TCF389: Public Key Cryptography

Text or data is encrypted (scrambled) according to a key that both sender & receiver have
Then it is decrypted using that key
One piece of software facilitating that is Pretty Good Privacy (PGP)

Pretty Good Privacy (PGP)

Two complementary keys are used to maintain secure communications:
1. Private key to which only you have access
2. Public key which you freely exchange with other PGP users.
  - Include your public key in an e-mail message,
    - It's just a block of text--e.g., see my public key on my homepage.
  - Copy it to a file and give them the file,
  - Post it on a public key server where anyone can get a copy when they need it. You can then put a link to it in your Web pages:
    - http://pgpkeys.mit.edu:11371/pks/lookup?op=get&search=0xECF82637
To send someone an encrypted, private e-mail message
- Use a copy of that person’s public key to encrypt the information, which only they can decipher by using their private key.
  - See hand-out.
- (When someone wants to send you encrypted mail, they use a copy of your public key to encrypt the data, which only you can decipher by using a copy of your private key.)
Signing e-mail with encryption--to authenticate that it was really sent by who it purports to be sent by
- Faking e-mail is extremely easy
1. You use your private key to sign a message, thus authenticating it with your PGP Signature.
  - See below.
2. Then recipients use their copy of a public key to determine if you really sent the e-mail and whether it has been altered while in transit.