I am trying to use the hardware encryption on the CC2420, using tinyOS-1.x with Tmote Sky nodes. So far, I have managed to use the in-line modes successfully (CTR, CBC-MAC and CCM). What I am having a little trouble with is using the in-line operations for higher layer protocol operations, i.e.
Write to the TXFIFO, CTR encrypt without sending and read TXFIFO back to the MCU Write to the RXFIFO, start CTR decryption cycle and read RXFIFO back to the MCU Both cycles appear to work, however as the volume of packets on the radio increaces, packets start to be incorrectly decrypted. I think the packets I am writing via the SPI interface to the RX buffer may be being overwritten (or partially overwritten) by incoming packets from the air interface as they are being decrypted. I have tried to switch off the receiver during decryption operations (using the CC2420_SRFOFF command before filling RXBUF, and CC2420_SRXON after the read) however this does not seem to help. Has anyone managed to get this style of operation to work? The CC2420 datasheet is a bit light on this feature, simply stating that you should not write to the RXFIFO via the SPI interface except for "debugging or higher layer security operations". I did start out tyrying to implement this using the stand alone encryption until I discovered that there appears to be no corresponding decryption facility. I'd be interested to know if anyone has attempted this before, thanks for any input, Andrew
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