Use HMAC SHA1 signature method to explain in detail

Encryption algorithm:
Use the ES1en-SHA1 signature method

    /**
     * @brief  use HMAC-SHA1 Algorithm to generate oauth_signature The signature value 
     *
     * @param $key   The key 
     * @param $str   The source string 
     *
     * @return  The signature value 
     */
    function getSignature($str, $key) {
        $signature = "";
        if (function_exists('hash_hmac')) {
            $signature = base64_encode(hash_hmac("sha1", $str, $key, true));
        } else {
            $blocksize = 64;
            $hashfunc = 'sha1';
            if (strlen($key) > $blocksize) {
                $key = pack('H*', $hashfunc($key));
            }
            $key = str_pad($key, $blocksize, chr(0x00));
            $ipad = str_repeat(chr(0x36), $blocksize);
            $opad = str_repeat(chr(0x5c), $blocksize);
            $hmac = pack(
                    'H*', $hashfunc(
                            ($key ^ $opad) . pack(
                                    'H*', $hashfunc(
                                            ($key ^ $ipad) . $str
                                    )
                            )
                    )
            );
            $signature = base64_encode($hmac);
        }
        return $signature;
    }