IETF Anoop Kumar Pandey Internet-Draft C-DAC Bangalore Intended status: Informational December 23, 2019 Expires: June 25, 2020 AutoAdd - Automatic Bootstrapping of IoT Devices draft-anoopmis-eap-autoadd-00 Abstract IoT devices are fast getting embedded into our lives, and when put together they have the potential to generate a precise and detailed history of our lives and store them forever. Their networking and communicational power can be unleashed for malicious and sabotage purposes, by a motivated attacker sitting in the far corner of the world. Attacks on Industrial IoT systems can cause greater disasters. It is therefore essential to inculcate the security aspect, right from design to development to operations. The first operation of an IoT device is to bootstrap itself, and due importance should be placed to ensure that this operation is carried out securely and with due diligence. However, it's easier said than done, and this paper outlines several approaches for secure automated bootstrapping and also proposes a new method, which is compared against the existing mechanisms for several qualitative factors. Status of This Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at https://datatracker.ietf.org/drafts/current/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." This Internet-Draft will expire on June 25, 2020. Copyright Notice Copyright (c) 2019 IETF Trust and the persons identified as the document authors. All rights reserved. Anoop Kumar Pandey Expires June 25, 2020 [Page 1] Internet-Draft AutoAdd December 2019 This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (https://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Table of Contents 1. Prologue . . . . . . . . . . . . . . . . . . . . . . . . . . 2 2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 2.1. Requirements Language . . . . . . . . . . . . . . . . . . 3 3. Prior and Ongoing Contributions . . . . . . . . . . . . . . . 3 3.1. TOFU (Trust on First Use) . . . . . . . . . . . . . . . . 4 3.2. Resurrecting Duckling . . . . . . . . . . . . . . . . . . 4 3.3. Enrollment over Secure Transport . . . . . . . . . . . . 4 3.4. BRSKI . . . . . . . . . . . . . . . . . . . . . . . . . . 4 3.5. EAP-NooB . . . . . . . . . . . . . . . . . . . . . . . . 5 3.6. AutoAdd (Work in Progress) . . . . . . . . . . . . . . . 5 3.6.1. Expiration of owner certificate . . . . . . . . . . . 6 3.6.2. Selling a device . . . . . . . . . . . . . . . . . . 7 4. Comparison Chart . . . . . . . . . . . . . . . . . . . . . . 7 5. Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . 8 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9 7. Security Considerations . . . . . . . . . . . . . . . . . . . 9 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 9 8.1. Normative References . . . . . . . . . . . . . . . . . . 9 8.2. Informative References . . . . . . . . . . . . . . . . . 9 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 10 1. Prologue Amazon launched "Amazon Alexa" in November 2014. Alexa is a virtual assistant which comes with Echo line of smart speakers. It is capable of voice interaction, control of smart home devices, music playback, setting alarms, making calls, checking weather and news and much more. Google Home series smart speakers were launched in November 2016. Google Assistant can be used to control thousands of smart-home products from several brands like LG, GE, Whirlpool, Nest etc... Google Home can be asked to change the temperature, dim the lights, turn on a microwave or kettle, and also start Roomba (robotic vacuum cleaners). It can also turn the TV on/off using Chromecast. The concept of smart home and devices is taking off very fast. It appears to make our lives quite easy and comfortable. But turning Anoop Kumar Pandey Expires June 25, 2020 [Page 2] Internet-Draft AutoAdd December 2019 your home into a computer means facing computer-like problems. The security and performance issues associated are much scary. It creates a method for transformation of the physical world into computer-based systems, resulting in performance and efficiency enhancement, financial gains, and reduces human involvement. The number of IoT devices increased 31% year-over-year to 8.4 billion in 2017 and it is estimated to have 30 billion IoT devices by 2020 [iotscale]. Many more devices are/will be connected through serial link. 2. Introduction Kevin Ashton coined the term "Internet of Things (IoT)" and defined it as a system where the internet is connected to the physical world