ieee80211_crypto (9)
Leading comments
Copyright (c) 2004 Bruce M. Simpson <bms@spc.org> Copyright (c) 2004 Darron Broad <darron@kewl.org> All rights reserved. Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met: 1. Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer. 2. Redistributions in binary form must reproduce the above copyright notice, this list of conditio...
NAME
ieee80211_crypto - 802.11 cryptographic supportSYNOPSIS
In net80211/ieee80211_var.hFt void Fn ieee80211_crypto_register const struct ieee80211_cipher * Ft void Fn ieee80211_crypto_unregister const struct ieee80211_cipher * Ft int Fn ieee80211_crypto_available int cipher
Ft void Fo ieee80211_notify_replay_failure Fa struct ieee80211vap * Fa const struct ieee80211_frame * Fa const struct ieee80211_key * Fa uint64_t rsc Fa int tid Fc Ft void Fo ieee80211_notify_michael_failure Fa struct ieee80211vap * Fa const struct ieee80211_frame * Fa u_int keyix Fc Ft int Fo ieee80211_crypto_newkey Fa struct ieee80211vap * Fa int cipher Fa int flags Fa struct ieee80211_key * Fc Ft int Fn ieee80211_crypto_setkey struct ieee80211vap * struct ieee80211_key * Ft int Fn ieee80211_crypto_delkey struct ieee80211vap * struct ieee80211_key * Ft void Fn ieee80211_key_update_begin struct ieee80211vap * Ft void Fn ieee80211_key_update_end struct ieee80211vap * Ft void Fn ieee80211_crypto_delglobalkeys struct ieee80211vap * Ft void Fn ieee80211_crypto_reload_keys struct ieee80211com *
Ft struct ieee80211_key * Fn ieee80211_crypto_encap struct ieee80211_node * struct mbuf * Ft struct ieee80211_key * Fn ieee80211_crypto_decap struct ieee80211_node * struct mbuf * int flags Ft int Fo ieee80211_crypto_demic Fa struct ieee80211vap * Fa struct ieee80211_key * Fa struct mbuf * Fa int force Fc Ft int Fo ieee80211_crypto_enmic Fa struct ieee80211vap * Fa struct ieee80211_key * Fa struct mbuf * Fa int force Fc
DESCRIPTION
The net80211 layer includes comprehensive cryptographic support for 802.11 protocols. Software implementations of ciphers required by WPA and 802.11i are provided as well as encap/decap processing of 802.11 frames. Software ciphers are written as kernel modules and register with the core crypto support. The cryptographic framework supports hardware acceleration of ciphers by drivers with automatic fall-back to software implementations when a driver is unable to provide necessary hardware services.CRYPTO CIPHER MODULES
net80211 cipher modules register their services using Fn ieee80211_crypto_register and supply a template that describes their operation. This Vt ieee80211_cipher structure defines protocol-related state such as the number of bytes of space in the 802.11 header to reserve/remove during encap/decap and entry points for setting up keys and doing cryptographic operations.Cipher modules can associate private state to each key through the Vt wk_private structure member. If state is setup by the module it will be called before a key is destroyed so it can reclaim resources.
Crypto modules can notify the system of two events. When a packet replay event is recognized Fn ieee80211_notify_replay_failure can be used to signal the event. When a TKIP Michael failure is detected Fn ieee80211_notify_michael_failure can be invoked. Drivers may also use these routines to signal events detected by the hardware.
CRYPTO KEY MANAGEMENT
The net80211 layer implements a per-vap 4-element ``global key table'' and a per-station ``unicast key'' for protocols such as WPA, 802.1x, and 802.11i. The global key table is designed to support legacy WEP operation and Multicast/Group keys, though some applications also use it to implement WPA in station mode. Keys in the global table are identified by a key index in the range 0-3. Per-station keys are identified by the MAC address of the station and are typically used for unicast PTK bindings.net80211 provides ioctl(2) operations for managing both global and per-station keys. Drivers typically do not participate in software key management; they are involved only when providing hardware acceleration of cryptographic operations.
Fn ieee80211_crypto_newkey is used to allocate a new net80211 key or reconfigure an existing key. The cipher must be specified along with any fixed key index. The net80211 layer will handle allocating cipher and driver resources to support the key.
Once a key is allocated it's contents can be set using Fn ieee80211_crypto_setkey and deleted with Fn ieee80211_crypto_delkey (with any cipher and driver resources reclaimed).
Fn ieee80211_crypto_delglobalkeys is used to reclaim all keys in the global key table for a vap; it typically is used only within the net80211 layer.
Fn ieee80211_crypto_reload_keys handles hardware key state reloading from software key state, such as required after a suspend/resume cycle.
DRIVER CRYPTO SUPPORT
Drivers identify ciphers they have hardware support for through the Vt ic_cryptocaps field of the Vt ieee80211com structure. If hardware support is available then a driver should also fill in the iv_key_alloc iv_key_set and iv_key_delete methods of each Vt ieee80211vap created for use with the device. In addition the methods iv_key_update_begin and iv_key_update_end can be setup to handle synchronization requirements for updating hardware key state.When net80211 allocates a software key and the driver can accelerate the cipher operations the iv_key_alloc method will be invoked. Drivers may return a token that is associated with outbound traffic (for use in encrypting frames). Otherwise, e.g. if hardware resources are not available, the driver will not return a token and net80211 will arrange to do the work in software and pass frames to the driver that are already prepared for transmission.
For receive, drivers mark frames with the M_WEP mbuf flag to indicate the hardware has decrypted the payload. If frames have the IEEE80211_FC1_PROTECTED bit marked in their 802.11 header and are not tagged with M_WEP then decryption is done in software. For more complicated scenarios the software key state is consulted; e.g. to decide if Michael verification needs to be done in software after the hardware has handled TKIP decryption.
Drivers that manage complicated key data structures, e.g. faulting software keys into a hardware key cache, can safely manipulate software key state by bracketing their work with calls to Fn ieee80211_key_update_begin and Fn ieee80211_key_update_end . These calls also synchronize hardware key state update when receive traffic is active.