Reference sites like: http://phpjs.org/ and http://www.php2python.com/wiki/function.iconv/ show mappings from PHP to js or python commonly used functions and vice versa. Is there any reference that maps from PHP to Go. Or are a reference to existing libraries where i can find common functions like:
base64_encode/decode
json_encode/decode
etc...
Ummm PHP has a lot of functions. Your only real solution to this is to browse the stdlib at http://golang.org/pkg/ and look for packages that let you do the tasks you are looking for.
The two encoding/decoding functions you listed can be found in http://golang.org/pkg/encoding/json and http://golang.org/pkg/encoding/base64 along with a whole bunch of other encoding packages.
Crypto packages are in the http://golang.org/pkg/crypto/ sections and so on and so forth.