3i Infotech Placement: Sample Questions 770 - 771 of 1245

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Question 770



What are the different events in Triggers?


Choice (4)


Define, Create


Drop, Comment


Insert, Update, Delete


None of the above




  • Trigger event specifies what DML statement can initiate the trigger- INSERT, DELETE, or UPDATE operation on the table or view, or a SELECT operation that queries the table.
  • Create trigger statement must specify one trigger event.
  • We can define triggers that are activated by INSERT, DELETE, UPDATE, or SELECT statements.
  • Multiple triggers on the same table or view can active different type of trigger by the same type of trigger event.
  • We cannot specify a DELETE event if the triggering table has a referential constraint that specifies ON DELETE CASCADE.
  • Guaranty is that triggering statement returns the same result with and without the trigger action on a table.
  • Statement from an external database server can activate the trigger.
  • The INSTEAD OF trigger replaces the trigger event with the specified trigger action.
  • Any number INSTEAD OF trigger can be defined for each type of INSERT, DELETE, or UPDATE triggering event.

Question 771


Describe in Detail


What is wide-mouth frog?


  • The simplest known key distribution centre authentication protocol.
  • A key distribution centre is part of a cryptosystem intended to reduce risks in exchanging keys.
  • Allows individuals communicating over a network to prove identity to each other preventing reply attack.
  • Provides detection of modification.
  • Prevention of unauthorized reading.
  • First described under the name “The Wide-mouthed-frog Protocol” in the paper “A Logic of Authentication” .
  • The protocol can be specified as follows in security protocol notation.
  • Security protocol notation:

  • The protocol has several problems:
  • Requires a global clock.
  • The server has access to all keys- single point of failure and attack
  • The value of the shared key between “A” and “B” is completely determined by “A” - an attacker can pretend to be “A”
  • Can replay messages within period when timestamp is valid.
  • “A” is not assured that “B” exists.
  • Protocol is stateful.

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