Devantech dS378, User Manual

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dS378
dS378
User Manual v2.19
To prevent re-play (or Playback) attacks the command packet includes a Nonce. This takes the
form of a 32-bit (4 byte) random number in positions 12, 13, 14 & 15 of the 16 byte data
packet. For example when you send a Get Status command (0x30) you will get a 16 byte block
returned. The first 8 bytes (0-7) will be as defined for the binary commands. Bytes 8-11 are
unused. Bytes 12-15 contain the Nounce.
Commands with generate and send you a Nounce are:
0x30 – Get Status
0x31 – Set Relay
0x32 – Set Output
Commands which require a Nounce to be sent by you are:
0x31 – Set Relay
0x32 – Set Output
A Nounce is only ever used once, you must always used the most recently issued Nounce.
The following example shows how the Nounce provided by the module is used in the next Set
Relay or Set Ouput command.
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
Get Status 0x30 xx xx xx xx xx xx xx xx xx xx xx xx xx xx xx
Response 0x23 0x02 0x12 0x01 0x02 0x7D 0x01 0x0B xx xx xx xx 0x89 0xAB 0xCD 0xEF
Set Relay 0x31 0x02 0x01 0x00 0x00 0x00 0x00 xx xx xx xx xx 0x89 0xAB 0xCD 0xEF
Response 0x00 xx xx xx xx xx xx xx xx xx xx xx 0x1A 0x2B 0x3C 0x4D
Set Relay 0x31 0x03 0x01 0x00 0x00 0x00 0x00 xx xx xx xx xx 0x1A 0x2B 0x3C 0x4D
Response 0x00 xx xx xx xx xx xx xx xx xx xx xx 0xF1 0xE2 0xD3 0xC4
Set Output 0x32 0x04 0x01 xx xx xx xx xx xx xx xx xx 0xF1 0xE2 0xD3 0xC4
Response 0x00 xx xx xx xx xx xx xx xx xx xx xx 0x5C 0x47 0x9B 0xED
If the Nounce you send with the command does not match the last one sent to you, then the
Relay (or Output) will not be changed.
No other commands either require or provide a Nounce.
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