[security] Introducing signing support to MySensors

[Anticimex]

@scalz Great! Thanks for finding and testing this.
I am not sure I understand your question. You mean to store the PSK of atsha_soft in encrypted form in the sketch? That is difficult since the encryption secret then needs to be stored somewhere as well.
I would recommend (if you do use atsha_soft) to burn the fuses to prevent memory readout to protect the PSK.
Normally, this implementation is stored in the gateway which should be physically protected in any case, so the need to protekt PSK in the gateway is less critical than in a node which may be located "outside".

Secure OTA is currently unsupported. It might be supported in the future.

[scalz]

Oh, sorry for my bad english!
Is signing just between a Node and a Gateway. or is the controller involved too? Maybe it's a dumb question, I have not checked yet the changes in message.
For OTA, I understand it is not suppported by signature as you explained in your tuto. But, in the other hand, I think that for initiating an ota, it should need a signed message, so I think it is good.

[Anticimex]

@scalz You decide if your component will require signatures when you create your signer. That is, if you want your gateway to be able to sign messages sent to an actuator (like a lock) but you don't want your gateway to require signed messages from your nodes, you pass a argument to the constructor like this:
MySigningAtsha204 signer(false);
That will

• Configure that node/gw to support signed message processing using HW ATSHA
• Have that node/gw inform others that it does not require signed messages
• Still permit that node/gw to sign messages sent to other nodes/gw who do requre signing

If you stick to default constructor arguments or pass true, the difference is that the node/gw will also inform others that it requires signed messages, and will ignore/discard any message that is not signed which it receive (and is targeted to that particular node/gw). It will not affect messages which are to be relayed, so the node will still work as a relay for unsigned messages.

[scalz]

@Anticimex:
ok, it is good to know. You have thought about everything!
If signer(true) for gateway, Will the controller (Jeedom, Domoticz..) see a crypted payload in serial transmission or will it work like before (I understand there are some changes in message structure, but what about crypted payload, does the controller need to decrypt?)

[Anticimex]

@scalz We only sign messages. There is no encryption involved. And the signature is stored without affecting the message contents so it is perfectly compatible with all controllers. The only thing that could affect a controller is the new sign bit in the message header but I don't think that will make any difference as it is not relevant to the controller. It is the gateway that manages this for it.

[scalz]

ok, it is new for me, so I am mixing vocabulary, but I understand the concept. Thank you, and now I have my answer. no big changes for controller side, great! It makes sense, but I was not sure.

[hek]

Fix pushed to development.

[Anticimex]

Thanks for that!

[jsondag]

I put together a garage door opening using code from korttoma. I used soft signing, and it works great. I was wanting to use a real atsha though.

I bought some atsha204a chips from amazon, and the chips are marked with only "3eas", and a "Y" in one corners. They are soic-8. Is that how this should be marked? I wired one up according to the data sheet. Gnd to Gnd, VCC to 5V, and SDA to A3. I ran the personalizer to generate a key and it said "Failed to wake device." in the serial console. Am I doing something wrong? or did I just get the wrong chip from the seller?

[Anticimex]

@jsondag I don't have a good explanation on the software signing not working. Maybe inadequate decoupling leads to a too noisy power rail?
About the HW issue, it is important that you use the single wire version of atsha204. NOT the i2c version. The i2c version also has an scl line while the single wire only has sda (and power and ground). That means your soic8 should have 5 unused pads. Atmel ordering code for that variant is ATSHA204A-SSHCZ-T but unfortunately it is not printed on the case. So unless you find that information from Amazon, I am afraid it is very difficult to determine the type of the chips you've got.

[jsondag]

@Anticimex. Software signing is working fine.

Thanks for the information though. I didn't realize the soic 8 couldn't do one wire. It's a ATSHA204-SH-DA-B according to the listing.

EDIT:
Looking at the datasheet, it says that the SCL pin can be ignored for single wire interface. perhaps I'll wire another one up and give it a go.

Just connect, SDA to A3, correct?

