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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19
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6answers
315 views

advances in usability for cryptography/authentication

I'm wondering if there have been any recent advances (say, the past 5-10 years) in human usability for cryptography and/or authentication? By that I mean something that makes it easier for an ...
15
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1answer
7k 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?
14
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3answers
3k views

Specification of the Megamos crypto algorithm

It has recently emerged that a paper that was scheduled to appear at Usenix Security 2013, titled "Dismantling Megamos Crypto: Wirelessly Lockpicking a Vehicle Immobiliser", has been censored ...
10
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1answer
207 views

Shadowed identity in cryptography

I was trying to implement zero knowledge protocol for authentication based on the paper "A Practical Zero-Knowledge Protocol Fitted to Security Microprocessor Minimizing Both Transmission and Memory". ...
10
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2answers
9k views

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 ...
9
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4answers
414 views

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 ...
8
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3answers
15k 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?
8
votes
2answers
2k views

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 ...
8
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2answers
2k views

What advantage does facebook's new encrypted access_token have?

When a user on facebook grants an app access to their account, an API key is issued to the app. This key is app and user-specific. This process is described in Facebook's developer documentation. ...
8
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2answers
870 views

How should I store passwords that need to be available in plain text?

Suppose I need to store login information for a third-party website for a few users, how would I go about doing it? Since I am logging into a third party website, I need the password in plain-text, ...
8
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2answers
345 views

What current authenticated key exchange standards exist?

If neither of the 'big two' of TLS Handshake and IKE are appropriate in a given situation, what alternative Authenticated Key Exchange (AKE) standards exist and are recommended? Many protocols have ...
7
votes
3answers
321 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 ...
7
votes
2answers
602 views

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. ...
7
votes
1answer
413 views

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 ...
7
votes
3answers
886 views

Is this a secure implementation of password reset email?

I am redesigning a password reset email mechanism because the existing implementation scares the hell out of me. My goal is to generate reset codes that are: Expired Tamper Resistant Single Use ...
7
votes
1answer
283 views

Is there any known malleability of scrypt outputs?

The scenario is single-use passphrase-based non-interactive message authentication. The obvious try to do this is to chose a random salt of the appropriate length and send: ...
6
votes
3answers
2k views

SHA1 usage for passwords, alternatives and advantages?

My application can authenticate via openid and oauth (facebook, twitter, etc) and also with its own authentication system. I previously switched hashing from MD5 to SHA1 and during migration I had to ...
6
votes
4answers
1k views

How can I validate a hashed password if all I have is another hash?

The Scenario I have a client-side web application that bounces requests against a server-side API. For the sake of simplicity, every request must pass a username and password. This is similar to ...
6
votes
3answers
554 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. ...
6
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2answers
1k views

RSA-based authentication and key-agreement protocol

An authentication and key-agreement protocol between devices shall mutually demonstrate their identity, and establish a shared random secret $R$ suitable for securing later communications. To that ...
6
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1answer
1k 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. ...
6
votes
4answers
184 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 ...
6
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1answer
127 views

Cryptography used for login and signing transactions

My bank uses a smartcard reader (separate module not connected to the computer) as depicted below: When I need to log into my account it provides me with a challenge and I need to provide some ...
5
votes
2answers
83 views

Why is this authentication procedure using Rabin crypto not useful?

A friend asked me the following, pointing out that the method is not very useful (my problem is I do not see why it is not good): Consider a person A which chooses $n$ as the public key for the ...
5
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2answers
2k views

What are advantages of using a HMAC over RSA with SHA-1 hashes?

I am currently studying for an exam and this was a previous question: Give one advantage of using HMACs over using RSA to sign SHA-1 hashes. My thoughts are that it has something to do with the ...
5
votes
1answer
294 views

Why are the random exponents so much bigger in the Socialist Millionaire protocol versus Diffie-Hellman key exchange?

Section 8, Security considerations, of RFC3526, which defines groups used for Diffie-Hellman has a table recommending some random exponent sizes. In particular, it says: The strength of a key ...
5
votes
1answer
249 views

What is 'Carry-forward verification' defense against MITM?

