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In lecture 2 we learn about authentication and basic cryptography. Authentication is identity of someone who generates data being verified. Authentication used to protect information or data from active attack. There are many classification to verify identity of someone, we can use password, by identity card such as smart card or passport, using physical characteristic such as finger print and retina, and also by signature. Password is a character of string that used to authenticate identity. To make password hard to guessed we must combine number and letter, uppercase and lowercase, and also include symbol in the password. Even though we already combine all those things to create password, is not impossible the password being guessed by the hacker. To prevent that there is a method, cryptography method. Cryptography is convert plain text into cipher text. The idea of cryptography is to disguise the information and make it meaningless to unauthorized user.

Cryptography terminology:

• Plain text is the original text.
• Cipher text is the coded text.
• Cipher - algorithm for transforming plaintext to ciphertext
• Key - info used in cipher known only to sender/receiver
• Encipher (encrypt) - converting plaintext to ciphertext
• Decipher (decrypt) - recovering ciphertext from plaintext
• Cryptography - study of encryption principles/methods
• Cryptanalysis (codebreaking) - study of principles/ methods of deciphering ciphertext without knowing key
• Cryptology - field of both cryptography and cryptanalysis

Caesar cipher is letters A to W is encrypted by being represented by the letter that occurs three places after it in the alphabet. This cipher used by Julius Caesar in Gallic wars. Another way to protect the information is using digital signature. Digital signature is like hand written signature, its depend on the sender and same for all the message.