work when press enter key in asp.net

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ASP.NET

I am create a web application. I am use three textbox and two buttons.
I one textbox and button for search and remain two textbox and button use for login.
but my problem is when user enter the login name and password then press enter key then work search button in place of loggin button.

so give any idea for when enter text in search text box and press enter key then work search button. and when enter the login name and password and press enter key then work login button.