Forum

The glossary of the CWSP study guide(page 486) says 3DES uses 2 secret keys, but the topic page in the book (page 222) says 3DES uses 3 keys altogether. It also says if any TWO keys of the 3 keys were same, it works back to same as normal DES.

I wanted to know just how many keys does 3DES uses for its encryption.

Could someone please help?

SMITH

3DES does use *three* keys. I think the way the text is written in the glossary might be referring to DES and how 3DES is an improvement upon DES. A bit confusing I agree.

Hi Smith of Toronto:

3DES uses either two or three keys, but never the same key with any two adjacent iterations.

DES-EEE3: 3 DES encryptions with 3 different keys
DES-EDE3: 3 DES operations, encrypt-decrypt-encrypt, with 3 different keys
DES-EEE2: same as EEE3 except first and third operations use same key
DES-EDE2: same as EDE3 except first and third operations use same key

I hope this helps. Thanks. /criss

NIST suggests the use of AES anyways (as a replacement for 3DES) ;)

However, going back to 3DES, there still are 3 keys. Its just depends on what key combinations you end up using. All 3 keys can be the same (don't know why you would want to do that though).

More information in RFC1851

It is incurrect to say that all three keys can be same. In fact, only two keys can be same or all three are different. What Chris said is correct?

3DES uses 48 rounds of computation where as, DES only used 16 rounds of computation.

AES is a replacement of DES as it can be broken. Just to give you an idea AES is 2^56 (2 to the power 56) times stronger than DES.

AES is a block cipher algorithem (similar to DES)but uses 128, 192, or 256 bit block sizes. The key sizes can also be 128, 192, or 256. And AES can be used using any of the nine combinations.

Hope this helps.

Kamran

Thanks for all of you. Yes, now I got an understanding of how 3DES works and also can compare with other techniques like AES, etc.

SMITH