Reading from Blown to Bits for next class
Bits
To appreciate encryption, we must learn a bit about bits. We’ll start with Semmy’s Digital Encodings lecture notes.
Bit strings
What is the number of bitstrings of length n.
| n | 2n | things to consider |
|---|---|---|
| 16 | 65536 | Common for “personal” computer in the 80’s |
| 32 | 4294967296 | Common for today’s computers Could cause problems in the year 2038 |
| 56 | 72057594037927936 | Number of DES keys |
| 64 | 18446744073709551616 | Number of Lucifer keys |
| 256 | ~ 1.15 × 1077 | Common for AES keys Number of observable atoms about 4 × 1080 |
| 2048 | ~ 3.2 × 10626 | Common for RSA keys |
| 4096 | ~ 1 × 101253 | Hard RSA keys |
Is it possible that Edward Snowden really doesn’t know how to decrypt all documents he has?
Chalkboard exercise
- What is 42 in binary?
- What does the binary number 00100110 represent?
Representing information
- Hexadecimal: as in The Martian
- Hexadecimal: as in HTML
- ASCII and Extended ASCII
- Unicode
- The CSCI 255 spreadsheet
Getting ready
Following instructions given in lab, do the following.
- Open a terminal session
- You can also try connecting to iotla.cs.unca.edu using ssh
- Create a directory called public_html/lab107
- Create a file public_html/lab107/hello.txt
- View http://www.cs.unca.edu/~yourname/lab107/hello.txt in your browser