Questions tagged [hmac]

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

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256
votes
7answers
102k 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. ...
174
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5answers
224k 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 ...
65
votes
4answers
81k 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 ...
59
votes
2answers
94k 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?
38
votes
1answer
10k 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. ...
36
votes
2answers
23k 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 ...
29
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3answers
16k 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?
29
votes
1answer
25k 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 ...
23
votes
1answer
10k 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 ...
21
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2answers
5k 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 ...
18
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1answer
2k views

FIDO, U2F Compatibility

I've been following the FIDO standard (a consumer-friendly public-key system similar to SSH key pairs) and it appears that it's close to being complete: both Google and PayPal have been testing it ...
18
votes
3answers
10k views

Securing a multi-tenant, multi-database REST API

I am looking to improve the security of an existing REST API accessed over SSL. The web service is multi-tenant, such that each tenant has an assigned TenantId. The problem I facing can be summarized ...
17
votes
1answer
3k views

When authenticating ciphertexts, what should be HMACed?

Some have argued for using AES-256-CTR with HMAC-SHA-256 for authenticated encryption over AEAD-specific modes like EAX and GCM. However, when doing, this, what should be HMAC'd? And how? ...
15
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2answers
2k views

How secure is the Ciphersweet library for searchable encryption, and why is a duplicate entry leak not a problem?

I'm currently managing a code base in which we've got a mysql database with all records encrypted using the php-encryption library. This works well for our current setup. We now got a new business ...
15
votes
1answer
21k views

Security for REST api (user/pass auth vs hmac vs oauth)

I have two servers (one on Hetzner (I am calling it H) and other in my office (calling it O) ). I need to run a basic CRUD web service on O and the only consumer of the service is H. Data on O is ...
13
votes
1answer
6k views

Shared secret when using JWT with an HMAC for authentication

I'm currently implementing user authentication on a REST-like API that is used by an Android client. After some research I think that JWT (JSON Web Token) is a good way to do it. The basic procedure ...
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 ...
12
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4answers
15k 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 ...
12
votes
1answer
6k views

Using RSA-SHA as/instead HMAC in OpenVPN?

While reading the manual of OpenVPN 2.3, I came across the --auth alg option. The manual says: Authenticate packets with HMAC using message digest algorithm alg. (The default is SHA1 ). HMAC is a ...
12
votes
1answer
3k views

HMAC needed with SSL/AccessToken in place?

Is using an HMAC in web service messages overkill if you are already using SSL and Access Tokens? I’m thinking of further ways to secure a service, and HMAC message signing is one. But it comes with ...
11
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3answers
3k views

HMAC Based Request Signing - Storing the Salt

I'm working on a (non high security) project that currently isn't live but might go live at some point. We have a REST API (implemented using Restlet and Neo4j) running on a server and an Android ...
11
votes
3answers
3k views

API message verification without storing private key?

I'm in the process of implementing a public API for my web service. Security is a key concern as money is involved. It seems the current common practice for "authenticating" users in API requests is ...
10
votes
1answer
5k 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 ...
9
votes
4answers
507 views

Major industry password leaks using salted HMAC but without eg PBKDF2, scrypt

I'm trying to convince higher-ups on a project to use an iterative strengthening function to secure password-storage for a new system. The current proposal would store something like an HMAC of a ...
9
votes
1answer
9k views

HMAC solution for a rest API

I'm trying to learn some things about REST apis and one of the topics that I'm having some trouble is security. I'm using angularjs for web interface ans slim framework for the php api. I've read ...
8
votes
1answer
13k views

How is the HMAC key exchanged?

Just wondering about this. Does it need a PKI to work?
8
votes
2answers
3k 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 ...
8
votes
2answers
6k views

JWT: Choosing between HMAC and RSA

It is my understanding that HMAC is a symmetric signing algorithm (single secret key) whereas RSA is an asymmetric signing algorithm (private/public key pair). I am trying to choose between these 2 ...
8
votes
1answer
2k views

Why isn't Amazon using a NONCE for REST Authentication?

