CODEWITHSUNDEEP
encryptiondes
nikky
nikky

Reputation: 1985

What is DES-X?

What is DES-X?

And

DES-X and DES, are they backwards compatible?

Upvotes: 0

Views: 2714

Answers (4)

wadesworld
wadesworld

Reputation: 13763

The summary of this paper says that DES-X is "compatible." However, I'm not sure if that includes backwards-compatibility.

http://www.cs.ucdavis.edu/~rogaway/papers/cryptobytes.ps

Upvotes: 0

Mike Dinescu
Mike Dinescu

Reputation: 55750

Well, DES-X is a variant of the DES block cipher (as I'm sure you already knew).

The reason for the introduction of the DES-X was an attempt to increase the security of the original DES algorithm (which was limited to a 56bit key). The proposed solution with DEX-X was to use two more 64-bit keys which would be applied to make it harder for an attacker to guess the key of the DES algorithm. Basically, the first additional key is XORed to the plain text which is then encrypted with DES. The second additional key is XORed to the resulting cypher.

However, as far the backwards compatibility.. I'm not sure what you mean by that? If you're asking if you can use DES to decrypt DES-X messages then NO (it the strict sense). If you're asking whether a DES-X implementation could be configured to encrypt/decrypt DES messages then the answer is YES.

Here's an example:

    DES(msg) = CYPHER
    DES-X(msg) = K2 X DES(K1 x msg) = CYPER-X

If you choose K2 and K1 to be the all 0 then:

    DES-x(msg) = K2 x DES(K1 x msg) [where K1 = 0, K2 =0] = DES(msg)

It should be pointed out that what I mean by making K1 and K2 0 is actually choosing a key which is 64 bits of 0 = {0,0,0,0,0...0} (64 times). Such a key does not modify the plaintext of the cypher at all when the XOR operation is applied.

Upvotes: 5

Paul Sonier
Paul Sonier

Reputation: 39510

Here's the wikipedia article on DES-X. DES-X increases the key size by appending XOR'd versions of the key before and after the encryption.

Upvotes: 0

mas
mas

Reputation: 1117

DES and DES-X are both block ciphers. See http://en.wikipedia.org/wiki/DES-X for more details. In short, DES-X adds key whitening.

Upvotes: 0

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