- Cryptography Tutorial
Key Generation. The round-key generator creates sixteen 48-bit keys out of a 56-bit cipher key. The process of key generation is depicted in the following illustration − The logic for Parity drop, shifting, and Compression P-box is given in the DES description. DES Analysis. The DES satisfies both the desired properties of block cipher. 2012-1-24 DES Weak Keys. DES uses 16 48-bits keys generated from a master 56-bit key (64 bits if we consider also parity bits). Weak keys: keys make the same sub-key to be generated in more than one round. Result: reduce cipher complexity. Weak keys can be avoided at key generation. DES has 4 weak keys – 0100101 – FEFEFEFE.
- Cryptography Useful Resources
- Selected Reading
The Data Encryption Standard (DES) is a symmetric-key block cipher published by the National Institute of Standards and Technology (NIST).
DES is an implementation of a Feistel Cipher. It uses 16 round Feistel structure. The block size is 64-bit. Though, key length is 64-bit, DES has an effective key length of 56 bits, since 8 of the 64 bits of the key are not used by the encryption algorithm (function as check bits only). General Structure of DES is depicted in the following illustration −
Since DES is based on the Feistel Cipher, all that is required to specify DES is −
- Round function
- Key schedule
- Any additional processing − Initial and final permutation
Initial and Final Permutation
The initial and final permutations are straight Permutation boxes (P-boxes) that are inverses of each other. They have no cryptography significance in DES. The initial and final permutations are shown as follows −
Round Function
The heart of this cipher is the DES function, f. The DES function applies a 48-bit key to the rightmost 32 bits to produce a 32-bit output.
-
Expansion Permutation Box − Since right input is 32-bit and round key is a 48-bit, we first need to expand right input to 48 bits. Permutation logic is graphically depicted in the following illustration −
-
The graphically depicted permutation logic is generally described as table in DES specification illustrated as shown −
-
XOR (Whitener). − After the expansion permutation, DES does XOR operation on the expanded right section and the round key. The round key is used only in this operation.
Windows 7 pro key generator. Windows 7 Professional Product Key 64 Bit 2020; Windows 7 Product Key Generator 32 / 64 Bit Latest is the best way to activate not registered windows 7. It supports both editions like 32bit and 64bit windows. It improves the performance of windows and unlocks more features of windows 7 64bit ISO. All keys are shared only for students. Mar 09, 2020 The Windows 7 product key generator can be gotten from different sources. You just have to choose the best that suits you. Some computer users find it difficult in locating a genuine and workable product key. But there is no special requirement needed in getting it. The requirement of Windows 7 Professional Product Key: One gigahertz (GHz) or faster 32-bit (x86) or 64-bit (x64) processor. 1 gigabyte (GB) RAM (32-bit) or 2 GB RAM (64-bit) 16 GB available disk that is hard (32-bit) or 20 GB (64-bit) DirectX 9 graphics unit with WDDM 1.0 or higher driver. 11th February 2020 11th February 2020 licenseguide license key, Windows Leave a Comment on Windows 7 Professional Product Key Generator + Crack Free Download Windows 7 Professional Product Key Generator extreme right border of the taskbar today sports sort of nub. Blot it over, and spacious windows become transparent, showing the background below.
-
Substitution Boxes. − The S-boxes carry out the real mixing (confusion). DES uses 8 S-boxes, each with a 6-bit input and a 4-bit output. Refer the following illustration −
-
The S-box rule is illustrated below −
-
There are a total of eight S-box tables. The output of all eight s-boxes is then combined in to 32 bit section.
-
Straight Permutation − The 32 bit output of S-boxes is then subjected to the straight permutation with rule shown in the following illustration:
Key Generation
The round-key generator creates sixteen 48-bit keys out of a 56-bit cipher key. The process of key generation is depicted in the following illustration −
The logic for Parity drop, shifting, and Compression P-box is given in the DES description.
3des Des
DES Analysis
The DES satisfies both the desired properties of block cipher. These two properties make cipher very strong.
-
Avalanche effect − A small change in plaintext results in the very great change in the ciphertext.
-
Completeness − Each bit of ciphertext depends on many bits of plaintext.
Des Encryption
During the last few years, cryptanalysis have found some weaknesses in DES when key selected are weak keys. These keys shall be avoided.
Des Key Generation Program In China
DES has proved to be a very well designed block cipher. There have been no significant cryptanalytic attacks on DES other than exhaustive key search.