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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47
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3answers
88k views

RSA encryption with private key and decryption with a public key

When using the RSA cryptosystem, does it still work if you instead encrypt with the private key and decrypt with the public key? What about in the case of using RSA for sender authentication?
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1answer
80k views

What are the differences between a digital signature, a MAC and a hash?

A message may be accompanied with a digital signature, a MAC or a message hash, as a proof of some kind. Which assurances does each primitive provide to the recipient? What kind of keys are needed?
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1answer
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Why does my SSH private key still work after changing some bytes in the file?

I (for a test) just randomly altered a private RSA key by opening it up in Vim and changing a few bytes. It is the private part of an SSH key pair used for logging in on a remote system. Puzzlingly, ...
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Is there a way to make RC4 (ARCFOUR) secure, or is it completely broken?

I need a method to authenticate a process with another in order to establish interprocess communication between them, to prevent malicious processes from trying to hook onto the system. Currently I ...
7
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1answer
3k views

What is “Implicit Authentication”?

What is “Implicit Authentication” in the context of authentication methods? I searched the Web but could not find any article that describes this. If anyone can describe it, that would be a great ...
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2answers
643 views

Is there a companion algorithm for OTP to ensure integrity and/or authentication?

One-Time Padding is (theoretically) perfect encryption algorithm. Let's assume that these problems are solved: Fast generation of independent and identically distributed random variables Perfect key ...
2
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1answer
177 views

How does Gilbert, MacWilliams, and Sloane's solution to “perfect integrity” work?

Gilbert, MacWilliams, and Sloane defined a solution to "perfect integrity" in Codes Which Detect Deception, unconditionally secure message authentication, not vulnerable to any cryptanalysis on its ...
9
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2answers
992 views

Is it safe to reuse ECDH asymmetric keys for authentication?

Alice, Bob, and Carol each generate ECDH keypairs. Alice and Bob establish a communication channel and negotiate an AliceBob secret. The question is: Is it safe for Alice and/or Bob to reuse their ...
44
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2answers
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Signatures: RSA compared to ECDSA

I'm signing very small messages using RSA, and the signature and public key are added to every message, which requires a lot of space compared to the actual content. I'm considering switching to ...
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6answers
4k views

Why not authenticate full-disk encryption?

Common FDE software (TrueCrypt, BitLocker, dm-crypt) doesn't authenticate ciphertext stored on the disk. The commonly cited reason is "it would take too much space", reasoning that you would need an ...
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Authenticated DH, what protocols are secure?

I read about STS + variants being insecure in the SIGMA paper, which then proposes SIGMA as a replacement. Are the SIGMA variants still considered secure or are there some other protocol that's ...
6
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3answers
2k views

Convert old and busted password encryption to something sensible

Given a TOTALLY HYPOTHETICAL scenario in which passwords for over a million accounts in over 200 databases have been stored using 3DES, a key derived from a (single) MD5 hash of a customer-controlled (...
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1answer
3k views

How can I encrypt + authenticate short strings into similar short ciphertexts?

I wish to manipulate short ASCII strings (namely unpredictable domain names) into a form which cryptographically assures authenticity and confidentiality, for use in the local part of email addresses. ...
9
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1answer
8k views

Where is the authentication tag stored in file encrypted using AES-GCM?

So I am using cryptopp to encrypt a file in a project and I am using AES-GCM. I have a 256bit key and a 128bit ivec and a 128bit tag that I use to encrypt files. However, I want to know where the ...
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1answer
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Why does SRP-6a use k = H(N, g) instead of the k = 3 in SRP-6?

I've been reading up on the Secure Remote Pasword protocol (SRP). There are a couple different versions of the protocol (the original published version being designated SRP-3, with two subsequent ...
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2answers
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AES-ECB as an authentication mechanism

ECB is considered to be insecure when used for confidentiality because identical plaintext result with identical ciphertext. But what if we use ECB for authentication? Assume A wants to transmit an ...
4
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2answers
397 views

Rivest's ring signatures with hashes instead of symmetric encryption

While studying ring signatures, I obviously stumbled on the Wikipedia article about ring signatures. It includes a piece of Python code to demonstrate "How to leak a secret" ring signatures. ...
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1answer
770 views

Inverse public-key encryption

I'm in the need of an inverse public-key encryption method where you encrypt with the private key and decrypt with the public key. In other words an asymetric encryption where you can't generate the ...
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1answer
347 views

Is this variant of SRP for peer-to-peer authentication practical?

I'm interested in using a modified form of SRP as a peer-to-peer authentication method. Since neither side is acting as a host, one of the primary design goals for SRP (that the client doesn't need ...
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1answer
283 views

Definition of Short Authentication String

I am studying for my cryptography final and I passed by the following term: short authentication string. Please, can anyone explain it to me, thank you very much.
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1answer
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Has GMAC mode a future outside GCM?

Once gcm has been implemented for providing both encryption & authentication solution , it appears obvious to consider that such implementation can also provide (if required by new user) a Mac ...
6
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1answer
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Security of authenticated encryption modes GCM & CCM

I have two questions for Clarification for AE mode choice criteria GCM : it appears to be actually the most popular and widely used AE mode of operation. however it is also well-known to be highly ...
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2answers
989 views

How did LinkedIn “salt” all their passwords?

First, just to make sure I understand "salting" correctly: You randomly generate a string to append to the password before hashing it, so as to increase its length and make precomputed tables much ...
3
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1answer
263 views

What does this Authentication protocol achieve and what information is shared?

