]> Huawei

liuchunchi@huawei.com

Security Automated Certificate Management Environment ACME RATS Zero Trust This document describes an approach where ACME Client can prove possession of a Remote Attestation Result to an ACME Server. About This Document The latest revision of this draft can be found at . Status information for this document may be found at . Discussion of this document takes place on the Automated Certificate Management Environment Working Group mailing list (), which is archived at . Subscribe at . Source for this draft and an issue tracker can be found at .

Introduction ACME is a standard protocol for issuing and renewing certificates automatically, widely used in the Internet scenario, help an ACME Client prove its ownership to an identifier like domain name or email address. In order to prevent issuing certificates to malicious devices, a few works are ongoing in the LAMPS and RATS WG.

• define trustworthy claims about device's platform generating the certification signing requests (CSR) and the private key resides on this platform.
• define a summary of a local assessment of posture for managed systems and across various layers.

In this document, we propose an approach where ACME Server checks if the ACME Clients possess a valid remote attestation result, for instance, EAT (entity attestation token). We define a new ACME "rats" identifier and "rats" challenge type for ACME Clients to prove their possession of EAT. In this way, we (as network administators) issue certificates only to devices that have a fresh attestation result, indicating such device has passed the most up-to-date security checks. By repeating this process and issue only short-lived certificates to qualified devices, we also fulfill the continuous monitoring/validation requirement of Zero-Trust principle. The example use case include an enterprise scenario where Network Operations Center (NOC) issue certificates to devices that are freshly appraised by the Security Operations Center (SOC), in order to help them work together. For ease of denotion, we omit the "ACME" adjective from now on, where Server means ACME Server and Client means ACME Client.

Extensions -- rats identifier An rats identifier type represents a unique identifier to an attestation result. It extends a "rats" identifier type and a string value.

type (required, string):

The string "rats".

value (required, string):

The identifier itself.

The following steps are the ones that will be affected: 1. newOrder Request Object - identifiers: During the certificate order creation step, the Client sends a /newOrder JWS request (Section 7.4 of ) whose payload contains an array of identifiers. The Client adds an rats identifier to the array. An example extended newOrder JWS request: 2. Order Object - identifiers: After a newOrder request is sent to the Server, the Account Object creates an Order Object (Section 7.1.3 of ) with "rats" identifiers and values from Step 1. An example extended Order Object: 3. Authorization Object - identifier: The Server creates an Authorization Object that has rats identifier (Section 7.1.4 of ) 4. Challenge Object - identifier: The Server creates a Challenge Object that has rats challenge type. An example extended Authorization Object (that contains a Challenge Object):

Extensions -- rats challenge type A rats challenge type help the Client prove ownership to its attestation result identifier. This section describes the challenge/response extensions and procedures to use them.

RATS-01 Challenge RATS-01 Challenge simply works with Passport Model of RATS. The corresponding Challenge Object is:

type (required, string):

The string "rats-01".

url (required, string):

The URL that the Client post its response to.

token (required, string):

Same as Section 8.3 of RFC8555.

The response sent to the url is: where the attestationResult is the entire EAT (in JWT format). The ACME Server verifies the attestationResult. If pass, set Order Object and Authorization Object's "status" Object to "valid", otherwise "invalid".

RATS-02 Challenge RATS-02 Challenge works with the Background Check Model of RATS. TODO: After the Client gets the "token", it include "token" as part of its RATS Evidence, appraise again. The new attestationResult now has a "token" claim. The retrival process is same.

Reusing HTTP challenge type We can also reuse http-01 challenge type in Section 8.3 of . This changes steps used in {#rats01}.

1. The Client creates the keyAuthorization string defined in {#rats01}.
2. The Client provisions the keyAuthorization string in the resource path defined in the original http-01 challenge -- "/.well-known/acme-challenge/", followed by the "token".
3. The Client sends an empty object ({}) to the url, notifying the Server it is ready to fetch.
4. The Server fetches the keyAuthorization string from the resource path. Verifies the "token", retrive the attestationResult.

Example use case -- enterprise access In an enterprise network scenario, it is hard to coordinate Security Operations Center (SOC) and Network Operations Center (NOC) to work together due to various of reasons:

1. Integration/compatibility difficulty: Integrating SOC and NOC requires plenty of customized, case-by-case developing work. Especially considering differrnt system vendors, system versions, different data models and formats due to different client needs... Let alone possible updates.
2. Conflict of duties: NOC people do not want SOC people to interfere with their daily work, and so do SOC people. Also, NOC people may have limited security knowledge, and SOC people vice versa. Where to draw the line and what is the best tool to help them collaborate is a question.

This work proposes a way to help SOC and NOC work together, with separated duties (to avoid conflict) and ease of working together (proper abstraction). An Endpoint Detection and Response (EDR) software and Security Operations Center (SOC) is responsible for checking the security status of an accessing end device. If the device passed latest security checks, EDR/SOC should issue fresh attestation results (consider as a security clearance). Otherwise, EDR/SOC should refuse to issue (new) attestation results. A Network Operations Center (NOC) could use ACME to issue short-lived certificates to only devices with fresh attestation results. In this way, the NOC can follow a Zero-Trust philosophy and issue network access to only devices that are continuously monitored and have no known security risks up-to-date. SOC can also have flexible security policies and decide what to check.

Security Considerations TODO Security

IANA Considerations This document has no IANA actions.

References Normative References Public Key Infrastructure using X.509 (PKIX) certificates are used for a number of purposes, the most significant of which is the authentication of domain names. Thus, certification authorities (CAs) in the Web PKI are trusted to verify that an applicant for a certificate legitimately represents the domain name(s) in the certificate. As of this writing, this verification is done through a collection of ad hoc mechanisms. This document describes a protocol that a CA and an applicant can use to automate the process of verification and certificate issuance. The protocol also provides facilities for other certificate management functions, such as certificate revocation. Informative References Entrust Limited Siemens Fraunhofer SIT Beyond Identity Intel Corporation A PKI end entity requesting a certificate from a Certification Authority (CA) may wish to offer trustworthy claims about the platform generating the certification request and the environment associated with the corresponding private key, such as whether the private key resides on a hardware security module. This specification defines an attribute and an extension that allow for conveyance of Evidence in Certificate Signing Requests (CSRs) such as PKCS#10 or Certificate Request Message Format (CRMF) payloads which provides an elegant and automatable mechanism for transporting Evidence to a Certification Authority. Including Evidence along with a CSR can help to improve the assessment of the security posture for the private key, and can help the Certification Authority to assess whether it satisfies the requested certificate profile. These Evidence Claims can include information about the hardware component's manufacturer, the version of installed or running firmware, the version of software installed or running in layers above the firmware, or the presence of hardware components providing specific protection capabilities or shielded locations (e.g., to protect keys). Transforming Information Security LLC Beyond Identity National Institute of Standards and Technology This document establishes an architectural pattern whereby a remote attestation could be issued for a complete set of benchmarks or controls that are defined and grouped by an external entity, preventing the need to send over individual attestations for each item within a benchmark or control framework. This document establishes a pattern to list sets of benchmarks and controls within CWT and JWT formats for use as an Entity Attestation Token (EAT).

Acknowledgments TODO acknowledge.