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Authentication is successfully validating that an entity you are communicating with is actually who they claim to be. The entity typically demonstrates who they are by showing they possess a secret that only they could know.

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How to generate tokens from a secret key?

The problem is simple: I want to be able to spit out 256-bit "tokens" that only I could've produced because I know my secret key $s$, and given any number of these tokens, no one can figure what $s$ ...
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Drawbacks of Schnorr Authentication that require Fiat-Shamir and Random Oracles?

I've been going through G. Maxwell's paper on the Borromean Ring Signature, and I don't fully understand this part on Schnorr Signature. If some could explain it more intuitively thank you. "...
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1answer
27 views

How does EAP-TLS authenticate?

I understand that a client and server certificate is required, however the validation process isn't clear to me. Is it simply that the certificates are check to ensure they're valid, aren't revoked, ...
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1answer
68 views

Where should I start to learn cryptography? [duplicate]

I want to learn cryptography. I just wanted to ask people who experienced about the field that where should I start? Any recommendation would be something for me. Thank you in advance.
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59 views

Is using a username and smart card two-factor authentication? [migrated]

Is username counted as one-factor, something you know? A smart card (which contains the username and user information inside the card) is something you have. What if the smart card doesn't contain ...
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0answers
24 views

Cost of asymmetric signature checks vs password hashing

This is a question about standard every day web authentication. I have the following assumptions: one of the reasons public key user authentication is not used as bread and butter on the web is that ...
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1answer
60 views

Is using a smart card and password two-factor authentication?

I use a smart card - as read only device - for user identity as well as a password: The smart card (holds the user ID) is something I have; The password is something I know. Is this still two-factor ...
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4answers
2k views

Using a blockchain for secure communication

I've recently heard of the idea of using a blockchain for secure communication. No details were given so it's a little hard for me to say that it can't be done. But as far as I know: Secure ...
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0answers
37 views

Is timing attack practical in a web developer's perspective?

Let's say my server has a non-constant-time compare function for checking if the visitor has a valid session id. The time it takes for the comparator to run would be very insignificant, usually within ...
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1answer
38 views

CCM authenticity bound

Can someone help me understanding the CCM authenticity bound by Phillip Rogaway? i-e Success probability < $q_{\text{dec}}/2^\tau + \sigma/2^b$. $\tau$ is tag length, where as $b$ is block length. ...
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1answer
55 views

Authentication scheme using HMAC

I have an authentication service, a client and an application service. The client needs to use the application, but they have to be authenticated first. I'm trying to create a simple scheme to do ...
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1answer
63 views

Using nested signatures to trust public key of inner signatures

I have a scenario where entity $A$ has an unauthentic copy of the public key $P_B$ of $B$ and an authentic copy of $P_C$ of $C$, trusted by both $A$ and $B$. Now $A$ wants to establish trust in $P_B$...
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2answers
57 views

Client-side password stretching - danger of the salt being public?

In case of using client-side password stretching (plus a single hash on the server) - the server would need to send the salt before authentication, of course. Though the salt is not considered a real ...
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2answers
204 views

passive corruption ?= Byzantine corruption in the UC framework?

Notations: We follow the convention in the UC framework. We use $\mathcal{A}$ to denote the adversary, $\mathcal{P}$ to denote a party in the model. We focus on two types of corruption in the UC ...
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1answer
66 views

Authentication and integrity

I was trying to solve this problem: Sometimes Alice needs to send a file to Bob, guaranteeing her identity and the file integrity (no confidentiality required); the two parties are sharing a secret w ...
4
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2answers
137 views

What is the point of using a cryptographic sequence number if you're not using it as a nonce?

