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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163 views

Offline app authentication - embedding hashed password inside an encrypted file

I am working on an occasionally connected app. To allow the users to authenticate I created a profile which is encrypted and placed on the users machine. The first byte of the file contains the IV ...
2
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1answer
531 views

Encrypt-then-MAC paradigm

I read that the Encrypt-then-MAC paradigm is provably secure. From what I understand, when using for example AES for encryption and HMAC_SHA256 for MAC generation (and the keys $K_1 \neq K_2$), this ...
2
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1answer
168 views

Signature scheme with two private keys, neither derivable from the other

Is there any scheme, ideally one widely used or at least widely available, where you can treat both the signing and verifying keys as secret? Basically, the functionality I'm looking for is this: ...
2
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1answer
86 views

Why is CBC-MAC with length appended not secure?

I've just read about CBC-MAC for the authentication of arbitrary length messages. In particular I cannot figure out why appending the message length before computing the MAC yields a non-secure MAC. I'...
2
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1answer
65 views

TLS Handshake : Server authentication or only Server ‘s Certificate authentication?

I have some difficulty understanding the way in which the Server is really authenticated by Client in TLS handshake (in case of using RSA key exchange). When Client receives Server ‘s Certificate and ...
2
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253 views

Chess Grandmaster Problem and “Valid” Attacks on Zero-Knowledge Proofs of Identity

A long question here, but I really want to motivate why I'm confused. Consider the following attack on the Schnorr Identification Scheme. Alice chooses a random $k$, computes $\gamma = \alpha^k \...
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1answer
88 views

Can adding nonces make challenge response authentications weaker?

In a custom protocol we want to replace an aged tiger32 based challenge response authentication. I suggested that we use something existing, so threw HMAC into the room. As per wikipedia it works as: ...
2
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1answer
59 views

Constant data as input to hash

I want to use hash function on some data, and part of this data, might be constant for a certain period. The output of the hash function is used as authentication data (MAC). I want to know if there ...
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1answer
118 views

Proof of shared secret through key derivation

Alice gives a random key $K$ (e.g. 32 bytes long) to Bob through a secure channel. Bob want to prove to Alice through an unsecured channel that he knows the key. Is it secure for Bob to send $s||...
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120 views

Genuine encryption from only one source?

Is there any technique so that if I encrypt data, the ciphertext would be genuine and if someone else tries to encrypt the same data the ciphertext could be determined as fake or just invalid? I want ...
2
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2answers
93 views

Is the security of an HMAC equally important as the security of the cipher itself?

I'm a little unclear on how hash based MAC works... So I would like to know, is the security of your hash function as important as the security of the overall cipher? Basically, if you can crack the ...
2
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111 views

Message security and also program copy detection

Imagine I have client and server running on different machines, each as a separate software. I want to ensure: message authenticity, integrity and confidentiality at least of messages coming from ...
2
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70 views

Implicit authentication aritcle

First, I want to know what is the logarithm used in the following system of equations (from the paper Flexible and Robust Privacy-Preserving Implicit Authentication - Domingo-Ferrer, Wu, Blanco-...
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116 views

State of the art techniques for Anonymous Authentication?

What are the state of the art techniques for Anonymous Authentication? What are the most popular ones? The problem domain I am considering is with respect to different users accessing cloud content; ...
2
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2answers
126 views

Client login without sending a password

I would love to have a system where the password is never send in plaintext (even with TLS) to authenticate a user. I've come up with this protocol, but I'd rather use something proven. Registration: ...
2
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1answer
100 views

How does the small n attack work?

I'm studying the Lamport's Hash one-time password scheme. This is the scheme: Alice wants to authenticate herself to Bob from a workstation that knows nothing about her. Alice only knows her ...
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42 views

N users must approve a request

I have a locked-down production system that we'd like to process specific requests, picked-up (poll) from a less-secure location. For security and "go slow, this is production" reasons, a request ...
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58 views

Security of MSS

I have started reading about the Merkle Signature Scheme. I am a little confused about why it is believed to be secure against quantum attacks, couldn't the hash function be attacked? What would make ...
2
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183 views

What is the advantage of using the socialist millionaire protocol to authenticate vs HMACing some random number?

Say Alice and Bob have a shared secret $s$. Alice and Bob establish an encrypted channel and verify that it hasn't been MitM'ed by exchanging $r_1$ and $r_2$, where $r_1$ and $r_2$ are randomly ...
2
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1answer
150 views

Secure way to store fixed size string of digits

I need to store a string of digits (0-9) of a fixed size in my database securely. I've already performed a rainbow table attack on a plain hash, and it broke it in a matter of seconds. One option I ...
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2answers
2k 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
150 views

With Encrypt-then-MAC, and flexible protocols, do I need to authenticate the authentication?

Sorry, the question is not easy to state (or wasn't for me, anyhow). So I'm writing a very flexible format for security. It allows for full choice of cipher, key size, and so on, along with key ...
2
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1answer
204 views

Can an encrypted nonce be used for authentication?

Would a scheme like the following work to allow authentication of a sender: A nonce is appended to data, and the result is encrypted. The encrypted pack is sent to the other party. The sender then ...
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417 views

implications of SSH server key compromission when authenticating users against a public key

Friday we had a disagreement with a colleague of mine about the implications of SSH server key compromission The question was stated as this : What could a hacker do while provided with the SSH ...
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980 views

Hash or encryption function for challenge-response protocol?

Say I have an authentication protocol where the shared secret is never transmitted. The server passes a challenge to the client and the client calculates a response using an algorithm where the ...
2
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1answer
59 views

How SAM modules secure transactions?

