3DES-CBC questoins

[Andrew]

A coworked has brought up a question that I cant answer and I am hoping somewhere here could. With 3des you encrypt the data with the first key, decrypt with the second and encrypt with the 3rd to get the encryprted message. He xor'ed the plain text with the encrypted message and obtained a key. He then could use that key to decrypt any other message. Now I know that if you know the plain text than you can get the key but the point was how is 3des any stronger than des if you only need one key to decrypt the message. Also it appears the key he found was only 56-bits, or maybe this is a mistake. So I guess the question is, if you only need one key to decrypt a 3des encrypted message then how is it strong. Thanks!   - Andrew ActiveSol.net [EMAIL PROTECTED]