I2NSF Working Group J. Jeong, Ed. Internet-Draft P. Lingga Intended status: Informational Sungkyunkwan University Expires: 3 August 2023 J. Park ETRI D. Lopez Telefonica I+D S. Hares Huawei 30 January 2023 Security Management Automation of Cloud-Based Security Services in I2NSF Framework draft-jeong-i2nsf-security-management-automation-05 Abstract This document describes Security Management Automation (SMA) of cloud-based security services in the framework of Interface to Network Security Functions (I2NSF). The security management automation in this document deals with closed-loop security control, security policy translation, and security audit. To support these three features in SMA, this document specifies an augmented architecture of the I2NSF framework with new system components and new interfaces. 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 3 August 2023. Copyright Notice Copyright (c) 2023 IETF Trust and the persons identified as the document authors. All rights reserved. Jeong, et al. Expires 3 August 2023 [Page 1] Internet-Draft I2NSF Security Management Automation January 2023 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 Revised BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Revised BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 3. Security Management Automation in I2NSF Framework . . . . . . 4 3.1. Components with I2NSF Framework for Security Management Automation . . . . . . . . . . . . . . . . . . . . . . . 4 3.2. Interfaces with SMA-Based I2NSF Framework . . . . . . . . 5 4. Security Policy Translation . . . . . . . . . . . . . . . . . 6 5. Security Audit System . . . . . . . . . . . . . . . . . . . . 9 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11 7. Security Considerations . . . . . . . . . . . . . . . . . . . 11 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 11 8.1. Normative References . . . . . . . . . . . . . . . . . . 11 8.2. Informative References . . . . . . . . . . . . . . . . . 12 Appendix A. Acknowledgments . . . . . . . . . . . . . . . . . . 14 Appendix B. Contributors . . . . . . . . . . . . . . . . . . . . 14 Appendix C. Changes from draft-jeong-i2nsf-security-management-automation-04 . . . 14 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 14 1. Introduction Interface to Network Security Functions (I2NSF) defines a framework and interfaces for interacting with Network Security Functions (NSFs) [RFC8192][RFC8329]. Note that an NSF is defined as software that provides a set of security-related services, such as (i) detecting unwanted activity, (ii) blocking or mitigating the effect of such unwanted activity in order to fulfill service requirements, and (iii) supporting communication stream integrity and confidentiality [RFC8329]. The NSF can be implemented as a Virtual Network Function (VNF) in a Network Functions Virtualization (NFV) environment [ETSI-NFV][I-D.ietf-i2nsf-applicability]. Jeong, et al. Expires 3 August 2023 [Page 2] Internet-Draft I2NSF Security Management Automation January 2023 This document describes Security Management Automation (SMA) of cloud-based security services in the I2NSF framework. The security management automation includes closed-loop security control, security policy translation, and security audit. This document specifies an augmented architecture of the I2NSF framework for the SMA services with new system components and new interfaces. For reliable management for networked security services, this document proposes a network management and verification facility using a secuirty audit system (e.g., remote attestation and blockchain [Bitcoin]). This security audit system can facilitate the non-repudiation of configuration commands and monitoring data generated in the I2NSF framework. Therefore, with the security service automation, this document facilitates the foundation of Intent-Based Networking (IBN) for autonomous security services [RFC9315]. 