Why hmac

Ajay Ohri 11 Feb They are used for verification while activating or creating the account They are also used while resetting the password for sending the one time hyperlink that is often used like OTP.

It can convert messages of any size into messages of fixed length 3 Working of HMAC Working here basically involves providing the requestor and involved server with the private key which is only in the knowledge of them. In Brief, they can be said as, Select K.

Append S2 with output of step 5. Apply SHA on step 7 to output n-bit hash code. From S1 to Pm each block is in b bits.

And M here is the number of blocks of plain text. The resultant thus is a hash code of n-bit. It is because of the hash functions used, which are quick both in terms of calculation as well as verification.

If I don't know the key then why would i trust that party? Sign up to join this community. The best answers are voted up and rise to the top. Stack Overflow for Teams — Collaborate and share knowledge with a private group.

Create a free Team What is Teams? Learn more. Ask Question. Asked 9 years, 2 months ago. Active 3 months ago. Viewed k times. Why is the key part of the hash?

Even if someone successfully used a "length-extension attack", how would that be useful to the attacker? Improve this question.

If anyone is curious what i wanted to know was hmac is a way to sign data using a symmetrical key. A friend of mine runs one of the largest "crypto currency" exchanges in the world.

His API requires HMAC signing of all api calls with the users Private api key it would be the "secret" you refer to in your question , which includes the public key in the hash.

This is the basic use case, as an additional layer of security for API calls. In the cryptocurrency world, his is the only platform yet to be hacked, despite millions of attempts. HMAC is useful, just make sure you know how to use it. Add a comment.

Active Oldest Votes. Improve this answer. Community Bot 1. Can the hmac code be shared? It seems confusing to me - It is a hash but can't be shared. R11G I don't understand your question. The fact that it's based on a hash is an implementation detail. Gilles Sorry. You can't go back from the HMAC to the input without the key. Even with the key, you can only go back by guessing the input and checking it. However, if you see the same HMAC twice, you know it has to be the same input with the same key.

Show 3 more comments. Because this is a very basic example of how JWT's work, it skips over some implementation details. However, if you want to learn more about the specifics, take a look at the explanation on jwt. If you feel that I missed anything important, or have any questions, feel free to contact me on twitter!

The Cosmos HackAtom is here! Get feral when you answer to the greatest interview in history Share your philosophy. An HMAC uses two rounds of hashing instead of one or none Each round of hashing uses a section of the secret key. How to Push an Empty Commit with Git by kodewithchirag. Recently I have been doing quite a bit of research and hacking in and around server APIs.

Authentication for these type APIs really depends on the type of service, and falls into a couple of general categories:. For infrastructure APIs I have had a look at a few options, these are explained in some detail below. This is the simplest to implement and for some implementations can work well, however it requires transport level encryption as the user name and password are presented with ever request.

For more information on this see Wikipedia Article. This is actually quite a bit closer to HMAC than basic, it uses md5 to hash the authentication attributes in a way which makes it much more difficult to intercept and compromise the username and password attributes.

Note I recommend reading over the Wikipedia page on the subject, in short it is more than secure than basic auth, however it is entirely dependent on how many of the safeguards are implemented in the client software and the complexity of the password is a factor.