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Detailed Software Supply Chain Uses Cases for SCITT

Document Type Active Internet-Draft (scitt WG)
Authors Henk Birkholz , Yogesh Deshpande , Dick Brooks (REA) , Bob Martin , Brian Knight
Last updated 2023-03-14
Replaces draft-birkholz-scitt-software-use-cases
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Network Working Group                                        H. Birkholz
Internet-Draft                                            Fraunhofer SIT
Intended status: Informational                              Y. Deshpande
Expires: 15 September 2023                                           ARM
                                                               D. Brooks
                                                               R. Martin
                                                               B. Knight
                                                           14 March 2023

          Detailed Software Supply Chain Uses Cases for SCITT


   This document includes a collection of representative Software Supply
   Chain Use Case Descriptions.  These use cases aim to identify
   software supply chain problems that the industry faces today and acts
   as a guideline for developing a comprehensive solution for these
   classes of scenarios.

About This Document

   This note is to be removed before publishing as an RFC.

   Status information for this document may be found at

   Discussion of this document takes place on the SCITT Working Group
   mailing list (, which is archived at  Subscribe at

   Source for this draft and an issue tracker can be found at

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

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   This Internet-Draft will expire on 15 September 2023.

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   document authors.  All rights reserved.

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   Please review these documents carefully, as they describe your rights
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   provided without warranty as described in the Revised BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Generic Problem Statement . . . . . . . . . . . . . . . . . .   3
   3.  Software Supply Chain Use Cases . . . . . . . . . . . . . . .   5
     3.1.  Verification that Signing Certificate is Authorized by
           Supplier  . . . . . . . . . . . . . . . . . . . . . . . .   5
     3.2.  Multi Stakeholder Evaluation of a Released Software
           Product . . . . . . . . . . . . . . . . . . . . . . . . .   6
     3.3.  Security Analysis of a Software Product . . . . . . . . .   6
     3.4.  Promotion of a Software Component by multiple entities  .   8
     3.5.  Post-Boot Firmware Provenance . . . . . . . . . . . . . .   9
     3.6.  Auditing of Software Product  . . . . . . . . . . . . . .  10
     3.7.  Authentic Software Components in Air-Gapped
           Infrastructure  . . . . . . . . . . . . . . . . . . . . .  11
     3.8.  Firmware Delivery to large set of constrained IoT
           Devices . . . . . . . . . . . . . . . . . . . . . . . . .  11
     3.9.  Software Integrator assembling a software product for a
           smart car . . . . . . . . . . . . . . . . . . . . . . . .  12
   4.  Normative References  . . . . . . . . . . . . . . . . . . . .  13
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  13

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1.  Introduction

   Modern software applications are an intricate mix of first-party and
   third-party code, development practices and tools, deployment methods
   and infrastructure, and interfaces and protocols.  The software
   supply chain comprises all elements associated with an application's
   design, development, build, integration, deployment, and maintenance
   throughout its entire lifecycle.  The complexity of software coupled
   with a lack of lifecycle visibility increases the risks associated
   with system attack surface and the number of cyber threats capable of
   harmful impacts, such as exfiltration of data, disruption of
   operations, and loss of reputation, intellectual property, and
   financial assets.  There is a need for a platform architecture that
   will allow consumers to know that suppliers maintained appropriate
   security practices without requiring access to proprietary
   intellectual property.  SCITT-enabled products and analytics
   solutions will assist in managing compliance and assessing risk to
   help prevent and detect supply chain attacks across the entire
   software lifecycle while prioritizing data privacy.

1.1.  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "OPTIONAL" in this document are to be interpreted as described in
   BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

2.  Generic Problem Statement

   Supply chain security is a paramount prerequisite to successfully
   protect consumers and minimize economic, public health, and safety
   impacts.  Supply chain security has historically focused on risk
   management practices to safeguard logistics, meet compliance
   regulations, demand forecasts, and optimize inventory.  While these
   elements are foundational to a healthy supply chain, an integrated
   cyber security-based perspective of the software supply chains
   remains broadly undefined.  Recently, the global community has
   experienced numerous supply chain attacks targeting weaknesses in
   software supply chains.  As illustrated in Figure 1, a software
   supply chain attack may leverage one or more lifecycle stages and
   directly or indirectly target the component.

