This article details the various

tables Table may refer to: * Table (furniture), a piece of furniture with a flat surface and one or more legs * Table (landform), a flat area of land * Table (information), a data arrangement with rows and columns * Table (database), how the table data ...

referenced in the

Data Encryption Standard The Data Encryption Standard (DES ) is a symmetric-key algorithm for the encryption of digital data. Although its short key length of 56 bits makes it too insecure for modern applications, it has been highly influential in the advancement of cry ...

(DES)

block cipher In cryptography, a block cipher is a deterministic algorithm operating on fixed-length groups of bits, called ''blocks''. Block ciphers are specified cryptographic primitive, elementary components in the design of many cryptographic protocols and ...

. All bits and bytes are arranged in

big endian In computing, endianness, also known as byte sex, is the order or sequence of bytes of a word of digital data in computer memory. Endianness is primarily expressed as big-endian (BE) or little-endian (LE). A big-endian system stores the most sig ...

order in this document. That is, bit number 1 is always the most significant bit.

Initial permutation (IP)

This table specifies the input permutation on a 64-bit block. The meaning is as follows: the first bit of the output is taken from the 58th bit of the input; the second bit from the 50th bit, and so on, with the last bit of the output taken from the 7th bit of the input. This information is presented as a table for ease of presentation; it is a vector, not a matrix.

Final permutation (IP⁻¹)

The final permutation is the inverse of the initial permutation; the table is interpreted similarly.

Expansion function (E)

The expansion function is interpreted as for the initial and final permutations. Note that some bits from the input are duplicated at the output; e.g. the fifth bit of the input is duplicated in both the sixth and eighth bit of the output. Thus, the 32-bit half-block is expanded to 48 bits.

Permutation (P)

The P permutation shuffles the bits of a 32-bit half-block.

Permuted choice 1 (PC-1)

The "Left" and "Right" halves of the table show which bits from the input

key Key or The Key may refer to: Common meanings * Key (cryptography), a piece of information that controls the operation of a cryptography algorithm * Key (lock), device used to control access to places or facilities restricted by a lock * Key (map ...

form the left and right sections of the key schedule state. Note that only 56 bits of the 64 bits of the input are selected; the remaining eight (8, 16, 24, 32, 40, 48, 56, 64) were specified for use as

parity bit A parity bit, or check bit, is a bit added to a string of binary code. Parity bits are a simple form of error detecting code. Parity bits are generally applied to the smallest units of a communication protocol, typically 8-bit octets (bytes) ...

Permuted choice 2 (PC-2)

This permutation selects the 48-bit subkey for each round from the 56-bit key-schedule state. This permutation will ignore 8 bits below: Permuted Choice 2 "PC-2" Ignored bits 9, 18, 22, 25, 35, 38, 43, 54.

Substitution boxes (S-boxes)

This table lists the eight S-boxes used in DES. Each S-box replaces a 6-bit input with a 4-bit output. Given a 6-bit input, the 4-bit output is found by selecting the row using the outer two bits, and the column using the inner four bits. For example, an input "011011" has outer bits "01" and inner bits "1101"; noting that the first row is "00" and the first column is "0000", the corresponding output for S-box S₅ would be "1001" (=9), the value in the second row, 14th column. (See

S-box In cryptography, an S-box (substitution-box) is a basic component of symmetric key algorithms which performs substitution. In block ciphers, they are typically used to obscure the relationship between the key and the ciphertext, thus ensuring Sha ...

Key Generation

The main key supplied from user is of 64 bits. The following operations are performed with it.

Drop Parity bits

Drop the bits of the grey positions (8x) to make 56 bit space for further operation for each round. After that bits are permuted according to the following table, The table is row major way, means, Actual Bit position = Substitute with the bit of row * 8 + column.

Bits Rotation

Before the round sub-key is selected, each half of the key schedule state is rotated left by a number of places. This table specifies the number of places rotated. • The key is divided into two 28-bit parts • Each part is shifted left (circular) one or two bits • After shifting, two parts are then combined to form a 56 bit temp-key again

Key Compression

• The compression P-box changes the 56 bits key to 48 bits key, which is used as a key for the corresponding round. The table is row major way, means, Actual Bit position = Substitute with the bit of row * 8 + column. After this return the Round-Key of 48 bits to the called function, ''i.e.'' the Round.

References

External links

The DES Algorithm Illustrated
{{Cryptography navbox , block Data Encryption Standard S-box