The guarantees offered by conventional servers may be violated by:

i) physical damage to the host;

ii) Errors or inconsistencies by system adminstrators or their managers;

iii)successful attacks on the security of the system software;

iv)hardware or software errors.

Give two examples of possible incidents for each type of violation. Which of them could be described as a breach of trust or a criminal act? Would they be breaches of trust if they occurred on a personal computer that was contributing some resources to a peer-to-peer service? Why is this relevant for peer-to-peer systems?

i) Power failure, earthquake, flood, act of war or sabotage, owner throws the computer away. The last two are breeches of trust for servers, but the owner of a PC is free to throw it away.

ii) Accidental deletion of a file, permission failure, there are many possible errors in system administration.
Maybe not a breach of trust, but repeated occurrences are a serious matter in a service, though not on a
PC.

iii)The attacks described in Section 7.1.1 are always a breach of trust or a criminal attack for servers. But for a PC the perpetrator may be the owner who may attack a user who is sharing the resources of their computer with impunity.

iv)Hard disk failures, network failures, program bugs. These are not normally due to breaches of trust or criminal acts. Servers are configured to ‘fail over’ to use alternative hardware and backup copies of data. The the software they run is probably more carefully validated before it is put into use.

The differences in what is ‘trusted behaviour’ for servers and PCs is relevant because peer-to-peer system must be designed to cope with the looser interpretation of trust for PCs.