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5

Same as the reason of why not switching to AES (or any other 80+ key bits algorithms available at the time). Because we want to reuse whatever "hardware" (chip design) resources available to do the blockcipher calculation, and re-designing the key schedule would prevent us from doing so since the existing hardware cannot compute the new key schedule.


2

Is the following build stronger than 2DES or 3DES with 2 different keys (or even normal DES)? $DES(DES(x,k),\overline{k})$ It is only slightly stronger than DES; it is considerably easier to attack than 2DES or 3DES. The most practical attack against DES is brute force; simply try the various possible keys until you stumble on the correct one. With a known ...


2

DES key schedule takes the 64-bit key and PC-1 (Permuted Choice 1) discards the parity check bits and applies a permutation to the remaining. Then for the rest they key bits are divided into 28-bit halves and for the each round They are rotated left one or two specified for each round. Then 48-bit bits are selected by PC-2 (Permuted Choice 2) which is ...


1

I solved the problem. So for people who are hunting for the answer, you need to consider what mechs your HSM supports. Every logic I had in the code was correct. The only problem was the mechanism that I used to derive the key was wrong. There are several mechs that are available to derive the key with, which was the hard part to figure out since it did not ...


1

The DES round keys are just certain secret key bits (48 of them for each round). Say $K_1,\ldots,K_{16}$ are the 48 bit round keys with $K_i$ the $i^{th}$ round subkey. Then, the EDE triple DES uses round keys in the following order $$K^{(1)}_1,K^{(1)}_2,\ldots,K^{(1)}_{16}$$ which are the subkeys of the first (E) followed by (D) $$K^{(2)}_{16},K^{(2)}_{...


1

Just changing the key schedule would improve the security of DES only moderately (at least in the model where high data complexity below exhausting the codebook does not render an attack impractical). For instance, chapter 4.6 of the book Differential Cryptanalysis of the Data Encryption Standard by Biham and Shamir describes an attack on DES with ...


1

The confidence that we have in the security of DES comes from years (decades) of cryptanalytic attempts and research. Any internal change would mean that we would have to re-analyze everything from scratch, and if we are doing that then we may as well just design a new block cipher that is better in many other ways. (For example: block size, speed, code size,...


1

Yes, It is what you understood. You use the same key for each encryption. If you think that they used different keys for each TDES (3DES) they need to store one million keys. This is not practical for the attacker but also for them. It can also be written as $c = \operatorname{TDES}^{(1000000)}_k(m)$ The point in the section distinguishing these iterated ...


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