salt - Check HMAC-SHA1 without key in C# -

i generating hmac-sha1 without key in c# , returns every time different hash same value, how can match hashes,

my code https://dotnetfiddle.net/3a3tip

• is possible or not match these hashes?
• i think hmac-sha1 not possible without key right?
• if above 'yes' why c# allow generate without key , how doing?

yes, because using parameterless constructor build hmacsha1 instance, , msdn says

hmacsha1() - initializes new instance of hmacsha1 class randomly generated key.

just add constant key , you'll same hash every time. e.g.

var hmacsha = new hmacsha1(encoding.utf8.getbytes("yourconstantkey")); 

and answering questions:

1. yes, use same key 2 generations.
2. yes.
3. it generates random key you