Cryptography or cryptology is the practice and study of techniques for secure communication in the presence of third parties called adversaries. More cryptography is about constructing and analyzing protocols that prevent third parties or the public from reading private messages. Modern cryptography exists at the intersection of the disciplines of mathematics, computer science, electrical engineering, communication science, physics. Applications of cryptography include electronic commerce, chip-based payment cards, digital currencies, computer passwords, military communications. Cryptography prior to the modern age was synonymous with encryption, the conversion of information from a readable state to apparent nonsense; the originator of an encrypted message shares the decoding technique only with intended recipients to preclude access from adversaries. The cryptography literature uses the names Alice for the sender, Bob for the intended recipient, Eve for the adversary. Since the development of rotor cipher machines in World War I and the advent of computers in World War II, the methods used to carry out cryptology have become complex and its application more widespread.
Modern cryptography is based on mathematical theory and computer science practice. It is theoretically possible to break such a system, but it is infeasible to do so by any known practical means; these schemes are therefore termed computationally secure. There exist information-theoretically secure schemes that provably cannot be broken with unlimited computing power—an example is the one-time pad—but these schemes are more difficult to use in practice than the best theoretically breakable but computationally secure mechanisms; the growth of cryptographic technology has raised a number of legal issues in the information age. Cryptography's potential for use as a tool for espionage and sedition has led many governments to classify it as a weapon and to limit or prohibit its use and export. In some jurisdictions where the use of cryptography is legal, laws permit investigators to compel the disclosure of encryption keys for documents relevant to an investigation. Cryptography plays a major role in digital rights management and copyright infringement of digital media.
The first use of the term cryptograph dates back to the 19th century—originating from The Gold-Bug, a novel by Edgar Allan Poe. Until modern times, cryptography referred exclusively to encryption, the process of converting ordinary information into unintelligible form. Decryption is the reverse, in other words, moving from the unintelligible ciphertext back to plaintext. A cipher is a pair of algorithms that create the reversing decryption; the detailed operation of a cipher is controlled both by the algorithm and in each instance by a "key". The key is a secret a short string of characters, needed to decrypt the ciphertext. Formally, a "cryptosystem" is the ordered list of elements of finite possible plaintexts, finite possible cyphertexts, finite possible keys, the encryption and decryption algorithms which correspond to each key. Keys are important both formally and in actual practice, as ciphers without variable keys can be trivially broken with only the knowledge of the cipher used and are therefore useless for most purposes.
Ciphers were used directly for encryption or decryption without additional procedures such as authentication or integrity checks. There are two kinds of cryptosystems: asymmetric. In symmetric systems the same key is used to decrypt a message. Data manipulation in symmetric systems is faster than asymmetric systems as they use shorter key lengths. Asymmetric systems use a public key to encrypt a private key to decrypt it. Use of asymmetric systems enhances the security of communication. Examples of asymmetric systems include RSA, ECC. Symmetric models include the used AES which replaced the older DES. In colloquial use, the term "code" is used to mean any method of encryption or concealment of meaning. However, in cryptography, code has a more specific meaning, it means the replacement of a unit of plaintext with a code word. Cryptanalysis is the term used for the study of methods for obtaining the meaning of encrypted information without access to the key required to do so; some use the terms cryptography and cryptology interchangeably in English, while others use cryptography to refer to the use and practice of cryptographic techniques and cryptology to refer to the combined study of cryptography and cryptanalysis.
English is more flexible than several other languages in which crypto
In cryptography, encryption is the process of encoding a message or information in such a way that only authorized parties can access it and those who are not authorized cannot. Encryption does not itself prevent interference, but denies the intelligible content to a would-be interceptor. In an encryption scheme, the intended information or message, referred to as plaintext, is encrypted using an encryption algorithm – a cipher – generating ciphertext that can be read only if decrypted. For technical reasons, an encryption scheme uses a pseudo-random encryption key generated by an algorithm, it is in principle possible to decrypt the message without possessing the key, for a well-designed encryption scheme, considerable computational resources and skills are required. An authorized recipient can decrypt the message with the key provided by the originator to recipients but not to unauthorized users. In symmetric-key schemes, the encryption and decryption keys are the same. Communicating parties must have the same key.
An example of a symmetric key scheme would be the one used by the German Enigma Machine that sent information from a central location to troops in various other locations in secret. When the Allies captured one of these machines and figured out how it worked, they were able to decipher the information encoded within the messages as soon as they could discover the encryption key for a given day's transmissions. In public-key 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. Public-key encryption was first described in a secret document in 1973. Although published subsequently, the work of Diffie and Hellman, was published in a journal with a large readership, the value of the methodology was explicitly described and the method became known as the Diffie Hellman key exchange. A publicly available public key encryption application called Pretty Good Privacy was written in 1991 by Phil Zimmermann, distributed free of charge with source code.
Encryption has long been used by governments to facilitate secret communication. It is now used in protecting information within many kinds of civilian systems. For example, the Computer Security Institute reported that in 2007, 71% of companies surveyed utilized encryption for some of their data in transit, 53% utilized encryption for some of their data in storage. Encryption can be used to protect data "at rest", such as information stored on computers and storage devices. In recent years, there have been numerous reports of confidential data, such as customers' personal records, being exposed through loss or theft of laptops or backup drives. Digital rights management systems, which prevent unauthorized use or reproduction of copyrighted material and protect software against reverse engineering, is another somewhat different example of using encryption on data at rest. 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, stolen ciphertext attacks, attacks on encryption keys, insider attacks, data corruption or integrity attacks, data destruction attacks, ransomware attacks.