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         Dependencies        Malicious 3rd-party package or version
        |           |
        |   Code    |        Compromise source control
        |           |
        |           |        Malicious plug-ins;
        |  Commit   |        Malcious commit
        |           |
        |           |        Modify build tasks or build environment;
        |   Build   |        Poison build agent/compiler;
        |           |        Tamper with build cache
        |           |        Compromise test tools;
        |    Test   |        Falsification of test results
        |           |
        |           |        Use bad package;
        |  Package  |        Compromise package repository
        |           |
        |           |        Modify release tasks;
        |  Release  |        Modify build drop prior to release
        |           |
        |           |
        |  Deploy   |        Tamper with versioning and update process
        |           |

                    Figure 1: Example Lifecycle Threats

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   DevSecOps often depends on third-party and open-source solutions.
   These dependencies can be quite complex throughout the supply chain
   and render the checking of lifecycle compliance difficult.  There is
   a need for manageable auditability and accountability of digital
   products.  Typically, the range of types of statements about digital
   products (and their dependencies) is vast, heterogeneous, and can
   differ between community policy requirements.  Taking the type and
   structure of all statements about digital and products into account
   might not be possible.  Examples of statements may include commit
   signatures, build environment and parameters, software bill of
   materials, static and dynamic application security testing results,
   fuzz testing results, release approvals, deployment records,
   vulnerability scan results, and patch logs.  In consequence, instead
   of trying to understand and describe the detailed syntax and
   semantics of every type of statement about digital products, the
   SCITT architecture focuses on ensuring statement authenticity,
   visibility/transparency, and intends to provide scalable
   accessibility.  The following use case illustrates the scope of SCITT
   and elaborate on the generic problem statement above.

3.  Software Supply Chain Use Cases

3.1.  Verification that Signing Certificate is Authorized by Supplier

   Consumers wish to verify the authenticity and integrity of software
   they use before installation.  To do this today, they rely on the
   digital signature of the software.  This can be misleading, however,
   as there is no guarantee that the certificate used to sign the
   software is authorized by the Supplier for signing.  For example, a
   malicious actor may obtain a signing certificate from a reputable
   organization and use that certificate to sign malicious software.
   The consumer, believing the software originated from the reputable
   organization, would then install malicious software.

   A consumer of software wants:

   *  to verify the authenticity and integrity of software they use
      before installation.

   There is no standardized way to:

   *  enable the consumer to verify that software originated from a
      'duly authorized signing party' on behalf of the supplier, and is
      still valid.

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3.2.  Multi Stakeholder Evaluation of a Released Software Product

   In IT industry it is a common practice that once a software product
   is released, it is evaluated on various aspects.  For example, an
   auditing company, a code review company or a government body will
   examine the software product and issue authoritative reports about
   the product.  The end users (consumers or distribution entities) use
   these report to make an accurate assessment as to whether the
   software product is deemed fit to use.

   There are multiple such authoritative bodies that make such
   assessments.  There is no assurance that all the bodies may be aware
   of statements from other authoritative entities or actively
   acknowledge them.  Discovery of all sources of such reports and/or
   identity of the authoritative bodies adds a significant cost to the
   end user or consumer of the product.

   A consumer of released software product wants:

   *  to offload the burden of identifying all relevant authoritative
      entities to an entity who does it on their behalf

   *  to offload the burden to filter from and select all statements
      that are applicable to a particular release of a multi release
      software product, to an entity who does this on their behalf

   *  to make an informed decisions on which authoritative entities to
      believe based on the best visibility of all authoritative entities

   There is no standardized way to:

   *  aggregate large numbers of related statements in one place and
      discover them

   *  referencing other statements via a statement

   *  identifying or discover all (or at least a critical mass) of
      relevant authoritative entities

3.3.  Security Analysis of a Software Product

   This use case is a specialization of the use case above.

   A released software product is often accompanied by a set of
   complementary statements about it's security compliance.  This gives
   enough confidence to both producers and consumers that the released
   software has a good security standard and is suitable to use.

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   Subsequently, multiple security researchers often run sophisticated
   security analysis tools on the same product.  The intention is to
   identify any security weaknesses or vulnerabilities in the package.

   Initially a particular analysis can identify itself as a simple
   weakness in a software component.  Over a period of time, a statement
   from another third-party illustrates that the weakness is exposed in
   the same software component in a way that it is an exploitable
   vulnerability.  The producer of the software product now provides a
   statement that confirms the linking of software component
   vulnerability with the software product and also issues an advisory
   statement on how to mitigate the vulnerability.  At first, the
   producer provides an updated software product that still uses the
   vulnerable software component but shields the issue in a fashion that
   inhibits exploitation.  Later, A second update of the software
   product includes a security patch to the affected software component
   from the software producer.  Finally, A third update includes a new
   release (updated version) of the formerly insecure software
   component.  For this release, both the software product and the
   affected software component are deemed secure by the producer and

   A consumer of a released software wants:

   *  to know where to get these security statements from producers and
      third-parties related to the software product in a timely and
      unambiguous fashion,

   *  how to attribute them to an authoritative issuer,

   *  how to associate the statements in a meaningful manner via a set
      of well-known semantic relationships, and

   *  how to consistently, efficiently, and homogeneously check their

   There is no standardized way to:

   *  know the various sources of statements,

   *  how to express the provenance and historicity of statements,

   *  how to related/link various heterogeneous statements in a simple
      fashion, and

   *  check that the statement comes from a source with authority to
      issue that statement.

