/* * The MySensors Arduino library handles the wireless radio link and protocol * between your home built sensors/actuators and HA controller of choice. * The sensors forms a self healing radio network with optional repeaters. Each * repeater and gateway builds a routing tables in EEPROM which keeps track of the * network topology allowing messages to be routed to nodes. * * Created by Henrik Ekblad * Copyright (C) 2013-2017 Sensnology AB * Full contributor list: https://github.com/mysensors/Arduino/graphs/contributors * * Documentation: http://www.mysensors.org * Support Forum: http://forum.mysensors.org * * This program is free software; you can redistribute it and/or * modify it under the terms of the GNU General Public License * version 2 as published by the Free Software Foundation. */ /** * @defgroup MySigninggrp MySigning * @ingroup internals * @{ * * @brief The signing driver provides a generic API for various signing backends to offer * signing of MySensors messages. * * Signing support created by Patrick "Anticimex" Fallberg * * @section MySigninggrpbackground Background and concepts * * Suppose two participants, Alice and Bob, wants to exchange a message. Alice sends a message to Bob. In MySensors “language” Alice * could be a gateway and Bob an actuator (light swich, electronic lock, etc). But to be generic, we will substitute the term * “gateway” with Alice and a “node” with Bob (although the reverse relationship is also supported). * * Alice sends a message to Bob. This message can be heard by anyone who wants to listen (and also by anyone that is within “hearing” * distance). Normally, this is perhaps not a big issue. Nothing Alice says to Bob may be secret or sensitive in any way. * However, sometimes (or perhaps always) Bob want to be sure that the message Bob receives actually came from Alice. In cryptography, * this is known as authenticity. Bob needs some way of determining that the message is authentic from Alice, when Bob receives it. * This prevents an eavesdropper, Eve, to trick Bob into thinking it was Alice that sent a message Eve in fact transmitted. Bob also needs * to know how to determine if the message has been repeated. Eve could record a message sent by Alice that Bob accepted and then send * the same message again. Eve could also in some way prevent Bob from receiving the message and delay it in order to permit the message * to arrive to Bob at a time Eve chooses, instead of Alice. Such an attack is known as a replay attack.
* Authenticity permits Bob to determine if Alice is the true sender of a message. * @image html MySigning/alicenfriends.png * @image latex MySigning/alicenfriends.eps "Alice with Eve and Bob" width=6cm * * It can also be interesting for Bob to know that the message Alice sent has not been tampered with in any way. This is the * integrity of the message. We now introduce Mallory, who could be intercepting the communication between Alice and Bob and * replace some parts of the message but keeping the parts that authenticate the message. That way, Bob still trusts Alice to be the * source, but the contents of the message was not the content Alice sent. Bob needs to be able to determine that the contents of the * message was not altered after Alice sent it.
* Mallory would in this case be a man-in-the-middle attacker.
* Integrity permits Bob to verify that the messages received from Alice has not been tampered with.
* This is achieved by adding a signature to the message, which Bob can inspect to validate that Alice is the author. * @image html MySigning/alicenfriends2.png * @image latex MySigning/alicenfriends2.eps "Alice with Mallory and Bob" width=9cm * * The signing scheme used, needs to address both these attack scenarios. Neither Eve nor Mallory must be permitted to interfere with the * message exchange between Alice and Bob. * * The key challenge to implementing a secure signing scheme is to ensure that every signature is different, even if the message is not. * If not, replay attacks would be very hard to prevent.
* One way of doing this is to increment some counter on the sender side and include it in the signature. This is however predictable.
* A better option would be to introduce a random number to the signature. That way, it is impossible to predict what the signature will be. * The problem is, that also makes it impossible for the receiver (Bob) to verify that the signature is valid.
* A solution to this is to let Bob generate the random number, keep it in memory and send it to Alice. Alice can then use the random number * in the signature calculation and send the signed message back to Bob who can validate the signature with the random number used. * This random number is in cryptography known as a nonce or * salt. * * However, Mallory might be eavesdropping on the communication and snoop up the nonce in order to generate a new valid signature for a * different message. To counter this, both Alice and Bob keep a secret that only they know. This secret is never transmitted over the air, * nor is it revealed to anybody. This secret is known as a pre-shared key (PSK). * * If Eve or Mallory are really sophisticated, he/she might use a delayed replay attack. This can be done by allowing Bob to transmit * a nonce to Alice. But when Alice transmits the uniquely signed message, Mallory prevents Bob from receiving it, to a point when Mallory * decides Bob should receive it. An example of such an attack is described * here.
