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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Byzantine Agreement: Why does OM need f+1 rounds in a synchronous setting?

To get Byzantine Fault Tolerance in a synchronous model you can use an Oral Message Algorithm. For n > 3f+1 it gets an Byzantine agreement in ...
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38 views

Did key-wrap modes see actual use?

Is there an IETF standard-track protocol have IANA-registered IDs for deterministic authenticated encryption yet? If not, what's preventing their adoption? What changes to protocols will DAEs likely ...
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1answer
28 views

Omitting a MAC which can be manipulated unrecognized by the receiver

I am given a cryptographic key exchange protocol, which is basically diffie-hellman, only the server authenticates its public part. After exchanging the public parts the client sends a message ...
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3answers
261 views

What's wrong with this digital signature scheme?

With regards to user authentication... The server sends Alice a randomly chosen number. Alice signs the number and sends the signature back to the server. The server checks the signature using Alice'...
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1answer
183 views

Getting unlimited amount of signatures - Risk?

Lets suppose we have a communication protocol given where messages $(1)$ and $(2)$ are send over an unsecure network. There are some prerequisites like distributed certificates etc., but they should ...
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39 views

No freshness protection for single messages, but for the overall protocol

I am given a key exchange protocol between a component $C$ and a key master $K$. During the overall execution 4 messages are transferred between $C$ and $K$. DH keypairs are always chosen randomly for ...
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1answer
31 views

Can I Implement a Well-Trusted Protocol with Well-Trusted Libraries in JavaScript securely?

Just for anyone reading this: DO NOT ROLL YOUR OWN ALGORITHM. Besides that, is implementing a well-trusted protocol with well-trusted algorithms and libraries a good idea? Is this likely to ...
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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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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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1answer
38 views

Reference books in security and privacy preservation [closed]

I am looking for books or reference guides to learn and teach "cryptography, security and privacy preservation techniques"? I need some advice to good resources that I can use.
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1answer
47 views

Is there an algorithm that allows to distribute elements securely between parties?

Let's say we have a set of numbers $n = \{ 1, 2, 3, 4, 5, \ldots \}$ and $m$ players ($m < \operatorname{sizeof}(n)$, of course). I want to know if there's a way for all $m$'s to pick different ...
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160 views

Efficient proof of knowledge using Carter-Wegman 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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2answers
128 views

Protocol to identify zone of potential agreement without revealing reservation prices and having to trust third parties?

A wants to buy a company from B. Before A and B enter negotiations, they want to make sure that there actually is a zone of potential agreement. Obviously, they don't want to communicate their ...
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144 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 ...
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1answer
48 views

Station-to-Station protocol questions

Basic Station-to-Station protocol which authenticates Bob and Alice if they safely shared their long-term asymmetric public keys. Alice sends Bob her public key $A_K$ Bob receives $A_K$ and computes ...
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1answer
87 views

Key derivation for AES-GCM using HKDF?

I have a system comprising N >1000 nodes. At each node I would like to use HKDF to derive a unique 256-bit key, Kn (for the nth node), from a pre-shared master key, K0, and a locally-generated random ...
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3answers
362 views

Existing works on pre-computing ElGamal ephermal keys

I was playing around with a problem in e-voting schemes that use additive homomorphic encryption to tally votes, namely that at the end of the day somebody (or somebodies, if the secret material has ...
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1answer
88 views

Are two keys derived from the same password vulnerable to a related key attack?

Background I am currently writing a password manager application. As usual, the passwords are put in a file encrypted using a user-entered password. I'm using the NaCl library but actually it's not ...
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1answer
101 views

Authentication protocol for communication with Arduino Uno

I am using an ECDH key exchange to establish a shared secret between an Arduino Uno and an Android device. For this purpose I am using this library and more specifically Curve25519. This is the ...
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1answer
91 views

Commitment to a polynomial

$A(x) \bmod B(x) = C(x)$ and $A(x) \bmod D(x) = E(x)$: A dealer knows $A(x)$ polynomial, which is a secret. He distributes $C(x)$ and $E(x)$ privately to $X$ and $Y$, respectively. $B(x)$ and $D(x)$ ...
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Security of MAC-Then-Encrypt without MAC key authentication

We have the following settings in our system: TLS 1.2 using legacy cipher suite - OFB mode (using 64 bit block cipher) and trunkated CBC-MAC (32 bit). The goal is to achieve authenticated encryption ...
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1answer
41 views

Needham–Schroeder fix by adding opponent's identity to the first message

Recap: Needham–Schroeder is as follows: $A \rightarrow B : \{A, N_a\}_{pk_B}$ $B \rightarrow A : \{N_a, N_b\}_{pk_A}$ $A \rightarrow B : \{N_b\}_{pk_B}$ Then, there is a MITM attack by Lowe ...
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1answer
163 views

Signal protocol: when, and why, is X3DH run again between the same two users?

This question concerns the Signal protocol's X3DH key agreement protocol as documented here. Obviously, if Alice and Bob have never contacted each other before, they need to run X3DH at least once to ...
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1answer
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specific scenario question relating to using NACL crypto_box in a protocol

Scenario 1: SenderA sends message1 to ReceiverB message1 is encrypted using NACL crypto_box using SenderA secret key and ReceiverB public key. we understand that the NACL crypto_box authenticator ...
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3answers
1k views

Selective format-compliant JPEG encryption?

I am working towards building a format-compliant encryption system for pictures. The aim of it is to be able to obscure specific areas of a picture (i.e. faces, car license numbers...) while keeping ...
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1answer
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What time is used in a TOTP counter?

I am currently working on a desktop TOTP client. From the TOTP spec at https://tools.ietf.org/html/rfc6238#section-4.1, the 6 digit OTP is generated from counter (in this case time). But what is "...
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HMAC key storage for a web app?