OSPF features the use of Auth Crypto Sequence Number however, from reading the RFC it would appear the sequence number is not being used as a nonce. In addition, ...
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2answers
130 views

Generating secure short activation code for offline applications

My application is as follows User has a hardware system (with an unique ID) that does not have connectivity but has a keypad for input. To make the hardware operational, the user has to go to central ...
3
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1answer
55 views

shared symmetric key

Suppose $R$ is a random challenge sent in the clear from Alice to Bob and $K$ is a symmetric key known only to Alice and Bob. Which of the following are secure session keys and which are not? Justify ...
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1answer
64 views

Attack on challenge response protocol using shared symmetric key and addition of random nonce [closed]

Consider the following mutual authentication protocol, where KAB is a shared symmetric key. Give two different attacks that Trudy can use to convince Bob that she is Alice.
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1answer
61 views

What can I do, if my SRP password verifier was stolen?

I've got a system that works like this: ...
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2answers
57 views

Password vs public key for authentication?

What's the difference password and key in terms of authentication? I think that they are potentially same. But, in practice, password involves some bias since it is created by human. On the other ...
2
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1answer
54 views

Encrypted Hash vs MAC [duplicate]

I (believe I) am aware of the general difference between a hash and a MAC; the former is used for integrity and the latter for integrity and authentication as it also takes a secret key as an input in ...
2
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2answers
58 views

Authentication scheme to protect against fake devices

I want two embedded devices (call them master and slave) to communicate with each other. For intellectual property protection, the master must reject fake slave devices (the other way around is a pre ...
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0answers
28 views

How can I encourage non-techie users to authenticate PGP-signed documents (with keys not at a keyserver)

How can I encourage non-techie users to authenticate PGP-signed documents by verifying 1) a PGP fingerprint published elsewhere against a PGP public key included in the document (and not at a key ...
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1answer
98 views

Why is this authentication protocol with a nonce and tree parties not secure?

Why is the following authentication service not secure? C⟶S: $I_C$ S⟶C: $N$ C⟶S: $E(K_{C,A}, N)$ S⟶A: $E(K_{S,A}, \{I_C, E(K_{C,A}, N)\})$ A⟶S: $E(K_{S,A}, N)$ where: C = client S = server A = ...
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1answer
92 views

Is authentication more computationally expensive than encryption?

newbie in crypto here. I've a application that needs integrity protection. Confidentiality would be nice but has less priority over performance throughput. So I test "openssl speed" on my laptop, and ...
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42 views

Challenge/Response approach for mutual authentication

Why is challenge/response approach unsuitable for connectionless type of applications?
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1answer
61 views

merkle tree motivation

Here author seems to give overview of merkle trees. However, I have one problem. As in the article author claims you can use merkle trees to verify authenticity of data, e.g. if piece of data is ...
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1answer
41 views

Why exactly is a root hash used in relation to hash lists?

Wikipedia has an rticle about hash lists, although I find it technically not very detailed. For example: We could solve same problem by sending (authenticated) hash of each data block, together with ...
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58 views

ABE (attribute based encryption) vs ABS (attribute based signature)

I want to know if there is any shortcoming that ABE cannot achieve and that the ABS complete it. I mean why the ABS is included if the authentication and the authorization are already ensured by the ...
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0answers
46 views

PKI Challenge Response: why is $h(r) = x$ enough to protect against chosen text attacks?

I think the question was asked somewhere else but not answered very precisely. Quoting from the "Handbook of applied cryptography": Identification based on PK decryption and witness. Consider ...
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0answers
50 views

How does the authd protocol work?

So far, I have been able to research on what it is: authentication; authorization; using resource authd. I still have not come across a definitive answer or ...
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2answers
86 views

Plausibly deniable authentication for agents on multiple teams

Here's a problem that I've been thinking about: An individual, Alice, wishes to authenticate herself. She may wish to authenticate to Bob (who is on the blue team) that they are both on the blue team....
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41 views

Any Idea on this identification scheme's problem?

I was looking at the exercises of Cryptography theory and practice and I could not find the answer to this question anyone has an idea?
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1answer
48 views

Is symmetric encryption with a key containing the userId passes as authentication?

