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.
2
votes
1answer
85 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 ...
1
vote
1answer
93 views
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 ...
3
votes
1answer
76 views
Can substrings of a long string be efficiently authenticated?
Suppose one has a (strong) shared secret key and wishes to authenticate a very long string in a way that will allow the verifier to verify small substrings without reading much of the stored data and ...
2
votes
1answer
79 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 ...
1
vote
1answer
34 views
Why does the server in S/KEY authentication only store a single password?
I've been reading about the S/KEY One-Time Password system on wikipedia here and was wondering why the server only stores a single password and not the list of one-time passwords like the client does. ...
1
vote
1answer
36 views
Difference entity authentication and implicit key authentication
From the Handbook of Applied Cryptography, in discussions of key sharing algorithms, I see definitions:
Implicit key authentication is when one party is assured that no other aside from a ...
3
votes
2answers
104 views
What are the potential security impacts of using CRAM-MD5 for Emails, when not using an SSL connection?
Background: My current server-provider tells me it's no problem to store the passwords in plain-text in the database, saying he has to do so because they use CRAM-MD5 for email authentication. But ...
1
vote
2answers
89 views
standard way to authenticate parties with public keys without certificates
Is there some standard protocol for mutual authentication of two parties when there is possibility to use public key cryptography? The problem is that two parties can use public key cryptography but ...
1
vote
0answers
59 views
Algorithm digipass-like
I'm pretty sure there are famous algorithms for my problem, but I don't have enough knowledge in this field, so I need your lights.
Here si the problem :
Alice sends key X to Bob.
Bob has an ...
2
votes
1answer
106 views
How to use salt if I am sending hashed password?
If have application that is sending username and hashed password to server for authentication, how would I use salt for this scenario ?
1
vote
1answer
119 views
AES Message Authentication Vulnerability
My securities instructor recently posed this question to the class and I am bending my brain in half trying to figure it out.
Suppose $y_1 = AES(K, x_1)$ and $y_2 = AES(K,x_2)$, and suppose you ...
0
votes
0answers
28 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 ...
4
votes
1answer
140 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 ...
3
votes
3answers
165 views
Efficient Symmetric Mutual Entity Authentication Protocol
I am looking for an Authentication protocol for access control. Let's say both the client and server would share a symmetric secret (256 bit key) and the client wants to access the server. Access ...
3
votes
2answers
149 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 ...
3
votes
1answer
543 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?
1
vote
3answers
151 views
Message authentication codes construction
I was reading the paper $[1]$ and came across the scheme that I show below. While I understand the scheme well, I don't understand why they prepend a 0 to the block containing $r$ and a 1 to all other ...
0
votes
0answers
61 views
Is this a valid real-time authentication scheme?
The scenario in Alice/Bob/Cindy terms:
Alice approaches someone she doesn't know, but thinks is Bob, and asks for some secret information. Bob doesn't know and doesn't trust Alice, but Alice says she ...
3
votes
6answers
317 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
149 views
Why shouldn't one build a MAC by XORing multiple message blocks?
I found this simple proposal for a MAC algorithm:
Let the MAC of message M (which consists of message blocks $M_1$,$M_2$, ..., $M_n$)
be the AES encryption with key K of the XOR of all the ...
1
vote
0answers
102 views
Computer appliance protocol
I build the computer appliance system that consist of software server and multiple controllers. The system I want to build must be pluggable in the sense that when I connect a controller C to the ...
2
votes
1answer
68 views
Authentication techniques being used by QKD Systems
As its well known that QKD systems are prone to simple MITM attacks, Any idea what authentication techniques are being used in QKD to prevent them in practice
1
vote
2answers
88 views
When is each key used when encrypting an email using OpenPGP?
When you send an email using PGP to encrypt emails, is the recipients public key used to encrypt the email, or is your private key used? Are they both used?
At what points do each of the four keys ...
2
votes
1answer
122 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 ...
1
vote
1answer
203 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 ...
1
vote
0answers
114 views
Is TOTP or a timestamp encryption a better timestamp-based authentication token system?
Are there advantages to using TOTP over encrypting a timestamp with a shared secret, in cases where the readability or ease of typing the token are not important?
4
votes
2answers
794 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 ...
2
votes
1answer
108 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 ...
4
votes
3answers
264 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 ...
5
votes
1answer
223 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 ...
4
votes
3answers
374 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
...
1
vote
2answers
2k 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 ...
0
votes
0answers
47 views
What happens when you use Windows credentials to sign a message?
I'm trying to dig into the messages that are exchanged when you sign a message using Windows credentials. I've modified the default service that is provided when you create a WCF service to use the ...
1
vote
2answers
84 views
KDF with low-entropy salts
I need to derive a key from a username and a password. These are the only two things I have access to. What I thought is using PBKDF2 with username as the salt and password as the master password.
...
1
vote
0answers
94 views
Setting protocol parameters to achieve concrete security
Background
One issue with modern security proofs is that they are usually asymptotic. In other words, such proofs are usually formulated as follows: For any polynomial-time adversary $\mathcal A$, we ...
4
votes
4answers
513 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 ...
5
votes
2answers
812 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 ...
3
votes
1answer
345 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 ...
7
votes
1answer
256 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:
...
5
votes
3answers
356 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. ...
1
vote
2answers
215 views
How to generate successive stream-cipher keys?
I've identified a weakness in a distributed simulation system I'm looking at, and I'm looking for some advice on how to fix it.
Clients initially negotiate an authentication token with a login server ...
4
votes
2answers
219 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.
...
2
votes
1answer
534 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 would be a great help.
...
3
votes
2answers
119 views
Helper data authentication in PUFs
As I understand, PUFs work by using two procedures: generation and reproduction. Generation reads a value $w$ from a fuzzy source and generates a key $R$ and helper data $P$. Then, in the reproduction ...
1
vote
1answer
118 views
How is the password sent across for verification?
I am familiar with Challenge-Response Authentication scheme.
However I would like to know actual message content sent between client and server for 1 way authentication, over an insecure channel.
...
3
votes
1answer
468 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 ...
5
votes
1answer
179 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 ...
2
votes
1answer
298 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 ...
5
votes
1answer
330 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 ...
1
vote
3answers
190 views
How does one provide a secure and authentic communication channel?
Let assume two participants Alice and Bob who perform a given protocol which is a sequence of messages exchange between them.
My question is: How can I provide a secure and authentic communication ...
