# INTRODUCTION

# BUSINESS CONTEXT
The electronic transfer of public health data involves the ability to securely and automatically send and receive information between computer systems, to achieve a "live" network for data exchange between partners in public health, i.e. the Public Health Information Network (PHIN). The Centers for Disease Control and Prevention has advanced a standards-based approach to secure, reliable, bi-directional message transport across the Internet. The resulting Public Health Information Network (PHIN) specification calls for ebXML messaging on top of SOAP web services, XML Encryption, XML Digital Signature, and SSL authentication using client side certificates and/or passwords. The use of these industry standard specifications ensures that public health data is securely, reliably and automatically sent and received between health data systems. To effectively exchange information, both sending and receiving parties must adhere to the same specifications. This provides guidance of how to implement systems that securely send and receive public health data.

# OBJECTIVES
The objective of the PHIN Secure Message Transport Guide is to provide:
- Requirements for secure message transport within the PHIN framework This specification attempts to generalize message transport processing so that existing or proposed public health applications can more easily be integrated into a PHIN compatible public health infrastructure.

# SCOPE
This document describes the processes, data flows, system components, and relevant standards and specifications that constitute the PHIN Secure Messaging. This document provides an architecture view of the work that is performed when an electronic message is created, routed, sent, and received between PHIN partner sites such as labs, public health departments or the CDC. This specification is not prescriptive as to how specific public health messages, such as an ELR HL7 2.3.x message are created nor does this guide address how messages are routed based on message content. For information on creating specific public health messages, please reference PHIN messaging implementation guides which can be found at . Scope of this specification is limited to high-level requirements of the PHIN Secure Messaging Integration Point. The document does not prescribe specific platforms, technologies or infrastructure components that constitute a physical instance of the integration point. These aspects of system architecture should be further defined in system design documents. The intent of this document is to provide enough specificity to promote rapid and consistent development of PHIN compatible messaging transport systems without unduly constraining the development of such systems. Implementations based on this guide should be able to interoperate ("over the wire") with CDC's PHIN Messaging System (PHINMS). Detailed interoperability features can be found in the ebXML Messaging Services Specification Version 2.0 (ebMS) at . However, there is no guarantee of interoperability until an implementation is tested using PHINMS.

# HIGH LEVEL OVERVIEW
Essential functional elements of the PHIN Secure Messaging integration point consist of the ability to securely send and receive public health messages between designated endpoints. The following illustration, Figure 1-1, is a business process diagram of the PHIN Secure Messaging in Business Process Modeling Notation (BPMN).

# MESSAGE TRANPORT FUNCTIONAL REQUIREMENTS
The requirements in the section describe the baseline functionality for secure message transport within the PHIN framework. These secure message transport requirements address: securely and reliably exchanging messages over the Internet using the ebXML protocol, and security controls to prevent unauthorized access to systems and data.

# SECURE MESSAGE TRANSPORT
Secure Message Transport refers to the secure, reliable, bi-directional exchange of information between public health partners. Security and privacy requirements necessitate that information generally be encrypted and that communications be performed in a way which ensures delivery to the intended recipient(s) only. Messages are securely transported over the Internet using standards such as ebXML, Public Key Infrastructure (PKI), and Secure Socket Layer (SSL), which are described in the following sections.
The CDC has developed PHIN Messaging Service (MS) as an implementation of the standards supporting secure message transport. Exchange partners must use a secure transport protocol that is compatible with PHIN MS . PHIN MS fully implements PHIN standards for secure messaging and is available from CDC. More information about PHIN MS is available at . However, the use of PHIN MS is not required as long as PHIN data exchange requirements can be met using a PHIN MS compatible solution. HTTPS is a web protocol that encrypts and decrypts user page requests as well as the pages that are returned by the web server. HTTPS is the use of SSL as a sub-layer under its regular HTTP application layering.

# Transport Standard The ebXML Messaging Service (ebMS) is the industry standard used by PHIN for message transport across the Internet for the exchange of sensitive health data information between partner organizations. It supports a neutral format for carrying messages between different systems, such as between legacy systems and web services applications. It is designed to work with any communications protocol, and the content of messages carried over ebMS can be in any format. The ebMS standard is a set of layered extensions on the
2.1.2.1.a For system-to-system communication over the Internet, the HTTPS protocol must be used to protect communication confidentiality at all times.
2.1.2.1.b HTTPS should be used for communication between DMZ components and Intranet components. DMZ, or "demilitarized zone", refers to a computer or sub network that sits between a trusted internal network and an untrusted external network.

# APPENDIX A -PHIN SECURE MESSAGE TRANSPORT STANDARDS