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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However, some FDE solutions use multiple keys for encrypting different partitions. If an attacker gains access to the computer at run-time, he has access to all files. Conventional file and folder encryption instead allows different keys for different portions of the disk. Thus an attacker cannot extract information from still-encrypted files and folders.

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Although this has the advantage that the disk cannot be removed from the device, it might create a single point of failure in the encryption. For example, if something happens to the TPM or the motherboard, you might not be able to access your data simply by connecting the hard drive to another computer, unless you also have a separate recovery key.

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The Hardware-based Full Disk Encryption solutions are considerably faster than the software-based solutions, and usually produce no overhead for the CPU or the hard disk drive. Hardware-based Full Disk Encryption, without some form of user authentication, provides absolutely no protection of data. Currently, there are two solutions providing Pre-Boot Authentication for Hardware-based Full Disk Encryption and a BIOS or ATA password can provide basic access control.

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A good hash function should map the expected inputs as evenly as possible over its output range. That is, every hash value in the output range should be generated with roughly the same probability. When testing a hash function, the uniformity of the distribution of hash values can be evaluated by the chi-square test.

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In computer science, geometric hashing is a method for efficiently finding two-dimensional objects represented by discrete points that have undergone an affine transformation. (Extensions exist to some other object representations and transformations.)

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Augmented methods have the added goal of ensuring that password verification data stolen from a server cannot be used by an attacker to masquerade as the client, unless the attacker first determines the password (e.g. by performing a brute force attack on the stolen data).

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More literacy, or opponent literacy, required actual cryptography. The main classical cipher types are transposition ciphers, which rearrange the order of letters in a message (e.g., 'hello world' becomes 'ehlol owrdl' in a trivially simple rearrangement scheme)An early substitution cipher was the Caesar cipher, in which each letter in the plaintext was replaced by a letter some fixed number of positions further down the alphabet.

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Encryption attempts to ensure secrecy in communications, such as those of spies, military leaders, and diplomats. There is record of several early Hebrew ciphers as well. Cryptography is recommended in the Kama Sutra as a way for lovers to communicate without inconvenient discovery.[5] Steganography (i.e., hiding even the existence of a message so as to keep it confidential) was also first developed in ancient times.

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The modern study of symmetric-key ciphers relates mainly to the study of block ciphers and stream ciphers and to their applications. A block cipher is, in a sense, a modern embodiment of Alberti's polyalphabetic cipher: block ciphers take as input a block of plaintext and a key, and output a block of ciphertext of the same size.

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That internal state is initially set up using the secret key material. RC4 is a widely used stream cipher; see Category:Stream ciphers.[10] Block ciphers can be used as stream ciphers; see Block cipher modes of operation. Cryptographic hash functions are a third type of cryptographic algorithm. They take a message of any length as input, and output a short, fixed length hash which can be used in (for example) a digital signature.

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Whilst the academic study of trust relationships and systems has long been the forte of intelligence services such as the American NSA, the growth of the internet in the 1990s and the contemporary declassification of related knowledge allowed for greater public discussion of the potential for anonymous banking services by groups such as the cryptoanarchists and cypherpunks.

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Note that if neither Alice nor Bob wishes the bank to know that they performed a transaction with each other, then it is hard for the bank to find out. However, in order to ensure this is the case many people need to be making transactions at the same time. Otherwise the bank can figure it out by the timing of the transactions, using traffic analysis.

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Typically, this involves use of computer networks, the internet and digital stored value systems. Electronic Funds Transfer (EFT) and direct deposit are examples of electronic money. Also, it is a collective term for financial cryptography and technologies enabling it.

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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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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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The term cypherpunk, derived from cipher and punk, was coined by Jude Milhon as a pun to describe cyberpunks who used cryptography. [1] In November 2006, the word was proposed for inclusion in the Oxford English Dictionary[2]. The Cypherpunks included several notable computer industry figures

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The diagram to the right shows Blowfish's F-function. The function splits the 32-bit input into four eight-bit quarters, and uses the quarters as input to the S-boxes. The outputs are added modulo 232 and XORed to produce the final 32-bit output.

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The algorithm's overall structure is shown in Figure 1: there are 16 identical stages of processing, termed rounds. There is also an initial and final permutation, termed IP and FP, which are inverses (IP "undoes" the action of FP, and vice versa). IP and FP have almost no cryptographic significance, but were apparently included in order to facilitate loading blocks in and out of mid-1970s hardware, as well as to make DES run slower in software.

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The output from the F-function is then combined with the other half of the block, and the halves are swapped before the next round. After the final round, the halves are not swapped; this is a feature of the Feistel structure which makes encryption and decryption similar processes.

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