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 advantage of using the socialist millionaire protocol to authenticate vs HMACing some random number?

Say Alice and Bob have a shared secret $s$. Alice and Bob establish an encrypted channel and verify that it hasn't been MitM'ed by exchanging $r_1$ and $r_2$, where $r_1$ and $r_2$ are randomly ...
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63 views

What are the well known protocols that offer perfect forward secrecy? [on hold]

As far as I know these are the well known protocols that offer PFS TLS/SSL (with DHE-RSA, DHE-DSS, ECDHE-RSA or ECDHE-ECDSA) SSH (RFC4253) OTR (Protocol Version 3 Spec) IPsec (with IKEv1 and IKEv2) ...
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0answers
44 views

How does double-encryption work with a client server model

With mobile applications like Accompli (now the base for the Android Outlook application), credentials are stored. Reading from the Accompli website: Each user’s credentials are double-encrypted ...
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49 views

How to attack this authentication protocol

Let us consider the following protocol, I have a project and I need help to attack this protocol : A -> B : A, Na B -> A : B, Nb A -> S : {A, Na, Nb} Kas S -> A : {A, Na, Nb, Ns, Kab} pub(A) A ...
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1answer
59 views

Non-repudiation and digital signature of a dishonest participant

Let's assume a dishonest Alice who sends, encrypts & digital signs a message to Bob. Bob stores the decrypted message and the digital signature in a database. However Alice is a bad girl and ...
2
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0answers
215 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 ...
1
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1answer
198 views

Rock-paper-scissors over network, how to protect from cheating server?

I'm trying to design cryptographic protocol to play Rock-Paper-Scissors with two parties, neither trusting each other, nor trusting server they use for communication, so game is 'provably fair'. So ...
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2answers
123 views

What cryptanalysis is possible against two independent keystreams XORed against plaintext?

If a wise person was unsure about which commercial cryptography standards are truly secure from the fascist powers that be, it would seem the obvious option for companies and individuals is to now use ...
0
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1answer
105 views

Key management protocol for end-to-end security on Advanced Metering Infrastructure

I am currently working on a research on end-to-end security implementation for Advanced Metering Infrastructure (AMI). Pardon me if I a bit off topic or not asking the right question as I am ...
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2answers
67 views

Where are the ChaCha20 test vectors/examples?

I see in the Salsa20 specification there are test examples throughout the document to help an implementer make sure every function works as designed. Consequently the whole algorithm would work ...
3
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2answers
68 views

Encryption for a short packet size

I have an 8051 microcontroller with a radio that can send packets with up to 32 bytes and I want to have the messages encrypted. It is a sensor network so I really only want to send one packet per ...
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0answers
54 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 ...
3
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1answer
74 views

Secure multiparty computation of conjunction

Suppose Alice and Bob each have bits a and b, respectively. How can Alice and Bob compute the function ...
0
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2answers
132 views

Voting system validation

I'm developing an application to run elections. A voting system. I would like to give the ability to the voters to check later if their vote were correct computed/casted. assumptions: each user has ...
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5answers
1k 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 ...
3
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3answers
160 views

Verifying DER encoded DSA/ECDSA signature with extra content?

Having a DSA/ECDSA signature which is supposed to be DER encoded as an ASN.1 sequence of $r$ and $s$ (as described in the RFC), and being given some bytes which are ...
126
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7answers
24k 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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3answers
133 views

In cryptographic protocols, what protects against an attacker dropping messages?

In some cryptographic protocols I have seen messages protected for confidentiality, authenticity, replaying attacks, reordering attacks, etc. What protects a protocol from an attacker in a ...
1
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1answer
69 views

Why is proving “parties' views are simulatable” enough in semi-honest model?

To prove a protocol is secure in semi-honest model, we have to prove: the view of each party, on each possible pair of inputs, can be efficiently simulated based solely on its own input and and ...
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1answer
55 views

Oblivious transfer variation question

Now I am doing a variation of the oblivious transfer, I have to use 2 people, pebbles, and boxes. I need to find out if who has a larger number between Alice and Bob (variation of Yao's Millionaires' ...
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0answers
51 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 ...
2
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2answers
174 views

Zero-knowledge proof of a product

I have non-negative integers $x,y,z$. I'm going to give you commitments $C(x),C(y),C(z)$ to them. Then, I would like to prove in zero knowledge that $xy=z$. I can choose the commitment scheme to ...
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0answers
31 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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3answers
1k views

How do public key rings work in cryptographic applications?

I am wondering if there are any links to articles or resources available online, or explanations that you can give, that would help me to understand the concept of a public key ring, and why I might ...
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0answers
41 views

Is Paillier cryptosystem commutative?

Is Paillier cryptosystem commutative? If not, how can we construct an oblivious decryption protocol based on Paillier?
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1answer
101 views

Is it possible to hand-negotiate an SSL/TLS session?

I'm interested in trying to hand-negotiate an SSL/TLS session. Similar to how one would use telnet to port 80 and type GET / HTTP/1.1. I know there's a lot of steps ...
1
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1answer
54 views

Where is defined the fact of having a “learning” and “challenge” phase in cryptography proofs?

