The Michael hash( MIC) is an additional encryption in WLANs. It protects the transmitted data packets against modification. For this purpose, the Michael hash (MIC) is appended to the data packet in addition to the cyclic block check (CRC).
The Michael hash is a hash algorithm specially developed for WLANs that involves a reasonable overhead. It is derived from the Pairwise Transient Key( PTK) or the Group Transient Key( GTK). The hash value, which includes the Michael key, cannot be calculated without knowledge of the Michael key, and modifications to data packets are thus detected.
If a WLAN card detects two Michael errors within a certain period of time, then communication between the WLAN client and the access point( AP) is interrupted for one minute. After that, both stations negotiate a new Temporal Key Integrity Protocol( TKIP) and a new Michael hash. The Michael hash is used in WiFi Protected Architecture(WPA), among other things.