* This needs to be addressed as well, and one way of doing this is to have Bob keep track of time between a transmitted nonce and a signed * message to verify. If Bob is asked for a nonce, Bob knows that a signed message is going to arrive “soon”. Bob can then decide that if the * signed message does not arrive within a predefined timeframe, Bob throws away the generated nonce and thus makes it impossible to verify * the message if it arrives late. * * The flow can be described like this: * @image html MySigning/alicenbob.png * @image latex MySigning/alicenbob.eps "Alice and Bob" width=8cm * The benefits for MySensors to support this are obvious. Nobody wants others to be able to control or manipulate any actuators in their home. * * @section MySigninggrpencryption Why encryption is not part of this * * Well, some could be uncomfortable with somebody being able to snoop temperatures, motion or the state changes of locks in the environment. * Signing does not address these issues. Encryption is needed to prevent this.
* It is my personal standpoint that encryption should not be part of the MySensors “protocol”. The reason is that a gateway and a node does * not really care about messages being readable or not by “others”. It makes more sense that such guarantees are provided by the underlying * transmission layer (RF solution in this case). It is the information transmitted over the air that needs to be secret (if user so desires). * The “trust” level on the other hand needs to go all the way into the sketches (who might have different requirements of trust depending on * the message participant), and for this reason, it is more important (and less complicated) to ensure authenticity and integrity at * protocol-level as message contents is still readable throughout the protocol stack. But as soon as the message leaves the “stack” it can be * scramble into “garbage” when transmitted over the air and then reassembled by a receiving node before being fed in “the clear” up the stack * at the receiving end. * * There are methods and possibilities to provide encryption also in software, but if this is done, it is my recommendation that this is done * after integrity- and authentication information has been provided to the message (if this is desired). Integrity and authentication is of * course not mandatory and some might be happy with only having encryption to cover their need for security. I, however, have only focused on * integrity and authenticity while at the same time keeping the current message routing mechanisms intact and therefore leave * the matter of secrecy to be implemented in the “physical” transport layer. With the integrity and authenticity handled * in the protocol it ought to be enough for a simple encryption (nonce-less AES with a PSK for instance) on the message as it is sent to the * RF backend. Atmel does provide such circuits as well but I have not investigated the matter further as it given the current size of the * ethernet gateway sketch is close to the size limit on an Arduino Nano, so it will be difficult to fit this into some existing gateway * designs.
* Also it is worth to consider that the state of a lock can just as readily be determined by simply looking at the door in question or * attempting to open it, so obfuscating this information will not necessarily deter an attacker in any way.
* Nevertheless, I do acknowledge that people find the fact that all information is sent “in the clear” even if it require some technical * effort for an intruder to obtain and inspect this information. So I do encourage the use of encrypting transport layers.
* This is however not covered by this implementation. * * @section MySigninggrphow How this is done * * There exist many forms of message signature solutions to combat Eve and Mallory.
* Most of these solutions are quite complex in term of computations, so I elected to use an algorithm that an external circuit is able to * process. This has the added benefit of protecting any keys and intermediate data used for calculating the signature so that even if * someone were to actually steal a sensor and disassembled it, they would not be able to extract the keys and other information from the * device.
* A common scheme for message signing (authenticity and integrity) is implemented using * HMAC which in combination with a strong * hash function provides a very strong level of protection.
* The Atmel ATSHA204A is a low-cost, low-voltage/current circuit that provides * HMAC calculation capabilities with SHA256 hashing which is a (currently) virtually unbreakable combination. If SHA256 were to be hacked, * a certain cryptocurrency would immediately be rendered worthless.
* The ATSHA device also contain a random number generator (RNG) which enables the generation of a good nonce, as in, * non-predictable.
* As I acknowledge that some might not want to use an additional external circuit, I have also implemented a software version of the ATSHA * device, capable of generating the same signatures as the ATSHA device does. 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. It also naturally claims more flash space due to the more complex software. But * for indoor sensors/actuators this might be good enough for most people. * * @section MySigninggrphowuse How to use this * * Before we begin with the details, I just want to emphasize that signing is completely optional and not enabled by default. If you do want * the additional security layer signing provides, you pick the backend of your choise in your sketch. Currently, two compatible backends are * supported; @ref MY_SIGNING_ATSHA204 (hardware backed) and @ref MY_SIGNING_SOFT (software backed). You can either enable these globally in * @ref MyConfig.h or in your sketch for sketch specific/local use. * * Firstly, you need to make sure to pick a backend to use as described above. * @code{.cpp} * //#define MY_SIGNING_SOFT * #define MY_SIGNING_ATSHA204 * #include * ... * @endcode * Make sure to set the define before the inclusion of MySensors.h. * It is legal to mix hardware- and software-based backends in a network. They work together. * * You also need to decide if the node (or gateway) in question require and verify signatures in addition to calculating them. * This has to be set by at least one of the node in a "pair" or nobody will actually start calculating a signature for a message. * Just set the flag @ref MY_SIGNING_REQUEST_SIGNATURES and the node will inform the gateway that it expects the gateway to sign all * messages sent to the node. If this is set in a gateway, it will @b NOT force all nodes to sign messages to it. It will only require * signatures from nodes that in turn require signatures. If it is desired that the gateway should require signatures from all nodes, * @ref MY_SIGNING_GW_REQUEST_SIGNATURES_FROM_ALL can be set in the gateway sketch.