When you look at Amazons RESTAuthentication you can see that it doesn't use a nonce: Authorization = "AWS" + " " + AWSAccessKeyId + ":" + Signature; Signature = Base64( HMAC-SHA1( ...
8
votes
2answers
872 views

How the AWS signature works in depth

I'm trying to understand how the AWS signature 4 works. I read the docs and I found a Python example where a signature is computed. I also ran into this answer which explains HMAC a bit. I'm curious ...
8
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1answer
1k views

Sending Encrypted Messages with Hybrid RSA, AES and HMAC SHA-256

Is this a Secure strategy for sending a large Encrypted Message using Hybrid RSA 2048, AES 256 and authenticated with HMAC SHA-256: Given the Alice already has Bob's RSA Public Key, Alice: Generates ...
7
votes
2answers
3k views

HOTP with as HMAC hashing algoritme a hash from the SHA-2 family

I'm looking into using a OTP solution. HOTP is a OTP solution that is based on a HMAC with as hashing algorithm SHA-1. The standards defines it this way. But... SHA1 (as we know) has been a weakness. ...
7
votes
1answer
3k views

Is there a method to get plain-text from cipher-text in HMAC SHA-1, given that the key is known?

This is technically not even an attack. We have all the resources at hand, except for the original plain-text. We have the cipher-text (to be converted back to plain-text), as well as the key. The ...
7
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 ...
7
votes
1answer
261 views

Detect duplicates without exposing underlying data

We have a scenario where we need to prevent two users from using the same identifier. The identifier is sensitive (e.g. a social security number), so we do not want to store it in our DB. We just want ...
7
votes
3answers
2k views

Why would I use MAC over digital signature?

As far as I've read, there is no benefit of a MAC over a digital signature - except the fact that it is faster to generate and process. Is this true? Digital signatures (asymmetric encryption) seem ...
7
votes
2answers
852 views

HMAC with or without data encryption?

I'm in the process of developing a system that periodically transmits a small amount of data (16/18 bytes), where the only part that will change is a 4 byte counter that will increment for each ...
7
votes
1answer
3k views

Is Django's approach to password reset tokens secure?

I am implementing a password reset feature for a web application and am contemplating adopting an implementation similar to Django. In a nutshell, Django creates a token who is comprised of a ...
6
votes
2answers
4k views

HMAC and key size

I generated a keyed hash using HMAC-MD5 and HMAC-SHA256 for an arbitrary file with various keys of different lengths. Do we have to use a key with a fixed size in HMAC? If so, what is the key size? ...
6
votes
1answer
5k views

How vulnerable is IPSec HMAC-SHA1

There are a few references out there that say HMAC-SHA2 must be used over HMAC-SHA1. If I am using an IPsec link with HMAC-SHA1, how vulnerable is it to being intercepted and cracked?
6
votes
1answer
393 views

Is this vault-less password manager/generator design safe?

Counter The counter is appended to the site name and incremented if you need to get a new password for a site or if the generated password is insecure because it randomly matches something like "...
6
votes
1answer
1k 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 ...
6
votes
2answers
3k views

Determining strength of truncated HMAC

I have data stored on a device which I must guarantee integrity, for ease of explanation the data is like numerical field representing 'credit balance available'. The device only ever interacts with ...
6
votes
1answer
248 views

4 bytes authentication problem

I have a classic security problem where Alice needs to prove its identity to Bob but with quite unusual requirements and constraints due to a M2M context. EDITs in bold The communication channel ...
6
votes
1answer
560 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 ...
6
votes
2answers
296 views

Securing a JavaScript app with RESTful backend

I went through the question Securing a JavaScript Single Page App with RESTful backend that has discussions / options around securing a Javascript client side app that invokes RESTful APIs. However, ...
6
votes
1answer
2k views

Unusual design aspects of AWS HMAC-based authentication, v4

I am designing a RESTful API in python. I want to use HMAC authentication. I could not find any suitable HMAC libraries, so I am rolling my own. However I want to use a well-known standard such as AWS ...
6
votes
1answer
2k views

How the HMAC secret key is exchanged?

I stumbled upon a code where the secret key for HMAC has been hard coded into C# client and server code. I've watched 5 videos about HMAC and many articles and none of them doesn't specify how the ...
5
votes
1answer
6k views

NIST test vectors for HMAC-SHA-256

I'm working on an implementation of HMAC-SHA-256 in classic ASP (legacy code). I currently have it working, and the resulting values are correct compared to some test cases I came up with along with ...
5
votes
1answer
2k views

Why aren’t collisions important with HMAC?

SHA-1 is broken because collisions can be found in substantially fewer hash operations than naive brute-force would suggest. HMAC-SHA1 is fine, however, because for HMAC “collisions aren’t important.” ...

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