[Anticimex]

@jsondag ok. From what I could read there are two different order codes for i2c and one-wire so I don't think you can take an i2c variant board and treat it as a one-wire board by just ignoring the scl pin. But if the board really is single-wire, the pinout will be the same as the i2c version, you can just ignore the scl pin as it is NC for the one-wire variant. And from the data sheet, SHDAB is i2c not "single-wire" so I am afraid you cannot use my libs for those. I only have drivers for single-wire chips i am afraid.

[TD22057]

I just received my chips today from digikey (part num ATSHA204A-STUCZ-TCT-ND) which are the small 3 pin versions. Holy cow these are things are tiny. These are going to be a lot more difficult than I expected to hand solder.

[Anticimex]

@TD22057 If you don't have a "inverse" tweezer to fixate the chip to the board, just glue it in place. With proper iron temp (at least 300 deg C, I use 330) it's very doable. Much easier than smd resistors/caps if you ask me :) (just don't forget to solder after you glue if you do that)

[TD22057]

@Anticimex said:

@TD22057 If you don't have a "inverse" tweezer to fixate the chip to the board, just glue it in place. With proper iron temp (at least 300 deg C, I use 330) it's very doable. Much easier than smd resistors/caps if you ask me :) (just don't forget to solder after you glue if you do that)

Thanks - I'll try that as soon as everything arrives. Watching parts trickle in from aliexpress shippers is killing me (I think I've become spoiled on Amazon prime shipping).

[tomkxy]

First of all I would like to thank Anticimex for this great piece of work!

I am playing around with signing right now. I set up a temp & humid sensor with soft signing support as well as a MQTT gateway with soft signing.

In principle it seems to work. At least sensor values are published to the MQTT broker. However, in the gateway output I see nonce tr errors and sign failures.

Started!
0;0;3;0;9;read: 21-21-0 s=1,c=3,t=16,pt=0,l=0,sg=0:
0;0;3;0;9;send: 0-0-21-21 s=255,c=3,t=17,pt=6,l=25,sg=0,st=ok:0107FD8
0;0;3;0;9;read: 21-21-0 s=1,c=1,t=0,pt=7,l=5,sg=1:25.1
publish: MyMQTT/21/1/V_TEMP 25.1
0;0;3;0;9;read: 21-21-0 s=2,c=3,t=16,pt=0,l=0,sg=0:
0;0;3;0;9;send: 0-0-21-21 s=255,c=3,t=17,pt=6,l=25,sg=0,st=ok:012B06D
0;0;3;0;9;send: 0-0-21-21 s=1,c=3,t=16,pt=0,l=0,sg=0,st=ok:
0;0;3;0;9;read: 21-21-0 s=2,c=1,t=1,pt=7,l=5,sg=1:59.0
publish: MyMQTT/21/2/V_HUM 59.0
0;0;3;0;9;sign fail
0;0;3;0;9;send: 0-0-21-21 s=2,c=3,t=16,pt=0,l=0,sg=0,st=fail:
0;0;3;0;9;nonce tr err
0;0;3;0;9;read: 21-21-0 s=255,c=3,t=17,pt=6,l=25,sg=0:01D5F523C2778AA
0;0;3;0;9;read: 21-21-0 s=1,c=3,t=16,pt=0,l=0,sg=0:
0;0;3;0;9;send: 0-0-21-21 s=255,c=3,t=17,pt=6,l=25,sg=0,st=ok:0104881
0;0;3;0;9;read: 21-21-0 s=1,c=1,t=0,pt=7,l=5,sg=1:25.1
publish: MyMQTT/21/1/V_TEMP 25.1
0;0;3;0;9;read: 21-21-0 s=2,c=3,t=16,pt=0,l=0,sg=0:
0;0;3;0;9;send: 0-0-21-21 s=255,c=3,t=17,pt=6,l=25,sg=0,st=ok:019A79B
0;0;3;0;9;send: 0-0-21-21 s=1,c=3,t=16,pt=0,l=0,sg=0,st=ok:
0;0;3;0;9;read: 21-21-0 s=2,c=1,t=1,pt=7,l=5,sg=1:59.2
publish: MyMQTT/21/2/V_HUM 59.2
0;0;3;0;9;sign fail
0;0;3;0;9;send: 0-0-21-21 s=2,c=3,t=16,pt=0,l=0,sg=0,st=fail:
0;0;3;0;9;nonce tr err
0;0;3;0;9;read: 21-21-0 s=255,c=3,t=17,pt=6,l=25,sg=0:0120D83204D1A06
0;0;3;0;9;read: 21-21-0 s=1,c=3,t=16,pt=0,l=0,sg=0:
0;0;3;0;9;send: 0-0-21-21 s=255,c=3,t=17,pt=6,l=25,sg=0,st=ok:01AB761
0;0;3;0;9;read: 21-21-0 s=1,c=1,t=0,pt=7,l=5,sg=1:25.1
publish: MyMQTT/21/1/V_TEMP 25.1
0;0;3;0;9;read: 21-21-0 s=2,c=3,t=16,pt=0,l=0,sg=0:
0;0;3;0;9;send: 0-0-21-21 s=255,c=3,t=17,pt=6,l=25,sg=0,st=ok:013CD41
0;0;3;0;9;read: 21-21-0 s=2,c=1,t=1,pt=7,l=5,sg=1:59.3
publish: MyMQTT/21/2/V_HUM 59.3
0;0;3;0;9;send: 0-0-21-21 s=1,c=3,t=16,pt=0,l=0,sg=0,st=fail:
0;0;3;0;9;nonce tr err
0;0;3;0;9;send: 0-0-21-21 s=2,c=3,t=16,pt=0,l=0,sg=0,st=fail:
0;0;3;0;9;nonce tr err

