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Encryption

In cryptography, encryption is the process of encoding information. This process converts the original representation of the information, known as plaintext, into an alternative form known as ciphertext. Ideally, only authorized parties can decipher a ciphertext back to plaintext and access the original information. Encryption does not itself prevent interference but denies the intelligible content to a would-be interceptor.

This article is about algorithms for encryption and decryption. For an overview of cryptographic technology in general, see Cryptography. For the album by Pro-jekt, see Encryption (album).

For technical reasons, an encryption scheme usually uses a pseudo-random encryption key generated by an algorithm. It is possible to decrypt the message without possessing the key but, for a well-designed encryption scheme, considerable computational resources and skills are required. An authorized recipient can easily decrypt the message with the key provided by the originator to recipients but not to unauthorized users.


Historically, various forms of encryption have been used to aid in cryptography. Early encryption techniques were often used in military messaging. Since then, new techniques have emerged and become commonplace in all areas of modern computing.[1] Modern encryption schemes use the concepts of public-key and symmetric-key.[1] Modern encryption techniques ensure security because modern computers are inefficient at cracking the encryption.

History[edit]

Ancient[edit]

One of the earliest forms of encryption is symbol replacement, which was first found in the tomb of Khnumhotep II, who lived in 1900 BC Egypt. Symbol replacement encryption is “non-standard,” which means that the symbols require a cipher or key to understand. This type of early encryption was used throughout Ancient Greece and Rome for military purposes.[2] One of the most famous military encryption developments was the Caesar Cipher, which was a system in which a letter in normal text is shifted down a fixed number of positions down the alphabet to get the encoded letter. A message encoded with this type of encryption could be decoded with the fixed number on the Caesar Cipher.[3]


Around 800 AD, Arab mathematician Al-Kindi developed the technique of frequency analysis – which was an attempt to systematically crack Caesar ciphers.[2] This technique looked at the frequency of letters in the encrypted message to determine the appropriate shift. This technique was rendered ineffective after the creation of the polyalphabetic cipher by Leon Battista Alberti in 1465, which incorporated different sets of languages. In order for frequency analysis to be useful, the person trying to decrypt the message would need to know which language the sender chose.[2]

19th–20th century[edit]

Around 1790, Thomas Jefferson theorized a cipher to encode and decode messages in order to provide a more secure way of military correspondence. The cipher, known today as the Wheel Cipher or the Jefferson Disk, although never actually built, was theorized as a spool that could jumble an English message up to 36 characters. The message could be decrypted by plugging in the jumbled message to a receiver with an identical cipher.[4]


A similar device to the Jefferson Disk, the M-94, was developed in 1917 independently by US Army Major Joseph Mauborne. This device was used in U.S. military communications until 1942.[5]


In World War II, the Axis powers used a more advanced version of the M-94 called the Enigma Machine. The Enigma Machine was more complex because unlike the Jefferson Wheel and the M-94, each day the jumble of letters switched to a completely new combination. Each day's combination was only known by the Axis, so many thought the only way to break the code would be to try over 17,000 combinations within 24 hours.[6] The Allies used computing power to severely limit the number of reasonable combinations they needed to check every day, leading to the breaking of the Enigma Machine.

Modern[edit]

Today, encryption is used in the transfer of communication over the Internet for security and commerce.[1] As computing power continues to increase, computer encryption is constantly evolving to prevent eavesdropping attacks.[7] With one of the first "modern" cipher suites, DES, utilizing a 56-bit key with 72,057,594,037,927,936 possibilities being able to be cracked in 22 hours and 15 minutes by EFF's DES cracker in 1999, which used a brute-force method of cracking. Modern encryption standards often use stronger key sizes often 256, like AES(256-bit mode), TwoFish, ChaCha20-Poly1305, Serpent(configurable up to 512-bit). Cipher suites utilizing a 128-bit or higher key, like AES, will not be able to be brute-forced due to the total amount of keys of 3.4028237e+38 possibilities. The most likely option for cracking ciphers with high key size is to find vulnerabilities in the cipher itself, like inherent biases and backdoors. For example, RC4, a stream cipher, was cracked due to inherent biases and vulnerabilities in the cipher.

