PHP encryption and decryption function Authcode specific use of methods Analysis _php Tutorial

The specific sample code for the PHP cryptographic decryption function Authcode is as follows:

2. Parameter interpretation
4. $string: Clear Text or redaction
6. $operation: Decode means decryption, other means encryption
8. $key: Key
10. $expiry: Ciphertext validity
12. function Authcode ($string, $operation =
    ' DECODE ', $key = ' ', $expiry = 0) {
14. Dynamic key length, the same plaintext will generate different ciphertext is dependent on the dynamic key
16. $ Ckey_length = 4 ;
18. Secret key
20. $ Key = MD5 ($key $key: $GLOBALS [' Discuz_auth_key ']);
22. Key A will participate in encryption and decryption
24. $ Keya = MD5 (substr ($key, 0,));
26. Key B will be used for data integrity verification.
28. $ keyb = MD5 (substr ($key, +));
30. Key C is used to change the generated ciphertext
32. $ KEYC = $ckey _length? ($ Operation = = ' DECODE '
    ? substr ($string, 0, $ckey _length): substr (MD5
    (Microtime ()),-$ckey _length)): ";
34. PHP Cryptographic decryption function Authcode key to participate in the operation
36. $ Cryptkey = $keya. MD5 ($keya. $KEYC);
38. $ Key_length = strlen ($cryptkey);
40. PlainText, the first 10 bits are used to hold the timestamp, to verify the validity of the data when decrypting,
    10 to 26 bits are used to hold the $KEYB (key B), and the decryption will verify the integrity of the data through this key.
42. If it is decoded, it will start from the $ckey_length bit, because the $ckey_ before the ciphertext
    Length bit holds dynamic key to ensure decryption is correct
44. $ string = $ Operation = = ' DECODE '? Base64_decode (substr
    ($string, $ckey _length)) : sprintf ('%010d ', $expiry?
    $expiry + Time (): 0). substr (MD5 ($string. $keyb), 0, +). $string;
46. $ String_length = strlen ($string);
48. $ result = '' ;
50. $ Box = Range (0, 255);
52. $ Rndkey = Array ();
54. PHP Cryptographic decryption function Authcode generate key book
56. For ($i = 0; $i <= 255; $i + +) {
58. $rndkey [$i] = Ord ($cryptkey [$i% $key _length]);
60. }
62. Using a fixed algorithm to disrupt the key book, to increase randomness, seems very complex,
    Actually, it doesn't increase the intensity of the ciphertext.
64. For ($J = $i = 0; $i < $i + +) {
66. $ J = ($j + $box [$i] + $rndkey [$i])%;
68. $ tmp = $box [$i];
70. $box [$i] = $box [$j];
72. $box [$j] = $tmp;
74. }
76. PHP Cryptographic decryption function Authcode core plus decryption part
78. For ($a = $J = $i = 0; $i < $string _length; $i + +) {
80. $ a = ($a + 1)%;
82. $ J = ($j + $box [$a])%;
84. $ tmp = $box [$a];
86. $box [$a] = $box [$j];
88. $box [$j] = $tmp;
90. PHP Cryptographic decryption function Authcode The key from the key book to the XOR, and then into the character
92. $result . = CHR (Ord ($string [$i]) ^ (
    $box [($box [$a] + $box [$j]) (% 256]));
94. }
96. if ($operation = = ' DECODE ') {
98. substr ($result, 0, 10) = = 0 Verify data validity
100. //substr ($result, 0, Ten)-time () > 0 Verifying data validity
102. SUBSTR ($result, ten, +) = = substr (MD5 (substr
     ($result, +). $keyb), 0, 16) Verifying data integrity
104. To verify data validation, see the format of unencrypted plaintext
106. if ((substr ($result, 0, 10) = = 0 | |
     substr ($result, 0, Ten)-time () > 0) &&
     SUBSTR ($result, ten, +) = = SUBSTR (MD5
     (Substr ($result, +). $keyb), 0, 16)) {
108. Return substr ($result, 26);
110. } else {
112. Return ';
114. }
116. } else {
118. PHP Cryptographic decryption function authcode The dynamic key in the ciphertext, which is why the same plaintext,
     Reasons for decrypting after producing different ciphertext
120. Because encrypted ciphertext can be some special characters,
     The copy process may be lost, so it is encoded with base64
122. Return $KEYC. Str_replace (' = ', ',
     Base64_encode ($result));
124. }
126. }

The above code is the PHP cryptographic decryption function Authcode the specific use of the method, I hope you can through the content of this article to master the meaning of this function.

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