I am somehow irritated concerning those failures logged after the publish logs. They seem not to be related to receiving and publishing the sensor data. What can be source of that? Why might the gateway trying to transmit?

A second question is related to personalization of the ATSHA204. Am I right that the key is displayed in the SlotConfig00 - SlotConfig0F?

The second personalization step fails with the message "Data lock failed". What could be the reason for that?

[Anticimex]

@tomkxy Thanks.
"nonce tr err" is sent if sendRoute() fails to send a nonce request. So it suggests the radio link is somewhat unreliable and that in turn causes signing to fail. From what I can see you want to sign messages in both directions, so maybe traimsission from the MQTT gateway is not as reliable as reception? message type 16 (command 3) is a nonce request and sometimes it succeeds

0;0;3;0;9;send: 0-0-21-21 s=1,c=3,t=16,pt=0,l=0,sg=0,st=ok:

and sometimes it fail (with that message as consequence):

0;0;3;0;9;send: 0-0-21-21 s=2,c=3,t=16,pt=0,l=0,sg=0,st=fail:
0;0;3;0;9;nonce tr err

But the failing one is to a different sensor (2) than the first one (1), so perhaps that node is down or at a long range? But last in your log you also fail a transmission to sensor 1. In any case, the nonce tr err is because of failing radio transmissions and as such not a signing issue as such. Sometimes it works (when there are no radio issues:

0;0;3;0;9;read: 21-21-0 s=1,c=3,t=16,pt=0,l=0,sg=0: (request for nonce to GW)
0;0;3;0;9;send: 0-0-21-21 s=255,c=3,t=17,pt=6,l=25,sg=0,st=ok:01AB761 (GW sends nonce back)
0;0;3;0;9;read: 21-21-0 s=1,c=1,t=0,pt=7,l=5,sg=1:25.1 (signed message with that nonce is received)
publish: MyMQTT/21/1/V_TEMP 25.1 (message/signature is accepted and forwarded)

"sign fail" is typically reported if nonce exchange times out. You can adjust the timeout using MY_VERIFICATION_TIMEOUT_MS if you have many hops or for other reasons cannot process messages fast enough.
I have not tested MQTT gateway myself, and perhaps it uses the MySensors library differently but I have tested both serial and ethernet gateway. But in this case, it probably fails because you never got the request for the nonce out so your sender never got a chance to send a nonce back, and therefore signing cannot succeed.
So the key is to determine why the transmission of the nonce request fail (a radio problem since you get st=fail). Or implement a retransmission at a higher level in your sketch if the radio link is "lossy". The signing backend assumes a working channel and do not handle retransmission for you on failures.

