[security] Introducing signing support to MySensors

[fleinze]

@Anticimex In your original post you said:

However, the difference is that the gateway will only require signed messages from nodes it knows in turn require signed messages.

I made pull request 208 to match this behavior in the code:
https://github.com/mysensors/Arduino/pull/208

• If node is not a gateway, everything is as always. (1 || x)
• if node is gateway and the sender requires signed messages, check signature (0 || 1)
• if node is gateway and the sender does not requires signed messages, do not check signature (0 || 0)
  please consider adding this.

[Anticimex]

@fleinze Ok, lets discuss this in the PR and conclude it in this thread later.

[Anticimex]

Ok, the problem is identified and @fleinze has provided a fix that resolves the issue which is now merged to the development branch.
Thanks for finding the issue and fixing it!
There is no change in the signing behavior as it is documented. Now gateway does as it is supposed to.

[mfalkvidd]

Great work @fleinze and @Anticimex !
Reading this thread (yes, all of it) has made me ready to start configuring my nodes to use signing. Better start now, while my sensor network is still small :)

[FotoFieber]

Compiling with the latest dev branch SecureActuator example

#define MY_SIGNING_REQUEST_SIGNATURES

I get following error:

In file included from /Users/mm/Documents/Arduino165/libraries/MySensors/MySensor.h:157:0,
                 from SecureActuator.ino:58:
/Users/mm/Documents/Arduino165/libraries/MySensors/core/MyTransport.cpp: In function 'void transportProcess()':
/Users/mm/Documents/Arduino165/libraries/MySensors/core/MyTransport.cpp:92:10: error: 'MY_IS_GATEWAY' was not declared in this scope
    if ((!MY_IS_GATEWAY || DO_SIGN(sender)) &&
          ^
/Users/mm/Documents/Arduino165/libraries/MySensors/core/MyTransport.cpp:93:20: error: 'nc' was not declared in this scope
     destination == nc.nodeId &&
                    ^
Fehler beim Kompilieren.```

Is this a problem of the code or of my setup?

[Anticimex]

@FotoFieber @hek something related to the recent refactoring? I have not had the opportunity to evaluate the effects on signing myself.

[hek]

@FotoFieber said:

MY_SIGNING_REQUEST_SIGNATURES

Let's see how Jenkins feels about this
https://github.com/mysensors/Arduino/pull/231

[Avamander]

@Anticimex Hello, I found this thread now. I'll ask a few more questions, sorry. This all seems really-really great.

1. If someone wishes to use TMRh20's RF24Mesh instead of MySensors how would one sign the messages sent with that library? Is is even possible? What should be done to use that functionality?

2. Also, as I understand it is possible to emulate the ATSHA204A, on what hardware is is possible (on Uno's ATMega too?)?

3. Is it also possible to use whitelisting with RF24Mesh somehow?

Again, sorry for any dumb questions and my poor English.

[Anticimex]

@Avamander

1. Signing as described in this post is specific to users of the MySensors library. I suppose you could use any rf backend you like but you will need to use the MySensors library to get the nonce exchange and such. Or manually port the signing specifics out from the MySensors library and integrate them into another library. It's all open source.
2. The software emulated atsha signing backend (for MySensors) is compatible with any Arduino product.
3. See 1.

Lastly, there are no dumb questions, only dumb answers :)

[Silver978]

Hello,

firstly, I must say that you're doing a great job and this section about security is very interesting.
Sorry, but I want to ask a question: as regards the whitelisting system, how can I add more nodes to the list of the trusted nodes of the gateway?
The part of code is this:

[...]
#ifdef MY_SECURE_NODE_WHITELISTING
whitelist_entry_t node_whitelist[] = {
  { //I want to add nodes HERE:
    .nodeId = 55, // Just some value, this need to be changed  to the NodeId of the trusted node
    .serial = {0x01,0x02,0x03,0x04,0x05,0x06,0x07,0x08,0x09} } // This need to change to the serial of the trusted node
};
MySigningAtsha204 signer(true, 1, node_whitelist);  // Select ATSHA204A software signing backend with one entry in the whitelist
[...]

but the gateway continue to fail the verification of the trusted nodes that I inserted.

To sum up, how can I add more nodeIDs and serials in addition to the number "55" presented in the example of the code?

Thank you very much in advance,
Silver978

[Anticimex]

@Silver978 Thanks!
Try something like this:

whitelist_entry_t node_whitelist[] = {
  {
    .nodeId = 55, // Just some value, this need to be changed  to the NodeId of the trusted node
    .serial = {0x01,0x02,0x03,0x04,0x05,0x06,0x07,0x08,0x09} // This need to change to the serial of the trusted node
  },
  {
    .nodeId = 56, // Just some value, this need to be changed  to the NodeId of the trusted node
    .serial = {0x01,0x02,0x03,0x04,0x05,0x06,0x07,0x08,0x09} // This need to change to the serial of the trusted node
  },
  {
    .nodeId = 57, // Just some value, this need to be changed  to the NodeId of the trusted node
    .serial = {0x01,0x02,0x03,0x04,0x05,0x06,0x07,0x08,0x09} // This need to change to the serial of the trusted node
  }
};
MySigningAtsha204 signer(true, 3, node_whitelist);  // Select ATSHA204A software signing backend with three entries in the whitelist

Note the changed argument in the constructor (3 and not 1)

[Silver978]

@Anticimex I tried also this syntax but I haven't changed the argument of the signer, so that number indicates how many nodes the gateway must trust?
Thank you!

[Anticimex]

@Silver978 The number gives the number of entries in the whitelist the backend is expected to iterate over. Having a number for this allows the use of a potenitally very large whitelist but where "uninteresting" entries to this particular node can be ignored by having them last in the list and make sure the number does not cover those entries when searching the list.

[Silver978]

@Anticimex Perfect, understood! Very good explanation and super-fast support, fantastic :)
Thank you very much again!

[Anticimex]

@Silver978 :+1:

[siod]

I would like to add security to my sensor network as well so I am very glad I found your thread. Your explanation are very detailed but I´m a guy who needs more practical examples. For example I would like to know, where exactly I have to activate this. I am using an arduino as an MQTT to Ethernet gateway and Mosquitto running on a raspberry pi. So all I have to do is activate the soft version in Myconfig.h, if not already activated, set a serial, re-upload to my arduino gateway and that´s it? I guess the Nodes have to get flashed again to get the serials as well, right?

[Anticimex]

@siod correct. You have to activate signing in both ends. The serial numbers you only need of you want to use whitelisting which is a bit more complex to set up. At the very least, for software signing, you need to enable it, have an unconnected analog pin on your boards, and set a hmac key.

[Anticimex]

EDIT: Topic post updates with a documentation link for those using the development branch.

[ahmedadelhosni]

Great topic as usual. I have a question please.

You mentioned "Because it is pure-software however, it does not provide as good nonces (it uses the Arduino pseudo-random generator) and the HMAC key is stored in SW and is therefore readable if the memory is dumped. "

Isn't this case also dangerous if the node which contains ATSHA chip was stolen ? The attacker will use the chip to be on the network ?

Thanks.

[Anticimex]

@ahmedadelhosni thanks!
Correct. That is why I also implemented whitelisting and node revocation. It's all described in the topic (and for development branch in doxygen, linked in the topic).