Internet DRAFT - draft-birkholz-scitt-software-use-cases
draft-birkholz-scitt-software-use-cases
Network Working Group H. Birkholz
Internet-Draft Fraunhofer SIT
Intended status: Informational Y. Deshpande
Expires: 19 August 2023 ARM
D. Brooks
REA
R. Martin
MITRE
B. Knight
Microsoft
15 February 2023
Detailed Software Supply Chain Uses Cases for SCITT
draft-birkholz-scitt-software-use-cases-01
Abstract
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
https://datatracker.ietf.org/doc/draft-birkholz-scitt-software-use-
cases/.
Discussion of this document takes place on the SCITT Working Group
mailing list (mailto:scitt@ietf.org), which is archived at
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https://www.ietf.org/mailman/listinfo/scitt/.
Source for this draft and an issue tracker can be found at
https://github.com/ietf-scitt/draft-birkholz-scitt-software-supply-
chain-use-cases.
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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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",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"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
possible
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
consumers.
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
authenticity.
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
provider,
* 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
artefact 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
procedures.
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
measurements
* 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
fashion
* 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
available
* the cost of audits to be manageable and scale well
* complete visibility and accessibility to documents required for
audits
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
fashion
* 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
challenges.
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Consumers and other interested parties of a firmware update ecosystem
wants:
* 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
logging?
* 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,
<https://doi.org/10.17487/RFC2119>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://doi.org/10.17487/RFC8174>.
Authors' Addresses
Henk Birkholz
Fraunhofer Institute for Secure Information Technology
Rheinstrasse 75
64295 Darmstadt
Germany
Email: henk.birkholz@sit.fraunhofer.de
Yogesh Deshpande
ARM
Email: yogesh.deshpande@arm.com
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Dick Brooks
REA
Email: dick@reliableenergyanalytics.com
Robert Martin
MITRE
Email: ramartin@mitre.org
Brian Knight
Microsoft
Email: brianknight@microsoft.com
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