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3.4.  Promotion of a Software Component by multiple entities

   A software component source (e.g., a library) released by a certain
   original producer is becoming popular.  The released software
   component source is accompanied by a statement of authenticity (e.g.,
   a detached signature).  Over time, due to its enhanced applicability
   to various products, there has been an increasing amount of multiple
   providers of the same software component version on the internet.

   Some providers include this particular software component as part of
   their release package bundle and provide the package with proof of
   authenticity using their own issuer authority.  Some packages include
   the original statement of authenticity, and some do not.  Over time,
   some providers no longer offer the exact same software component
   source but pre-compiled software component binaries.  Some sources do
   not provide the exact same software component but include patches and
   fixes produced by third-parties, as these emerge faster than
   solutions from the original producer.  Due to complex distribution
   and promotion lifecycle scenarios, the original software component
   takes myriad forms.

   A consumer of a released software wants:

   *  to understand if a particular provider is actually the original
      provider or a promoter,

   *  to know if and how the source, or resulting binary, of a promoted
      software component differs from the original software component,

   *  to check the provenance and history of a software component's
      source back to its origin, and

   *  to assess whether to trust a promoter or not.

   There is no standardized way to:

   *  to reliably discern a provider that is the original producer from
      a provider that is a trustworthy promoter or from an illegitimate

   *  track the provenance path from an original producer to a
      particular provider

   *  to check for the trustworthiness of a provider

   *  to check the integrity of modifications or transformations done by
      a provider

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3.5.  Post-Boot Firmware Provenance

   In contrast to operating systems or user space software components of
   a large and complex systems, firmware components are often already
   executed during boot-cycles before there is an opportunity to
   authenticate them.

   Authentication takes place, for example, by validating a signed
   artifact against a Reference Integrity Manifest (RIM).  Corresponding
   procedures are often called authenticated, measured, or secure boot.
   The output of these high assurance boot procedures is often used as
   input to more complex verification known as remote attestation

   If measurements before execution are not possible, static after-the-
   fact analysis is required, typically by examining artifacts.  When
   best practices are followed, in such cases measurements (e.g., a hash
   or digests) are stored in a protected or shielded environment (e.g.,
   TEEs or TPMs).  After finishing a boot sequence, these measurements
   about foundational firmware are retrieved after-the-fact from
   shielded locations and must be compared to reference values that are
   part of RIMs.  A verifying system appraising the integrity of a boot
   sequence must identify, locate, retrieve, and authenticate
   corresponding RIMs.

   A consumer of published software wants:

   *  to easily identify sources for RIMs

   *  to select appropriate RIMs and download them for the appraisal of

   *  to be able to assure the authenticity, applicability, and
      freshness of RIMs over time

   There is no standardized way to:

   *  identify, locate, retrieve and authenticate RIMs in a uniform

   *  to uniquely identify among multiple potential available RIMs
      (e.g., by age, source, signing authority, etc.)

   *  to store RIMs in a fashion that enables their usage in appraisal
      procedures years after they were created in a secure and
      believable fashion

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3.6.  Auditing of Software Product

   An organization has established procurement requirements and
   compliance policies for software use.  In order to allow the
   acquisition and deployment of software in certain security domains of
   the organization, a check of software quality and characteristics
   must succeed.  Compliance and requirement checking includes audits of
   the results of organisational procedures and technical procedures,
   which can originate from checks conducted by the organization itself
   or checks conducted by trusted third parties.  Consecutively,
   consumers of statements about a released software can be auditors.
   Examples of procedure results important to audits include: available
   fresh and applicable code reviews, certification documents (e.g.,
   FIPS or Common Criteria), virus scans, vulnerability disclosure
   reports (fixed or not fixed), security impact or applicability
   justification statements.  Relevant compliance, requirement, and
   check result documents originate from various sources and include a
   wide range of representations and formats.

