Network security
Network security

This free course is available to start right now. Review the full course description and key learning outcomes and create an account and enrol if you want a free statement of participation.

Free course

Network security

7.3 Sequence numbers

Sequence numbers are an alternative way of indicating freshness. If Alice is sending a stream of messages to Bob she can bind each one to a sequential serial number, and encryption will prevent an eavesdropper from altering any sequence number. If Bob is suspicious he can check that the numbers in Alice's messages are incremented sequentially. It would be a straightforward matter for him to spot a replayed message since the sequence order would be incorrect and its number would duplicate that of an earlier message.

SAQ 10

In a connectionless packet-switched network, would sequence numbers provide effective freshness indicators?

Answer

In a packet-switched network, messages between two points could take different routes and might arrive out of sequence. It would be impossible for Bob to determine whether this was a result of network delays or some malicious intent. However, the sequence numbers would still provide a means of identifying duplicated messages.

T823_1

Take your learning further

Making the decision to study can be a big step, which is why you'll want a trusted University. The Open University has over 40 years’ experience delivering flexible learning and 170,000 students are studying with us right now. Take a look at all Open University courses.

If you are new to university level study, find out more about the types of qualifications we offer, including our entry level Access courses and Certificates.

Not ready for University study then browse over 900 free courses on OpenLearn and sign up to our newsletter to hear about new free courses as they are released.

Every year, thousands of students decide to study with The Open University. With over 120 qualifications, we’ve got the right course for you.

Request an Open University prospectus