via ubiquitous sensors. While, the scale of IoT is going pretty bigger day by day, the task of adding new devices and bootstrapping it at such a large scale, remains at large. Manual bootstrapping requires a human to add an IoT device to a network (network discovery), connect to registrar (system where a device can be registered), setting up the key for future secure communication and finally all configuration of the device for its functioning in the network domain. Automatic bootstrapping methods are still evolving and are under testing and scrutiny for various environments and scenarios. While security experts and engineers are toiling hard to mitigate risks associated with automatic bootstrapping, we propose a system AutoAdd (work in progress), which ensures automatic addition and initial bootstrapping of an IoT device while it is put on the network. There are billions of devices and at least thousands of manufacturers. So how do we identify and trust a device? Similarly there are many networks, how does the device know that I am working only with my owner and not with some imposter network? Remember, there are hostile devices on the network, and there are hostile networks that might attempt to take over the device. Basically, we need to establish the identity/authenticity of the device; Check if device is compromised or not; establish the identity of the network/ domain; and finally check if the domain is the correct one. 2.1. Requirements Language The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119 [RFC2119]. 3. Prior and Ongoing Contributions Anoop Kumar Pandey Expires June 25, 2020 [Page 3] Internet-Draft AutoAdd December 2019 3.1. TOFU (Trust on First Use) TOFU (Trust on First Use) calls for accepting and storing a public key or credential associated with an asserted identity, without authenticating that assertion. Subsequent communication that is authenticated using the cached key or credential is secure against an MiTM attack, if such an attack did not succeed during the vulnerable initial communication. 3.2. Resurrecting Duckling In 'Resurrecting Duckling' [stajano1999resurrecting], a device recognises as its owner the first entity that sends it a secret key and will stay loyal to its owner for the rest of the life. It may come to EoL (end of life), or may be reset. The ownership of the device may also be transferred. It is analogous to imprinting in ducks, where duckling emerging from its egg will recognise as its mother the first moving object it sees that makes a sound, regardless of what it looks like. 3.3. Enrollment over Secure Transport In Enrollment over Secure Transport (EST) RFC 7030 [RFC7030], the client starts a TLS based HTTPS session with an EST server. Through a part of URI, a specific EST service is requested during the session. The client authenticates the server and the server authenticates the client. The server verifies if the client is authorized to use the requested service. Similarly the client verifies if the server has proper authorization to serve this client. Upon complete authentication and authorization check of both the parties, the server responds to the client request. 3.4. BRSKI An ongoing internet draft BRSKI (Bootstrapping Remote Secure Key Infrastructures) [I-D.ietf-anima-bootstrapping-keyinfra] lists steps for auto bootstrapping as follow: o Pledge discovers a communication channel to a Registrar. o Pledge identifies itself. This is done by presenting an X.509 IDevID credential to the discovered Registrar (via the Proxy) in a TLS handshake. (The Registrar credentials are only provisionally accepted at this time) o Pledge requests to join the discovered Registrar using a voucher request. Anoop Kumar Pandey Expires June 25, 2020 [Page 4] Internet-Draft AutoAdd December 2019 o Registrar sends the voucher request to the MASA (manufacturer). URL of MASA can be in the voucher request or embedded in Registrar. o MASA sends the voucher which is passed to pledge. o MASA sends the voucher which is passed to pledge. o Pledge verifies the voucher and imprints to the registrar by send voucher status telemetry. o Registrar verifies the voucher and enrolls the pledge to the domain Here pledge is the device to be added to network/domain; registrar is the registration authority where devices are registered; MASA is manufacturer authorized signing authority; IDevID is an Initial Device Identity X.509 certificate installed by the vendor on new equipment and voucher is a signed statement from the MASA service that indicates to a Pledge the cryptographic identity of the Registrar it should trust. 