* If you want to have two nodes communicate securely directly with each other, the nodes that require signatures must send a presentation * message to all nodes it expect signed messages from (only the gateway is informed automatically). See @ref signerPresentation().
* A node can have three "states" with respect to signing: * 1. Node does not support signing in any way (neither @ref MY_SIGNING_ATSHA204 nor @ref MY_SIGNING_SOFT is set) * 2. Node does support signing but don't require messages sent to it to be signed (@ref MY_SIGNING_REQUEST_SIGNATURES is not set) * 3. Node does support signing and require messages sent to it to be signed (@ref MY_SIGNING_REQUEST_SIGNATURES is set) * * Secondly, you need to verify the configuration for the backend.
* For hardware backed signing it is the pin the device is connected to. In MyConfig.h there are defaults which you might need to adjust to * match your personal build. The setting is defined using @ref MY_SIGNING_ATSHA204_PIN and the default is to use pin A3.
* Similar to picking your backend, this can also be set in your sketch: * @code{.cpp} * #define MY_SIGNING_ATSHA204 * #define MY_SIGNING_ATSHA204_PIN 4 * #define MY_SIGNING_REQUEST_SIGNATURES * #include * ... * @endcode * For the software backed signingbackend, an unconnected analog pin is required to set a random seed for the pseudo-random generator. * It is important that the pin is floating, or the output of the pseudo-random generator will be predictable, and thus compromise the * signatures. The setting is defined using @ref MY_SIGNING_SOFT_RANDOMSEED_PIN and the default is to use pin A7. The same configuration * possibilities exist as with the other configuration options. * * Thirdly, if you use the software backend, you need to personalize the node (see @ref personalization). * @code{.cpp} * #define MY_SIGNING_SOFT * #define MY_SIGNING_SOFT_RANDOMSEED_PIN 7 * #define MY_SIGNING_REQUEST_SIGNATURES * #include * ... * @endcode * * An example of a node that require signatures is available in @ref SecureActuator.ino. * * @anchor personalization If you use the “real” ATSHA204A, before any signing operations can be done, the device needs to be personalized. * This can be a daunting process as it involves irreversibly writing configurations to the device, which cannot be undone. I have however tried * to simplify the process as much as possibly by creating a helper-sketch specifically for this purpose in @ref SecurityPersonalizer.ino * Note that you also need to do personalization for software signing, but then the values are stored in EEPROM. * * To personalize a ATSHA204A do the following procedure: * 1. Enable @ref GENERATE_KEYS_ATSHA204A
* This will lock the ATSHA204A and generate random keys for HMAC (signing) and AES (encryption). * Copy the keys generated and replace the corresponding definitions under * "User defined key data", specifically @ref MY_HMAC_KEY and @ref MY_AES_KEY. * 2. Disable @ref GENERATE_KEYS_ATSHA204A and enable @ref PERSONALIZE_ATSHA204A
* This will store the HMAC key to the ATSHA204A and the AES key to EEPROM. It will also write * a checksum of the personalization data in EEPROM to be able to detect if the data is * altered.
* Personalization is now complete. * * To personalize for software signing do the following procedure: * 1. Enable @ref GENERATE_KEYS_SOFT
* This will generate random keys for HMAC (signing) and AES (encryption). * Copy the keys generated and replace the corresponding definitions under * "User defined key data", specifically @ref MY_HMAC_KEY and @ref MY_AES_KEY. * 2. Disable @ref GENERATE_KEYS_SOFT and enable @ref PERSONALIZE_SOFT
* This will store the HMAC key and the AES key to EEPROM. It will also write * a checksum of the personalization data in EEPROM to be able to detect if the data is * altered.
