1. Cryptography

2. Introduction Encryption  The art (or science) of putting messages into a code, and the study of those coding techniques. Decryption  The means by which to bring out the meaning from a coded message.

3. Simple Techniques Original text “testing”  Reversing text “gnitset”  Shifting text “uftujoh”  Flipping text “ettsnig”  Caeser cipher Multi-shift (this one is by 2) “vguvkpi” Examples

4. Cryptography Public Key Encryption  You create a private key/public key pair If a message is encrypted with your private key, only your public key will decrypt it Publish your public key on web sites or send it to people via e-mail  Uses If you want to send a private message to another person, encrypt it with their public key (only they can decrypt it with their private key) Digital Signatures  Encrypt with your private key first and then their public key  PGP (Pretty Good Privacy) One version of this technology Example