Computer security- attacks on protocols

Classical attacks on security protocols

Note: most follow man in the middle attacks where intruder sniffs information

Out of context attacks

Using messages generated in one context in another

May be using a message generated in protocol 1 for protocol 2

So if using the Needham-Schroeder protocol we know that

A sends b a nonce NA and identity, encrypted with B’s public key

B replies with nonce NB as well as NA, encrypted with A’s public key

A then replies with B’s nonce, encrypted by public key of B

BUT

MiM would receive message from a with pb key of MiM

Would copy A’s message but send to B, encrypted by B’s public key

Receive nonce from B encrypted with A’s public key

Forwards B’s reply to A and receives Nonce of B encrypted MiM public key

Then send to B encrypted by B’s public key

Now has B’s nonce

However this can be prevented with more identification checks

B should include identity in reply

Replay attacks

Replay attacks

Simply replaying protocol message to disrupt session

A may be establishing a session with B but if Intruder copies A’s message

B may think two sessions from A, and intruder has easily got some info

Attacks on multiple layers of encryption

Data at rest

Data on move- can’t always just add encryption to protect

Simple attack- A -> C(pretending to be B): A, Encrypt(M, KpbB), B

Later on C sends this to B and then B would reply with message but encrypted with public key of C

C now has M

All that had to be done to prevent is for A to sign off that it is from A to B and B do the same!

With multiple encryption the message will just be the inner encryption