]> China Automotive Innovation Corporation

yangyanzhao@t3caic.com

China Automotive Innovation Corporation

guopeng@t3caic.com

Purple Mountain Laboratories, China

yujiabao@pmlabs.com.cn

Device authentication LTE-D This document describes a physical layer device authentication protocol based on the physical layer unclonable fingerpint (PUF) technique for LTE Direct (LTE-D), a subprotocol of LTE V2X (Vehicle-to-Everything), to help the LTE-D message receiver confirm the identity of the LTE-D message sender. PUF utilizes intrinsic nonlinear characters of the transmission signal to identificate the devices and coresponding wireless signal transmitters, and is suitable for critical vehicular communication scenarios by its immunity against traditional cryptographic attacks. The protocol can be seamlessly integrated into the LTE-D communication system, and compatible with the traditional cryptography-based authentication mechanism.

Introduction LTE Direct (LTE-D), a subprotocol of LTE V2X (Vehicle-to-Everything), is designed for device-to-device communication within vehicular environments. LTE-D lies in its potential to enable direct, efficient, and low-latency communication between nearby devices, fostering enhanced safety, cooperative driving, and diverse applications in the automotive landscape. To realize the benefits and ensure the integrity and security of communications, authentication mechanisms for high-level security are imperative. A novel technique called physical layer unclonable fingerprint (PUF) is proposed for device authentication, which does not rely on cryptographic algorithms or keys, but utilizes intrinsic nonlinear characters of the transmission signal to identify devices with corresponding wireless signal transmitters, and is suitable for enhancing the security of critical vehicular communication scenario by tis immunity against traditional cryptographic attacks. A PUF system is composed by two kinds of components, the capturing frontends and the identification backend. A PUF capture frontend is often implemented by a Software Radio Platform (SRP), which captures wireless signals and extracts device characters (device fingerprint) from them. A PUF identification backend is a program with a database of pre-collected device fingerprints of varied devices, which takes device fingerprint as input and outputs the identification result. This document describes an physical layer device authentication protocol based on the PUF technique to help the LTE-D message receiver confirm the identity of the LTE-D message sender. The protocol can be seamlessly integrated into the LTE-D communication system, and compatible with the traditional cryptography-based authentication mechanism.

Conventions and Definitions The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 when, and only when, they appear in all capitals, as shown here.

Device Authentication Protocol The device authentication protocol contains only two messages and only involves the receiver, equipped with a PUF capture frontend, and the authenticator, equipped with a PUF identification backend. Notice that the sender does not need more interactions than normal LTE-D communication processes, and the traditional first step of authentication, i.e. initiating the authentication, is understood by the action of sending messages.

Device Authentication Request The Receiver initiates the authentication process by sending a request to the Authenticator.

Table of fields included in the request +---------------------------+---------+ | Field | Length | +---------------------------+---------+ | Message Type | 8 bits | +---------------------------+---------+ | Endian Type | 1 bits | +---------------------------+---------+ | Reserved | 7 bits | +---------------------------+---------+ | Receiver ID | 16 bits | +---------------------------+---------+ | Serial Number | 32 bits | +---------------------------+---------+ | Timestamp | 64 bits | +---------------------------+---------+ | Nonce | 64 bits | +---------------------------+---------+ | Signal Data Length | 32 bits | +---------------------------+---------+ | Signal Data | variable| | | length | +---------------------------+---------+

1. Message Type (8 bits) 8 bits for fixed message type, i.e., 0x10, for Device Authentication Request.
2. Endian Type (1 bits) 0 for little endian, 1 for big endian.
3. Receiver ID (32 bits) Unique identifier for the Receiver.
4. Serial Number (32 bits) A serial number indicating the receive order of the message.
5. Timestamp (64 bits) A timestamp indicating when the request was generated.
6. Nonce (64 bits) A random value generated by the device to prevent replay attacks.
7. Signal Data Length (32 bits) The length of the following signal data, in octets.
8. Signal Data (variable length) Data captured by the SRP of the receiver that contains enough information to authentication.

Device Authentication Response The Authenticator processes the request, comparing the signal data with the pre-collected fingerprints and decoding the data by the PUF Backend, then sends the result back to the Receiver.

Table of fields included in the response +---------------------------+---------+ | Field | Length | +---------------------------+---------+ | Message Type | 8 bits | +---------------------------+---------+ | Endian Type | 1 bits | +---------------------------+---------+ | Confidence Coefficient | 7 bits | +---------------------------+---------+ | Sender ID | 16 bits | +---------------------------+---------+ | Serial Number | 32 bits | +---------------------------+---------+ | Timestamp | 64 bits | +---------------------------+---------+ | Nonce | 64 bits | +---------------------------+---------+ | Decoded Data Length | 32 bits | +---------------------------+---------+ | Decoded Data | variable| | | length | +---------------------------+---------+

1. Message Type (8 bits) 8 bits for fixed message type, i.e., 0x20, for Device Authentication Response.
2. Endian Type (1 bits) 0 for little endian, 1 for big endian.
3. Confidence Coefficient (7 bits) The confidence coefficient of the following calculated sender ID given by the PUF backend, in percent, from 0 to 100. Any value above 100 is illegal.
4. Sender ID (32 bits)
   • Unique identifier for the Sender, identified by the Authenticator with the pre-collected fingerprints.
   • The ID 0xFFFFFFFF is reserved for unknown sender.
5. Serial Number (32 bits) A serial number corresponding with the request.
6. Timestamp (64 bits) A timestamp indicating when the response was generated.
7. Nonce (64 bits) A random value generated by the device to prevent replay attacks.
8. Decoded Data Length (32 bits) The length of the following decoded data, in octets.
9. Decoded Data (variable length) Data decoded by the signal data from the corresponding authentication request message.

Security Considerations To ensure the confidentiality, integrity, and authenticity of communication within the LTE-D Physical Layer Device Authentication Protocol, it is crucial to employ strong encryption and integrity mechanisms for the exchanged messages among all the parties of the protocol. Leveraging Transport Layer Security (TLS)[RFC8446] is highly recommended for this purpose.

IANA Considerations This document does not require any actions or registrations with the Internet Assigned Numbers Authority (IANA).

Normative References In many standards track documents several words are used to signify the requirements in the specification. These words are often capitalized. This document defines these words as they should be interpreted in IETF documents. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements. RFC 2119 specifies common key words that may be used in protocol specifications. This document aims to reduce the ambiguity by clarifying that only UPPERCASE usage of the key words have the defined special meanings. This document specifies version 1.3 of the Transport Layer Security (TLS) protocol. TLS allows client/server applications to communicate over the Internet in a way that is designed to prevent eavesdropping, tampering, and message forgery. This document updates RFCs 5705 and 6066, and obsoletes RFCs 5077, 5246, and 6961. This document also specifies new requirements for TLS 1.2 implementations.