This article discusses hardware which is used to implement the technique (for cryptographic aspects of the problem see disk encryption). Compared to access restrictions commonly enforced by an OS, this technique allows to protect data even when the OS is not active, for example, if data is read directly from the hardware.

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Although these concepts overlap to some extent, each has its own uses and requirements and is designed and optimised differently. The HashKeeper database maintained by the National Drug Intelligence Center, for instance, is more aptly described as a catalog of file fingerprints than of hash values.

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The same techniques can be used to find equal or similar stretches in a large collection of strings, such as a document repository or a genomic database. In this case, the input strings are broken into many small pieces, and a hash function is used to detect potentially equal pieces, as above.

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This principle is widely used in computer graphics, computational geometry and many other disciplines, to solve many proximity problems in the plane or in three-dimensional space, such as finding closest pairs in a set of points, similar shapes in a list of shapes, similar images in an image database, and so on.

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In these applications, the set of all inputs is some sort of metric space, and the hashing function can be interpreted as a partition of that space into a grid of cells. The table is often an array with two or more indices (called a grid file, grid index, bucket grid, and similar names), and the hash function returns an index tuple. This special case of hashing is known as geometric hashing or the grid method.

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Good hash functions, in the original sense of the term, are usually required to satisfy certain properties listed below. Note that different requirements apply to the other related concepts (cryptographic hash functions, checksums, etc.).

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The same technique can be used to map two-letter country codes like 'us' or 'za' to country names (26²=676 table entries), 5-digit zip codes like 13083 to city names (100000 entries), etc. Invalid data values (such as the country code 'xx' or the zip code 00000) may be left undefined in the table, or mapped to some appropriate 'null' value.

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A perfect function for a given set of n keys, suitable for use in a hash table, can be found in time proportional to n, can be represented in less than 3*n bits, and can be evaluated in a constant number of operations. There are generators that will emit optimized executable code to evaluate a perfect hash for a given input set.

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For instance, most patrons of a supermarket will live in the same geographic area, so their telephone numbers are likely to begin with the same 3 to 4 digits. In that case, if n is 10000 or so, the division formula (z × n) ÷ N, which depends mainly on the leading digits, will generate a lot of collisions; whereas the remainder formula z mod n, which is quite sensitive to the trailing digits, may still yield a fairly even distribution of hash values.

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Although several of the forms of EKE in this paper were later found to be flawed, the surviving, refined, and enhanced forms of EKE effectively make this the first method to amplify a shared password into a shared key, where the shared key may subsequently be used to provide a zero-knowledge password proof or other functions.

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In cryptography, a password-authenticated key agreement method is an interactive method for two or more parties to establish cryptographic keys based on one or more party's knowledge of a password. Password-authenticated key agreement.

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Until modern times cryptography referred almost exclusively to encryption, which is the process of converting ordinary information (plaintext) into unintelligible gibberish (i.e., ciphertext).[2] Decryption is the reverse, in other words, moving from the unintelligible ciphertext back to plaintext. A cipher (or cypher) is a pair of algorithms which create the encryption and the reversing decryption.

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Before the modern era, cryptography was concerned solely with message confidentiality (i.e., encryption) — conversion of messages from a comprehensible form into an incomprehensible one and back again at the other end, rendering it unreadable by interceptors or eavesdroppers without secret knowledge (namely the key needed for decryption of that message). In recent decades, the field has expanded beyond confidentiality concerns to include techniques for message integrity checking, sender/receiver identity authentication, digital signatures, interactive proofs and secure computation, among others.

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Since messages are almost always longer than a single block, some method of knitting together successive blocks is required. Several have been developed, some with better security in one aspect or another than others. They are the modes of operation and must be carefully considered when using a block cipher in a cryptosystem.

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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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One rare success has been Hong Kong's Octopus card system, which started as a transit payment system and has grown into a widely used electronic cash system. Singapore also has an electronic money implementation for its public transportation system (commuter trains, bus, etc), which is very similar to Hong Kong's Octopus card and based on the same type of card (FeliCa). There is also one implementation in the Netherlands, known as Chipknip.

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Symmetric-key algorithms can be divided into stream ciphers and block ciphers. Stream ciphers encrypt the bytes of the message one at a time, and block ciphers take a number of bytes and encrypt them as a single unit. Blocks of 64 bits have been commonly used; the Advanced Encryption Standard algorithm approved by NIST in December 2001 uses 128-bit blocks.

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However, lack of randomness in those generators or in their initialization vectors is disastrous and has led to cryptanalytic breaks in the past. Therefore, it is essential that an implementation uses a source of high entropy for its initialization.

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At the time Blowfish was released, many other designs were proprietary, encumbered by patents or were commercial/government secrets. Schneier has stated that, "Blowfish is unpatented, and will remain so in all countries. The algorithm is hereby placed in the public domain, and can be freely used by anyone."

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Another member of the DES team, Walter Tuchman, is quoted as saying, "We developed the DES algorithm entirely within IBM using IBMers. The NSA did not dictate a single wire!"[6] In contrast, a declassified NSA book on cryptologic history states:

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