Questions tagged [authentication]

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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225 views

AES-CTR and AES-CMAC using the same temporary key

Is it a severe security issue using a short-lived dynamic key for both AES-CTR and AES-CMAC? CMAC is generated on the cleartext and 32 bit of it are attached to the message (MAC-and-Encrypt) The key ...
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Public key cryptography instead of passwords for web authentication

The usual way for a user to authenticate themselves to a website at the application layer is with a shared secret - the user's password. If a user is connecting to a bank, they give the bank their ...
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What constructions for data authentication are subject to the birthday paradox?

$H(m\mathbin\Vert k)$ as an authentication algorithm, where $H: \{0, 1\}^* \rightarrow \{0, 1\}^{n}$, has at most a strength equivalent to $\frac{n}{2}$ bits. $H((k^\prime \oplus \mathrm{opad})\...
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HMAC based challenge-response authentication

Would a challenge response HMAC authentication be secure? i.e. Client sends id Server sends a challenge(32byte value) Client calculates hmac_sha256 of the challenge value with its key and sends the ...
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60 views

Desirability of chaining an LCG in an authentication scheme

Suppose that: $E(k, x)$ is the encryption of data block $x$ with key $k$ using a block cipher. $L_{Key}$ is the key size of the block cipher in bits. $L_{Block}$ is the block size of the block cipher ...
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477 views

Authentication of data using XOR and a secure function

Suppose that: $i$ is a zero-based index. $K$ is a secret key. $X$ is a stream of data. $x_{i}$ denotes the $i$th block of data in $X$. $s$ is the number of blocks in $X$. $X = x_{0}\mathbin\|x_{1}\...
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How does “one-pass” authentication differ from “two-pass”?

The meaning of "one-pass authentication" as well as its difference from "two-pass authentication" has not been explained to my satisfaction. CCM mode, EAX mode, and HMAC are examples of the first type;...
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Checking a file for integrity and authentication

A checksum is a small-sized datum derived from a block of digital data for the purpose of detecting errors which may have been introduced during its transmission or storage. It is usually applied to ...
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Can cryptography help create tamper proof voting systems?

After hearing about what happened with the election in Kenya and the related discussion about a “tamper proof voting system”, I was wondering how the use of cryptography could be used to make a tamper ...
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Store encrypted MAC key inside encrypted file?

In order to have an encrypted file who's key can be changed without needing to encrypt the whole file again, I'd like to encrypt the file with a main key ,and then encrypt that main key with another ...
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Is Encrypt(m||k2, k1) secure authenticated encryption?

I don't fully understand the need for MAC algorithms to authenticate encrypted messages. As I understand, the standard is to send something like $\mathrm{E}(m,k) \| \mathrm{MAC}(m,k)$ where $E$ is an ...
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Questions about the certificate authority procedures

I am beginner in cryptography and now I try to understand certificate process. I read this answer and have some questions about the enrollment process: The general procedure to issue certificates ...
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698 views

Can ECDH be used for authentication?

Is it safe to use ECDH for challenge-response authentication, with server key being ephemeral? The goal is that server does not store sensitive data (hashes) and allow clients to use additional ...
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1answer
57 views

Is it a good or bad idea to include a password's salt in the calculation of a MAC?

Say there's a cryptosystem where encryption and authentication of data is done using a key derived from a user-given password using something like PBKDF2. Is it a good or bad idea to include the ...
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99 views

Ensuring no unintended leaking before authentication

Assume my authentication system consists of querying an endpoint to get sign in parameters cost and salt, ...
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56 views

Authenticating PBKDF2 params from the server

In my app, I use PBKDF2 to stretch a user inputted password. I split the result in two: the first half is stored locally as an encryption key (and never sent to the server), and the second half is ...
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579 views

Machine learning to break imperfect randomness

I have a shared randomness between two user. But to make situation worse Eve can listen to exchanges and guess noisy or error prone version of shared randomness, whose correlation varies depending on ...
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Are there any attacks / weak points with HMAC-SHA3?

I read about SHA3 and would like to study its weak point, Are there any cryptographic attacks on SHA3-based HMAC?
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zero knowledge proof application

Suppose I have a secret 'X'. Which can be use as a seed to a deterministic random number generator to generate a number 'Y'. Is there any way to prove to others, that I have the secret 'X' which ...
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Should a certificate be validated every time it is used?

In contrast to private keys, public keys don't need to be stored on a secure place. But what if somebody changes a certificate with a public key to just another one? To ensure certificate authenticity,...
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Is the “Pico” alternative to passwords vulnerable to man-in-the-middle?

Maybe someone has already heard about "Pico" by Frank Stajano. In short: It is a model for an alternative for using passwords for authentication and seems to be very interesting. Regarding the paper, ...
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777 views

Does humanly verifiable one time pad authentication exist?

Firstly some predicates:- Sufficient hardware generated one time pad key material. No pad reuse. Messages of 160 characters length (think Twitter). 28 characters only in use (A-Z, space and full stop ...
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1answer
397 views

Is it a vulnerability (for message authentication) to have a variable iteration-count for PBKDF2?

The scenario: A user clicks on an encrypted file, and enters his password, in order to decrypt and authenticate it using HMAC (when its key is derived using PBKDF2). If the iteration-count is fixed, ...
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85 views

Is creating an authentication-key (mac) from the encryption password a vulnerability?