2. Terminology This document uses the terminology described in [RFC8329] and [I-D.ietf-i2nsf-applicability]. In addition, the following terms are defined below: * Security Management Automation (SMA): It means that a high-level security policy from a user (or administrator) is well-enforced in a target I2NSF system. The high-level security policy can be translated into the corresponding low-level security policy by a security policy translator and dispatched to appropriate NSFs. Through the monitoring of the NSFs, the activity and performace of the NSFs is monitored and analyzed. If needed, the security rules of the low-level security policy are augmented or new security rules are generated and configured to appropriate NSFs. * Security Policy Translation (SPT): It means that a high-level security policy is translated to a low-level security policy that can be understood and configured by an NSF for a specific security service, such as firewall, web filter, deep packet inspection, DDoS-attack mitigation, and anti-virus. * Feedback-Based Security Management (FSM): It means that a security service is evolved by updating a security policy (having security rules) and adding new security rules for detected security attacks by processing and analzing the monitoring data of NSFs. Jeong, et al. Expires 3 August 2023 [Page 3] Internet-Draft I2NSF Security Management Automation January 2023 +------------+ | I2NSF User | +------------+ ^ | Consumer-Facing Interface v +-------------------+ Registration +-----------------------+ |Security Controller|<-------------------->|Developer's Mgmt System| +-------------------+ Interface +-----------------------+ ^ ^ | | | | Analytics Interface +-----------------------+ | +------------------------>| I2NSF Analyzer | | +-----------------------+ | NSF-Facing Interface ^ ^ ^ | | | | | | | | | +------------------------------+ | | | | +-----------------------+ | | | | Monitoring Interface | v v v v +----------------+ +---------------+ +-----------------------+ | NSF-1 |-| NSF-2 |...| NSF-n | | (Firewall) | | (Web Filter) | |(DDoS-Attack Mitigator)| +----------------+ +---------------+ +-----------------------+ Figure 1: Security Management Automation in I2NSF Framework 3. Security Management Automation in I2NSF Framework This section summarizes the I2NSF framework as defined in [RFC8329]. As shown in Figure 1, an I2NSF User can use security functions by delivering high-level security policies, which specify security requirements that the I2NSF user wants to enforce, to the Security Controller via the Consumer-Facing Interface (CFI) [I-D.ietf-i2nsf-consumer-facing-interface-dm]. 3.1. Components with I2NSF Framework for Security Management Automation The following are the system components for the SMA-based I2NSF framework. * I2NSF User: An entity that delivers a high-level security policy to Security Controller. Jeong, et al. Expires 3 August 2023 [Page 4] Internet-Draft I2NSF Security Management Automation January 2023 * Security Controller: An entity that controls and manages other system components in the I2NSF framework. It translates a high- level security policy into the corresponding low-level security policy and selects appropriate NSFs to execute the security rules of the low-level security policy. * Developer's Management System (DMS): An entity that provides an image of of a virtualized NSF for a security service to the I2NSF framework, and registers the capability and access information of an NSF with Security Controller. * Network Security Function (NSF): An entity that is a Virtual Network Function (VNF) or Container Network Function (CNF), which is called Cloud-native Network Function, for a specific network security service such as firewall, web filter, deep packet inspection, DDoS-attack mitigation, and anti-virus. * I2NSF Analyzer: An entity that collects monitoring data from NSFs and analyzes such data for checking the activity and performance of the NSFs using machine learning techniques (e.g., Deep Learning [Deep-Learning]). If there is a suspicious attack activity for the target network or NSF, I2NSF Analyzer delivers a report of the augmentation or generation of security rules to Security Controller. For SMA-based security services with Feedback-Based Security Management (FSM), I2NSF Analyzer is required as a new I2NSF component for the legacy I2NSF framework [RFC8329] to collect monitoring data from NSFs and analyzing the monitoring data. The actual implementation of the analysis of monitoring data is out of the scope of this document. 