Computer World. Матросова Т.А. - 107 стр.

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106
The Elements of Encryption
There are many different ways that you can use a computer to encrypt or decrypt
information. Nevertheless, each of these so-called encryption systems share common
elements :
Encryption algorithm
The encryption algorithm is the function, usually with some mathematical
foundations, which performs the task of encrypting and decrypting your data.
Encryption keys
Encryption keys are used by the encryption algorithm to determine how
data is encrypted or decrypted. Keys are similar to computer passwords: when
a piece of information is encrypted, you need to specify the correct key to
access it again. But unlike a password program, an encryption program doesn't
compare the key you provide with the key you originally used to encrypt the
file, and grant you access if the two keys match. Instead, an encryption
program uses your key to transform the ciphertext back into the plaintext. If
you provide the correct key, you get back your original message.
Key length
As with passwords, encryption keys have a predetermined length. Longer
keys are more difficult for an attacker to guess than shorter ones because there
are more of them to try in a brute-force attack. Different encryption systems
allow you to use keys of different lengths; some allow you to use variable-
length keys.
Plaintext
The information which you wish to encrypt.
Ciphertext
The information after it is encrypted.
Cryptographic Strength
Different forms of cryptography are not equal. Some systems are easily
circumvented, or broken. Others are quite resistant to even the most determined
attack. The ability of a cryptographic system to protect information from attack is
c alled its strength. Strength depends on many factors, including:
• The secrecy of the key.
• The difficulty of guessing the key or trying out all possible keys (a key search).
Longer keys are generally harder to guess or find.
• The difficulty of inverting the encryption algorithm without knowing the
encryption key (breaking the encryption algorithm).
• The existence (or lack) of back doors, or additional ways by which an
encrypted file can be decrypted more easily without knowing the key.

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