Regarding personalization, key is never displayed. It is stored in slot 0. Slotconfigs are used to set the permissions of the slots. They don't store keys themselves.
You should get the reason for the data lock failure in the code that is sent together with the message. It is the ATSHA circuit itself that provide this value (or the library communicating with it in case of communication problem).

[tomkxy]

Thanks for your fast reply. Regarding the communication failures: I was testing this with both transmitters lying side by side. Do you have any idea why the gateway might want to have a nonce. Is it part of the sensor protocol?
The two sensors displayed in the log are basically the same sensor (DHT22 providing temp and humidity).

With respect to the key topic: The first personalization step provides the following output:

Device revision: 00020009
Device serial:   {0x01,0x23,0x48,0xC9,0x51,0x6A,0x1A,0x06,0xEE}
012348C9516A1A06EE
Chip configuration:
           SN[0:1]           |         SN[2:3]           | 01   23 | 48   C9   
                          Revnum                         | 00   09   04   00   
                          SN[4:7]                        | 51   6A   1A   06   
    SN[8]    |  Reserved13   | I2CEnable | Reserved15    | EE | 13 | 00 | 00   
  I2CAddress |  TempOffset   |  OTPmode  | SelectorMode  | C8 | 00 | 55 | 00   
         SlotConfig00        |       SlotConfig01        | 8F   80 | 80   A1   
         SlotConfig02        |       SlotConfig03        | 82   E0 | A3   60   
         SlotConfig04        |       SlotConfig05        | 94   40 | A0   85   
         SlotConfig06        |       SlotConfig07        | 86   40 | 87   07   
         SlotConfig08        |       SlotConfig09        | 0F   00 | 89   F2   
         SlotConfig0A        |       SlotConfig0B        | 8A   7A | 0B   8B   
         SlotConfig0C        |       SlotConfig0D        | 0C   4C | DD   4D   
         SlotConfig0E        |       SlotConfig0F        | C2   42 | AF   8F   
  UseFlag00  | UpdateCount00 | UseFlag01 | UpdateCount01 | FF | 00 | FF | 00   
  UseFlag02  | UpdateCount02 | UseFlag03 | UpdateCount03 | FF | 00 | FF | 00   
  UseFlag04  | UpdateCount04 | UseFlag05 | UpdateCount05 | FF | 00 | FF | 00   
  UseFlag06  | UpdateCount06 | UseFlag07 | UpdateCount07 | FF | 00 | FF | 00   
                      LastKeyUse[0:3]                    | FF   FF   FF   FF   
                      LastKeyUse[4:7]                    | FF   FF   FF   FF   
                      LastKeyUse[8:B]                    | FF   FF   FF   FF   
                      LastKeyUse[C:F]                    | FF   FF   FF   FF   
  UserExtra  |    Selector   | LockValue |  LockConfig   | 00 | 00 | 55 | 55  

Can I provide any key in the second personalization step or does it have to be same than in the first step being generated?

[Anticimex]

@tomkxy The protocol is described in the first post. Any node that is sending a signed message to another node (that has requested to get signed messages) will ask for a nonce. So you have configured your gateway to require signed messages as well as your node.
Regarding the personalization, I do t understand your question. The output is the chip configuration. It does not list any keys. I am not sure I understand what you mean by second step. You can generate a random key and that key you store and after you store it you have an option to also lock it, but then you have no way of ever changing it. I have documented the personalization flow also in the sketch itself.

[Anticimex]

I should emphasise that if you personalize multiple atsha:s you have to have the same key stored in all of them. But the sketch offer to generate a random key (but you can skip that and use any key or password you like). But the key must be the same for all members of a secure network that want to talk to each other.