OSI Security Architecture:-

1)SECURITY ATTACK:
Any action that compromises the security of information owned by an organisation.

-Passive Attack:
   -Release of message contents
   -Traffic control
-Active attack:
   -Masquerade
   -Replay
   -Modification of message
   -Denial of service

2)SECURITY MECHANISM:
A process that is design to detect,prevent or recover from a security attack.

3)SECURITY SERVICES:
A processing or communication service that enhances the security of the data processing systems and the information transfers of an organisation.

-Authentication
-Access control
-Data confidentiality
-Data Integrity
-Non repudiation