As you know SAM Modules are used mainly in the electronic payment industry. Due to the low security of key storing in general storage devices or MCUs, Manufacturers used SAM modules for secure storing ...
2
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1answer
61 views

Perfect Forward Secrecy in PGP/asynchronous email

Looking at the RFC for PGP email/asynchronous chat with PFS here https://tools.ietf.org/html/draft-brown-pgp-pfs-03 can anyone tell me why the following scheme is no good? Alice and Bob retrieve each ...
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39 views

Should I authenticate memory data which was loaded from authenticated disk file?

Encrypted fields are loaded from disk file to process memory only after file's HMAC validation is successful. Data is still encrypted in memory and will be decrypted later, on demand, when it needs to ...
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79 views

Can we use the authentication tag as Nonce / IV for the next message?

Let's assume we're in some scenario requiring transfer of large amounts of data. This means we can only use AES-GCM chunk-for-chunk as its maximal size is restricted to a few GiBs. This means we have ...
2
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1answer
74 views

Could this alternative hash based MAC construction be as, or even more secure than an HMAC?

Begin hashing (Key||Message) Encrypt the hash state (or some part of it, such as the first 128 or 256 bits), with the key. Add the encrypted hash state to the hash ...
2
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1answer
107 views

Is this a valid scheme to authenticate through a 'human-readable' certificate?

Let's say Alice wants to talk securely to Bob over the internet, and Eve is not only eavesdropping, but has managed to get into a MITM position. In this scheme Alice and Bob exchange $n$ (example $n =...
2
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3answers
518 views

Key derivation of public key without knowledge of private key

I'm looking for a convenient way to share a set of public keys across multiple services, while preserving privacy by preventing these services from tying the identity of these public key sets together ...
2
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1answer
78 views

Symmetric-key login protocol

I'm trying to analyze a login protocol based on symmetric key cryptography. I'm just starting out, so this may very likely be a very bad idea, but nonetheless I'd like to hear your thoughts on it. ...
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2answers
342 views

ECDH anonymous key exchange to avoid PKI

I want to use TLS to encrypt the communication between peers in a P2P network. Each peer has a well known 256bit peer identifier (the public key of a 256bit elliptic curve keypair). Both peers need ...
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98 views

Why would splitting a password output be better than separate HMACs for encryption/authentication key derivation?

In a recent question I asked here on crypto.se, an answer was given that surprised me a bit. As mentioned in the referenced question, I'm looking to derive encryption and authentication keys from ...
2
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1answer
127 views

DH key exchange with only one end authenticated

We know there is a man in the middle vulnerability with unauthenticated DH key establishment. And the way to negate that is to use authenticate the keys used. But what if I only verify the signature ...
2
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1answer
166 views

Is there need for message authentication if a public key is transmitted and then used to encrypt a symmetric key?

First I'd like to note that I'm really a beginner at cryptography, and while this interests me and while I have researched it in the past few months, there is still a lot of things that simply aren't ...
2
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1answer
192 views

Off-the-record communication

Is my protocol correct? For fun, I tried to design a protocol that would allow off-the-record communication. I'm not sure it works, I have a feeling there might be a problem with it that I'm not ...
2
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1answer
196 views

Authentication of machine before installation (to stop piracy) [closed]

I have a web-software project which needs a bit of protection in form of authencitation… This web based software runs on an intranet. There is no access to the internet from these terminal machines. ...
2
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1answer
425 views

Verifying Self-signed SSL Client Certificates

I have a service and I want to authenticate my clients using SSL client certificates. Now I want the key exchange process to be as simple as possible, kind of like SSH: You generate a keypair and ...
2
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1answer
152 views

Using plain Diffe-Hellman for server authentication with known public key

Other considerations aside, is it possible to use DH with an established public key (together with fixed g, p, q) to safely authenticate a server instead of using some signing algorithm? In other ...
2
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1answer
135 views

How can I validate generated session keys in SRP-6a protocol

I have genereted two equal session keys on client and server successfully. But I couldn't understand how each other should validate that they have same session keys. On the client I generated a SHA1 ...
2
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1answer
394 views

Is it considered insecure in an HOTP implementation to publicly provide the next counter?

I am working on a project that needs to securely authenticating one or more smartphone clients with a server running on a microcontroller so it has very limited resources. I have found plenty of ...
2
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1answer
121 views

Authentication protocol which detects client impersonation from another machine

Consider following authentication protocol. Client ClientA knows some initial secret KeyA shared with server. Client also knows IP of legitimate server. Now when client wants to establish connection ...
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62 views

StoredKey in Salted Challenge Response Mechanism (SCRAM)

In SCRAM (RFC5802, page 8) the client generates ClientKey to server, which is a derivation of the original password. This is communicated to the server in a secure ...
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39 views

David Chaum's anonymous credential

I am a newbie in cryptography (I know the basic RSA, AES stuffs) and am interested in anonymous authentication systems. Looks like David Chaum is the godly figure in the field. I see lots of people ...
2
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0answers
63 views

Proposed unidirectional authentication scheme

I've been looking around for a way to authenticate a client to the server and deliver a message, but in a unidirectional fashion - that is, the client sends messages to the server, but the server ...
2
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0answers
112 views

Does the initial exchange of random tokens in SKID3 authentication assure against replay attacks?

As the question suggests, I wanted to get a sanity-check on this issue... is it the case that the use of a random token exchange during SKID3 authentication itself constitute a prevention of a replay ...
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674 views

Challenge-response based on public-key decryption, why send public key

Quoting the handbook of applied cryptography, chapter 10.3.3 (i): Identification based on PK decryption and witness. Consider the following protocol: $A \leftarrow B: h(r), B, P_A(r,B)$ $...
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45 views

Validity of authentication scheme?

Here's an authentication scheme I had in mind that combines the simplicity of HTTP Digest Authentication and the security of real crypto primitives. I have in mind the user-level authentication, ie ...