I'm having trouble with the following question from my class: "What is the purpose of the protocol, and how does it achieve this purpose and what shared information does A and B end up after ...
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1answer
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What is a man-in-the-middle attack (for instance in Diffie-Hellman)?

I'm new to cryptography and I just started learning about the Diffie-Hellman key agreement. I read that this system is vulnerable to a man-in-the-middle attack when used alone. What kind of attack is ...
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3answers
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How does a rolling code work?

I have general questions regarding rolling codes. Basically there is a sender and a receiver. Both have a sequence generator. The receiver checks if the received sequence matches the newly generated. ...
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6answers
780 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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3answers
1k views

How to authenticate over open channel?

I am making an arduino project to open my garage door. I want to make it so users with the passphrase can open the door. Due to computational restrictions it is unlikely encryption is possible. ...
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3answers
657 views

Can one have an authentic, but repudiable, message without a previously shared secret?

Bob wants to send a message to Alice, such that Alice can be sure that the message came from Bob, but can't prove it to anyone else. If I understand right, this means that the same message could have ...
6
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1answer
8k views

How exactly does certificate based authentication work?

I know the concept of key generation, as well as encryption and decryption using public and private keys. When it comes to authenticating a user by a server, in general there are three types: ...
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2answers
9k views

Digital Signature using symmetric key cryptography

Generally digital signature is a public key cryptography concept.But it needs high overhead. So is there any publication or link available where 'digital signature using symmetric key' has been ...
2
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1answer
455 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 ...
7
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3answers
560 views

What is the reason to separate domains in the internal hash algorithm of a merkle tree hash?

From rfc 6962 It is stated that: Note that the hash calculations for leaves and nodes differ. This domain separation is required to give second preimage resistance. That means that ...
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6answers
2k views

Is there an authenticated encryption scheme where the recipient can attribute the message to a single sender?

With a standard authenticated encryption scheme (or MAC), Alice and Bob share a symmetric key. When Alice sends something to Bob, Bob can check that it is authentic. At that point, Bob can deduce ...
6
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1answer
174 views

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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2answers
8k views

Diffie-Hellman Key Exchange with Authentication: Man-in-the-Middle query

I have been reading up on MiTM attacks, and the prevention of them using public key certificates. Recently I learnt about Diffie-Hellman Key Exchange with Authentication, and how it uses signed ...
5
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4answers
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Diffie-Hellman and man-in-the-middle attacks

See here for the man-in-the-middle attack on Diffie-Hellman that I'm concerned about: What is Diffie-Hellman? How do we combat this? I have two questions: Is one solution for both Alice and Bob just ...
5
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1answer
346 views

Implementing CD serial key system

I am trying to create a system where to unlock the application one needs to enter a serial code. I have read many articles on the theme but there are two problems bugging me. One is, If I have a ...
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1answer
2k views

Is there a generic attack on encrypted CRC32 when used as a MAC?

I am examining a protocol that uses CRC32 as a MAC (see note 1) the weaknesses of this method but I would nevertheless like to see if it is just weak or actually relatively easily to break. The ...
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2answers
2k views

Why does TLS do Authenticate-then-Encrypt instead of Encrypt-then-Authenticate?

Encrypt-then-Authenticate (EtA) seems to generally be considered the better option, compared to Authenticate-then-Encrypt (AtE) (see this Crypto.SE question, for example). The people writing the RFC ...
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0answers
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Can you help me understand this toy example of ECDSA signing and verification? [closed]

I'm a complete newbie to ECC. but I was trying to get my feet wet with (what I thought would be) a TRIVIAL/EXTREMELY SIMPLE example of ECDSA signing and verification (that I could check by hand). I'd ...
2
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1answer
192 views

Unconditional authentication

I have a few questions regarding universal-hash functions: Is there a way universal hash functions can be used to provide unconditional authentication in the way the OTP provides unconditional ...
9
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2answers
6k views

Can a salt for a password hash be public?

For my understanding salts in password hashes are used to prevent the precomputation of $plaintext \to hashvalues$ (rainbow tables). I know from different threads, it is not necessary to keep the ...
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2answers
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Authenticated encryption mode for stream cipher?

Block ciphers have modes like GCM or OCB that combine primitives to provide both authentication and encryption. Are there similar constructs for stream ciphers, which provide both authentication and ...
9
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1answer
3k views

The difference between MAC algorithms and what to use

I've been looking into message authentication codes and found several ways to create integrity for a message. I know of the following algorithms: HMAC, this can use any cryptograhpic hash function ...
8
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2answers
1k views

Is the HMAC construction really neccessary for a fixed length message?

The HMAC Construction is defined as: Hash( (Key XOR opad) || Hash((Key XOR ipad) || Message) ) This was designed because a simpler construction such as: ...
6
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2answers
1k views

Is there another resource for Carter-Wegman-style message authentication?

I'm wondering if there are other resources that cover Carter-Wegman style message authentication, besides the sources themselves. Is there an online text or a book that covers their ideas? I'd ...
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4answers
241 views

Authenticating data generated by a particular build of an open source program

[I was torn between posting here or security.stackexchange.com. In the end, I felt that this was more of a design question, rather than an implementation question and so chose this forum.] My ...
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1answer
395 views

What authentication techniques can be used by QKD Systems?

As it is well known that QKD systems are prone to simple MITM attacks… what authentication techniques are being used in QKD to prevent those attacks in practice?
5
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3answers
941 views

Is including the key as AAD actually dangerous?

In a recent answer, Maarten mentioned including the key is a bad idea as well. This got my curious. Is there any scientific / cryptographic analysis whether including the key in the ...