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T-DES v.s. 3DES

Triple DES (T-DES)

Triple DES, just like standard DES, comes in various flavors: ECB, CBC, etc.

True Triple DES uses a 168-bit key, 3 times the length of a single-DES 56-bit key. As Triple DES requires new encryption hardware (older DES hardware cannot be used) and or software, and is quite a bit slower than 56-bit DES (especially for software), several new forms of Triple DES have come about to shrink the encryption/decryption time and allow current DES devices to be used as follows:

TDES-EDE & 3DES-EDE

This EDE form of Triple DES comes in two flavors also.

Unknown to many people, T-DES and 3-DES are two completely different forms of DES. I don't know if you can really call them Triple DES or not.

Many people mistake Triple DES (abbreviated TDES) and (TDES-EDE) as one in the same too, but THEY ARE NOT!!!

Triple DES, as mentioned above uses a single 168-bit DES key.

T-DES-EDE or TDES-EDE3 uses three single 56-bit keys which total 168 bits, but they are not one single key. They are in fact, three separate DES-56 bit keys (instead of a single 168-bit key) and they are used as follows:

  1. The 1st 56-bit Key is used to Encrypt data.

  2. The 2nd 56-bit Key is used to Decrypt the data encrypted with the 1st Key.

  3. The 3rd 56-bit Key is then used to re-Encrypt the Decrypted data.

    Also, T-DES-EDE (when compared to 56-bit DES) isn't 3 times as slow when encrypting/decrypting, but is more like 2.5 times slower.

3-DES-EDE or TDES-EDE2 on the other hand, uses only two single 56-bit keys and doesn't total 168-bits but rather 112-bits if you add them together, but you can't really add them like that. They are in fact, two separate DES-56 bit keys used in EDE form with one key used twice (instead of a single 168-bit key) and are used as follows:

  1. The 1st 56-bit Key is used to Encrypt data.

  2. The 2nd 56-bit Key is used to Decrypt the data encrypted with the 1st Key.

  3. The 1st 56-bit Key is then re-used to re-Encrypt the Decrypted data.

    Common sense will tell you that 3DES is weaker than TDES and you better believe it, because if you know or can find the first key, then you also know the 3rd key!

Both TDES-EDE and 3DES-EDE appeared only after Triple DES was conceived and neither have been proven to be stronger or weaker than the 168-bit Key version. As they are both (as of yet) unproven, we CANNOT consider them SAFE! We PRESUME them to be, but until we can PROVE them to be SAFE, we must assume that they are not!

So where does this leave us with Triple DES?

Triple DES is a supposedly stronger than the proven DES encryption method, all of Triple DES's (168-bit Key) weak keys have yet to be found. TDES-EDE and 3DES-EDE (as they use 56-bit keys) have their weak keys known and published, but they haven't been proven to be safer than Triple DES (168-bit Key) or even DES (56-bit Key) either!!!

Triple DES (168-bit) and TDES-EDE & 3DES-EDE may be stronger than DES-ECB which the DES Cracker was able to crack, but does that make them stronger than the 56-bit DES-CBC (with IV) which Financial Organizations and Governments have been clinging to so dearly?

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