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# Cryptographic algorithm

## Cryptographic algorithm definition

Cryptographic algorithms, or ciphers, are mathematical procedures used to encrypt and decrypt data. These algorithms play a crucial role in secure communications, protecting information by transforming it into an unreadable format. Only someone with the appropriate decryption key can understand it.

## Brief history of cryptographic algorithms

• Ancient times. The Greeks and Romans used simple substitution ciphers. For example, the Caesar cipher replaced each letter in a message by a letter a fixed number of positions down the alphabet.
• Middle Ages. More complex ciphers, such as the Vigenère cipher, were developed during the Middle Ages. These ciphers involved several Caesar ciphers in sequence with different shift values.
• World War II. Cryptography played a critical role in World War II, with the Enigma machine used by Germany being one of the most famous examples. The device used mechanical rotors to achieve a complex form of substitution cipher. Breaking the Enigma code by the Allies is considered a significant event in the history of cryptography.
• Modern cryptography. The advent of computers led to the development of much more complex cryptographic algorithms. In the 1970s, symmetric key cryptography was revolutionized after IBM introduced the Data Encryption Standard (DES). The invention of asymmetric key cryptography followed, and the RSA algorithm became a standard.

## Cryptographic algorithm types

• Symmetric key algorithms use the same key for converting plaintext data into ciphertext (encryption) and the other way around (decryption). Examples include AES (Advanced Encryption Standard) and DES (Data Encryption Standard). Symmetric key algorithms are relatively fast and useful for bulk data encryption.
• Asymmetric key algorithms use two different keys: a public key for encryption and a private key for decryption. The public key can be freely shared while the private key remains secret. This allows secure communication between parties who have never met. RSA (Rivest–Shamir–Adleman) and ECC (Elliptic Curve Cryptography) are examples of asymmetric key algorithms.
• Hash functions transform an input of any size into a fixed-size string of text, which uniquely represents the input. Hash functions have various uses, such as data integrity checks and secure password storage. Examples include SHA-256 (Secure Hash Algorithm 256) and MD5 (Message Digest Algorithm 5).

## Cryptographic algorithm uses

• Secure communication. Cryptography allows safely transmitting data across insecure networks. It is used in HTTPS (the secure version of HTTP), email encryption, and VPNs.
• Data protection. Cryptography can protect data at rest, such as files on your hard drive. If someone gains unauthorized access, the data will be unreadable without the decryption key.
• Digital signatures and certificates. Cryptography helps verify the integrity and origin of data. A digital signature proves that data hasn't been tampered with and verifies the sender's identity.
• Password storage. Websites don't store your actual password but rather a hash of it. When you log in, the password you enter is hashed again and compared with the stored hash. This way, even if someone breaches the website's password database, the actual passwords remain safe.