Information Science

1. Coding

2. Error detection/correction code

Example: When the message is a₁a₂a₃a₄, the code word is a₁a₂a₃a₄c₁c₂c₃, where
c₁ = a₁+a₂+a₃, c₂ = a₁+a₃+a₄, c₃ = a₂+a₃+a₄


1: message, 2: code word, 3: received code, 4: error correction

Assume the weight of a binary code is t. The code will detect (though not fix) t-1 errors. If t is odd, the code will correct (t-1)/2 errors, if t is even, the code will correct (t-2)/2 errors. For example, the weight of the above code is 3 (see Table 17.1, page 620), so it can either detect 2 errors or correct 1 error.

Another distance-based explanation of error correcting code.

3. Compression coding

Huffman Coding

4. Cryptography

Vigenere cipher

A	B	C	D	E	F	G	H	I	J	K	L	M	N	O	P	Q	R	S	T	U	V	W	X	Y	Z
0	1	2	3	4	5	6	7	8	9	10	11	12	13	14	15	16	17	18	19	20	21	22	23	24	25

Credit card number, in binary code, can be encrypted and decrypted by adding the same binary key.

Public Key Encryption

Cryptogram

Assignment: Chapter 17 Exercises No. 1-5, 7, 9, 11, 20-21, 27, 29-32, 35, 38-39, 43, 51