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Our Lecture 2.1 ((2) Terminology :neutral_face: :frowning_face: :cry:…
Our Lecture
2.1
(2)
Terminology
:neutral_face: :frowning_face: :cry:
Cryptanalysis
Cryptology
Cryptography
Plaintext
Decryption or Deciphering
Ciphertext
Cipher
Key
Encryption or Enciphering
Conventional Encryption Principles(An encryption scheme has five ingredients)
(3) Requirements for :warning: Secure Use :warning:
:check:Strong encryption algorithm
At a minimum, if opponent
knows the algorithm
Has access to one or more ciphertexts and the corresponding plain texts
:check:Sender and receiver must obtain secret key securely
(1) Security Objectives
:cop:
Availability
Authenticity
Integrity
Non-repudiation
Confidentiality
(4) Cryptographic Protocols aims
:+1:
Proof of the sender’s identity
Message shouldn’t be corrupted in transit
Only the recipient should get it
Only the recipient should see it
Messages should be transmitted to destination
Message should be sent/received once only
(5) Types of ciphers
:red_flag:
Private key cryptosystems/ciphers
(The secret key is shared between two parties)
composed of two algorithms:
encryption algorithm E
decryption algorithm D
Vulnerabilities:
Passive Attacker (Eavesdropper)
Active Attacker
Weaknesses
Key Management issue:
Need a key for each pair of users
n users need n*(n-1)/2 keys
Key Storage
: If the secret key (and cryptosystem) is compromised, the adversary will be able to decrypt all traffic and produce fake messages
Key Distribution
must be done secretly (difficult when parties are geographically distant, or don't know each other)
Public key cryptosystems/ciphers
(The secret key is not shared and two parties can still communicate using their public keys)