Cryptographic Key

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

• many processes have been used to produce keys
  • one-time pads
    • in theory, is the only truly unbreakable encryption process, when used correctly
  • pseudorandom numbers
    • commonly used as keys
    • sender and recipient each have a copy of the same pseudorandom number generator algorithm
    • uses a seed value to start with
    • sequence of pseudorandom numbers from provides either
      • a one-time pad of encryption keys
      • or a keystream for stream cipher use
  • Hardware random and pseudorandom number generators combined with software functions
    • can generate keys or keystreams
    • latest versions can use quantum computing technologies to generate unique keystreams

Key Strength

Cryptologic key strength is a way to measure or estimate how much effort would be required to break (illicitly decrypt) a cleartext message encrypted by a given algorithm using such a key.

• often directly related to the key size
  • defined by how many bits makes up the key
• key strength determines the size of the key space
  • the total number of values that such a key can take on
  • e.g.,
    • 8-bit key can represent the decimal numbers 0-255
      • means 8-bit key space has 256 unique values in it
    • SSL uses a 256-bit key as its session key

Key Distribution and Management

Key material is a term that collectively refers to all materials and information that govern how keys are generated and distributed to users in a cryptographic system.

Key management processes govern how long a key can be used and what users and systems managers must do if the key has been compromised.

Key distribution describes how newly generated keys are issued to each legitimate user, along with any updates to the rules for their period of use and their safe disposal.

• follows same topological considerations as networks:
  • point-to-point
    • connects only 2 users and requires only one pair
  • star
    • for a given set of users, star requires pairs of keys to keep traffic secure and private between each user and central site
  • full-mesh
    • requires sets of keys for unique secure communication for each pair of users