3.5. EAP-NooB EAP-NooB (Extensible Authentication Protocol Nimble out of Band) [I-D.aura-eap-noob] method is intended for bootstrapping all kinds of Internet-of-Things (IoT) devices that have a minimal user interface and no pre-configured authentication credentials. The method makes use of a user-assisted one-directional OOB (out of band) channel between the peer device and authentication server. The secure bootstrapping in this specification makes use of a user-assisted out- of-band (OOB) channel. The security is based on the assumption that attackers are not able to observe or modify the messages conveyed through the OOB channel. EAP-NooB follows the common approach of performing a Diffie-Hellman key exchange over the insecure network and authenticating the established key with the help of the OOB channel in order to prevent impersonation and man-in-the-middle (MitM) attacks. 3.6. AutoAdd (Work in Progress) We propose AutoAdd: an automatic bootstrapping method for IoT devices. This is a work in progress and open for comments. When a device is purchased in real world, usually an invoice is issued in the name of the purchaser with stamp of vendor/ manufacturer. We propose that similarly, a digital invoice can be issued which will contain the public key(s) of the and digitally signed by the manufacturer. The Anoop Kumar Pandey Expires June 25, 2020 [Page 5] Internet-Draft AutoAdd December 2019 digital invoice may be embedded in the device along with the IDevID. A digital invoice may be contain the IDevID of the device and Public key of Registrars (Ri), digital signed by Manufacturer (M) and can be represented as below. Dig_Invoice = DigSignM {IDevID, PubKey: [R1, R2, .., Rn]} When the device starts the registration process, it will present the digital invoice along with IDevID. The Registrar can verify the digital signature of the manufacturer on the digital invoice and sent a signed note of acceptance to the device. Flag = VerifyDigSignManufacturer (Dig_Invoice, PubKeyM) if (flag) Acceptance_Note = DigSignRi {Note} The device can verify the signed note using the public key(s) mentioned in the digital invoice, thereby verifying its true owner. VerifyDigSignRegistrar (Acceptance_Note, PublicKeyFromDigInvoiceRi) This process with eliminate all the communication overhead with MASA and multiple level verification (voucher request, voucher, telemetry etc. at Registrar/ MASA/Device. From security point of view, we can claim that given that the digital invoice is digitally signed by manufacturer, the public key of domain owner embedded in the digital invoice can't be changed, otherwise verification of digital signature of manufacturer at Registrar end will fail. We would also like to share few use cases for the sake of understanding the complete ecosystem of AutoAdd. 3.6.1. Expiration of owner certificate The device has domain owner's or registrar's public key embedded in its digital invoice which is used to verify the digital signature on the note of acceptance and thereby authenticating the owner. If the owner's digital signature certificate expires or is changed or is revoked, the digital signature of the owner can't be verified and the owner authentication will fail. To overcome such situation, before the expiration of the certificate, the owner will require to create another digital invoice by specifying it's own new public key digitally signed by his old private key and embedding it into the device. This will basically create a chain of digital invoices. This process is similar to attestation of own signature in real world. The verification will basically verify the chain of digital invoices. For the sake of clarity, let us consider R1_old as old public key of Registrar and original digital invoice be Anoop Kumar Pandey Expires June 25, 2020 [Page 6] Internet-Draft AutoAdd December 2019 Dig_Invoice_Original = DigSign (PvtM, {IDevID, PubKey: [R1_old]}) Let R1_new be the new public key of the registrar and Pvt_R1_Old be the old private key of the reigstrar. The registrar need to create a new digital invoice digitally signed by his old private key. Dig_Invoice_New = DigSign (Pvt_R1_Old , {IDevID, PubKey: [R1_new]} ) Let note of acceptance signed with new private key of R1 as follow: Acceptance_Note = DigSign(Pvt_R1_new, {Note}) Verification will be done as per following steps: Flag1 = VerifyDigSignDigInvoiceNew (Dig_Invoice_New, PublicKeyFromDigInvoiceOriginalR1) If(flag1) flag2 = VerifyDigSignRegistrar (Acceptance_Note, PublicKeyFromDigInvoiceNewR1) If(flag2) Output "Registrar or Owner verified" These steps can be chained for multiple chain of digital invoices. 