Limitations[edit]

Encryption is used in the 21st century to protect digital data and information systems. As computing power increased over the years, encryption technology has only become more advanced and secure. However, this advancement in technology has also exposed a potential limitation of today's encryption methods.


The length of the encryption key is an indicator of the strength of the encryption method.[27] For example, the original encryption key, DES (Data Encryption Standard), was 56 bits, meaning it had 2^56 combination possibilities. With today's computing power, a 56-bit key is no longer secure, being vulnerable to brute force attacks.[28]


Quantum computing utilizes properties of quantum mechanics in order to process large amounts of data simultaneously. Quantum computing has been found to achieve computing speeds thousands of times faster than today's supercomputers.[29] This computing power presents a challenge to today's encryption technology. For example, RSA encryption utilizes the multiplication of very large prime numbers to create a semiprime number for its public key. Decoding this key without its private key requires this semiprime number to be factored, which can take a very long time to do with modern computers. It would take a supercomputer anywhere between weeks to months to factor in this key. However, quantum computing can use quantum algorithms to factor this semiprime number in the same amount of time it takes for normal computers to generate it. This would make all data protected by current public-key encryption vulnerable to quantum computing attacks.[30] Other encryption techniques like elliptic curve cryptography and symmetric key encryption are also vulnerable to quantum computing.


While quantum computing could be a threat to encryption security in the future, quantum computing as it currently stands is still very limited. Quantum computing currently is not commercially available, cannot handle large amounts of code, and only exists as computational devices, not computers.[31] Furthermore, quantum computing advancements will be able to be utilized in favor of encryption as well. The National Security Agency (NSA) is currently preparing post-quantum encryption standards for the future.[32] Quantum encryption promises a level of security that will be able to counter the threat of quantum computing.[31]

Attacks and countermeasures[edit]

Encryption is an important tool but is not sufficient alone to ensure the security or privacy of sensitive information throughout its lifetime. Most applications of encryption protect information only at rest or in transit, leaving sensitive data in clear text and potentially vulnerable to improper disclosure during processing, such as by a cloud service for example. Homomorphic encryption and secure multi-party computation are emerging techniques to compute encrypted data; these techniques are general and Turing complete but incur high computational and/or communication costs.


In response to encryption of data at rest, cyber-adversaries have developed new types of attacks. These more recent threats to encryption of data at rest include cryptographic attacks,[33] stolen ciphertext attacks,[34] attacks on encryption keys,[35] insider attacks, data corruption or integrity attacks,[36] data destruction attacks, and ransomware attacks. Data fragmentation[37] and active defense[38] data protection technologies attempt to counter some of these attacks, by distributing, moving, or mutating ciphertext so it is more difficult to identify, steal, corrupt, or destroy.[39]

(1939), Cryptanalysis: A Study of Ciphers and Their Solution, New York: Dover Publications Inc, ISBN 978-0486200972

Fouché Gaines, Helen

(1967), The Codebreakers - The Story of Secret Writing (ISBN 0-684-83130-9)

Kahn, David

(2000), "Advances in Cryptology – EUROCRYPT 2000", Springer Berlin Heidelberg, ISBN 978-3-540-67517-4

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(1966): Elementary Cryptanalysis: A Mathematical Approach, Mathematical Association of America. ISBN 0-88385-622-0

Sinkov, Abraham

Tenzer, Theo (2021): SUPER SECRETO – The Third Epoch of Cryptography: Multiple, exponential, quantum-secure and above all, simple and practical Encryption for Everyone, Norderstedt,  978-3-755-76117-4.

ISBN

Lindell, Yehuda; Katz, Jonathan (2014), Introduction to modern cryptography, Hall/CRC,  978-1466570269

ISBN

Ermoshina, Ksenia; Musiani, Francesca (2022), (PDF), Manchester, UK: matteringpress.org, ISBN 978-1-912729-22-7, archived from the original (PDF) on 2022-06-02

Concealing for Freedom: The Making of Encryption, Secure Messaging and Digital Liberties (Foreword by Laura DeNardis)(open access)