US Robotics USR2450 Informations techniques télécharger pdf (Page 42)

V 2.2 Copyright SystemExperts 2001,2002,2003

Problem: Message Authentication

n The Cyclical Redundancy Check (CRC)

chosen for the authentication is weak

n It is designed for errors, not authentication

n It is possible to modify a message such that

the CRC will be valid for the messages, but is

not the messages that was sent

n Can also inject messages in much the same

manner

V 2.2 Copyright SystemExperts 2001,2002,2003

Current Status of WEP

n IEEE 802.11 Task Group I (tgi)

n Message Integrity Check (MIC): Doc 594

n Re-keying

n Add MIC to data before encrypting

n Algorithm not yet selected

n No replay protection (done with IV)

n Temporal Key Hash: Doc 550

n Temporal key to derive per-packet key

n Countermeasure to key-scheduling algorithm

n Re-Keying

n Re-key Proposal: Doc 540

n Re-key faster than the attacker can attack

n Authenticated Key Exchange at the MAC Layer: Doc 508

n A different way J

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US Robotics USR2450 Informations techniques Page 42