programming-for-dummies

Chapter 5: Encryption Algorithms
In This Chapter
Encryption basics
Symmetric and asymmetric encryption
Cracking encryption with attacks
Encryption involves scrambling information, or plaintext, and converting
it into another format — ciphertext — essentially turning ordered data
into seemingly random gibberish. By encrypting information, you can keep
data information out of the hands of other people, which can be useful for
sending coded messages for military use, sending credit card information
over the Internet to online shopping Web sites, or just hiding your personal
documents from the prying eyes of family members, co-workers, or strangers.
The simplest form of encryption is substitution cipher, which basically
replaces each letter with a specific symbol, such as another letter. A substitution
cipher simply replaces one letter with another letter from the alphabet
a fixed distance away, such as replacing the letter A with the letter Z, the
letter B with the letter A, the letter C with the letter B, and so on.
In this case, each letter gets replaced by the previous letter in the alphabet,
like this:
I AM HOT
Replacing the letter I with the letter H, the letter A with the letter Z, and so
on creates the following ciphertext:
H ZL GNS
This information may be scrambled, but after someone discovers that each
letter in the ciphertext actually represents the next letter in the alphabet,
this simple substitution cipher can be cracked easily. When an encryption
method can be broken easily, it’s weak encryption. If an encryption method
can’t be broken easily, it’s strong encryption.
The key to deciphering the substitution cipher is recognizing both the method
it’s using (replacing one letter with another) and the specific way it implements
that method (replacing each letter with the previous letter in the
alphabet). A slightly more-complicated substitution cipher might replace