* Personalization is now complete. * * If you want to use soft signing and you want to use whitelisting (the ability to revoke/ban * compromised nodes in the network) and your target does not provide a unique device ID, you have * to generate a unique serial and store it in EEPROM. This can be done by replacing * @ref PERSONALIZE_SOFT in step 2 above with @ref PERSONALIZE_SOFT_RANDOM_SERIAL. See the output * under "Hardware security peripherals" to determine if this is necessary. * * When you have personalized your first device after step 2 above, you can run the same sketch on * all devices in your network that needs to be personalized in a compatible manner. Pick * @ref PERSONALIZE_ATSHA204A or @ref PERSONALIZE_SOFT as needed by the hardware. * * If a node does require signing, any unsigned message sent to the node will be rejected.
* This also applies to the gateway. However, the difference is that the gateway will only require signed messages from nodes it knows in turn * require signed messages (unless @ref MY_SIGNING_GW_REQUEST_SIGNATURES_FROM_ALL is set).
* A node can also inform a different node that it expects to receive signed messages from it. This is done by transmitting an internal message * of type @ref I_SIGNING_PRESENTATION and provide flags as payload that inform the receiver of the signing preferences of the sender.
* All nodes and gateways in a network maintain a table where the signing preferences of all nodes are stored. This is also stored in EEPROM so * if the gateway reboots, the nodes does not have to retransmit a signing presentation to the gateway for the gateway to realize that the node * expect signed messages.
* Also, the nodes that do not require signed messages will also inform gateway of this, so if you reprogram a node to stop require signing, * the gateway will adhere to this as soon as the new node has presented itself to the gateway. Note however, that if the gateway sets * @ref MY_SIGNING_GW_REQUEST_SIGNATURES_FROM_ALL a node that does not support signing will be unable to send any data to the gateway. * * The following sequence diagram illustrate how messages are passed in a MySensors network with respect to signing: * @image html MySigning/signingsequence.png * @image latex MySigning/signingsequence.eps "Signing sequence diagram" width=9cm * * None of this activity is “visible” to you (as the sensor sketch implementor). All you need to do is to set your preferences in MyConfig.h or * in your sketch. Depending on chosen backend, do personalization or key configurations and set @ref MY_SIGNING_REQUEST_SIGNATURES on the node that * you want protected. That is enough to enable protection from both Eve and Mallory in your network (although if you do not also enable encryption, * Eve can eavesdrop, but not do anything about, your messages). * * @section MySigningwhitelisting Whitelisting and node revocation * * Consider the situation when you have set up your secure topology. We use the remotely operated garage door as an example: * - You have a node inside your garage (therefore secure and out of reach from prying eyes) that controls your garage door motor.\n * This node requires signing since you do not want an unauthorized person sending it orders to open the door. * - You have a keyfob node with a signing backend that uses the same PSK as your door opener node. * * In this setup, your keyfob can securely transmit messages to your door node since the keyfob will sign the messages it sends and the door node * will verify that these were sent from a trusted node (since it used the correct PSK). If the keyfob does not sign the messages, the door node * will not accept them. * * One day your keyfob gets stolen or you lost it or it simply broke down. * * You now end up with a problem; you need some way of telling your door node that the keyfob in question cannot be trusted any more. Furthermore, * you maybe locked the data region in your door nodes ATSHA device and is not able to revoke/change your PSK, or you have some other reason for * not wanting to replace the PSK. How do you make sure that the "rogue" keyfob can be removed from the "trusted chain"? * * The answer to this is whitelisting. You let your door node keep a whitelist of all nodes it trusts. If you stop trusting a particular node, you * remove it from the nodes whitelist, and it will no longer be able to communicate signed messages to the door node. * * In case you want to be able to "whitelist" trusted nodes (in order to be able to revoke them in case they are lost) you also need to take note * of the serial number of the ATSHA device or the software value stored in EEPROM. This is unique for each device. The serial number is printed * in a copy+paste friendly format by the personalizer for this purpose.
* The whitelist is stored on the node that require signatures. When a received message is verified, the serial of the sender is looked up in a * list stored on the receiving node, and the corresponding serial stored in the list for that sender is then included in the signature verification * process. The list is stored as the value of the flag that enables whitelisting, @ref MY_SIGNING_NODE_WHITELISTING.
* * Whitelisting is achieved by 'salting' the signature with some node-unique information known to the receiver. In the case of ATSHA204A this is the * unique serial number programmed into the circuit. This unique number is never transmitted over the air in clear text, so Eve will not be able to * figure out a "trusted" serial by snooping on the traffic.
