Glossary for cryptography
Tuesday, January 29, 2008, 22:13
algorithm
A procedure or mathematical formula. Cryptographic algorithms convert plaintext to and from ciphertext.
cipher
Synonym for “cryptographic algorithm”
cryptanalysis
To solve or “break” a cryptosystem.
EAR
Export Administration Regulations. The rules under which the export of cryptographic software from the US are governed now.
escrow
A third party able to decrypt messages sent from one person to another. Although this term is often used in connection with the US Government’s “Clipper” proposals, it isn’t limited to government-mandated ability to access encrypted information at will. Some corporations might wish to have their employees use cryptosystems with escrow features when conducting the company’s business, so the information can be retrieved should the employee be unable to unlock it himself later, (if he were to forget his passphrase, suddenly quit, get run over by a bus, etc.) Or, someone might wish his spouse or lawyer to be able to recover encrypted data, etc., in which case he could use a cryptosystem with an escrow feature.
initialization vector
One of the problems with encrypting such things as files in specific formats (i.e., that of a word processor, email, etc.) is that there is a high degree of predictability about the first bytes of the message. This could be used to break the encrypted message easier than by brute force. In ciphers where one block of data is used to influence the ciphertext of the next (such as CBC), a random block of data is encrypted and used as the first block of the encrypted message, resulting in a less predictable ciphertext message. This random block is known as the initialization vector. The decryption process also performs the function of removing the first block, resulting in the original plaintext.
ITAR
International Traffic in Arms Regulations. These are the rules by which munitions, as defined by the US State Department, may (or may not) be exported from the US. Until recently, this also included the export of cryptography. The exportability of cryptography is now in the hands of the Bureau of Export Administration, under the US Department of Commerce.
key
A piece of data that, when fed to an algorithm along with ciphertext, will yield plaintext. (Or, when fed to an algorithm along with plaintext, will yield ciphertext.
random session key
This is a temporary key that is generated specifically for one message. Typically, in public key cryptosystems, the message to be sent is encrypted with a symmetric key that was specifically generated for that message. The encrypted version of that message, as well as the associated session key can then be encrypted with the recipient’s public key. When the recipient decrypts the message, then, the system will actually decrypt the message it gets (which is the ciphertext message and the symmetric key to decrypt it), and then use the symmetric key to decrypt the ciphertext. The result is the plaintext message. This is often done because of the tremendous difference in the speed of symmetric vs. asymmetric ciphers.
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