Cryptography Overview

“I'm more interested in the future than in the past, because the future is where I intend to live.” --Albert Einstein

• What is Cryptography?

1. The Science and Study of Hiding information.
   -Hiding information by converting plaintext into ciphertext(E)
   -The back from ciphertext to plaintext(D).

• Benefits of Cryptography

1. Confidentiality
   - Protecting data in transit.
   -Protecting data in rest.
2. Non-repudiation & authentication
   - A message encrypted with your private key or signed with your digital signature had to come from you
3. Access Control
   *- With symmetric encryption only the secret key holder can decrypt the ciphertext.
   -With a symmetric encryption a digital certificate can be used to authentication and thus access control.
4. Integraty
   
   - Message digest can be used to know if a message was tampered with during transit.

• How Cryptography Works

1. A cipher & a key(s)
   -An algorithm encrypts data by applying a key to plaintext.
   -Another algorithm decrypts data by applying key to ciphertext.
2. Different ciphers|algorithms are stronger than others.
3. Longer keys make stronger encryption
   - 40-bit key is not secure.
   

• Classic Ciphers

1. Substitution Cipher
2. Transposition Cipher

• Substitution Cipher Example

1. Caesar Substitution Cipher
   

• Transposition Cipher Example

1. Reversing Transportation Cipher
2. Scytale Transposition Cipher
   

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