View page as slide show

CT30A8800 Secured Communications

Pekka Jäppinen


  • Lecturer: Pekka Jäppinen
    • Contact: 1. period Tue: 14-15 Room 6624
  • Lectures: 1st period Tue: 12-14 room 4309-4310
  • Exercises: Thu: 12-14 room 6328
  • Seminars: Presentation: reserve time for 2nd period during first perios
    Written part: End of 2nd period
  • Coding work: By the end of January (can be returned as soon as it is finished)


  • Schneier: Applied Cryptography
    • The old bible of cryptography
  • Trappe & Washington: Introduction to Cryptography with Coding Theory
    • An update to what is going on.
  • Menezes et al: Handbook of Applied Cryptography
    • Good description of all the algorithms
  • Stallings: Cryptography and network Security


  • Maximum points from the course is 100
    • 50 points to pass
    • Exam : 50p (min 25p)
  • Practical work: 25p (min 10p)
  • Seminar: 25p (min 15)
    • Written part (10p)
    • Presentation (15p)
  • Bonus points can be gained by participating exercises and being active in seminars


  • Seminar is done in groups of 2 or three persons
  • This year the seminar topics will be focus on (wireless) security protocols
    • You can suggest topic that interests you
    • Protocol families can be divided for two groups
  • Written part
    • Write a document that describes what is the target of the protocol and what kind of problems it solves
    • Write also evaluation of the protocols good and bad points.
  • Presentation ~30 minutes
    • Sharing the important issues to your audience e.g. the other students.
  • Discussion: ~15 minutes
    • Audience can give their own questions and comments about protocol.
    • Activity and showing knowledge and understanding here will give extra points and can enhance your grade.

Practical assignment

  • Create a secured communication channel between two computers.
  • Any programming language can be used
    • Python is recommended
  • One security method should be created “by hand” i.e. programmed from scratch by yourself, for others existing libraries can be used.
    • The more you do yourself, the more points you get.
  • Assigments are returned personally and their functionality is demonstrated to the lecturer. There will be questions about the implementation during your presentation, so you better be able to justify your solutions.
    • If you do not understand what you have done, you can forget about getting grade.

Secured Communications

What is the course all about?

What is communication

  • Communication is transfer of data between two or more communicating partners.
    • Between communicating partners is formed a communication channel
    • Communication channel can be formed over variety of communication mediums
      • Information can be transmitted in digital or analog form
    • This course concentrates on digital transmissions
  • The focus of course is to understand the security problems of communication channel and how to create a secure channel
    • Basic cryptographic methods are learned and the principles behind them.
      • This is not however a cryptology course. Focus is on how to use the primitives correctly
    • Some special environments will be introduced and the challenges they provide for designing the security solution.

Basic threats against communication channel

  • Unauthorised connection
    • Fabrication of identity
  • Eavesdropping of communication
  • Transmitted data:
    • Modification
    • Repetition
  • Denying of the data transfer
  • Fabrication of data

Communication medium

  • Different communication mediums have different challenges that require different solutions
  • Wired
    • Copper cable
      • Information is transmitted in electricity
      • Eavesdropping is possible by using inductance
    • Fiber
      • Information is transmitted as light, eavesdropping on wire is not possible
  • Wireless
    • Infrared (IrDA)
      • Signal is directed, but is easily reflected all around and thus possible to eavesdrop
    • Radio (802.11*,GSM,GPRS,Bluetooth,zigbee…)
      • Signal travels freely in the air and there are lot of potential eavesdroppers.
      • Authentication is very important
    • Sonic communications
      • same problems than Radio based systems

General defence methods

  • Physical defence
    • Prevent attacker to have access on transmission path
    • Hard and expensive in many cases
  • Software based defence
    • Authentication: Verifies the identity of the communication partners
    • Encryption : protects from eavesdrop and data modification (modification can be noticed)
    • Digital signatures: Verifies the authenticity of the data, protects against denying, reveals changes in data.
    • Timestamps: Prevents message repetitions

General simple secure communication protocol

  • Can be used for practical assignment
  • Tasks done prior the connection forming (offline)
    1. Creation of asymmetric keys
    2. Exchange of asymmetric keys (could be done during the connection creation too)
  • The actual phases of protocol
    1. (authentication of communication partners if desired)
    2. Creation and exchange of symmetric key (authentication can be done during keyexchange also)
    3. Encryption of the data packet with symmetric cipher (Confidentiality)
    4. Calculation and signing of hash value of the packet (Integrity)
    5. Transmitting the packet
    6. Receiving the packet
    7. Decryption of packet
    8. Validation of the signature with hash


  • Cryptographic primitive
    • any cryptographic function or algorithm (hash, symmetric crypto…)
  • Cryptographic algorithm
    • specific rules for manipulatin data
  • Cryptographic protocol
    • combination of cryptographic primitives to achieve desired secure communications.
Last modified: 2013/07/01 14:42