ThomasReggi ThomasReggi - 1 year ago 175
Node.js Question

How can I decrypt a HMAC?

I can make an HMAC using the following:

var encrypt = crypto.createHmac("SHA256", secret).update(string).digest('base64');


I am trying to decrypt an encoded HMAC with the secret:

var decrypt = crypto.createDecipher("SHA256", secret).update(string).final("ascii");


The following was unsuccessful. How can I decrypt a HMAC with the key?

I get the following error:

node-crypto : Unknown cipher SHA256

crypto.js:155
return (new Decipher).init(cipher, password);
^
Error: DecipherInit error

Answer Source

HMAC is a MAC/keyed hash, not a cipher. It's not designed to be decrypted. If you want to encrypt something, use a cipher, like AES, preferably in an authenticated mode like AES-GCM.

The only way to "decrypt" is guessing the whole input and then comparing the output.

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