Encryption

Encryption is the process in which a clearly readable text ( plain text) (or other types of information such as audio or video recordings) using an encryption process ( cryptosystem ) to an " illegible ", that is not easily interpretable string ( ciphertext ) converted will. As a critically important parameter of the encryption in this case, one or even use multiple keys.

The scientific research field that deals with encryption method and its history is called cryptography. Cryptography is a branch of cryptology.

Introduction

Example for encrypting a plaintext into a ciphertext:

DiesisteinKlartextunderwirdnunverschluesselt GLHVLVWHLQNODUWHAWXQGHUZLUGQXQYHUVFKOXHVVHOW In this example, the plaintext was encrypted using the method of the Caesar cipher using the key "C". The reverse process, ie the transformation of ciphertext back into plaintext is called decryption. The algorithms for encryption and decryption are not necessarily identical. Also possible to use different keys for encryption and decryption. For symmetrical, particularly in the conventional encoding methods, however, is always identical secret key is used for encryption and decryption. Cryptographic methods with different keys for encryption and decryption are as asymmetric method (English: Public key methods ) respectively. Here, the sender uses the recipient's public key to encrypt and the beneficiary is kept secret, not publicly known so-called private key for decryption.

Linguistically to separate from the decryption, ie reconvert the activities of the authorized receiver of a secret message, using the in his possession (secret) key, the ciphertext in a clearly readable text ( plain text), the term " decoding ". When deciphering the art is known, the ciphertext to wrest his secret message without being in possession of the key. This is the work of a "Code Buster " (English: Codebreaker ). The area of ​​research that deals with the decipherment of ciphertext is called cryptanalysis (including cryptanalysis ) and is adjacent to the second part of cryptography cryptology. The cryptanalysis it is not limited only to the unauthorized decryption of secret messages, but it also deals very much with testing the efficacy and safety of cryptographic algorithms.

In interpersonal communication encryption is generally the exchange of information that is transmitted to a counterpart by means of symbols, there is accordingly an interpretation of the symbols. As symbols serve here as language, facial expressions, gestures, Lautierungen. The correct understanding of a message can be problematic in certain circumstances, because a correct interpretation of the symbols within the meaning of the intention of the sender is not always possible (see Four-sided model).

Distinction between

Encryption is a function of a key transferred depends a plaintext into a ciphertext, such that there is an inverse function of the decryption with which one again obtains the plaintext from the ciphertext.

Cryptographers strive for a definition of terms that are commonly used interchangeably. Examples:

• Cipher: When encryption all characters are encoded separately by means of an encryption method. Example is the Caesar encryption, in which a character from the alphabet is used as key and based on the position of the letter, the letters of the plaintext are shifted cyclically in the alphabet.
• Encoding: Encoding is the all characters in a character set be assigned to a different character set. An example of this is the encoding of all the alphabetic characters in the ASCII code.
• Decoding: transmitting a cipher text into plain text without known key (see also: Breaking ).

Encryption methods

A rough distinction between symmetric and asymmetric encryption systems arises from the manner in which cryptographic keys to the parties to the proceedings will be covered:

For symmetric systems, both communication partners have the same key and have to have these replaced safely before the start of communication (for example using Diffie -Hellman key exchange, or send by mail ). A well-known classical symmetric encryption is the Caesar cipher, which was used for the first time BC by Julius Caesar. The cipher by Alberti in the 15th century was the first mechanical cryptologic device. The most well known method from the time of the mechanical encryption machine (about 1920-1960 ) is the Enigma. The era of modern symmetric algorithms in the 19th and 20th century by the information-theoretically secure one -time pad (OTP ) and the Data Encryption Standard ( DES) ushered in the 1970s. The modern and in August 2013 considered to be safe procedures include the Rijndael, Twofish, and 3DES, with the Rijndael by his elevation in 2000 to the Advanced Encryption Standard ( AES) and due to its preference by State U.S. authorities play a prominent role.

Modern symmetric methods are further subdivided into two classes:

• In the block cipher, the plaintext before encryption is divided into blocks of equal size. As the blocks are encrypted, the operation mode determined. Here to small blocks must be filled with meaningless characters so that they take a higher transmission capacity to complete.
• In the stream cipher the plaintext character or bit encrypted. Such algorithms are referred to as " online algorithms ".

Asymmetric systems are characterized by the fact that for each participant, a key pair is generated. A key of each pair is released, the other remains secret. It enables the transfer of the key must not be held secret, but can only be authenticated to ensure that the communication partner is using the correct key. The asymmetry arises because data that has been encrypted with the public key of the key pair can only be decrypted with the private key of the key pair. The best known of these methods is the RSA cryptosystem. Often both types of encryption are combined in hybrid methods.

Key distribution

To distribute the key, there are three techniques:

Transmission of the message

An encrypted message has to be transmitted normally through several stages. Today, these are mostly individual computer systems, that is, the encrypted message is transmitted over a computer network. One distinguishes two fundamentally different ways of transmission:

• In the line encryption, the message is only one of the neighboring computer encrypted ( Point-to- Point Encryption ). This decrypts the message, encrypts it again ( with a possibly different method ) and sends it to its neighbors - and so on to the target computer. The advantage of this method is that only neighboring computers must agree on an encryption method and key used. In addition, this mode of transmission can be located at a very low level protocol (eg already in transmission hardware). The disadvantage is that each individual computer must be trustworthy and secure during transmission.
• In the end-to -end encryption, the message is encrypted by the sender and transmitted unchanged in this form for several other PCs. Here none of the transmitting computer has access to the plaintext of the message. The disadvantage, however, is that the sender must agree with each possible receiver on an encryption method and associated key (s).

Cryptography and Cryptanalysis

As representatives of opposing interests to cryptographers and cryptanalysts are facing. The development of encryption techniques took place mostly in the military. One side ( cryptographers ) tried their messages to encrypt - the other side ( cryptanalyst ) trying to decipher them. Today, the research in the field of encryption is much wider. There are numerous individuals as well as institutions that develop both new encryption technologies when trying simultaneously to break existing.

Hoping to give a cryptographic method by additional security, encryption algorithms have been like to be kept secret, which is called security by obscurity. Cryptographers argue thus climb the risk of illicit, but routine attacks on encrypted information or transportation. Therefore, scientists strive today to let analyze the algorithms of a broad public. For as long as many professionals find any vulnerability, a method is still considered safe. The disclosure of the method is Kerckhoffs ' principle.

Form ways of cryptanalysis, among other brute force ( ie try all possible keys ) and side channel attacks.