Encryption

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Encryption is the process of encoding or scrambling a message. 

Decryption is the process of decoding or unscrambling a message.

An encryption algorithm or cipher is a type of cryptographic process that scrambles the characters used in a message so that the message can be seen but not understood or modified unless it can be deciphered.

• composed of:
  • different types of cipher/algorithm (used interchangeably)
  • one or more keys
• assures confidentiality
• use cases:
  • a secure means of transmitting data and authenticating users
  • storing data securely

Algorithms

• Modern encryption algorithms use the basic techniques of substitution and transposition in complex ways that can defeat attempts at cryptanalysis
  • Substitution Cipher
  • Transposition Cipher

Properties of Encryption Algorithms

Secure encryption algorithm has 2 properties:

• Confusion
  • is a secure encryption algorithm property that ensures that changing a single bit of an encryption key impacts most of the ciphertext bits.
  • this property hides the relationship between a ciphertext and the encryption key
• Diffusion
  • is a secure encryption algorithm property that ensures that changing a single plaintext bit changes about half of the ciphertext bits and changing a single ciphertext bit changes about half of the plaintext bits.
  • hides the relationship between a plaintext and a cipher text

Cryptographic Key

A cryptographic key is a set of data that the encryption algorithm combines with the input plaintext to produce the encrypted, protected output—the ciphertext.

Encryption algorithms must be decrypted using a key linked to the initial encryption process.

• size of the key is one factor in determining the strength of the encryption
• A keyspace is the range of values that the key could be
  • Modern ciphers use large keyspaces with trillions of possible key values
  • makes key more resistant to brute force
• Keys for modern symmetric ciphers use a pseudorandomly generated number of bits
  • key length is the size of the encryption key measured in bits
  • a bit has a value of 0 or 1
    • possible key values is
  • e.g., Advanced Encryption Standard (AES)
    • AES-128 uses a 128-bit key length ()
    • AES-256 uses 256-bit key length ()
      • trillions of times bigger than 128-bit
• key stretching is the process of artificially increasing a key’s length and complexity
  • makes keys more resistant to brute-force attacks
• drawback of larger keys:
  • computer uses greater memory and processor cycles

Types

• Symmetric Encryption
• Asymmetric Encryption