is a protocol designed to define a common key of arbitrary length between two partners in quantum cryptography. If the key has the size of the message, then the encryption and decryption is equivalent to a One Time Pad.

Back Orifice (BO, BO2K)

is a hacking tool created by the Cult of the Deac Cow (cDc).  Back Orifice is a remote administration system which allows a user to control a  machine over a network using a simple console or GUI application. On a local LAN or across the internet, Back Orifice gives its user more control of the remote Windows system than the person at the keyboard of that machine.  It is available for Windows and Unix.  It is an open source project.

Bell LaPadula

is a security model designed in 1973 by David Bell and Len LaPadula. It is also known as multilevel security. It aims at managing access data at different levels. It enforces two properties:

    • No process may read data at a higher level.
    • No process may write data to a lower level

Birthday attack

is of the class of the brute force attacks. It is based on the property that if a function returns one of k equally like values, then by repeatedly evaluating the function for different inputs, we expect to find the same output after about

1.2  . K 1/2 trials.

Black hat

is the term describing hackers that act with evil purposes.  It is opposed to white hats.

Blind data

is the fact to hide data with a randomly chosen number. Thus, the recipient is not able to access the blind data. Knowing the random number, the emitter is able to retrieve his data.

Blind signature schemes

allow a person to get a message signed by another party without revealing any information about the message to the other party. They are used for digital time stamping, and digital cash.

Blinding factor

is the random quantity used to blind a data in a blind signature.

Block cipher

transforms a fixed length block of data into a block of cipher data of the same length. This transformation uses a user provided secret key. Decryption uses the reverse transformation. There are four main standardized modes of usage.

    • ECB (Electronic Code Block): Each plain text block is encrypted independently with the block cipher. Concurrent processing is easy.
    • CBC (Cipher Block Chaining Mode): Each plain text block is XORed with the previous cipher text block, then encrypted. The advantage over ECB is that patterns in plain text are removed in the cipher text. This is the preferred mode for DES.
    • CFB (Cipher Feedback): If two successive plain texts are identical, then this scheme removes the transparency inherent to ECB and CBC.
    • OFB (Output Feedback): This scheme does not propagate errors due to transmission in the decrypted text.


is a 64-bit block cipher designed by Bruce SCHNEIER. The key has a variable length up to 448 bits. It is currently considered as a secure cryptosystem.

Buffer Overflow attack

is one of the most exploited flaws in software. A common basic error in software engineering is that data entering a buffer may overflow the allocated size. Skilled hackers may so download malicious code in the memory of the computer that will be executed by the CPU.

Bulk cipher

is a symmetric encryption algorithm used to encrypt large quantities of data.

Brut Force Attack

is the technique of cryptanalysis trying every possible key. It is necessary to have a cipher text and the corresponding clear text.  This is an exhaustive search.

The best-known attack against DES finds a key in an individual session of 4.5 days using custom hardware costing approximately $250,000

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