Questions tagged [hmac]

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

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226
votes
7answers
83k views

Password Hashing: add salt + pepper or is salt enough?

Please Note: I'm aware that the proper method for secure password storage hashing is either scrypt or bcrypt. This question isn't for implementation in actual software, it's for my own understanding. ...
32
votes
1answer
8k views

Why can't I use the same key for encryption and MAC?

I wrote a simple file encryption program as an example of how to do encryption correctly, but after reading a questions about encryption + MAC, I think I made a mistake by using the same key for both. ...
132
votes
5answers
163k views

How and when do I use HMAC?

I was reading HMAC on wikipedia and I was confused about a few points. Where do I use HMAC? Why is the key part of the hash? Even if someone successfully used a "length-extension attack", how would ...
17
votes
2answers
4k views

Timing attack against HMAC in authenticated encryption?

In an answer to another question of mine, it was noted that a class using standard string comparison functions when checking the HMAC in authenticated encryption would make the class vulnerable to ...
47
votes
4answers
54k views

What are requirements for HMAC secret key?

I'm creating HTTP REST service which will be available over tls only. For authentication purposes I plan to generate JWT token for every user using HMAC HS256. I need a secret key for HMAC. What are ...
2
votes
2answers
325 views

Finding hash collision

for instance, sha-1 is known as weak hash function. If attacker finds collision in hash function, can he generate valid MAC for given message m? I mean it is possible to generate valid mac for any ...
6
votes
1answer
473 views

MasterSecret expansion into keys

I'm trying to deeply understand the steps during a TLS handshake. I've read this answer (which is btw pretty complete), but I still got a question about the utilization of the MasterSecret, in the ...
28
votes
2answers
18k views

Salted hashes vs HMAC?

Most of discussions involving access credentials include references to "hashing salted passwords". Is this another way to referring to the HMAC algorithm or a totally different operation? Different or ...
23
votes
3answers
14k views

Is a HMAC-ed password is more secure than a bcrypt-ed or scrypt-ed password?

Given an option , which one should I choose , a HMAC for storing a password securely or a bcrypt or scrypt library?
22
votes
1answer
18k views

When to use HMAC alongside AES?

One of my clients wants to provide an URL to each of his customers to register in a system. This URL would contain a query string parameter with some data (e.g. code, email and name) from his clients ...
10
votes
1answer
4k views

Using HMAC to generate secret keys

I am developing a platform that uses several secret keys for several usages: key1 for hashing passwords (using pbkdf2-hmac-sha256), key2 to generate non-repeating unpredictable uuids (using aes-128 ...
8
votes
2answers
2k views

Why does node.js scrypt function use HMAC this way?

According to the documentation, the scrypt hash function works like so: The hash function does the following: Adds random salt. Creates a HMAC to protect against active attack. Uses the ...
3
votes
1answer
1k views

Signing (HMAC) cookie identifier

Related to this other question about sharing the secret to sign the cookies, my question is more trivial: how really secure is to sign a simple cookie identifier? In example, expressjs#session ...
-5
votes
2answers
185 views

Protection of online image file (ancient manuscript) [duplicate]

I am going to protect an image file (ancient manuscript) which will be available online for everyone to download. I want to protect the file in these situations: When it's on the server, I need to ...
43
votes
2answers
59k views

What's the difference between HMAC-SHA256(key, data) and SHA256(key + data)

Is there anything different about how secure these two hashing algorithms are? Does HMAC "fuse" the data and the key in a special way that's more security-aware?
12
votes
4answers
13k views

HMACSHA512 versus Rfc2898DeriveBytes for password hash

We are currently using HMACSHA512 in .net, with a 128Char (64byte) validation key The salt is 64 char randomly generated string. We allocated 2048 length on the database for the hashed base64 string ...
19
votes
1answer
7k views

Why a symmetric key for HMAC?

I am working on securing a RESTful API and am using the Amazon AWS HMAC model as my guide. I am struggling with coming up with a secure way to store the symmetric keys on my end. What is the standard ...
6
votes
1answer
11k views

How is the HMAC key exchanged?

Just wondering about this. Does it need a PKI to work?
13
votes
1answer
1k views

Secure backup encryption with OpenSSL

I know, the general advice is "keep your hands off crypto stuff". And the standard way to encrypt backup data securely would be using GnuPG. However, for a rather academic exercise, I would like to ...
6
votes
4answers
5k views

HMAC/PBKDF2 vs Simple hashing algorithm for web service authentication?

We are in the process of creating a web service and have been investigating ways of securing it. In reality, the service is likely to get very little traffic and the data is likely to be of little use ...
6
votes
1answer
952 views

Should password hashes be encrypted or HMACed?

Assume I am hashing user passwords with PBKDF2, bcrypt, scrypt, or some other secure key derivation function. Are there: tangible security benefits, precedents, and respected research for ...
4
votes
1answer
2k views

SSO via HMAC and shared key. Can this be improved?

Given an authenticated user on A.com, we want to redirect the user to B.com so that she'll be immedaitely authenticated. The scheme I'm considering is very basic: A.com and B.com both share key S. ...
2
votes
1answer
97 views

Is D parameter of the RSA strong enough to be used as secret for HMAC calculation?

Short question: Is the D parameter of the RSA alghorithm crypthographically strong enough to be used as a secret key for generating SHA-256 hash value? Long question: I'm working on windows platform. ...
2
votes
2answers
727 views

What does it mean that Hmac is secure?

I'm not taking about general collision attack on weak hash function such as MD5 or SHA-1. I'm wondering security of HMAC which is based on weak hash function If there are key k, message m Hmac(k,m) =...