Converting PHP function to C# -

i've finished converting php script c# 1 use in asp.net.

i've converted match the correct result far:-

function sign_url($url, $key, $secret) {     if (strpos($url,'?') !== false)     {         $url .= "&";     }     else     {         $url .= "?";     }     $url .= "applicationkey=" . $key;      $signature = hash_hmac("sha1", urldecode($url), $secret);     $url .= "&signature=" . hex_to_base64($signature);      return $url; } 

here part i'm struggling with:-

function hex_to_base64($hex){   $return = '';   foreach(str_split($hex, 2) $pair){     $return .= chr(hexdec($pair));   }   return base64_encode($return); } 

from can gather splits input string ($hex) sets of 2 characters.
converts these hexadecimal strings decimal numbers before getting chr() value of number.
storing these conversions in $return string.
base 64 conversion.

i'm struggling find best way in c#, particularly splitting 2 characters while doing other conversions.

old, good, c-style code not use linq , megabytes of other libraries:

static string hextobase64(string hex) {     byte[] buf = new byte[hex.length / 2];     (int = 0; < hex.length / 2; i++)     {         buf[i] = convert.tobyte(hex.substring(i*2,2), 16);     }     return convert.tobase64string(buf); }