Find the DES encryption algorithm for C or C

The DES encryption algorithm is as follows:

1. Introduction to DES encryption algorithms.

DES (Data Encryption Standard) is one of the most popular encryption algorithms. DES is symmetrical, meaning it uses the same key to encrypt and decrypt data.

DES is also a packet encryption algorithm that processes a fixed-length data segment at a time, called packets. The size of the DES group is 64 bits, and if the length of the encrypted data is not a multiple of 64 bits, you can fill the digits according to some specific rules.

Essentially, the security of DES relies on false appearances, which in cryptography terms rely on the principle of "chaos and proliferation". The purpose of confusion is to hide any relationship between plaintext and ciphertext, or keys, while the purpose of diffusion is to make as many ciphertexts as possible with the valid bits and keys in the plaintext. The combination of the two makes for a relatively high level of security.

The DES algorithm encrypts the plaintext by performing a series of permutation and substitution operations. The crux of the process is a function that gets 16 subkeys from a given initial key. To encrypt a set of plaintext, each subkey is applied to the data in a series of bit operations in order (1-16), once per subkey, for a total of 16 repetitions.

Each iteration is called a round. The same procedure can be used to decrypt the ciphertext, except that the subkeys are processed in reverse order (16-1).

2. The encryption principle of DES encryption algorithm.

DES is encrypted in packets. Using a 64-bit packet length and a 56-bit key length, the 64-bit input is transformed into a 64-bit output. The DES algorithm uses multiple combinations of substitution algorithms and transposition algorithms to turn plaintext into ciphertext with high cryptographic strength through the interaction of obfuscation and diffusion.

The same steps and the same key are used for decryption.

64-bit data is encrypted in a group;

The initial substitution is based on an 8*8 substitution table, which shuffles the 64-bit plaintext.

The initial ciphertext is formed with a 56-bit key after 16 rounds of iterative operations.

Finally, the final ciphertext of the grouping is obtained by initial reverse permutation.

DES encrypts 64-bit blocks of data with a 56-bit key and encodes 64-bit blocks for 16 rounds.

With each round of encoding, a 48-bit "per round" key value is derived from the full 56-bit key.

DES takes a long time to decode with software, while decoding with hardware is very fast.

But luckily, most hackers didn't have enough equipment at the time to make such a hardware device.

In 1977, it was estimated that it would cost $20 million to build a computer dedicated to the decryption of DES.

And it takes 12 hours to crack to get the result.

So, at that time, DES was considered a very strong encryption method.

1.DEA encryption with key K1.

2.DES decryption of the results of step 1 with k2.

3.DES encryption with the result of step 2 using key k1.

The disadvantage of this method is that it takes three times as long, and on the other hand, the 112-bit key length of the triple DES is a very "strong" encryption method.

DES Encryption Algorithm Principle:

The DES algorithm uses a 56-bit key with an additional 8-bit parity bit to produce a maximum packet size of 64 bits. is an iterative block cipher in which the encrypted text is split into two halves. Use the subkey to apply a looping function to one half of them, and then "XOR" the output with the other half; The two halves are then exchanged, and the process continues, digging but the last cycle is not exchanged.

DES uses 16 rounds of cycles, using XOR, permutation, substitution, and shift to operate four basic operations.

Data encryption algorithms.

Data encryption algorithm DES

The Data Encryption Standard (DES) is a description of the specification, which comes from the research work of IBM and was formalized by the United States in 1997. It is probably the most widely used key system of Lunzheng, especially in the security of financial data, where the DES was originally developed and embedded in the hardware. Typically, automated teller machines (ATMs) use DES.

DES uses a 56-bit key with an additional 8-bit parity bit to produce a maximum packet size of 64 bits. This is an iterative block cipher that uses a technique called feistel, in which an encrypted block of text is split in half. Use the subkey to apply a looping function to one half of them, and then "XOR" the output with the other half; The two halves are then swapped, and the process continues, but the last cycle is not swapped.

DES uses 16 loops.

The main form of attack des is known as brute force or thorough key searching, where various keys are tried repeatedly until there is one match. If DES uses a 56-bit key, the number of possible keys is 2 to the power of 56. As the capabilities of computer systems continue to evolve, DES is much less secure than it was when it first appeared, but it can still be considered sufficient for non-critical practical reasons.

However, DES is now only used for the authentication of older systems, and more of a new encryption standard, the Advanced Encryption Standard (AES), is chosen.

A common variant of DES is triple DES, a mechanism that uses a 168-bit key to encrypt data three times; It usually (but not always) provides extremely strong security. If all three 56-bit child elements are identical, then triple des are backwards compatible with des.

IBM had a patent for DES for several years, but it expired in 1983 and is in the public domain, allowing it to be used without royalties under certain conditions.