A Reversible Encryption Routine for PHP
By Tony Marston2005-04-15
Manipulating the index number between the two strings
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This involves an additional step in between converting a character into an index number using STRING1 and converting that index number into a character from STRING2. This additional step adjusts the index number at runtime according to some fixed rules. The rules must be fixed so that the same source string will always result in the same target string, otherwise it will not be possible to verify a password with one that is held on file. This method means that if the same character appears in the input string more than once that it will not generate the same corresponding character in the output string, thus making the hacker's job that much more difficult.
A common method is to use a separate character string as a 'key'. This key is reduced to an array of numbers, and it is this array of numbers that is used to adjust the index number between STRING1 and STRING2. The method I use is to take the first number from the array, add it to the index number, then move this number from the beginning to the end of the array in a rotation movement.
The beauty of this method is that even if you know the exact encryption algorithm being used it is totally useless without the key.
Tutorial Pages:
» A Reversible Encryption Routine for PHP
» Rotating each character a fixed number of positions
» Swapping between two different character strings
» Manipulating the index number between the two strings
» Customising the Encryption Algorithm
» Class Variables
» Class Constructor
» The ConvertKey function
» The ApplyFudgeFactor function
» The CheckRange Function
» The Decrypt function
» Using the Encryption Class
» Summary
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