The scenario: There is a web application where ownership check is time expensive so during the development all users were able to access all other user's objects (let's say apples) by changing the ...
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122 views

Unknown key-share attack

In the unknown key-share attack a dishonest entity C tempts two honest entities A and B to establish a key shared between them. At the end of the attack, A believes she shares the key with B, but B ...
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1answer
77 views

Primitive root in a finite field

Wen-Her Yang and Shiuh-Pyng Shieh proposed two password authentication schemes by employing smart cards, one is timestamp-based and the other one is nonce-based. Their scheme consists of 3 phases: ...
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1answer
59 views

SCRAM Iteration Count Attack

I'm not sure if this questions belongs here or in the Information Security Stack Exchange, but here goes... With SCRAM (RFC5802), is there anything that prevents an attacker masquerading as the ...
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2answers
65 views

One-Time MAC's data block length and q

When 128-bit long data blocks are unavailable for one-time MAC: Could 64 bits be used instead? Should $q$ then be >=64 bits? E.g. $2^{64}+5$ Can this be scaled even further downwards to 32, 16, … ...
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1answer
71 views

Understanding the big picture with regard to how anonymous credentials work

I'm trying to learn about anonymous credential systems. I started with Lysyanskaya's thesis, which gives an outline of how to build an AC system given some particular primitives (signature scheme, ...
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1answer
36 views

Is it possible to personalize eToken PASS?

I am wondering if it is possible to personalize an eToken to PASS with the following method: On the server side we configure a physical device eToken to PASS when it belongs to Mr. Bob. So when he ...
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64 views

Possibility to combine keys for asymmetric signature creation

There is an asymmetric algorithm which signs with a private key and verifies with a public key. Private and public keys are created in pairs. Assume we have 2 pairs of private and public keys. Is ...
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26 views

Authenticate sender post-communication over out-of-band channel

I have the following problem to solve: Assumptions: A sender "Alice" and a receiver "Bob" An Attacker "Mallory" an insecure one-way channel for sending data (Mallory can read and manipulate data ...
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1answer
61 views

CBC-MAC 8 octet ICV compatable with 16 octet block size?

I'm trying to use DTLS in Preshared key mode for CoAP which necessitates using CipherSuite TLS_PSK_WITH_AES_128_CCM_8 I'm trying to start with the CBC-MAC but I'm not sure how to get an 8 octet ICV ...
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0answers
42 views

Are authenticated encryption (AE) aproaches such as EtM, E&M and MtE equally secure? [duplicate]

There are different approaches of implementing authenticated encryption (AE) and authenticated encryption with associated data (AEAD) such as: Encrypt-then-MAC (EtM) Encrypt-and-MAC (E&M) MAC-...
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2answers
331 views

What is the benefit of zero knowledge identification (Fiat Shamir) over a standard digital signature?

Let's say there is a public key $v$. Peggy has to prove to Victor that she has the corresponding private key $a$. Of course she doesn't want to disclose $a$ to Victor, but just to prove that she has ...
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1answer
341 views

understanding NTLM authentication

The flow is like this. Client sends GET to Server Server responds with 401 UNAUTHORIZED and the authentication protocol: NTLM Client re-sends the request including authentication information. I don'...
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1answer
180 views

Diffie-Hellman based password challenge response scheme

A very commonly used (examples: HTTP digest auth/CHAP/Kerberos) authentication scheme is something that looks like: Setup. Client and server both know a password $p$. Authentication. Server sends ...
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1answer
55 views

Why not generate the authentication key from the key and nonce in GCM?

In Galois/counter mode, the authentication key $H$ is leaked if two distinct messages are encrypted using the same nonce. If someone did end up doing that, then they would need to rekey to get a new $...
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1answer
66 views

RSA public key verification based on a secret

I'm attempting to develop my messanging app with encryption evolved. For now I came up with algorithm for authorization and message exchange. P.S. conneciton between server and client is over https ...