# How to perform the initial permutations 64-Bit DES to derive $K$?

Perform DES encryption on the first 64-bit plaintext only, what are these 0's and 1's? Do they mean that I need to use this value 111101 to derive $$K$$?

I want to know how to use initial permutation to derive $$K$$ using permuted choice 1 and permute choice 2.

• It is absolutely unclear what you're asking. Mar 24, 2020 at 7:03
• Welcome to crypto.SE. Exactly what part fo the specification of DES do you have a problem with?
– fgrieu
Mar 24, 2020 at 7:41

I want to know how to use initial permutation to derive $$K$$ using permuted choice 1 and permute choice 2
You start with the DES key $$K$$, usually expressed as 8 bytes. That's 64 bits. DES number these bits from 1 to 64, starting with high-order bit on the first byte in reading order, moving to lower-order bit, then after the 8th bit of a byte moving to the next byte in reading order, so that bit 42 is the second-highest-order bit of to the 6th byte in reading order, testable by binary AND of that byte with 40h.
From these bits 64 bits of $$K$$ it is extracted two 28-bit quantities $$C_0$$ and $$D_0$$ by picking bits per table $$PC1$$. The top (resp. bottom) of this table gives the bit numbers in $$K$$ of the bits forming $$C_0$$ (resp. $$D_0$$). You'll notice that $$PC1$$ contains no multiple of 8, meaning that the low-order bit of each byte of $$K$$ is ignored. This deliberately weakens DES.
Bits of $$C_0$$ are numbered 1 to 28, and bits of $$D_0$$ are numbered 29 to 56, in reading order of $$PC1$$.
For the first round of encryption, from $$C_0\mathbin\|D_0$$ it is extracted eight 6-bit quantities (the subkeys 1 to 8 for the first round) by picking bits per table $$PC2$$, which lines gives the bit numbers in $$C_0\mathbin\|D_0$$ of the bits forming each 6-bit quantities. Eight bits of $$C_0\mathbin\|D_0$$ are left aside, but will be used in the next round, after some rotation of $$C_0$$ (resp. $$D_0$$) yielding $$C_1$$ (resp. $$D_1$$).