Convert a Java function to PHP

rewrite the following Java code in PHP: public static String createSign(String param) throws Exception { StringBuffer result = new StringBuffer(); MessageDigest md5 = [login to view URL]("MD5"); [login to view URL]([login to view URL]("UTF-8")); byte[] b = [login to view URL](); for(int i=0;i< [login to view URL];++i) { int x = b[i]&0xFF; int h = x>>>4; int l = x&0x0F; [login to view URL]((char)(h+((h<10)?'0':'a'-10))); [login to view URL]((char)(l+((l<10)?'0':'a'-10))); } return [login to view URL]().substring(8, 24); }