Is it possible to reverse a sha1?
I'm thinking about using a sha1 to create a simple lightweight system to authenticate a small embedded system that communicates over a unencrypted connection.
Let's say that I create a sha1 like this with input from a "secret key" and spice it with a timestamp so that the sha will change all the time.
sha1("My Secret Key"+"a timestamp")
Then I include this sha1 in the communication and the server, that can do the same calculation. And hopefully nobody would be able to figure out the "secret key".
But is this really true?
If you know that this is how I did it, you would know that I did put a timestamp in there and you would see the sha1.
Can you then use those two and figure out the "secret key"?
secret_key = bruteforce_sha1(sha1, timestamp)
I guess you could brute force in some way, but how much work would that actually be?
I don't plan to encrypt any data, I just would like to know who sent it.