* Instead the value is hashed together with the senders NodeId into the HMAC signature to produce the final signature. The receiver will then take * the originating NodeId of the signed message and do the corresponding calculation with the serial it has stored in it's whitelist if it finds a * matching entry in it's whitelist. * * Whitelisting is an optional alternative because it adds some code and configuration options which might not be desirable for every user. So if * you want the ability to use whitelists, you need to enable @ref MY_SIGNING_NODE_WHITELISTING.
* The whitelist is provided as value of the flag that enable it as follows (example is a node that require signing as well): * @code{.cpp} * #define MY_SIGNING_ATSHA204 * #define MY_SIGNING_REQUEST_SIGNATURES * #define MY_SIGNING_NODE_WHITELISTING {{.nodeId = GATEWAY_ADDRESS,.serial = {0x09,0x08,0x07,0x06,0x05,0x04,0x03,0x02,0x01}},{.nodeId = 2,.serial = {0x01,0x02,0x03,0x04,0x05,0x06,0x07,0x08,0x09}}} * #include * ... * @endcode * In this example, there are two nodes in the whitelist; the gateway, and a separate node that communicates directly with this node (with signed * messages). You do not need to do anything special for the sending nodes, apart from making sure they support signing. * * The "soft" backend of course also support whitelisting. Example: * @code{.cpp} * #define MY_SIGNING_SOFT * #define MY_SIGNING_SOFT_RANDOMSEED_PIN 7 * #define MY_SIGNING_REQUEST_SIGNATURES * #define MY_SIGNING_NODE_WHITELISTING {{.nodeId = GATEWAY_ADDRESS,.serial = {0x09,0x08,0x07,0x06,0x05,0x04,0x03,0x02,0x01}},{.nodeId = 2,.serial = {0x01,0x02,0x03,0x04,0x05,0x06,0x07,0x08,0x09}}} * #include * ... * @endcode * * For a node that should transmit whitelisted messages but not receive whitelisted messages, you do not need any special configurations: * @code{.cpp} * #define MY_SIGNING_SOFT * #define MY_SIGNING_SOFT_RANDOMSEED_PIN 7 * @endcode * Remember that you always need to select a signing backend for all nodes that communicate to a node that require whitelisting. * Also, note that a node that use whitelisting will not accept messages from nodes that are not present in it's whitelist. * And you have to personalize all nodes that use signing with a common HMAC key but different serial numbers (ATSHA204A always has unique serials). * * @section MySigningtechnical The technical stuff * * How are the messages actually affected by the signing?
* The following illustration shows what part of the message is signed, and where the signature is stored: * @image html MySigning/signingillustrated1.png * @image latex MySigning/signingillustrated1.eps "Message structure" width=11cm * * The first byte of the header is not covered by the signature, because in the network, this byte is used to track hops in the network and therefore * might change if the message is passing a relay node. So it cannot be part of the signature, or the signature would be invalid when it arrives to * its destination. The signature also carries a byte with a signing identifier to prevent false results from accidental mixing of incompatible * signing backends in the network. Thus, the maximum size for a payload is 29-7 bytes. Larger payloads are not possible to sign. Another thing to * consider is that the strength of the signature is inversely proportional to the payload size. * * As for the software backend, it turns out that the ATSHA does not do “vanilla” HMAC processing. Fortunately, Atmel has documented exactly how * the circuit processes the data and hashes thus making it possible to generate signatures that are identical to signatures generated by the circuit. * * The signatures are calculates in the following way: * @image html MySigning/signingillustrated2.png * @image latex MySigning/signingillustrated2.eps "HMAC processing" width=10cm * * Exactly how this is done can be reviewd in the source for the ATSHA204SOFT backend and the ATSHA204A * datasheet. * In the MySensors protocol, the following internal messagetypes handles signature requirements and nonce requests:
* @ref I_SIGNING_PRESENTATION
* @ref I_NONCE_REQUEST
* @ref I_NONCE_RESPONSE
* * Also, the version field in the header has been reduced from 3 to 2 bits in order to fit a single bit to indicate that a message is signed. * * @section MySigninglimitations Known limitations * * Due to the limiting factor of our cheapest Arduino nodes, the use of diversified keys is not implemented. That mean that all nodes in your * network share the same PSK (at least the ones that are supposed to exchange signed data). It is important to understand the implications of * this, and that is covered in the "Typical use cases" chapter below.
* Also be reminded that the strength of the signature is inversely proportional to the size of the message. The larger the message, the weaker * the signature. * * @section MySigningusecases Typical use cases * * "Securely located" in this context mean a node which is not physically publicly accessible. Typically at least your gateway.
