[17] SECURITY

• Asymmetric key cryptography

  sender + receiver have pair of public + private keys

  message sent

  encrypted by recipient public key

  message recieved

  decrypted recipient private key
• Drawbacks asymmetric encryption

  slower than symmetric

  more complex
• Benefit of asymmetric encryption

  Strong guarantee messaged will be sent use of digital signature
• Quantum cryptography

  unconditional secure communication

  High level security

  uses physics of photons
• Digital signature used to verify message

  message + signature decrypted with receiver private key

  Digital signature decrypted with sender public key to recover digest

  Decrypted message hashed with hashing algorithm to proceed digest

  two message digests are compared

  If same, not altered
• use of quantum

  Military

  High level Gov communications
• TLS

  improved SSL; latest industry standard encryption protocol

  Authenticates client and server and encrypts data sent

  Data encrypted so eavesdroppers cannot see private info
• real life Examples use of SSL/TLS

  Online

  secure transactions

  email

  Healthcare
• SSL/TLS in client server communication (5)

  client connects to server

  SSL/TLS certificate sent

  authenticates client + server

  Encrypts data (eavesdroppers)

  new session begins with handshake
• Digital certificate content

  Name of sender

  Name of CA

  Public key
• symmetric key cryptography

  Agree secret / private key

  sender encrypts data

  Sends cipher text

  same key used to decrypt
• How Digital signature used to verify message

  message + signature decrypted with receiver private key

  Digital signature decrypted with sender public key to recover digest

  Decrypted message hashed to proceed digest two message digests are compared

  If same, not altered
• SSL process in client server communication web browser (6)

  • Web browser connects to SSL secured website

  • Request to identify

  • Copy of SSL certificate sent

  • Certificate checked

  • Acknowledgment for receiving request

  • Encrypted two-way data transfer
• How is digital signature produced (3)

  data hashed with hashing algorithm

  produce message digest

  digest encrypted with sender private key to form Digital signature
• Digital certificate obtained (5)

  Enquiry made to CA

  details checked by CA

  If details verified, public key agreed

  CA creates certificate included public key

  encrypted data sent
• Reasons to use key cryptography (4)

  non repudiation authenticity integrity confidentiality
• Drawback of Quantum cryptography (3)

  limited range

  Specialist hardware + dedicated fibre optic line required

  cost of installing
• Benefits of Quantum cryptography (3)

  Eavesdroppers identified

  guaranteed integrity

  more secure keys
• Drawback symmetric encryption (3)

  Key needs to be exchanged securely

  if compromised, same key can be used to encrypt + decrypt messages

  Cannot ensure non-repudiation
• SSL/TLS purpose (4)

  protocols provide secure communication over internet

  Provide encryption

  enable 2 parties to authenticate each other

  Communicate with confidentially/integrity
• text before encrypted vs after

  plain text vs cipher text

  jumbled - cannot understand
• Private Key (3)

  unpublished secret key

  has matching public key

  used to decrypt data which was encrypted with matching public key
• Public key


  available to all users and used to encrypt message
• Two differences between Asymmetric + symmetric encryption

  symmetric = single key / asymmetric = pair of keys

  Symmetric key used by all / only one asymmetric key available to all + one kept secret
• non repudiation

  neither sender or reciever can deny transmission occured
• authenticity

  message came from a trusted source
• Explain how the customer’s and the company’s computers use a hashing algorithm to assure the customer that: the software has come from the company (is authentic) and no one has altered it.

  Software is put through a hashing algorithm by company

  Hash total is encrypted with company's private key

  Company sends software and encrypted hash

  Customer decrypts hash with public key of company

  Customer uses hash algorithm to hash software

  If hashes match unaltered else altered