Ch 20 + 21 - Symmetric/Public Key Encryption & Message Confidentiality

Symmetric Encryption

A conventional form of public key encryption that uses the same key for both encryption and decryption.

Encryption Ingredients

• encryption and decryption algorithms

• input plaintext

• output ciphertext

• secret key.

Cryptography Classifications

Divided into:

• types of operation (substitution, transposition)

• number of keys (symmetric, asymmetric)

• plaintext processing (block cipher, stream cipher).

Substitution Cipher

Mapping method in encryption that is prone to brute force attacks.

Transposition Cipher

An encryption method that rearranges the elements of the plaintext.

Block Cipher

Processes data one block of elements at a time.

Stream Cipher

Processes data elements continuously.

Secure Encryption Criteria

The cost and time to decrypt should exceed the value and relevance of the information.

Electronic Code Book (ECB)

A method of encryption where blocks are encoded using the same key.

Cipher Block Chaining (CBC)

A method of encryption using XOR to encode blocks of plaintext + ciphertext

Cipher Feedback (CFB)

A method of encryption that encodes with ciphertext then uses XOR with plaintext to produce another ciphertext

Output Feedback (CFB)

A method of encryption that encodes with ciphertext then uses DES with plaintext to produce another ciphertext

Counter (CTR)

A method of encryption that encodes via XOR and a counter that increments every block

Match the block ciphers with their application:

• Cipher Feedback (CFB)

• Output Feedback (CFB)

• Electronic Code Book (ECB)

• Cipher Block Chaining (CBC)

• Counter (CTR)

• Used for encrypting single values

• Used for noisy channels

• Useful for high speed requirements

• Used for General Purpose/Authentication
  

• Cipher Feedback (CFB) - Used for General Purpose/Authentication

• Cipher Block Chaining (CBC) - Used for General Purpose/Authentication

• Electronic Code Book (ECB) - Used for encrypting single values

• Output Feedback (CFB) - Used for noisy channels

• Counter (CTR) - Useful for high speed requirements

The biggest challenge in symmetric key encryption is _____

Key Distribution

Hash Function

Transforms data without using a key, creating a hash that summarizes the data. If the data is tampered with, a different hash is creeated

Secure Hash Algorithm (SHA)

A method that creates high bit hash values aimed at strengthening encryption.

HMAC

A combination of an encryption algorithm key and SHA hashing for added authentication while maintaining easy keys

RSA

The foundation of public key encryption, vulnerable to various attacks such as brute force and mathematical attacks.

Timing Attack

An unexpected attack that derives a private key from the time taken to decrypt information.

Diffie-Hellman Key Exchange

The first public key algorithm for secure secret key exchange, which is subject to man-in-the-middle attacks.

Blinding

A countermeasure against timing attacks that involves multiplying ciphertext before exponentiation.