Data fragmentation 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, corrupt, or destroy. Encryption is used to protect data in transit, for example data being transferred via networks, mobile telephones, 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. Data should be encrypted when transmitted across networks in order to protect against eavesdropping of network traffic by unauthorized users. Encryption, by itself, can protect the confidentiality of messages, but other techniques are still needed to protect the integrity and authenticity of a message. Standards for cryptographic software and hardware to perform encryption are available, but using encryption to ensure security may be a challenging problem. A single error in system design or execution can allow successful attacks.
Sometimes an adversary can obtain unencrypted information without directly undoing the encryption. See, e.g. traffic analysis, TEMPEST, or Trojan horse. Digital signature and encryption must be applied to the ciphertext when it is created to avoid tampering. Encrypting at the time of creation is only secure if the encryption device itself has not been tampered with. Conventional methods for deleting data permanently from a storage device involve overwriting its whole content with zeros, ones or other patterns – a process which can take a significant amount of time, depending on the capacity and the type of the medium. Cryptography offers a way of making the erasure instantaneous; this method is called crypto-shredding. An example implementation of this method can be found on iOS devices, where the cryptographic key is kept in a dedicated'Effaceable Storage'; because the
The Clipper chip was a chipset, developed and promoted by the United States National Security Agency as an encryption device that secured “voice and data messages" with a built-in backdoor. It was intended to be adopted by telecommunications companies for voice transmission, it can decipher messages. It was part of a Clinton Administration program to “allow Federal and local law enforcement officials the ability to decode intercepted voice and data transmissions." “Each clipper chip ha a unique serial number and a secret ‘unit key,’ programmed into the chip when manufactured." This way, each device was meant to be different from the next. It was announced in 1993 and by 1996 was defunct; the Clipper chip used a data encryption algorithm called Skipjack to transmit information and the Diffie–Hellman key exchange-algorithm to distribute the cryptokeys between the peers. Skipjack was invented by the National Security Agency of the U. S. Government; the government did state that it used an 80-bit key, that the algorithm was symmetric, that it was similar to the DES algorithm.
The Skipjack algorithm was declassified and published by the NSA on June 24, 1998. The initial cost of the chips was said to be $16 or $26, with its logic designed by Mykotronx, fabricated by VLSI Technology, Inc. At the heart of the concept was key escrow. In the factory, any new telephone or other device with a Clipper chip would be given a cryptographic key, that would be provided to the government in escrow. If government agencies "established their authority" to listen to a communication the key would be given to those government agencies, who could decrypt all data transmitted by that particular telephone; the newly formed Electronic Frontier Foundation preferred the term "key surrender" to emphasize what they alleged was occurring. The Clinton Administration argued that the Clipper chip was essential for law enforcement to keep up with the progressing technology in the United States. While many believed that the device would act as an additional way for terrorists to receive information, the Clinton Administration said it would increase national security.
They argued that because “terrorists would have to use it to communicate with outsiders — banks and contacts — the Government could listen in on those calls.” Organizations such as the Electronic Privacy Information Center and the Electronic Frontier Foundation challenged the Clipper chip proposal, saying that it would have the effect not only of subjecting citizens to increased and illegal government surveillance, but that the strength of the Clipper chip's encryption could not be evaluated by the public as its design was classified secret, that therefore individuals and businesses might be hobbled with an insecure communications system. Further, it was pointed out that while American companies could be forced to use the Clipper chip in their encryption products, foreign companies could not, phones with strong data encryption would be manufactured abroad and spread throughout the world and into the United States, negating the point of the whole exercise, and, of course, materially damaging U.
S. manufacturers en route. Then-Senators John Ashcroft and John Kerry were opponents of the Clipper chip proposal, arguing in favor of the individual's right to encrypt messages and export encryption software; the release and development of several strong cryptographic software packages such as Nautilus, PGP and PGPfone was in response to the government push for the Clipper chip. The thinking was that if strong cryptography was available on the internet as an alternative, the government would be unable to stop its use. In 1994, Matt Blaze published the paper Protocol Failure in the Escrowed Encryption Standard, it pointed out that the Clipper's escrow system has a serious vulnerability: the chip transmitted a 128-bit "Law Enforcement Access Field" that contained the information necessary to recover the encryption key. To prevent the software that transmitted the message from tampering with the LEAF, a 16-bit hash was included; the Clipper chip would not decode messages with an invalid hash. A brute-force attack would produce another LEAF value that would give the same hash but not yield the correct keys after the escrow attempt.
This would allow the Clipper chip to be used as an encryption device, while disabling the key escrow capability. In 1995 Yair Frankel and Moti Yung published another attack, inherent to the design and which shows that the key escrow device tracking and authenticating capability of one device, can be attached to messages coming from another device and will be received, thus bypassing the escrow in real time. In 1997, a group of leading cryptographers published a paper, "The Risks of Key Recovery, Key Escrow, Trusted Third-Party Encryption", analyzing the architectural vulnerabilities of implementing key escrow systems in general, including but not limited to the Clipper chip Skipjack protocol; the technical flaws described in this paper were instrumental in the demise of the Clipper chip as a public policy option. While many leading voices in the computer science community expressed opposition to the Clipper chip and key recovery in general, some supported the concept, including Dorothy E. Denning.
The Clipper chip was not embraced by consumers or manufacturers and the chip itself was no longer relevant by 1996. The U. S. government continued to press for key escrow b