HMAC is a method for constructing a message authentication code based on a cryptographic hash function.

learn more… | top users | synonyms

4
votes
1answer
336 views

Memory-hard operations in work-factor hash functions

I'm playing around with work-factor hash functions, and I'm looking for a memory-hard operation to make it resistant to GPU / parallel hardware attacks. I considered a very large (i.e. 64K) s-box that ...
5
votes
2answers
264 views

Is my HMAC secure if I have a complete series of HMAC'd prefix strings

Let's say I have a long sentence, like "The quick brown fox jumped over the lazy dog." Let's further say that I need to keep this string encrypted, so I use an HMAC. Let's further further say I want ...
7
votes
2answers
3k 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
170 views

DIfferent inner and outer hash functions for NIST Recommended HMAC?

The NIST recommended HMAC uses $$\operatorname{HMAC}_k(text) = H_\mathrm{out}( (k \oplus \mathrm{opad}) \operatorname\| H_\mathrm{in}((k \oplus \mathrm{ipad}) \operatorname\| text) )$$ Is it ...
7
votes
1answer
532 views

Why does a broken hash function undermine an HMAC?

For instance, what makes MD4 a bad choice for an HMAC? In this case I am asking about MD4 because its less than ideal. I know that a preimage attack can be used to undermine the system, but why? ...
6
votes
3answers
709 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. ...
4
votes
1answer
274 views

Undecrypt using the OpenSSL EVP API?

I'm writing a client-server encryption scheme for homework, and I've stumbled upon what might be a fatal blow to my current implementation. When using AES-256-CBC on the two sides, it's important ...
8
votes
4answers
591 views

Can I determine if a user has the wrong symmetric encryption key?

We're using the Objectivity/DB object database with a custom encryption plugin that encrypts serialized objects on disk. Encryption uses AES with a shared secret key held by all users. I would like to ...
1
vote
1answer
173 views

ID-Secret Scheme

I have an ID-Secret scheme and I'd like to hear if there are any vulnerabilities present. Party 1 and Party 2 hold some credentials, an ID and a Secret. Party 1 Creates this message: ...
11
votes
1answer
737 views

Security of N bit HMAC

Lets say that I am using 128 bit HMAC. How many operations are needed to find a "non secure" message. Is a birthday attack possible?