RE: 802.15.4 problem with encryption and promiscuous mode

kapi — Tue, 20 Mar 2018 11:09:04 GMT

Hi,

Here is the information you asked for. I hope you find it helpful.

Source and destination addresses cannot be populated (set to 0x00) when operating in promiscuous mode. According to the 802.15.4-2006 specification:

"When in promiscuous mode, the MAC sublayer shall process received frames according to 7.5.6.2 and pass
all frames correctly received to the next higher layer using the MCPS-DATA.indication primitive. The
source and destination addressing mode parameters shall each be set to 0x00, the MSDU parameter shall
contain the MHR concatenated with the MAC payload (see Figure 41), and the msduLength parameter shall
contain the total number of octets in the MHR concatenated with the MAC payload. The mpduLinkQuality
shall be valid."

And another fragment from the specification:
"In promiscuous mode, the MAC sublayer shall pass all frames received after the first
filter directly to the upper layers without applying any more filtering or processing."

FYI, the first filter just checks if CRC (FCS field, present in MAC frame) is correct. That's why, in the promiscuous mode, you get raw messages without any field parsing. In this case you can ignore most of the fields that you receive in the indication (exceptions: msdu, link_quality, timestamp).

Since there is little interpretation of incoming frame in promiscuous mode at MAC layer level, the msdu payload is not decrypted by the stack.