I can think of at least one problem with it - that testing for a correct key (when brute forcing) is simpler with a mac key (at least for short messages) and therefore can help brute force decryption.
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134 views

Using crypto to build a clone resistant system

My question is related to using cryptography to build clone resistant system. I am building an embedded system with ARM based commodity hardware board. Thus the intellectual property which makes the ...
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214 views

Authentication in TLS protocol

TLS session keys are derived as a result of authenticated key agreement. Is being able to decrypt a record at an endpoint after receiving change_cipher_spec sufficient guarantee that the endpoint is ...
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1answer
100 views

MAC providing sender authentication (follow up question)

I was looking at the responses posted on the following question: How is digital signature different from a message authentication code (MAC)? I read the following comment to the first answer: So ...
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242 views

Securing an end-to-end encrypted cloud based address book

I am analyzing an existing end-to-end encrypted, cloud based service (e.g. email, file storage or chat) which also has a public cloud based address book (for managing contacts) so that users of the ...
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1k views

PGP-key-based authentication system

Consider we implement remote service, which will be accessible via API(i.e. restful http or grpc). All users are authenticated via pgp keys and each user has pgp keypair. How to implement ...
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1answer
508 views

MITM defense in Diffie-Hellman protocol

Let's consider that Alice and Bob both know a shared secret $secret$ and don't know each other DH public keys. They want to authenticate each other and their keys using only $secret$. Let's also ...
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140 views

Authenticated encryption using asymmetric keys

I know this may be marked duplicate. It is based off of this question and this answer. However, I feel like I'm missing something... My example: Bob wants to encrypt a message and send it to Alice ...
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102 views

Token generation using Mac?

I'm writing a web service that gives a unique token per client connection. And the following are the desired properties. I'm assuming server's issued token db is lost and untrustable client presents ...
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1answer
403 views

Enc-Mac (AES CTR+CBC) mixing AES-256 and AES-128 and splitting keys

I'm looking to accomplish a Enc-then-Mac approach using AES-CTR and ECBC-MAC Now ECBC-MAC requires 2 distinct keys, one for the MAC, and one to encrypt the Tag. If I do this: Use AES256-CTR for the ...
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What is mac-and-continue?

I've seen the term mentioned in a paper by the Keccak team here, and by Adam Langley here when talking about properly authenticating stream ciphers. What does it actually mean, and how does it work? ...
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559 views

Does DTLS in WebRTC protect from active Man-in-the-Middle?

I wonder if it does. It seems to me that there is no way for participants to authenticate each other securely. There are, though, signaling servers, but I don't think that they are capable of key ...
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1answer
233 views

Semantic security of the OCB mode

As defined in the specification of OCB, the tag depends only on the checksum (that is just the binary sum of plain blocs), so if we construct two messages that have the same sum (this is very easy to ...
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1k views

Why is the GHASH output in GCM mode encrypted to calculate the tag?

To calculate the authentication tag in the Galois/Counter mode (GCM), first a MAC is calculated using GHASH over the cipher text and the additional data. After that, this MAC is encrypted using GCTR (...
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NFC with AES : how works the exchange of key

I'm trying since days to understand the security protocols on NFC devices. I'm not a professional in security, I'm just a student and want to understand (additionally, English is absolutely not my ...
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259 views

Single roundtrip authentication

I have a server and a client that need to authenticate to that server. The idea is that we have user/pass and the authentication ...
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6k views

Security services provided by digital signature

Which of the security services can be provided by digital signature? data integrity nonrepudiation sender authentication receiver authentication I think it can provide nonrepudiation. Because ...
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Is this authentication system insecure or not

So I want to create a simple, fast and yet secure authentication in two steps for a PC - microcontroller communication. The first step is a seed request, the second step is an authentication request. ...
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263 views

A login token algorithm

Hi illuminated crowd of cryptography. I am currently working on a login token for a web API. The feature for the token is to be a mostly featureless identifier. The only property I need is, that I ...
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standard way of authentication via token

I'm relatively new to authentication and I'm using JWT.io in following manner. Server Side Once user logs in, I generate a token with userid embedded inside and ...
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171 views

Is it a bad idea to make multiple SHA-* with the same header?

I'm trying to figure out a simple way to verify ownership over a short period of time (typically 8 - 24h), to be used in a mobile application. One of the ideas I came up with is to hash the following ...
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1answer
95 views

Hybrid authenticated protocol

Let's suppose that two entities, A and B, are establishing a secure channel and then require a mutual authentication. A has only a RSA key pair and B has an ECDSA key pair. Both of them trust the ...
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How to improve long-term duration of standard checksum for authenticity purposes?

Official CMS's of Government gazettes (in the third world), need to publish the checksum of each article and each cited external documentin (eg. full-text contracts) in a permanent support medium like ...
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1answer
625 views

Key management in Java + Remembering passwords

I'm new within the area of crypto so I apologise if I am bad at explaining this, or have misunderstood certain areas. I'm currently developing a Java Fx application which includes the use of a '...
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1answer
54 views

How can companies authenticate messages sent between different security components in the company?

How can companies authenticate messages sent between different security components in the company? (say SIEM for monitoring and IDS for intrusion detection)? What protocols do they use in order to ...
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An example of an appropriate use case for AES-CBC encryption without authentication?

I have been learning a lot by studying the questions and answers here on crypto.stackexchange.com and an grateful for this community. Recently in this question AES in CBC Mode Is totally unsecure if ...
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How exactly does ASKE (Alpha Secure Key Establishment) in Zigbee work?

I am working on Zigbee security. For key establishment, some approaches are given in Zigbee. Some of them are: ASKE (Alpha Secure Key Establishment), ASAC (Alpha Secure Access Control), and SKKE (...