Wikipedia article on Man-in-the-middle attack mentions, in the list of defenses against it, some method called "Carry-forward verification", but it does not explain it. I am curious about different ...
5
votes
1answer
338 views

Authenticated encryption mode for stream cipher?

E. g. block ciphers have GCM or OCB, that take single cryptographic primitive (block cipher) and provide both authentication and encryption. Are there similar constructs for stream ciphers, which ...
5
votes
1answer
723 views

What is the proper way to use a client nonce?

I've implemented an API for one of my clients, it relies on nonces and a shared secret. The structure: Client's Site (CS) requests nonce from My App (MA), posting their username MA verifies the ...
5
votes
2answers
138 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 ...
5
votes
1answer
111 views

Authentication protocols for authenticating devices to a server

The requirement is to authenticate 1000s of devices to a server when the devices try to contact the server. The problem I face is that all authentication protocols require some kind of shared secret ...
5
votes
2answers
123 views

Does data authenticity always, implicitly, provide data integrity?

Does a scheme which provides data authenticity (e.g. HMAC or RSA signature) always implicitly provide integrity? It seems, to me at least, that it must by necessity. However, I have seen ...
4
votes
6answers
502 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 ...
4
votes
3answers
450 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 ...
4
votes
3answers
459 views

How to perform authentication without central server in P2P?

How can one be sure that the man who you're talking with is the one who you think he is? i.e. How can one perform authentication in P2P network without a central trust server or Certificate Authority? ...
4
votes
4answers
215 views

What is the difference between authenticating and signing a document?

Authenticating a document means to verify it is from the sender. But it seems like signing a document also verifies it’s from the sender. What exactly is the relationship or difference between ...
4
votes
2answers
368 views

X.509 CSR: Why does CA remove signature?

I just read this article on Wikipedia: Certificate Signing Request I'm not a PKI or Crypto expert. As I understand, a CSR (certification request) is always signed by the PKCS#10-Request creator. ...
4
votes
2answers
138 views

Spoofing protocol nonce

Amy and Betty have a shared key $k$, and the protocol below is to provide a mutual authentication for both Betty and Amy. A sends B : $n_a$ B sends A : $n_b \;\|\; E(k, n_a)$ A sends B : $E(k, n_b)$ ...
4
votes
1answer
313 views

HMAC for short messages

I am using HMAC (hmac-sha256 to be precise) message authentication without encryption. My question is, is having a short message make it easy to determine what my secret key is? My C# code is as ...
4
votes
2answers
552 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 ...
4
votes
1answer
59 views

Authenticating Very Short (Sub-Block) Data

If I'm encrypting very short/small data - like an int or a long (32 or 64 bits), does it make any sense to authenticate the ciphertext, when using an "online" mode of operation (like EAX)? ...
4
votes
3answers
185 views

Why can an RSA signature be authenticated ONLY with the signer's public key?

I'm an undergraduate Math student currently taking a cryptology course. I have a question about the RSA signature authentication mechanism. An RSA signature can be authenticated with the public key ...
4
votes
3answers
599 views

Can I use PBKDF2 for authentication and decryption?

I want to store a hash for authenticating a password. I also want to use the same password for decryption. Can I use PBKDF2 for both? (I plan to use different salts for the authentication and the ...
4
votes
1answer
339 views

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 ...
4
votes
1answer
144 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?
4
votes
1answer
560 views

Need an introduction to SPKI (or “SPKI for dummies”)

I am familiar with concepts such as the following: PKI and CAs ID based cryptography Certificateless cryptography PGP web of trust more or less anything in basic Crypto that is taught in a college ...
4
votes
3answers
434 views

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 ...
4
votes
1answer
743 views

Efficient and stateless anti-forgery method

One use of an anti-forgery token is to prevent Cross-Site Request Forgery (CSRF) attacks. The attacker doesn't need to sniff the wire in order to carry out a CSRF attack. This attack relays on the ...
4
votes
1answer
1k 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 ...
4
votes
1answer
133 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 ...