In cryptography, encryption is the process of Code 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 wouldbe interceptor.
For technical reasons, an encryption scheme usually uses a pseudorandom encryption key generated by an algorithm. It is possible to decrypt the message without possessing the key but, for a welldesigned 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. Modern encryption schemes use the concepts of publickey and symmetrickey. Modern encryption techniques ensure security because modern computers are inefficient at cracking the encryption.
Around 800 AD, Arab mathematician AlKindi developed the technique of frequency analysis – which was an attempt to systematically crack Caesar ciphers. 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 Leone 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.
A similar device to the Jefferson Disk, the M94, was developed in 1917 independently by US Army Major Joseph Mauborne. This device was used in U.S. military communications until 1942.
In World War II, the Axis powers used a more advanced version of the M94 called the Enigma machine. The Enigma Machine was more complex because unlike the Jefferson Wheel and the M94, 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. 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.
Many complex cryptographic algorithms often use simple modular arithmetic in their implementations.
In publickey encryption schemes, the encryption key is published for anyone to use and encrypt messages. However, only the receiving party has access to the decryption key that enables messages to be read.Bellare, Mihir. "PublicKey Encryption in a Multiuser Setting: Security Proofs and Improvements." Springer Berlin Heidelberg, 2000. p. 1. Publickey encryption was first described in a secret document in 1973; beforehand, all encryption schemes were symmetrickey (also called privatekey).Oded Goldreich Foundations of Cryptography: Volume 2, Basic Applications. Vol. 2. Cambridge university press, 2004. Although published subsequently, the work of Diffie and Hellman was published in a journal with a large readership, and the value of the methodology was explicitly described. The method became known as the DiffieHellman key exchange.
RSA (Rivest–Shamir–Adleman) is another notable publickey cryptosystem. Created in 1978, it is still used today for applications involving digital signatures. Using number theory, the RSA algorithm selects two , which help generate both the encryption and decryption keys.
A publicly available publickey encryption application called Pretty Good Privacy (PGP) was written in 1991 by Phil Zimmermann, and distributed free of charge with source code. PGP was purchased by NortonLifeLock in 2010 and is regularly updated.
Encryption is also used to protect data in transit, for example data being transferred via computer network (e.g. the Internet, ecommerce), , wireless microphones, wireless intercom systems, Bluetooth devices and bank automatic teller machines. There have been numerous reports of data in transit being intercepted in recent years.Fiber Optic Networks Vulnerable to Attack, Information Security Magazine, November 15, 2006, Sandra Kay Miller Data should also be encrypted when transmitted across networks in order to protect against eavesdropping of network traffic by unauthorized users.
The length of the encryption key is an indicator of the strength of the encryption method. 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 56bit key is no longer secure, being vulnerable to hacking by brute force attack.
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. 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 in, 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 publickey encryption vulnerable to quantum computing attacks. 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. Furthermore, quantum computing advancements will be able to be utilized in favor of encryption as well. The National Security Agency (NSA) is currently preparing postquantum encryption standards for the future. Quantum encryption promises a level of security that will be able to counter the threat of quantum computing.
In response to encryption of data at rest, cyberadversaries have developed new types of attacks. These more recent threats to encryption of data at rest include cryptographic attacks, stolen ciphertext attacks, attacks on encryption keys, Insider threat, data corruption or integrity attacks, data destruction attacks, and ransomware attacks. Data fragmentationExamples of data fragmentation technologies include TahoeLAFS and Storj. and Active Defense 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. CryptoMove is the first technology to continuously move, mutate, and reencrypt ciphertext as a form of data protection.
Integrity protection mechanisms such as MACs and digital signatures must be applied to the ciphertext when it is first created, typically on the same device used to compose the message, to protect a message endtoend along its full transmission path; otherwise, any node between the sender and the encryption agent could potentially tamper with it. Encrypting at the time of creation is only secure if the encryption device itself has correct keys and has not been tampered with. If an endpoint device has been configured to trust a root certificate that an attacker controls, for example, then the attacker can both inspect and tamper with encrypted data by performing a maninthemiddle attack anywhere along the message's path. The common practice of TLS interception by network operators represents a controlled and institutionally sanctioned form of such an attack, but countries have also attempted to employ such attacks as a form of control and censorship.
Padding a message's payload before encrypting it can help obscure the cleartext's true length, at the cost of increasing the ciphertext's size and introducing or increasing bandwidth overhead. Messages may be padded randomly or deterministically, with each approach having different tradeoffs. Encrypting and padding messages to form padded uniform random blobs or PURBs is a practice guaranteeing that the cipher text leaks no metadata about its cleartext's content, and leaks asymptotically minimal $O(\backslash log\backslash log\; M)$ information via its length.

