Examples of software that can be used for file encryption are special-purpose software (e.g., GNU Privacy Guard and PGP), file archivers, and even some text editors (e.g., emacs or vi). This section lists features commonly found in disk encryption software, though not all functions may be provided in any given system. Some disk encryption systems offer two levels of Plausible Deniability, which might be useful in case a user is required to reveal the password of an encrypted volume.

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If used properly, someone finding a lost device will have access only to inaccessible encrypted files. Software encryption is a fundamental part of all aspects of modern computer communication and file protection and may include features like file shredding.

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If the disk encryption hardware is integrated with the media itself the media may be designed for better integration. One example of such design would be through the use of physical sectors slightly larger than the logical sectors.

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A hash function is any well-defined procedure or mathematical function which converts a large, possibly variable-sized amount of data into a small datum, usually a single integer that may serve as an index into an array.

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Hash functions are primarily used in hash tables, to quickly locate a data record (for example, a dictionary definition) given its search key (the headword). Specifically, the hash function is used to map the search key to the hash. The index gives the place where the corresponding record should be stored. Hash tables, in turn, are used to implement associative arrays and dynamic sets.

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The meaning of 'small enough' depends on how much memory is available for the hash table. A typical PC (as of 2008) might have a gigabyte of available memory, meaning that hash values of up to 30 bits could be accommodated. However, there are many applications that can get by with much less.

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The term "hash" comes by way of analogy with its non-technical meaning, to "chop and mix". Indeed, typical hash functions, like the mod operation, "chop" the input domain into many sub-domains that get "mixed" into the output range to improve the uniformity of the key distribution.

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In the most general form of EKE, at least one party encrypts an ephemeral (one-time) public key using a password, and sends it to a second party, who decrypts it and uses it to negotiate a shared key with the first party.

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In the most stringent password-only security models, there is no requirement for the user of the method to remember any secret or public data other than the password. Augmented PAKE is a variation applicable to client/server scenarios, in which an attacker must perform a successful brute-force attack in order to masquerade as the client using stolen server data.

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As well as being aware of cryptographic history, cryptographic algorithm and system designers must also sensibly consider probable future developments while working on their designs. For instance, continuous improvements in computer processing power have increased the scope of brute-force attacks, thus when specifying key lengths, the required key lengths are similarly advancing

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The potential effects of quantum computing are already being considered by some cryptographic system designers; the announced imminence of small implementations of these machines may be making the need for this preemptive caution less than merely speculative.

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Symmetric-key cryptography refers to encryption methods in which both the sender and receiver share the same key (or, less commonly, in which their keys are different, but related in an easily computable way). This was the only kind of encryption publicly known until June 1976.

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Because of the blinding process, the Bank is not able to associate R'' with R' or R, so it is unable to determine that Bob and Alice are doing business together, preserving the anonymity of the transaction. Alice unblinds R''' to generate the original value R, which she sends to Bob.

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Using cryptography, anonymous ecash was introduced by David Chaum. He used blind signatures to achieve unlinkability between withdrawal and spend transactions.[1] In cryptography, e-cash usually refers to anonymous e-cash. Depending on the properties of the payment transactions, one distinguishes between on-line and off-line e-cash. The first off-line e-cash system was proposed by Chaum and Naor.

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The main focuses of digital cash development are 1) being able to use it through a wider range of hardware such as secured credit cards; and 2) linked bank accounts that would generally be used over an internet means, for exchange with a secure micropayment system such as in large corporations (PayPal).

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The transfer of digital currencies raises local issues such as how to levy taxes or the possible ease of money laundering. There are also potential macroeconomic effects such as exchange rate instabilities and shortage of money supplies (total amount of digital cash versus total amount of real cash available, basically the possibility that digital cash could exceed the real cash available). These issues may only be addressable by some type of cyberspace regulations or laws that regulate the transactions and watch for signs of trouble.

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Events such as the GURPS Cyberpunk raid lent weight to the idea that private individuals needed to take steps themselves to protect their privacy. In its heyday, the list discussed the public policy issues related to cryptography, as well as more practical nuts-and-bolts mathematical, computational, technological, and cryptographic matters themselves.

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This prevents its use in certain applications, but is not a problem in others. In one application, it is actually a benefit: the password-hashing method used in OpenBSD uses an algorithm derived from Blowfish that makes use of the slow key schedule; the idea is that the extra computational effort required gives protection against dictionary attacks. See key strengthening.

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The Data Encryption Standard (DES) is a block cipher (a form of shared secret encryption) that was selected by the National Bureau of Standards as an official Federal Information Processing Standard (FIPS) for the United States in 1976 and which has subsequently enjoyed widespread use internationally.

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DES is now considered to be insecure for many applications. This is chiefly due to the 56-bit key size being too small; in January, 1999, distributed.net and the Electronic Frontier Foundation collaborated to publicly break a DES key in 22 hours and 15 minutes (see chronology).

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