I've read Bellare and Rogaway 2004 and Shoup 2004 about game-based cryptography proofs, but I lack precisions about how should be built the "learning" and "challenge" phases, since my games will ...
2
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1answer
91 views

Encrypted read-only message queue

I'm creating a prototype for a messaging queue with some custom logic (can't re-use any existing solution). One requirement is to have all messages encrypted. There are three classes of nodes ...
0
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1answer
113 views

Is this chat protocol safe?

I am in the design phase of a secure chat application at the moment. I am trying to make this as secure as possible. The Serverprovider should not have access to the messagedata. So my idea was the ...
2
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2answers
167 views

Skein or Keccak stream cipher construction

I am wondering if using Skein or the Keccak hash algorithm in this construction (as a stream cipher) is secure: $H$ = Keccak or Skein hash with a 256 bit output $K$ = The main 256 bit random key, ...
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1answer
71 views

Basic question about design of program with data encryption

I need to store encrypted files on a hard disk. The actual code side is not important for me now (I plan to use C# and AES-GCM encryption from Bouncy Castle library, please tell me if you think that's ...
3
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2answers
178 views

Ways to make a “doomsday” cryptocurrency which becomes untradable

As a social experiment (not a money-making scheme), I'm interested in developing a crazy cryptocurrency which, by its very design, will become worthless and untradable after a certain point. Ideally, ...
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1answer
77 views

How Could the Music Industry Go About Implementing Crypto? [closed]

So I'm currently doing the Dan Boneh online Crypto course. In the last problem set there was a question on AACS for DVDs and wondered if a similar method could be used for music. Have the music ...
1
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1answer
85 views

How often do I need to rotate AES 256 keys

I'm trying to design a protocol for a resource constrained environment. The device has to communicate with a server through an insecure node. My plan is to use AES 256 end to end for all ...
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0answers
44 views

Is there a practical succinct interactive argument for fortress draws in chess endgames?

(In theory, it is known that collision-resistant hashing suffices for the type of protocol that I'm asking about: page 3.) Is there a known practical candidate protocol for succinctly (and ...
10
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1answer
372 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 ...
25
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1answer
2k views

Prevent double-spending with decentralized digital currencies without all transactions being public?

A recent approach to creating a decentralized online currency, called Bitcoin, has been generating some interest. The goal is to have a way to transfer currency without a central authority and without ...
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1answer
139 views

Burn after read algorythm. Software verification on compromised environment. Software smart card

Please help me pick right design of software… I have to design client-server software, where the server should verify that the client runs software from specific source code. It has to be verifiable ...
1
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2answers
204 views

Are SSL/TLS used for maintaining data confidentiality?

In SSL/TLS, we use symmetric and asymmetric keys to encrypt the data. Does that mean that the keys are used to encrypt the data (preserve the integrity) or provide a secure channel for the data to be ...
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0answers
101 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 ...
3
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3answers
164 views

Asymmetric algorithm for one time signing of small cleartext

I want to generate a key pair such that the private key can be used once to sign a small message (1024 bytes) at some indeterminate point in the future and the public key can be used to verify that ...
3
votes
1answer
116 views

Secure Deduplication and Encryption in a data store

Assume: We have a centralized data store that can store whatever we need Every user is online Function $f : File \to Key$ gets access to the store, and is the same for all users. $g : Key \to File$ ...
15
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1answer
1k views

Why do new versions of TLS use an explicit IV for CBC suites?

SSL 3.0 and TLS 1.0 used an insecure scheme to generate implicit IVs when encrypting records in CBC mode: they used the last part of the previous record, a value that can be predicted by the attacker. ...
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0answers
86 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 ...
4
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1answer
284 views

Why does the SRP-6 calculation of B include a multiplier k = 3?

In SRP-6 $B$ is calculated as $B=kv+ g^b, k=3$. What is the purpose of $k$, and why was it fixed as $3$? (In SRP-6a, this value $3$ is replaced by $k = H(N,g)$, but this question is about SRP-6.)
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2answers
5k views

Why is TLS susceptible to protocol downgrade attacks?

A recent blog post from Ivan Ristić (expert extraordinaire on all things SSL) says: all major browsers are susceptible to protocol downgrade attacks; an active MITM can simulate failure conditions ...
3
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4answers
503 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
299 views

What does well-typed mean?

I am currently studying Cryptography and I don't really understand what does 'well-typed' mean when talking about secure cryptographic protocols. I can't find any reasonable explanation on the ...
4
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1answer
82 views

Diffie-Hellman when $p$ and $g$ are pre-agreed and hidden from Eve

During a regular Diffie–Hellman public key exchange, Alice and Bob agree to use a prime number $p$ and a base $g$… which are both made public and are therefore also assumed to be known by Eve. Alice ...
2
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1answer
103 views

Secure MultiParty Computation with secret inputs for secret outputs

I want to know if it’s possible to use a SMPC (Secure Multi-Party Computation) to have $N$ entities compute the outcome of a known mathematical operation with two or more secret inputs, where each ...