* "Public" in this context mean a node that is located outside your "trusted environment". This includes sensors located outdoors, keyfobs etc. * * @subsection MySigninglock Securely located lock * * You have a securely located gateway and a lock somewhere inside your "trusted environment" (e.g. inside your house door, the door to your * dungeon or similar).
* You should then keep the data section of your gateway and your lock node unlocked. Locking the data (and therefore the PSK) will require you * to replace at least the signing circuit in case you need to revoke the PSK because some other node in your network gets compromised.
* You need to make your node require signed messages but you do not necessarily need to make your gateway require signed messsages (unless you * are concerned that someone might spoof the lock status of your lock).
* Configuration example for the secure lock node:
* @code{.cpp} * #define MY_SIGNING_ATSHA204 * #define MY_SIGNING_REQUEST_SIGNATURES * #include * ... * @endcode * If you do also want your gateway to require signatures from your lock you just enable the same (or similar if using software signing) settings * in the gateway. * * @subsection MySigningpatio Patio motion sensor * * Your gateway is securely located inside your house, but your motion sensor is located outside your house. You have for some reason elected * that this node should sign the messages it send to your gateway. You should lock the data (PSK) in this node then, because if someone were * to steal your patio motion sensor, they could rewrite the firmware and spoof your gateway to use it to transmit a correctly signed message * to your secure lock inside your house. But if you revoke your gateway (and lock) PSK the outside sensor cannot be used for this anymore. * Nor can it be changed in order to do it in the future. You can also use whitelisting to revoke your lost node.
* This is an unlikely use case because there really is no reason to sign sensor values. If you for some reason want to obfuscate sensor data, * encryption is a better alternative.
* Configuration example for a motion sensor:
* @code{.cpp} * #define MY_SIGNING_SOFT * #define MY_SIGNING_SOFT_RANDOMSEED_PIN 7 * #define MY_SIGNING_REQUEST_SIGNATURES * #include * ... * @endcode * * The gateway needs to be configured with a whitelist (and it has to have an entry for all nodes that send and/or require signed messages):
* @code{.cpp} * #define MY_SIGNING_SOFT * #define MY_SIGNING_SOFT_RANDOMSEED_PIN 7 * #define MY_SIGNING_REQUEST_SIGNATURES * #define MY_SIGNING_NODE_WHITELISTING {{.nodeId = MOTION_SENSOR_ID,.serial = {0x12,0x34,0x56,0x78,0x90,0x12,0x34,0x56,0x78}}} * #include * ... * @endcode * @subsection MySigningkeyfob Keyfob for garage door opener * * Perhaps the most typical usecase for signed messages. Your keyfob should be totally locked down. If the garage door opener is secured * (and it should be) it can be unlocked. That way, if you loose your keyfob, you can revoke the PSK in both the opener and your gateway, * thus rendering the keyfob useless without having to replace your nodes. You can also use whitelisting to revoke your lost keyfob.
* Configuration example for the keyfob (keyfob will only transmit to another node and not receive anything):
* @code{.cpp} * #define MY_SIGNING_ATSHA204 * #include * ... * @endcode * * Configuration example for the door controller node (should require signing from anyone who wants to control it):
* @code{.cpp} * #define MY_SIGNING_SOFT * #define MY_SIGNING_SOFT_RANDOMSEED_PIN 7 * #define MY_SIGNING_REQUEST_SIGNATURES * #define MY_SIGNING_NODE_WHITELISTING {{.nodeId = GATEWAY_ADDRESS,.serial = {0x00,0x11,0x22,0x33,0x44,0x55,0x66,0x77,0x88}},{.nodeId = KEYFOB_ID,.serial = {}}} * #include * ... * @endcode * * @subsection MySigningsketches Relevant sketches * * - @ref SecureActuator.ino * - @ref SecurityPersonalizer.ino */ /** * @file MySigning.h * * @brief API declaration for MySigning signing backend */ #ifndef MySigning_h #define MySigning_h #include "MySensorsCore.h" #include "drivers/ATSHA204/ATSHA204.h" #ifdef MY_SIGNING_NODE_WHITELISTING typedef struct { uint8_t nodeId; /**< @brief The ID of the node */ uint8_t serial[SHA204_SERIAL_SZ]; /**< @brief Node specific serial number */ } whitelist_entry_t; #endif /** @brief Helper macro to determine the number of elements in a array */ #define NUM_OF(x) (sizeof(x)/sizeof(x[0])) /** * @brief Initializes signing infrastructure and associated backend. * * This function makes sure that the internal states of the signing infrastructure * is set to a known initial state. * \n@b Usage: This fuction should be called before any signing related operations take place. */ void signerInit(void); /** * @brief Validates personalization data * * This function checks that the personalization details are in order. * \n@b Usage: This fuction should be called before any signing related operations take place. * * @returns @c true if personalization data is valid. */ bool signerValidatePersonalization(void); /** * @brief Does signing specific presentation for a node. * * This function makes sure any signing related presentation info is shared with the other part. * The presentation of the gateways signing preferences is done in @ref signerProcessInternal(). * \n@b Usage: This function should be called by the presentation routine of the mysensors library. * You only need to call this directly from a sketch to set up a node to node signed message exchange. * If you do call this directly from a sketch, and you at some point change your sketch to go from * requireing signing to not requireing signatures, you need to present this change