I just want to know how to decode this string I'm getting from web page: I4fTj5k9pw9RPr0Rh3BNHTkjCWMPLRcH4iR2bSTSigBnniVyVcYHkNtLw1q2rZvwxNFV0d8tMcgrE1doD4CD+nzfdQNacY/O0WvU0iz3BHQY7hVoiPTd5lbE6mo+leF0Owy/Gp2XWXpcYiW This is not encoded using encode64 php function. Also it's a govt site, so I'm sure very simple logic is used to encode it. This is a partial string. Full string is very long. It's present in the page: http://www.indiapost.gov.in/pin/pinsearch.aspx When this page loads: 1) click on District 2) Select a district from the combo box and press Search button Open the page source of the resulting window. I want to know what's there in the values of the form variables: __VIEWSTATE & __EVENTVALIDATION I suspect some php library function has been used to encrypt the data.