Decrypt a HMACSHA1 encrypted password?

[mattgcon]

Here is my question. I am encrypting user login passwords using HMACSHA1 and I would like to know how to decrypt the passwords for displaying to managers and when emailing the password to the user if they forget. Here is the code to encrypt but does anyone know how to decrypt using HMACSHA1?

byte[] byteKey = Encoding.UTF8.GetBytes(strEncrKey);
string regitPWD = this.txtEncrypRaw.Text;
HMACSHA1 hmac = new HMACSHA1(byteKey);
 
byte[] bytePWD = Encoding.UTF8.GetBytes(regitPWD);
byte[] byteHash = hmac.ComputeHash(bytePWD);
this.txtEncrypted.Text = Convert.ToBase64String(byteHash);

Thank you in advance

Matthew

[tlhintoq]

TIP: When you are writing your question, there is a button on the tool bar that wraps the [code] tags around your copy/pasted code. It helps a bunch. Its the button with a '#' on it. More on tags. They're cool. Check'em out.