1. RSA
   1. A public key cryptography algorithm developed by Rivest Shamir and Adleman. Commonly used in e-commerce.
   2. RSA public and private key usage:
      1. Send an encrypted message:
         1. Uses the receiver's public key
      2. Decrypt an encrypted message:
         1. Uses the receiver's private key
      3. Send an encrypted signature:
         1. Uses the sender's private key
      4. Decrypt an encrypted signature:
         1. Uses the sender's public key
2. Diffie-Hellman
   1. Invented in the 1970s, the first practical method for establishing a shared secret key over an unprotected communications channel.
3. Elliptic Curve
   1. Elliptic Curve Cryptography (ECC):
      1. A type of public key cryptography based on the structure of an elliptic curve.
   2. Elliptic Curve Diffie-Hellman Ephemeral (ECDHE):
      1. An asymmetric algorithm created by Diffie and Hellman that is based on elliptic curve cryptography and runs in ephemeral mode.
4. Other
   1. One-Time Pad (OTP)
      1. A cipher that encrypts plaintext with a secret random key that is the same length as the plaintext.
   2. PGP
      1. Pretty Good Privacy (PGP):
         1. An encryption program used primarily for signing, encrypting, and decrypting e-mails in an attempt to increase the security of e-mail communications.
      2. GNU Privacy Guard (GPG):
         1. A free alternative to PGP that is compliant with OpenPGP.
   3. Pseudorandom Number Generators
      1. Pseudorandom Number Generator (PRNG):
         1. Used by cryptographic applications that require unpredictable output.
         2. Example:
            1. SHA2PRNG
         3. Threat:
            1. RNG Attack
         4. Prevention:
            1. Additional randomness, AES, SHA256 or higher, and physical control of the system.