3.6.2. Selling a device A device may be resold and in the new environment, the public key of the new owner may need to be embedded in the device, else owner verification will fail. Addition of the public key of the new owner will follow similar steps as described in the previous section (3.6.1) where the old owner will create a new digital invoice by specifying the new owner's public key and digitally signing it. The verification of the note of acceptance by the new owner will follow similar steps as illustrated in section 3.6.1. 4. Comparison Chart Anoop Kumar Pandey Expires June 25, 2020 [Page 7] Internet-Draft AutoAdd December 2019 +--------------+-----------------------+----------------------------+ | Approach | Security | Constraints/Consequence | +--------------+-----------------------+----------------------------+ | TOFU | Vulnerable initial | No authentication of | | | communication | initial assertion | +--------------+-----------------------+----------------------------+ | Resurrecting | No owner | Anyone can be the owner | | Duckling | authentication | | +--------------+-----------------------+----------------------------+ | EST | TLS secured HTTP | Need some pre-provisioned | | | session between | credentials to establish | | | client and Server | secure communication | +--------------+-----------------------+----------------------------+ | BRSKI | Online service | Online service | | | authenticating both | authenticating both device | | | device and domain | and domain & MASA should | | | | be always online; No | | | | autorun of BRSKI on | | | | network or ownership | | | | change | +--------------+-----------------------+----------------------------+ | EAP-NooB | Security dependent on | Manual intervention for | | | Ephemeral Elliptic | OOB authentication; Not | | | Curve Diffie-Hellman | Scalable | | | (ECDHE) key exchange | | | | and manual assistance | | +--------------+-----------------------+----------------------------+ | AutoAdd | Easy offline | Public key is required for | | | authentication of | each buyer. | | | both device and | | | | domain | | +--------------+-----------------------+----------------------------+ Table 1: Comparison of various bootstrapping methods 5. Conclusion We have outlined a number of approaches that are currently followed for bootstrapping of IoT devices along with their merits and demerits. We have also highlighted several security concerns that would have to be addressed for booting up and bringing an IoT device for operations. We have also presented AutoAdd and have done a qualitative comparison against the existing methods in terms of security and ease-of-use. AutoAdd can serve as a secure automatic bootstrapping method for IoT devices. We are also working on a internet draft to incorporate device certificates with EAP-NOOB. Anoop Kumar Pandey Expires June 25, 2020 [Page 8] Internet-Draft AutoAdd December 2019 6. IANA Considerations This memo includes no request to IANA. 7. Security Considerations This draft proposes an automatic bootstrapping method for IoT devices. The security of the protocol is inherent from the security of unforgeable digital signature and PKI. A detailed security analysis is pending. 8. References 8.1. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, . [RFC7030] Pritikin, M., Ed., Yee, P., Ed., and D. Harkins, Ed., "Enrollment over Secure Transport", RFC 7030, DOI 10.17487/RFC7030, October 2013, . 8.2. Informative References [I-D.aura-eap-noob] Aura, T. and M. Sethi, "Nimble out-of-band authentication for EAP (EAP-NOOB)", draft-aura-eap-noob-07 (work in progress), October 2019. [I-D.ietf-anima-bootstrapping-keyinfra] Pritikin, M., Richardson, M., Eckert, T., Behringer, M., and K. Watsen, "Bootstrapping Remote Secure Key Infrastructures (BRSKI)", draft-ietf-anima-bootstrapping- keyinfra-31 (work in progress), December 2019. [iotscale] Nordrum, Amy., "Popular Internet of Things Forecast of 50 Billion Devices by 2020 Is Outdated", 2016, . Anoop Kumar Pandey Expires June 25, 2020 [Page 9] Internet-Draft AutoAdd December 2019 [stajano1999resurrecting] Frank, Stajano., "The resurrecting duckling", 1999, . Author's Address Anoop Kumar Pandey C-DAC Bangalore #68, Electronics City Bangalore 560100 India Email: anoop@cdac.in Anoop Kumar Pandey Expires June 25, 2020 [Page 10]