3.2. Interfaces with SMA-Based I2NSF Framework The following are the interfaces for the SMA-based I2NSF framework. Note that the interfaces are modeled with YANG [RFC6020] and security policies are delivered through either RESTCONF [RFC8040] or NETCONF [RFC6241]. * Consumer-Facing Interface: An interface between I2NSF User and Security Controller for the delivery of a high-level security policy [I-D.ietf-i2nsf-consumer-facing-interface-dm]. * NSF-Facing Interface: An interface between Security Controller and an NSF for the delivery of a low-level security policy [I-D.ietf-i2nsf-nsf-facing-interface-dm]. Jeong, et al. Expires 3 August 2023 [Page 5] Internet-Draft I2NSF Security Management Automation January 2023 * Registration Interface: An interface between a DMS and Security Controller for the registration of an NSF's capability and access information with the Security Controller or the query of an NSF for a required low-level security policy [I-D.ietf-i2nsf-registration-interface-dm]. * Monitoring Interface: An interface between an NSF and I2NSF Analyzer for collecting monitoring data from an NSF to check the activity and performance of an NSF for a possible malicious traffic [I-D.ietf-i2nsf-nsf-monitoring-data-model]. * Analytics Interface: An interface between I2NSF Analyzer and Security Controller for the delivery of an analytics report of the augmentation or generation of security rules to Security Controller [I-D.lingga-i2nsf-analytics-interface-dm]. This interface lets Security Controller get the report for security rules to its security policy management. For SMA-based security services with FSM, Analytics Interface is required as a new I2NSF interface for the legacy I2NSF framework [RFC8329] to deliver an analytics report of the augmentation or generation of security rules to Security Controller through the analysis of the monitoring data from NSFs. 4. Security Policy Translation To facilitate Security Policy Translation (SPT), Security Controller needs to have a security policy translator that performs the translation of a high-level security policy into the corresponding low-level security policy. For the automatic SPT services, the I2NSF framework needs to bridge a high-level YANG data model and a low- level YANG data model in an automatic manner [I-D.ietf-i2nsf-applicab ility][I-D.yang-i2nsf-security-policy-translation]. Note that a high-level YANG data model is for the I2NSF Consumer-Facing Interface [I-D.ietf-i2nsf-consumer-facing-interface-dm], and a low-level YANG data model is for the I2NSF NSF-Facing Interface [I-D.ietf-i2nsf-nsf-facing-interface-dm]. Figure 2 shows automatic mapping of high-level and low-level data models. Automatic Data Model Mapper takes a high-level YANG data module for the Consumer-Facing Inteface and a low-level YANG data module for the NSF-Facing Interface. It then constructs a mapping table associating the data attributes (or variables) of the high- level YANG data module with the corresponding data attributes (or variables) of the low-level YANG data module. Also, it generates a set of production rules of the grammar for the construction of an XML file of low-level security policy rules. Jeong, et al. Expires 3 August 2023 [Page 6] Internet-Draft I2NSF Security Management Automation January 2023 Figure 3 shows high-to-low security policy translation. A security policy translator is a component of Security Controller. The translator consists of three components such as Data Model Mapper, Data Extractor, Data Converter, and Policy Generator. High-level YANG Data Module Low-level YANG Data Model | | V V +---------+------------------------------+---------+ | Policy Data Model Mapper | +------------------------+-------------------------+ | V Data Model Mapping Table Figure 2: Automatic Mapping of High-level and Low-level Data Models Jeong, et al. Expires 3 August 2023 [Page 7] Internet-Draft I2NSF Security Management Automation January 2023 +--------------------------------------------------+ | I2NSF User | +------------------------+-------------------------+ | Consumer-Facing Interface | High-level Security Policy | Security Controller V +------------------------+--------------------------------+ | Security Policy | | | Translator V | | +---------------------+-----------------------------+ | | | | | | | | V | | | | +-----+-----+ +----------+ | | | | | Data | |Data Model| | | | | | Extractor | | Mapper | | | | | +-----+-----+ +----------+ | | | | Extracted Data from | Mapping | | | | | High-Level Policy V Model V | | | | +-----+-----+ +----+---+ | | | | | Data |<--------->| NSF DB | | | | | | Converter | +--------+ | | | | +-----+-----+ | | | | | Required Data for | | | | V Target NSFs | | | | +--------+---------+ | | | | | Policy Generator | | | | | +--------+---------+ | | | | | | | | | V | | | +---------------------+-----------------------------+ | | | | | V | +------------------------+--------------------------------+ | NSF-Facing Interface | Low-level Security Policy | V +------------------------+-------------------------+ | NSF(s) | +--------------------------------------------------+ Figure 3: High-to-Low Security Policy Translation Jeong, et al. Expires 3 August 2023 [Page 8] Internet-Draft I2NSF Security Management Automation January 2023 Data Model Mapper maps the attributes and their values of a high- level security policy to the corresponding attributes and their values of a low-level security policy. Note that the values of a high-level security policy may involve a human language and must be converted to an appropriate value for a low-level security policy (e.g., employees -> 192.0.1.0/24). Data Extractor extracts the values of the attributes related to a security policy from a high-level security policy that was delivered by an I2NSF User to a Security Controller through the Consumer-Facing Interface [I-D.ietf-i2nsf-consumer-facing-interface-dm]. Data Converter converts the values of the high-level policy's attributes into the values of the corresponding low-level policy's attributes to generate the low-level security policy [I-D.ietf-i2nsf-nsf-facing-interface-dm]. Policy Generator generates the corresponding low-level security policy that is delivered by the Security Controller to an appropriate NSF through NSF-Facing Interface [I-D.ietf-i2nsf-nsf-facing-interface-dm]. 5. Security Audit System The I2NSF framework is weak to both an insider attack and a supply chain attack since it trusts in NSFs provided by Developer's Management System (DMS) and assumes that NSFs work for their security services appropriately [I-D.ietf-i2nsf-applicability]. To detect the malicious activity of either an insider attack by a malicious DMS or a supply chain attack by a compromised DMS, a security audit system is required by the I2NSF framework. This security audit system can facilitate the non-repudiation of configuration commands and monitoring data generated in the I2NSF framework. A security audit system has the following four main objectives: * To check the existence of a security policy, a management system, and its procedures; * To identify and understand the existing vulnerabilities and risks of either an insider attack or a supply chain attack; * To review existing security controls on operational and administrative issues; Jeong, et al. Expires 3 August 2023 [Page 9] Internet-Draft I2NSF Security Management Automation January 2023 * To provide recommendations and corrective actions to Security Controller for further security improvement. +-----------------------------+ +----------------+ | I2NSF User | |Developer's Mgmt| | +------------+ | System | +--------------+--------------+ | +--------+-------+ | Consumer-Facing Interface | | | | Remote | High-level Security Policy | Attestation | | | Interface | | | | V | V +--------------+--------------+ | +---------+--------+ | | V | Security | | Security Controller +------------+---->| Audit | | | ^ | System | +--------------+--------------+ | +---------+--------+ | NSF-Facing Interface | ^ | | Remote | Low-level Security Policy | Attestation | | | Interface | V | | +--------------+--------------+ | +--------+-------+ | NSF(s) +------------+ | I2NSF Analyzer | | +------------------>| | +-----------------------------+ Monitoring +----------------+ Interface Figure 4: Activity Auditing with Security Audit System Figure 4 shows activity auditing with a security audit system in the I2NSF framework. All the components in the I2NSF framwork report its activities (such as configuration commands and monitoring data) to Security Audit System as transactions