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Facets of trustworthiness in networked computing
systems
– Availability
– Security
Availability
– Intrinsic reliability: software bugs, configuration and operation,
emergent behavior -> techniques for fault tolerance and graceful
crash recovery: equipment redundancy, data replication, data
persistence
– Security: countering deliberate threats
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Security measures
– The integrity of the message.
– The signature provides authentication, which means a provable i
dentification.
– Confidential.
– The inability of Alice to later deny she sent the message is called
nonrepudiation.
– Trusted authority
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Fig 13.1
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Examples of threats to messages communicated using the
network
– Interruption: the delivery of a legitimate message is prevented.
– Interception: a message is observed by an intruder and its contents
noted.
– Modification: a message is modified before it is passed to the recipient.
– Fabrication: a message is fabricated, including a false identity for the
sender.
– Computer virus
– Denial of service attack: injecting vast amounts of artificial work or
communications that cause a host or network to become overloaded
and degrade the performance for legitimate users or crash the
application altogether.
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Confidentiality
– Encryption and Decryption
– Symmetric and asymmetric systems
– Fig 13.3
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– The asymmetric locking key is called a public key and the
asymmetric unlocking key is called a secret key.
– Fig 13.4
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Encryption algorithms
– Confidentiality does not depend on the secrecy of the algorithm
s.
– Symmetric protocol: ESK(P) -> C, DSK(C) -> P where E: encryptio
n, D: decryption, SK: secret key, P: plaintext, C: ciphertext
– Asymmetric protocol: EBPK(P) -> C, DBSK(C) -> P where E: encryp
tion, D: decryption, BPK: Bob’s public key, BSK: Bob’s secret ke
y, P: plaintext, C: ciphertext
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– Fig 13.5
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authentication
– Verifying the identity of a party over the network
– Impersonation is easy over the network
– Authentication depends on a trusted third party, called an
authority
– Biometrics
– Challenge-response protocol
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– Fig 13.6
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– Digital certificate and certificate authorities (Fig 13.7)
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– Digital signature (Fig 13.8)
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Open issues
– Increasing vulnerability
– National security and law enforcement