If one is going to use an HMAC, I.E: http://php.net/manual/en/function.hash-hmac.php, where exactly are they storing the key? Without some sort of secure storage (i.e not in a local file or code), I ...
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1answer
195 views

How to construct a yes/no election protocol, such that only the result is revealed?

Can we use a threshold scheme to construct a (yes/no)-election protocol, such that every voter can give a positive or negative vote or he can abstain, and such that only the result of the election is ...
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1answer
70 views

Dynamic accumulator with only non-membership witness

Goal: Construct a dynamic accumulator which can add elements and provide non-membership witnesses. I wanted to know if my construction is correct. Consider a group $Z_p$ where $p$ is prime number. ...
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3answers
1k views

Cryptographic Challenge: How to Say Something Confidentially to Snowden?

The Snowden situation raises an intereting cryptograpic problem. At present, how can something be sent confidentially to Snowden? Claim: I have no particular political orientation. The above ...
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1answer
170 views

Proving Sigma Protocol on a Schnorr Protocol Variant

Let p, q be chosen as in Schnorr's protocol, and let $g_1, g_2, h$ be elements in $Z^*_P$ of order q. Assume that the prover P gets as input $w_1,w_2$ where $h = (g_1^{w_1}g_2^{w_2}) \mod q$. ...
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Are there conventions for signing JSON as a tree, to allow proofs of signed subtrees?

Given some JSON with a chosen encoding, you can obviously cryptographically-sign the whole thing as a binary blob. However, it might be useful if the logical structure of the JSON-compatible object ...
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1answer
216 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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2answers
97 views

How to sell a piece of data through blockchain?

User A attempts to sell a piece of data D (byte level) to user B at price C through the blockchain. A and B do not trust each other. A worry: After the data D is delivered, B does not complete the ...
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0answers
26 views

Is there a scheme to force a party to generate a fresh key?

Is there a way to force one party to generate a fresh key, such that another party can be convinced that the key was freshly generated, without that party also knowing the key? I'm motivated by a ...
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4answers
300 views

Changing algorithms during encryption

Inspired by "Guarding against cryptanalytic breakthroughs: combining multiple hash functions", I am curious if there is a cryptographic reason to use only one algorithm during encryption. For example,...
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3answers
150 views

Is there any protocol for proving that a message was written at a certain time?

Does there exist a way to cryptographically prove that a message was written at a certain time? I know that one can write messages in bitcoin transactions to that the message is preserved in the ...
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3answers
199 views

Why won't a BFT protocol using simple signing/voting work?

PBFT and most consensus algorithms are more complicated than a simple voting scheme. By simple voting I mean the following: we require all nodes to sign their local copy of the state and send this ...
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1answer
133 views

Could time lock encryption be implemented through indistinguishable obfuscation?

In the paper "How to build time-lock encryption", the authors give a theoretical solution to build time-lock encryption using multi-linear based witness encryption and blockchain. However, an ...
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1answer
199 views

Zero-knowledge transfer of value protocol II [closed]

This is an improvement of the protocol described here. The protocol does not require trusted setup and is very efficient (much more efficient than anything else I could find). The protocol allows the ...
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1answer
40 views

Privacy and warrants to obtain information

How could a site issue a `warrant'*, a document which: 1) Others can verify was issued from that site 2) Contains a date stamp, a named site and instructions which can be presented to a third site by ...
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3answers
222 views

RSA - What's to stop someone from using the same ciphertext to mimic private key holder?

I've recently looked into fundamentals of RSA and think I understand how it works. However, there's one basic problem I can't seem to figure out. If someone received ciphertext for a given message, ...
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3answers
2k views

Examples of protocols that are insecure when run concurrently

I was reading Canetti00 Universally Composable security paper. The first page of introduction says that there are some MPC protocols and Zero knowledge protocols that are insecure under concurrent ...
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1answer
58 views

Is the following non-interactive zero-knowledge set membership protocol provable secure?

Given the following Zero-knowledge set-membership protocol https://infoscience.epfl.ch/record/128718/files/CCS08.pdf]. That is given in the following steps (Please refer to page 9). The Verifier -...
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1answer
73 views

Time-release Protocol Implementation

“How to Build Time-Lock Encryption” by Jager “Time-release Protocol from Bitcoin and Witness Encryption for SAT” by Liu, Garcia, and Ryan I looked through the references, googled, searched GitHub ...
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1answer
213 views

Obfuscating functions that are mostly zero

Let $f_k(x)$ be a boolean function of two arguments with two properties: The function $f$ can be efficiently computed. The output is always 0 or 1, and for any fixed $k$, if we choose $x$ randomly, $\...
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2answers
89 views

Choice between appending or prepending nonces to ciphertexts

I understand that when using CTR mode it is usually secure to append or prepend the nonce to the resulting ciphertext, whether the nonce is before or after the ciphertext being unimportant. However, ...
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1answer
106 views

Does such a cryptographic protocol exist?

Persons A, B and C put x€, y€ and z€ in a pot, respectively. Suppose that anyone can make a withdrawal from the pot as long as they prove they have such a right and that the y€ that B deposited is ...
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5answers
69k views

Should we sign-then-encrypt, or encrypt-then-sign?

We often want to send messages that are both (a) encrypted, so passive attackers can't discover the plaintext of the message, and (b) signed with a private-key digital signature, so active attackers ...
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1answer
64 views

Can the encrypt-and-authenticate method result in secure authenticated encryption if the MAC scheme has unique tags(non-deterministic)?

If we use non-deterministic MACs in encrypt-and-authenticate approach, is it secure?