through Remote Attestation Interface [I-D.yang-i2nsf-remote-attestation-interface-dm]. The security audit system can analyze the reported activities from the I2NSF components to detect malicious activities such as an insider attack and a supply chain attack. Note that such a security audit system can be implemented by remote attestation [RFC9334][I-D.yang-i2nsf-remote-attestation-interface-dm] or Blockchain [Bitcoin]. The details of the implementation of the security audit system are out of the scope of this document. Jeong, et al. Expires 3 August 2023 [Page 10] Internet-Draft I2NSF Security Management Automation January 2023 In order to determine a minimum set of controls required to reduce the risks from either an insider attack or a supply chain attack, the security audit system should analyze the activities of all the components in the I2NSF framework periodically, evaluate possible risks, and take an action to such risks since vulnerabilities and threats may change in different environments over time. 6. IANA Considerations This document does not require any IANA actions. 7. Security Considerations The same security considerations for the I2NSF framework [RFC8329] are applicable to this document. The development and introduction of I2NSF Analyzer and Security Audit System in the I2NSF Framework may create new security concerns that have to be anticipated at the design and specification time. The usage of machine learning to analyze monitoring data of malicious NSFs may add a risk to its model to be attacked (e.g., adversarial attack) and can result in a bad security policy that is deployed into the I2NSF system. 8. References 8.1. Normative References [RFC8192] Hares, S., Lopez, D., Zarny, M., Jacquenet, C., Kumar, R., and J. Jeong, "Interface to Network Security Functions (I2NSF): Problem Statement and Use Cases", RFC 8192, DOI 10.17487/RFC8192, July 2017, . [RFC8329] Lopez, D., Lopez, E., Dunbar, L., Strassner, J., and R. Kumar, "Framework for Interface to Network Security Functions", RFC 8329, DOI 10.17487/RFC8329, February 2018, . [RFC6020] Bjorklund, M., Ed., "YANG - A Data Modeling Language for the Network Configuration Protocol (NETCONF)", RFC 6020, DOI 10.17487/RFC6020, October 2010, . [RFC8040] Bierman, A., Bjorklund, M., and K. Watsen, "RESTCONF Protocol", RFC 8040, DOI 10.17487/RFC8040, January 2017, . Jeong, et al. Expires 3 August 2023 [Page 11] Internet-Draft I2NSF Security Management Automation January 2023 [RFC6241] Enns, R., Ed., Bjorklund, M., Ed., Schoenwaelder, J., Ed., and A. Bierman, Ed., "Network Configuration Protocol (NETCONF)", RFC 6241, DOI 10.17487/RFC6241, June 2011, . [I-D.ietf-i2nsf-consumer-facing-interface-dm] Jeong, J. P., Chung, C., Ahn, T., Kumar, R., and S. Hares, "I2NSF Consumer-Facing Interface YANG Data Model", Work in Progress, Internet-Draft, draft-ietf-i2nsf-consumer- facing-interface-dm-24, 7 November 2022, . [I-D.ietf-i2nsf-nsf-facing-interface-dm] Kim, J. T., Jeong, J. P., Jung-Soo, J., Hares, S., and Q. Lin, "I2NSF Network Security Function-Facing Interface YANG Data Model", Work in Progress, Internet-Draft, draft- ietf-i2nsf-nsf-facing-interface-dm-29, 1 June 2022, . [I-D.ietf-i2nsf-registration-interface-dm] Hyun, S., Jeong, J. P., Roh, T., Wi, S., and J. Jung-Soo, "I2NSF Registration Interface YANG Data Model for NSF Capability Registration", Work in Progress, Internet- Draft, draft-ietf-i2nsf-registration-interface-dm-22, 8 November 2022, . [I-D.ietf-i2nsf-nsf-monitoring-data-model] Jeong, J. P., Lingga, P., Hares, S., Xia, L., and H. Birkholz, "I2NSF NSF Monitoring Interface YANG Data Model", Work in Progress, Internet-Draft, draft-ietf- i2nsf-nsf-monitoring-data-model-20, 1 June 2022, . [I-D.lingga-i2nsf-analytics-interface-dm] Lingga, P., Jeong, J. P., and Y. Choi, "I2NSF Analytics Interface YANG Data Model", Work in Progress, Internet- Draft, draft-lingga-i2nsf-analytics-interface-dm-01, 30 January 2023, . 