to the node at least * once, so it can update its requirements tables accordingly. Or it will keep believing that this node * require signatures and attempt to send signed messages to it. * * @param msg Message buffer to use. * @param destination Node ID of the destination. */ void signerPresentation(MyMessage &msg, uint8_t destination); /** * @brief Manages internal signing message handshaking. * * This function takes care of signing related message handshaknig such as nonce exchange. * \n@b Usage: This function should be called by the incoming message handler before any further message * processing is performed on internal messages. This function should only be called for @ref C_INTERNAL class * messages. * * @param msg Message buffer to process. * @returns @c true if caller should stop further message processing. */ bool signerProcessInternal(MyMessage &msg); /** * @brief Check timeout of verification session. * * Nonce will be purged if it takes too long for a signed message to be sent to the receiver. * \n@b Usage: This function should be called on regular intervals, typically within some process loop. * * @returns @c true if session is still valid. */ bool signerCheckTimer(void); /** * @brief Get nonce from provided message and store for signing operations. * * Returns @c false if subsystem is busy processing an ongoing signing operation.
* Returns @c false if signing identifier found in message is not supported by the used backend.
* If successful, this marks the start of a signing operation at the sending side so * implementation is expected to do any necessary initializations within this call. * \n@b Usage: This function is typically called as action when receiving a @ref I_NONCE_RESPONSE * message. * * @param msg The message to get the nonce from. * @returns @c true if successful, else @c false. */ bool signerPutNonce(MyMessage &msg); /** * @brief Signs provided message. All remaining space in message payload buffer is used for * signing identifier and signature. * * Nonce used for signature calculation is the one generated previously within @ref signerProcessInternal().
* Nonce will be cleared when this function is called to prevent re-use of nonce.
* Returns @c false if subsystem is busy processing an ongoing signing operation.
* Returns @c false if not two bytes or more of free payload space is left in provided message.
* This ends a signing operation at the sending side so implementation is expected to do any * deinitializations and enter a power saving state within this call. * \n@b Usage: This function is typically called as action when receiving a @ref I_NONCE_RESPONSE * message and after @ref signerPutNonce() has successfully been executed. * * @param msg The message to sign. * @returns @c true if successful, else @c false. */ bool signerSignMsg(MyMessage &msg); /** * @brief Verifies signature in provided message. * * Nonce used for verification is the one previously set using @ref signerPutNonce().
* Nonce will be cleared when this function is called to prevent re-use of nonce.
* Returns @c false if subsystem is busy processing an ongoing signing operation.
* Returns @c false if signing identifier found in message is not supported by the used backend.
* This ends a signing operation at the receiving side so implementation is expected to do any * deinitializations and enter a power saving state within this call. * \n@b Usage: This function is typically called when receiving a message that is flagged as signed * and @ref MY_SIGNING_REQUEST_SIGNATURES is activated. * * @param msg The message to verify. * @returns @c true if successful, else @c false. */ bool signerVerifyMsg(MyMessage &msg); /** * @brief Initialize a hash calculation session. * * Any ongoing calculation session will be terminated/reset. */ void signerSha256Init(void); /** * @brief Add data to an ongoing hash calculation session. * * More data can be added by repeated calls to this function. * * @param data Buffer with data to add. * @param sz Size of data buffer. */ void signerSha256Update(const uint8_t* data, size_t sz); /** * @brief Finalize an ongong hash calculation session and return the hash. * * The returned hash size is always 32 bytes. Buffer can be assumed to be valid * until @ref signerSha256Init() is called again. * * @returns Buffer with 32-byte hash. */ uint8_t* signerSha256Final(void); /** * @brief Do a timing neutral memory comparison. * * The function behaves similar to memcmp with the difference that it will * always use the same number of instructions for a given number of bytes, * no matter how the two buffers differ and the response is either 0 or -1. * * @param a First buffer for comparison. * @param b Second buffer for comparison. * @param sz The number of bytes to compare. * @returns 0 if buffers match, -1 if they do not. */ int signerMemcmp(const void* a, const void* b, size_t sz); #endif /** @}*/ /** * @defgroup MySigningTroubleshootinggrp Troubleshooting * @ingroup MySigninggrp * @{ * * @section MySigningTroubleshootingSymptoms Symptoms and solutions * * The first thing to do if you suspect signing is causing problems, is to enable the verbose debug * flag for the signing backend. @see MY_DEBUG_VERBOSE_SIGNING * * If you are having trouble getting signing to work, please see the following troubleshooting tips. * * @subsection MySigningTroubleshootingSymptomStFail Signing fails and logs show st=fail on transmissions * * This is actually not a signing problem, although ofthen st=fail becomes st=ok when signing is disabled. * This is by far the most commonly reported problem with signing, but the problems is not with signing, * it is with radio performence.
