Timeline for Why triple DES used in EDE mode?
Current License: CC BY-SA 2.5
9 events
| when toggle format | what | by | license | comment | |
|---|---|---|---|---|---|
| Apr 2, 2011 at 13:24 | comment | added | Bruno Rohée | I'd like to add this is mostly useful to save silicon in hardware implementation, in software there is no good reasons for one to use 3DES to do DES, save a love for global warming. | |
| Jan 30, 2011 at 19:30 | comment | added | D.W. | @AviD, OK, let's try explaining it this way. We use EDE instead of EEE for historical reasons. The historical reasons are as PulpSpy explained: for backwards compatibility with single DES (something that was important at the time 3DES was standardized, but is no longer important now). Regarding the 2 vs 3 different keys part of your comments, I don't understand what's being asked. | |
| Jan 30, 2011 at 8:03 | comment | added | AviD♦ | @D.W., the OP asked, "Why do we use EDE?". Since single-key mode is not relevant, "Why do we use EDE with 2 or 3 different keys?" is the implied question here. Why do you say its not what was asked? | |
| Jan 30, 2011 at 5:33 | comment | added | D.W. | @AviD, It doesn't explain those things, because that's not what the original poster asked. | |
| Jan 27, 2011 at 8:03 | comment | added | AviD♦ | @D.W. right, thats what I said in my comment (sorry, was that not clear...?) Using the same identical K for all keyparts will allow you to "recreate" DES, thus providing for backwards compatibility... But that doesn't explain either why to use EDE with 2 or 3 different keys. Especially since K1=K2=K3 is not recommended, supported, or secure. | |
| Jan 27, 2011 at 6:15 | comment | added | D.W. | I just want to emphasize that PulpSpy's answer is right: the only reason is for backwards compatibility. @AviD's 2nd comment is confused about what is meant by backwards compatibility. Backwards compatibility means that if you have a hardware implementation of 3-key 3DES (which accepts a message M and keys K1,K2,K3), you can use it to implement single-DES as follows: to single-DES-encrypt M under DES key K, set K1=K, K2=K, K3=K, and send M,K1,K2,K3 to your hardware 3DES encryptor. (As PulpSpy correctly points out, K1,K2 can be arbitrary so long as K1=K2 and K3=K.) | |
| Jan 26, 2011 at 7:15 | comment | added | AviD♦ | Backwards compatibility only applies where the same keypart (56 bits) is used for all 3 operations (which anyway has long been unrecommended). | |
| Jan 25, 2011 at 22:26 | comment | added | AviD♦ | Just one note, the first two operations will only cancel out if it is the same key - but EDE also allows for the 3 keyparts to be different... | |
| Jan 25, 2011 at 14:52 | history | answered | PulpSpy | CC BY-SA 2.5 |