8.2. Informative References Jeong, et al. Expires 3 August 2023 [Page 12] Internet-Draft I2NSF Security Management Automation January 2023 [I-D.ietf-i2nsf-applicability] Jeong, J. P., Hyun, S., Ahn, T., Hares, S., and D. Lopez, "Applicability of Interfaces to Network Security Functions to Network-Based Security Services", Work in Progress, Internet-Draft, draft-ietf-i2nsf-applicability-18, 16 September 2019, . [RFC9315] Clemm, A., Ciavaglia, L., Granville, L. Z., and J. Tantsura, "Intent-Based Networking - Concepts and Definitions", RFC 9315, DOI 10.17487/RFC9315, October 2022, . [I-D.yang-i2nsf-security-policy-translation] Jeong, J. P., Lingga, P., Yang, J., and J. Kim, "Guidelines for Security Policy Translation in Interface to Network Security Functions", Work in Progress, Internet-Draft, draft-yang-i2nsf-security-policy- translation-12, 24 October 2022, . [RFC9334] Birkholz, H., Thaler, D., Richardson, M., Smith, N., and W. Pan, "Remote ATtestation procedureS (RATS) Architecture", RFC 9334, DOI 10.17487/RFC9334, January 2023, . [I-D.yang-i2nsf-remote-attestation-interface-dm] Yang, P., chenmeiling, Su, L., Lopez, D., Jeong, J. P., and L. Dunbar, "I2NSF Remote Attestation Interface YANG Data Model", Work in Progress, Internet-Draft, draft-yang- i2nsf-remote-attestation-interface-dm-01, 5 June 2022, . [ETSI-NFV] "Network Functions Virtualisation (NFV); Architectural Framework", Available: https://www.etsi.org/deliver/etsi_gs/ nfv/001_099/002/01.01.01_60/gs_nfv002v010101p.pdf, October 2013. [Bitcoin] Nakamoto, S., "Bitcoin: A Peer-to-Peer Electronic Cash System", URL: https://bitcoin.org/bitcoin.pdf, May 2009. [Deep-Learning] Goodfellow, I., Bengio, Y., and A. Courville, "Deep Learning", Publisher: The MIT Press, URL: https://www.deeplearningbook.org/, November 2016. Jeong, et al. Expires 3 August 2023 [Page 13] Internet-Draft I2NSF Security Management Automation January 2023 Appendix A. Acknowledgments This work was supported in part by Institute of Information & Communications Technology Planning & Evaluation (IITP) grant funded by the Korea Ministry of Science and ICT (MSIT) (2020-0-00395-003, Standard Development of Blockchain based Network Management Automation Technology). This work was supported by the IITP grant funded by the Korea MSIT (R-20160222-002755, Cloud based Security Intelligence Technology Development for the Customized Security Service Provisioning). Appendix B. Contributors This document is made by the group effort of I2NSF working group. Many people actively contributed to this document, such as Linda Dunbar, Yoav Nir, and Qin Wu. The authors sincerely appreciate their contributions. The following are co-authors of this document: Jeonghyeon Kim - Department of Computer Science and Engineering, Sungkyunkwan University, 2066 Seobu-ro Jangan-gu, Suwon, Gyeonggi-do 16419, Republic of Korea. EMail: jeonghyeon12@skku.edu Yunchul Choi - Electronics and Telecommunications Research Institute, 218 Gajeong-Ro, Yuseong-Gu, Daejeon, 34129, Republic of Korea. EMail: cyc79@etri.re.kr Younghan Kim - School of Electronic Engineering, Soongsil University, 369, Sangdo-ro, Dongjak-gu, Seoul 06978, Republic of Korea. EMail: younghak@ssu.ac.kr Appendix C. Changes from draft-jeong-i2nsf-security-management- automation-04 The following changes are made from draft-jeong-i2nsf-security- management-automation-04: * This version updates the references. Authors' Addresses Jeong, et al. Expires 3 August 2023 [Page 14] Internet-Draft I2NSF Security Management Automation January 2023 Jaehoon Paul Jeong (editor) Department of Computer Science and Engineering Sungkyunkwan University 2066 Seobu-Ro, Jangan-Gu Suwon Gyeonggi-Do 16419 Republic of Korea Phone: +82 31 299 4957 Email: pauljeong@skku.edu URI: http://iotlab.skku.edu/people-jaehoon-jeong.php Patrick Lingga Department of Electronic, Electrical and Computer Engineering Sungkyunkwan University 2066 Seobu-Ro, Jangan-Gu Suwon Gyeonggi-Do 16419 Republic of Korea Phone: +82 31 299 4957 Email: patricklink@skku.edu Jung-Soo Park Electronics and Telecommunications Research Institute 218 Gajeong-Ro, Yuseong-Gu Daejeon 305-700 Republic of Korea Phone: +82 42 860 6514 Email: pjs@etri.re.kr Diego R. Lopez Telefonica I+D Jose Manuel Lara, 9 41013 Seville Spain Phone: +34 682 051 091 Email: diego.r.lopez@telefonica.com Jeong, et al. Expires 3 August 2023 [Page 15] Internet-Draft I2NSF Security Management Automation January 2023 Susan Hares Huawei 7453 Hickory Hill Saline, MI 48176 United States of America Phone: +1-734-604-0332 Email: shares@ndzh.com Jeong, et al. Expires 3 August 2023 [Page 16]