RSA is a waste of time: doesn't it depend on what is placed in-between the two encryptions?. What would happen if a permutation was ...
2
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1answer
189 views

Transparent cipher

I'm trying to implement this protocol: Alice has her permanent key $K_1$. She computes $E(K_1, P)$. She wants to share $P$ with Bob, Carol and Dave. For each of them she: 2.1. Generates $K_2$. ...
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1answer
99 views

How to design a secure data container?

I want to design a secure data container that can be used to transfer encrypted data over a public network that can defeat common attacks. Data is already encrypted before entering this container so ...
2
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2answers
203 views

Alice's forgetful banking

Alice has a bank account number, but has forgotten which bank it is for. There are 4 banks, run by Bob, Carlos, David, and Eve. She could find out by going to all of the banks and asking if they have ...
44
votes
7answers
4k 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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1answer
191 views

ID-based key exchange protocol with PFS

The traditional authenticated DH protocol with PFS against active adversaries, ensures that the compromise of both party's long-term private keys after the session is completed will not help the ...
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1answer
500 views

If you had to implement the BGN Cryptosystem, how would you do it?

If you had to implement BGN, how would you do it? I'm looking for an implementation of the public-key cryptosystem due to Boneh, Goh, and Nissim (aka BGN), or at least some suggestions on ...
3
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4answers
400 views

Is there a symmetric-key cryptography based on key establishment techniques?

Most of the current key exchange techniques are based on public-key cryptography. Are there any key exchange/establishment techniques based on symmetric-key cryptography too? In my setup primary ...
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2answers
152 views

Can you distinguish encryption methods from the output?

Suppose that you see all IP communication packets between two computers for a day, as they pass through a connecting router, and this amounts to 10MB. You additionally know that all data transmission ...
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1answer
112 views

Efficiency of computing $e(P,Q)$ Vs $g^a \pmod{p}$?

The definition of $e$ can be seen here. I want to know the accurate comparison of efficiency between $e(\cdot,\cdot)$ and $g^a \pmod{p}$. If computing $e(P,Q)$ is less efficient than computing $g^a ...
3
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1answer
205 views

Protocol for Randomized Oblivious Transfer?

If we define Oblivious Transfer as following: Alice inputs $(x_0,x_1) \in F^2$, where $F$ is a field, and Bob inputs $b\in\{0,1\}$, then Alice gets a dummy output(for which she knows nothing about ...
2
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1answer
113 views

Security of cloud computational protocols in UC Framework?

The universal composability allows one to the analyze security of cryptographic protocols . But it does have some gaps when it comes to analyzing few protocols especially two party cases when there is ...
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0answers
112 views

Cryptanalysis not based on method used to encrypt? [closed]

When doing cryptanalysis on RSA or something number theory based, there are various attacks that all seem to involve number theory (Wikipedia: RSA_(algorithm) ~ Attacks_against_plain_RSA). Similarly, ...
2
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1answer
284 views

How do TLS 1.1 and 1.2 generate IVs (initialization vectors) for each record?

According to RFC 4346 Explicit IVs [CBCATT] describes a chosen plaintext attack on TLS that depends on knowing the IV for a record. Previous versions of TLS [TLS1.0] used the CBC ...
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1answer
179 views

how to mathematically prove a key exchange algorithm [closed]

I want to know the basic methodology that can be used to prove that a key exchange algorithm is secure. I am not asking about any specific algorithm. I want to know what should be proven and how to ...