* This is a typical log which might look like a signing related issue but isn't: * @code{.unparsed} * 0;255;3;0;9;Skipping security for command 3 type 16 * 0;255;3;0;9;read: 3-3-0 s=255,c=3,t=16,pt=0,l=0,sg=0: * 0;255;3;0;9;Signing backend: ATSHA204Soft * 0;255;3;0;9;SHA256: 86DEAE1DAF50D577A4E2262B33ABF9DEE05DD8FAF84F94F50900000000000000 * 0;255;3;0;9;Skipping security for command 3 type 17 * 0;255;3;0;9;send: 0-0-3-3 s=255,c=3,t=17,pt=6,l=25,sg=0,st=fail:86DEAE1DAF50D577A4E2262B33ABF9DEE05DD8FAF84F94F509 * 0;255;3;0;9;Failed to transmit nonce! * 0;255;3;0;9;Message is not signed, but it should have been! * 0;255;3;0;9;verify fail * @endcode * * The reason for this is that when signing is used, the messages transmitted become relatively large.
* Because of this, the message is more sensitive to noise, and the chance for a message to get scrambled * increase with the message size. Please refer to the troubleshooting section at the MySensors forum for * information on how to improve radio performence.
* This is a good place to start: https://forum.mysensors.org/topic/666/debug-faq-and-how-ask-for-help * * @subsection MySigningTroubleshootingSymptomNonce Failed to generate nonce * * The signing backend failed to generate the nonce needed to sign a message. This indicate a hardware * problem. Please post the debug info on the forum together with a description of your hardware setup. * * @subsection MySigningTroubleshootingSymptomSign Failed to sign message * * The signing backend failed to sign the message. Typically this happens if your message is so large, * that there is no room left in the buffer to store a signature. * * @subsection MySigningTroubleshootingSymptomWrongSource Nonce did not come from the destination (XX) of the message to be signed! It came from YY * * This should not really happen. The reason for this message is that the signing backend is only capable * of handling one signed message session at any time. If for some reason multiple nodes send a nonce message to * the same node, only the nonce from a node that is the destination of the current message signing session will be * accepted. Any other nonces will be dropped. This should not happen as no node should send a nonce unless asked to, * and a node will only ask for a nonce to one destination for every signing session.
* If you see this message, please post the debugging details on the MySensors forum so it can be investigated further * together with a description of your setup. * * @subsection MySigningTroubleshootingSymptomNotSigned Message is not signed, but it should have been * * A node has failed to comply with the signing preferences of this node. Check that the node has received a * signing presentation message from this node. This is automatically transmitted to gateways. For other nodes, * you need to transmit the presentation from the sketch. @see signerPresentation * * @subsection MySigningTroubleshootingSymptomNotSignedGeneral "Messages do not appear to be signed but I think they should be..." * * Make sure you have enabled the flag to require signatures to require signatures and have enabled one of the signing * backends. @see MY_SIGNING_REQUEST_SIGNATURES @see MY_SIGNING_ATSHA204 @see MY_SIGNING_SOFT * * @subsection MySigningTroubleshootingSymptomNotWorkingWhitelisting Signature verification failed! * * Make sure both source and destination of the signed message has undergone @ref personalization with the same HMAC key.
* Also, if whitelisting is used, make sure the proper serial is paired with the proper node ID at the destination. * Whitelisting preferences are communicated with the signing presentation (done automatically from nodes to gateway but * has to be explicitly done by sketch for node to node communication). @see signerPresentation */ /** @}*/