Gutmans_ch05 Page 122 Thursday, September 23, 2004 2:41 PM in .NET Insert barcode code39 in .NET Gutmans_ch05 Page 122 Thursday, September 23, 2004 2:41 PM

How to generate, print barcode using .NET, Java sdk library control with example project source code free download:
Gutmans_ch05 Page 122 Thursday, September 23, 2004 2:41 PM using barcode implement for none control to generate, create none image in none applications. Console application How to Write a Web Application with PHP Chap. 5 /* apply functions to the variables, you can use the standard PHP * functions none none , but also use your own for added flexibility. */ if (isset($sig["function"])) { $tmp[$name] = {$sig["function"]}($tmp[$name]); } } $vars = $tmp; } $sigs = array( "prod_id" => array("required" => true, "type" => "int"), "desc" => array("required" => true, "type" => "string", "function" => "addslashes") ); sanitize_vars(&$_GET, $sigs, "http:// {$_SERVER["SERVER_NAME"]}/error.php cause=vars"); >.

5.5.2 HMAC Veri cation If you need to prevent bad guys from tampering with variables passed in the URL (such as for a redirect as shown previously, or for links that pass special parameters to the linked script), you can use a hash, as shown in the following script:.

< php fu none none nction create_parameters($array) { $data = ""; $ret = array(); /* For each variable in the array we a string containing * "$key=$value" to an array and concatenate * $key and $value to the $data string. */ foreach ($array as $key => $value) { $data .= $key .

$value; $ret[] = "$key=$value"; } /* We also add the md5sum of the $data as element * to the $ret array. */ $hash = md5($data); $ret[] = "hash=$hash"; return join ("&", $ret); }. Gutmans_ch05 Page 123 Thursday, September 23, 2004 2:41 PM 5.5 Techniques to Make Scripts Safe echo "<a href="script.php ". create_parameters(array("cause" => "vars"))."">err!</a>"; > Running thi none for none s script echoes the following link:. <a href="script.php cause=vars&hash=8eee14fe10d3f612589cdef079c025f6"> err!</a> However, th none none is URL is still vulnerable. An attacker can modify both the variables and the hash. We must do something better.

We re not the rst ones with this problem, so there is an existing solution: HMAC (Keyed-Hashing for Message Authentication). The HMAC method is proven to be stronger cryptographically, and should be used instead of home-cooked validation algorithms. The HMAC algorithm uses a secret key in a two-step hashing of plain text (in our case, the string containing the key/value pairs) with the following steps: 1.

If the key length is smaller than 64 bytes (the block size that most hashing algorithms use), we pad the key to 64 bytes with \0s; if the key length is larger than 64, we rst use the hash function on the key and then pad it to 64 bytes with \0s. 2. We construct opad (the 64-byte key XORed with 0x5C) and ipad (the 64byte key XORed with 0x36).

3. We create the inner hash by running the hash function with the parameter ipad . plain text.

(Because we use an iterative hash function, like md5() or sha1(), we don t need to seed the hash function with our key and then run the seeded hash function over our plain text. Internally, the hash will do the same anyway, which is the reason we padded the key up to 64 bytes). 4.

We create the outer hash by running the hash function over opad . inner_result that is, using the result obtained in step 3. Here is the formula to calculate HMAC, which should help you understand the calculation:.

H(K XOR opa d, H(K XOR ipad, text)). With H. The ha sh function to use K. The key padded to 64 bytes with zeroes (0x0) opad.

The 64 bytes of 0x5Cs. Gutmans_ch05 Page 124 Thursday, September 23, 2004 2:41 PM How to Write a Web Application with PHP Chap. 5 ipad. The 64 bytes of 0x36s text. The plain text for which we are calculating the hash Great so mu none none ch for the boring theory. Now let s see how we can use it with a PEAR class that was developed to calculate the hashes..

5.5.3 PEAR: :Crypt_HMAC The Crypt_HMAC class implements the algorithm as described in RFC 2104 and can be installed with pear install crypt_hmac.

Let s look at it:. class Crypt none for none _HMAC { /** * Constructor * Pass method as first parameter * * @param string method - Hash function used for the calculation * @return void * @access public */ function Crypt_HMAC($key, $method = "md5") { if (!in_array($method, array("sha1", "md5"))) { die("Unsupported hash function "$method"."); } $this->_func = $method; /* Pad the key as the RFC wishes (step 1) */ if (strlen($key) > 64) { $key = pack("H32", $method($key)); } if (strlen($key) < 64) { $key = str_pad($key, 64, chr(0)); } /* Calculate the padded keys and save them (step 2 & 3) */ $this->_ipad = substr($key, 0, 64) ^ str_repeat(chr(0x36), 64); $this->_opad = substr($key, 0, 64) ^ str_repeat(chr(0x5C), 64); }. First, we m ake sure that the requested underlying hash function is actually supported (for now, only the built-in PHP functions md5() and sha1() are supported). Then, we create a key, according to steps 1 and 2, as previously.
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