• The security of a distributed system 
  • The processes
  • The communication channels
  • The objects
• Protecting the objects
• Access rights: who is allowed to perform the operations of an object
• Principal: the authority who has some rights on the object
  
  
  

The Enemies

• Threats to processes
  • To servers: invocate with a false identity, e.g. cheating a mail server
  • To clients: receive false result, e.g. stealing account password
• Threats to communication channels
• Copy, alter or inject messages
• Save and replay, e.g. retransfer money from one account to another
  
  
  
• Denial of service
  • excessive and pointless invocation on services or message transmissions in a network
  • result in overloading of physical resources (network bandwidth, server processing capacity)
• Mobile code
• malicious mobile program, e.g. Trojan horse attachment

Secure Channel

• Each process knows reliably the identities of the principal on whose behalf the other process is executing
• Ensure the privacy and integrity of the data transmitted across it
• Each message includes physical or logical time stamp