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How to write a HMAC SHA1 code to compare the check sum generated by a PHP code and JSP code
// Adjust key to exactly 64 bytes
    if (strlen($key) > 64) {
        $key = str_pad(sha1($key, true), 64, chr(0));
    }
    if (strlen($key) < 64) {
        $key = str_pad($key, 64, chr(0));
    }

    // Outter and Inner pad
    $opad = str_repeat(chr(0x5C), 64);
    $ipad = str_repeat(chr(0x36), 64);

    // Xor key with opad & ipad
    for ($i = 0; $i < strlen($key); $i++) {
        $opad[$i] = $opad[$i] ^ $key[$i];
        $ipad[$i] = $ipad[$i] ^ $key[$i];
    }

    return sha1($opad . sha1($ipad . $data, true));
}