   A consumer of a released software wants:

   *  to provide methods with different levels of complexity to auditors
      of a released software

   *  expects the creator or distributor of released software to enable
      audit procedures and make corresponding documents visible and

   *  the cost of audits to be manageable and scale well

   *  complete visibility and accessibility to documents required for

   There is no standardized way to:

   *  discover and associate relevant documents and check results
      required for various types of audits

   *  assert the authenticity and provenance of documents relevant to
      audits in a deterministic and uniform fashion

   *  check the validity of identity statements about relevant documents
      after the fact (when they were made) in a consistent, long-term

   *  allow for more than one level of complexity of audit procedures
      (potentially depending on criticality)

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3.7.  Authentic Software Components in Air-Gapped Infrastructure

   Some software is deployed on systems not connected to the Internet.
   Authenticity checks for off-line systems can occur at time of
   deployment of released software.  Off-line systems require
   appropriate configuration and maintenance to be able to conduct
   useful authenticity checks.  If the off-line systems in operation are
   part of constrained node environments, they do not possess the
   capabilities to process and evaluate all kinds of different
   authenticity proofs that come with a released software.

   A consumer of a released software wants:

   *  a proof of authenticity that can be checked by an off-line system
      for vast periods of time after system deployment

   *  a proof of authenticity to be small and as uniform as possible to
      allow for application in constrained node environments

   *  a simple and low cost way to update the configuration of a system
      component in charge of validity or authenticity checking

   There is no standardized way to:

   *  provide an authenticity proof that can be checked by off-line
      systems in a simple and uniform fashion

   *  enable rich systems, regular systems, and constrained systems to
      conduct authenticity checks via the same procedure / code base

   *  to verify the authenticity and integrity of software in a fashion
      that scales from applications such as global open source
      repositories down to off-line constrained devices

3.8.  Firmware Delivery to large set of constrained IoT Devices

   Firmware is a critical component for successful execution of any
   constrained IoT device.  It is often the bedrock on which the
   security story of the devices it powers.  For example, personal
   health monitoring devices (eHealth devices) are generally battery
   driven and offer health telemetry monitoring, such as temperature,
   blood pressure, and pulse rate.  These devices typically connect to
   the Internet through an intermediary base station using wireless
   technologies.  Through this connection, the telemetry data and
   analytics transfer, and devices receive firmware updates when
   published by the vendor.  The public network, open distribution
   system, and firmware update process create several security

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   Consumers and other interested parties of a firmware update ecosystem

   *  to know that the received firmware for system update is not faulty
      or malicious

   *  to know if the signing identity used to assert the authenticity of
      the firmware is somehow used to sign unintended updates

   *  to ascertain that the released firmware is not subverted or
      compromised due to an insider risk - be it malicious or otherwise

   *  to confirm that the publishers know if their deliverable has been
      compromised.  Can they trust their key protection or audit

   *  to know how the update client on an instance of a health
      monitoring system discerns a general update from one specially
      crafted for just a small subset of a fleet of devices

   There is no standardized way to:

   *  provide an update framework that allows validation of authenticity
      of firmware revisions

   *  to verify that the firmware update seen by a single device, is
      indeed the same as seen by all the devices.

   *  reliably discern an update that has been signed by the appropriate
      and intended signing identity

   *  make an informed judgement on all available information about
      firmware at the install time.  For example, the firmware is still
      in a good state or otherwise?

3.9.  Software Integrator assembling a software product for a smart car

   Software Integration is a complex activity.  This typically involves
   getting various software components from multiple suppliers and
   producing an integrated package deployed as part of device assembly.
   For example, car manufacturers source integrated software for their
   autonomous vehicles from third parties that integrates software
   components from various sources.  Integration complexity creates a
   higher risk of security vulnerabilities to the delivered software.

   Consumer of an integrated software wants:

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   *  all components presents in a software product listed, and the
      ability to identify and retrieve them from a secure and tamper-
      proof location

   *  to receive an alert when a vulnerability scan detects a known
      security issue on a running software component

   *  verifiable proofs on build process and build environment with all
      supplier tiers to ensure end to end build quality and security

   There is no standardized way to:

   *  provide a tiered and transparent framework that allows for
      verification of integrity and authenticity of the integrated
      software at both component and product level before installation

   *  notify software integrators of vulnerabilities identified during
      security scans of running software

   *  provide valid annotations on build integrity to ensure conformance

4.  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,

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <>.

Authors' Addresses

   Henk Birkholz
   Fraunhofer Institute for Secure Information Technology
   Rheinstrasse 75
   64295 Darmstadt

   Yogesh Deshpande

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   Dick Brooks

   Robert Martin

   Brian Knight

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