Usage of the php encryption and decryption function authcode _ php instance

The authcode function can be said to have made significant contributions to the PHP field in China. Including kangsheng's own products, and most Chinese companies that use PHP use this function for encryption. authcode is the core tip for encryption and decryption using exclusive or operations: KANG Sheng's authcode function can be said to have made significant contributions to the Chinese PHP community. Including kangsheng's own products, and most Chinese companies that use PHP use this function for encryption. authcode uses exclusive or operations for encryption and decryption.

KANG Sheng's authcode function can be said to have made significant contributions to the Chinese PHP community. Including kangsheng's own products, and most Chinese companies that use PHP use this function for encryption. authcode uses exclusive or operations for encryption and decryption.

The principle is as follows:

Encryption

Plaintext: 1010 1001

Key: 1110 0011

Ciphertext: 0100 1010

The ciphertext 0100 1010 is obtained, and the decryption must be different from the key or lower.

Decryption

Ciphertext: 0100 1010

Key: 1110 0011

Plaintext: 1010 1001

There is no advanced algorithm, and the key is very important. The key is how to generate the key.

Let's take a look at how kangsheng's authcode works.

// Parameter description // $ string: plaintext or ciphertext // $ operation: DECODE indicates decryption, and others indicate encryption // $ key: key // $ expiry: ciphertext Validity Period function authcode ($ string, $ operation = 'decode', $ key = '', $ expiry = 0) {// dynamic key length, the same plaintext will generate different Ciphertext Based on the dynamic key $ ckey_length = 4; // key $ key = md5 ($ key? $ Key: $ GLOBALS ['discuz _ auth_key ']); // key a participates in encryption and decryption $ keya = md5 (substr ($ key, 0, 16 )); // key B is used for data integrity verification $ keyb = md5 (substr ($ key, 16, 16 )); // key c is used to change the generated ciphertext $ keyc = $ ckey_length? ($ Operation = 'decode '? Substr ($ string, 0, $ ckey_length): substr (md5 (microtime (),-$ ckey_length )):''; // calculate the key $ cryptkey = $ keya. md5 ($ keya. $ keyc); $ key_length = strlen ($ cryptkey); // plaintext. The first 10 digits are used to save the timestamp. Data Validity is verified during decryption, 10 to 26 bits are used to save $ keyb (Key B). During decryption, the key will be used to verify data integrity. // if the key is decoded, it will start from the $ ckey_length bit, because the $ ckey_length bit before the ciphertext stores the dynamic key to ensure correct decryption $ string = $ operation = 'decode '? Base64_decode (substr ($ string, $ ckey_length): sprintf ('% 010d', $ expiry? $ Expiry + time (): 0 ). substr (md5 ($ string. $ keyb), 0, 16 ). $ string; $ string_length = strlen ($ string); $ result = ''; $ box = range (0,255); $ rndkey = array (); // generate a key book for ($ I = 0; $ I <= 255; $ I ++) {$ rndkey [$ I] = ord ($ cryptkey [$ I % $ key_length]);} // use a fixed algorithm to disrupt the key book and increase randomness. It seems complicated, in fact, the ciphertext strength is not added. for ($ j = $ I = 0; $ I <256; $ I ++) {$ j = ($ j + $ box [$ I] + $ rndkey [$ I]) % 256; $ tmp = $ box [$ I]; $ box [$ I] = $ box [$ j]; $ box [$ j] = $ tmp ;} // core encryption and decryption part for ($ a = $ j = $ I = 0; $ I <$ string_length; $ I ++) {$ a = ($ a + 1) % 256; $ j = ($ j + $ box [$ a]) % 256; $ tmp = $ box [$ a]; $ box [$ a] = $ box [$ j]; $ box [$ j] = $ tmp; // The keys obtained from the key book are different or, then convert it into a character $ result. = chr (ord ($ string [$ I]) ^ ($ box [($ box [$ a] + $ box [$ j]) % 256]);} if ($ operation = 'decode') {// substr ($ result, 0, 10) = 0 verify the data validity // substr ($ result, 0, 10) -time ()> 0 verify Data Validity // substr ($ result, 10, 16) = substr (md5 (substr ($ result, 26 ). $ keyb), 0, 16) verify data integrity // verify data validity. Please refer to the unencrypted plaintext format if (substr ($ result, 0, 10) = 0 | substr ($ result, 0, 10)-time ()> 0) & substr ($ result, 10, 16) = substr (md5 (substr ($ result, 26 ). $ keyb), 0, 16) {return substr ($ result, 26) ;}else {return '';}} else {// Save the dynamic key in the ciphertext, this is also the reason why different ciphertext texts can be decrypted in the same plain text. // because the encrypted ciphertext may be special characters, the replication process may be lost, therefore, return $ keyc is encoded in base64 format. str_replace ('=', '', base64_encode ($ result ));}}