Difference between @secure_password, secure_password

Hello,
I have a User object that extends ActiveRecord::Base.
And I have the following defined in it:

after_validation :crypt_password


def crypt_password

write_attribute(“secure_password”, User.encrypt(password))

self.secure_password = User.encrypt(password)

end

And this works. Where I am getting confused about is the difference
between the following:
secure_password,
@secure_password
self.secure_password

Because these versions of crypt_password method don’t work:
def crypt_password
secure_password = User.encrypt(password)
end

def crypt_password
@secure_password = User.encrypt(password)
end

When I debug the app by placing a breakpoint right after the assigment
operation
in crypt_password, and ask for values:
@secure_password returns ‘nil’
but
secure_password returns the encrypted password…

Which is very puzzling.
First of all, I thought @ was used for instance variables. So
@secure_password should be the one with the encrypted value assigned not
secure_password…

Let’s forget that…If secure_password contains the encrypted value as I
see on the console, why would secure_password = User.encrypt(password)
call not do what I expect it to do?

Obviously, I’m pretty confused about the usage of @ vs. non-@, self,
etc…

Thanks,
Cagan