obfuscate or encrypt some plain text data in PHP

Question

I need to obfuscate or encrypt some plain text data in my php 5.2 application.

I'd prefer a solution that would have input string and output string retain the same length.

This does not need to extremely strong, as there are numerous other layers of security in place. Strong would be good, but this will just keep programmers/dba/support people/etc from accidentally reading the text from within the database.

key considerations

• EDIT ADD I'd prefer a solution that would have input string and output string retain the same length.
• only string text will be obfuscated/encrypted for storage in a database
• the php application will need to obfuscate/encrypt the data before the database save and will need to un-obfuscate/dencrypt following the database read
• this is a modification to an existing application
• only some columns will need to be obfuscated/encrypted
• only some rows will need to be obfuscated/encrypted, based on a Type field
• there are only a few load/save points to handle
• max column size is already determined for some fields, but not for others, but I'd prefer a solution to work within the existing size of the restricted fields
• EDIT, ADD the key will be probably be a composite of some Primary key info +uneditable fields

here is a sample database table and data:

int           char(1) varchar(24)              int      date
MyPrimaryKey  RowType UserText                 UserNo   DateChange
------------  ------- ------------------------ -------- ----------------
1             N       nothing special here     43       6/20/2009 12:11am
2             N       same thing, wow!         78       6/23/2009 1:03pm
3             S       fBJKg}.jkjWfF78dlg@45kjg 43       6/25/2009 6:45am
4             N       same old, same old text  21       6/25/2009 8:11am

The application would load and display rows 1,2, and 4 normally. However it would conditionally (based on row type) handle the text in row 3 using this obfuscate/encrypt and un-obfuscate/decrypt logic.

Can anyone provide obfuscate/encrypt and un-obfuscate/decrypt functions code, links, and or pointer that would help here?

thanks!

EDIT
I like the simple base64 encoding idea, but is there a method that can keep the data within a fixed size. All methods listed so far have the output value larger than the input value. This will be a problem for some columns, where the user can enter in 50 characters and it is stored in a varchar(50) column.

Answer 1

for simple obfuscation use strtr() - Translate certain characters:
string strtr ( string $str , string $from , string $to )

to encode in php:

$readable='This is a special test string ABC123 ([+,-!#$%&*])';    
$unreadable=strtr($readable,' !"#$%&\'()*+,-./0123456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\]^_`abcdefghijklmnopqrstuvwxyz{|}~€‚ƒ„…†‡ˆ‰Š‹ŒŽ‘’“”•–—˜™š›œžŸ ¡¢£¤¥¦§¨©ª«¬­®¯°±²³´µ¶·¸¹º»¼½¾¿ÀÁÂÃÄÅÆÇÈÉÊËÌÍÎÏÐÑÒÓÔÕÖ×ØÙÚÛÜÝÞßàáâãäåæçèéêëìíîïðñòóôõö÷øùúûüýþÿ'
                           ,'¡¢£¤¥¦§¨©ª«¬­®¯°±²³´µ¶·¸¹º»¼½¾¿ÀÁÂÃÄÅÆÇÈÉÊËÌÍÎÏÐÑÒÓÔÕÖ×ØÙÚÛÜÝÞßàáâãäåæçèéêëìíîïðñòóôõö÷øùúûüýþÿ !"#$%&\'()*+,-./0123456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\]^_`abcdefghijklmnopqrstuvwxyz{|}~€‚ƒ„…†‡ˆ‰Š‹ŒŽ‘’“”•–—˜™š›œžŸ '
                      );
print $unreadable; //outputs: "ÕéêôAêôAâAôñæäêâíAõæôõAôõóêïèAÂÃIJ³´A©Ü¬­®¢¤¥¦§«Þª"

to decode in php:

$unreadable='ÕéêôAêôAâAôñæäêâíAõæôõAôõóêïèAÂÃIJ³´A©Ü¬­®¢¤¥¦§«Þª';
$readable=strtr($unreadable,'¡¢£¤¥¦§¨©ª«¬­®¯°±²³´µ¶·¸¹º»¼½¾¿ÀÁÂÃÄÅÆÇÈÉÊËÌÍÎÏÐÑÒÓÔÕÖ×ØÙÚÛÜÝÞßàáâãäåæçèéêëìíîïðñòóôõö÷øùúûüýþÿ !"#$%&\'()*+,-./0123456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\]^_`abcdefghijklmnopqrstuvwxyz{|}~€‚ƒ„…†‡ˆ‰Š‹ŒŽ‘’“”•–—˜™š›œžŸ '
                           ,' !"#$%&\'()*+,-./0123456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\]^_`abcdefghijklmnopqrstuvwxyz{|}~€‚ƒ„…†‡ˆ‰Š‹ŒŽ‘’“”•–—˜™š›œžŸ ¡¢£¤¥¦§¨©ª«¬­®¯°±²³´µ¶·¸¹º»¼½¾¿ÀÁÂÃÄÅÆÇÈÉÊËÌÍÎÏÐÑÒÓÔÕÖ×ØÙÚÛÜÝÞßàáâãäåæçèéêëìíîïðñòóôõö÷øùúûüýþÿ'

               );
print $readable; //outputs: "This is a special test string ABC123 ([+,-!#$%&*])"

you can easily replicate this logic in the DB if necessary (without looping): Using a Table of Numbers, by Erland Sommarskog