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Home Backend Development PHP Tutorial 求一个可逆的加密算法,要求有点高

求一个可逆的加密算法,要求有点高

Jun 23, 2016 pm 02:17 PM

要求:
1.加密后的长度和加密前的长度一样长
2.加密后的字符串中只允许出现a到z中的字母和0到9的数字
3.根据秘钥可以再算回来
加密前的字符串也都是字母和数字的组合
如加密前的字符串:us3kqvu


回复讨论(解决方案)

你可以试试凯撒加密和栅栏加密,或者将两种方法都用进去

凯撒密码

$key = '3ae';$s = caesar_encode('us3kqvu', $key);echo "$s\n";echo caesar_decode($s, $key);function caesar_encode($s, $k) {  $k = "$k";  for($i=0; $i<strlen($k); $i++) {    $d = base_convert($k{$i}, 36, 10);    $t = '';    for($j=0; $j<strlen($s); $j++)      $t .= base_convert((base_convert($s{$j}, 36, 10)+$d)%36, 10, 36);    $s = $t;  }  return $t;}function caesar_decode($s, $k) {  $k = "$k";  for($i=0; $i<strlen($k); $i++) {    $d = 36 - base_convert($k{$i}, 36, 10);    $t = '';    for($j=0; $j<strlen($s); $j++)      $t .= base_convert((base_convert($s{$j}, 36, 10)+$d)%36, 10, 36);    $s = $t;  }  return $t;}
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密文:ljubhml
原文:us3kqvu

凯撒密码

$key = '3ae';$s = caesar_encode('us3kqvu', $key);echo "$s\n";echo caesar_decode($s, $key);function caesar_encode($s, $k) {  $k = "$k";  for($i=0; $i<strlen($k); $i++) {    $d = base_convert($k{$i}, 36, 10);    $t = '';    for($j=0; $j<strlen($s); $j++)      $t .= base_convert((base_convert($s{$j}, 36, 10)+$d)%36, 10, 36);    $s = $t;  }  return $t;}function caesar_decode($s, $k) {  $k = "$k";  for($i=0; $i<strlen($k); $i++) {    $d = 36 - base_convert($k{$i}, 36, 10);    $t = '';    for($j=0; $j<strlen($s); $j++)      $t .= base_convert((base_convert($s{$j}, 36, 10)+$d)%36, 10, 36);    $s = $t;  }  return $t;}
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密文:ljubhml
原文:us3kqvu
这种加密解密方式 存在重复性的概率大吗

凯撒密码 通过移动字符表映射来实现的,理论上不存在重复的可能性

所谓 移动字符表映射 就是例如
原文 abcd
移动距离 4
密文 efgh

一个字节有8位(bit),6位则有2^6=64种可能,字母+数字合计62个
所以有个映射表就能压缩到6位内

6位转6位的位运算就多的是了,任君选择,再反向映射为字母数字

上面的过程都是可逆的

凯撒加密和栅栏加密

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