[Spec] NuGet Config schema changes to enable trusted signers

Status: Reviewing

Issue

Issue for spec - NuGet/Home#6524
Parent spec - Repository-Signatures
Related spec - NuGet-Package-Signing-Client-Policy

Problem

As the next wave of package signing, consumers need to be able to trust specific package signers. Further, the trust information needs to be stored into the user's machine.

Who is the customer?

All NuGet package consumers.

Scenarios

• Enable package consumers to store repository and author trust information.

Solution

• Update the schema for the nuget.config file to be able to store repository and author trust information.
• Define a gesture for users to be able to trust.

Signers trust information

• Trusted signer key -
  Allows a user add a friendly name to identify the signer's trust information. If a trusted repository uses the same name as a source, it allows for correlation from a source to a trusted repository.

• Untrusted root -
  Indicates if it is allowed that a source's signing certificate chains to an untrusted root. Defaults to disallow.

Further for each certificate used by the repository, we should store the following -

• Certificate fingerprint -
  Used to assert the package being verified has been signed by the trusted repository. The fingerprint should be a calculated based on the Repository Certificate Fingerprint Algorithm described below.

• Certificate fingerprint algorithm -
  Allows for crypto-agility while calculating the certificate fingerprint. The algorithm currently supported are -

  • SHA256
  • SHA384
  • SHA512

Repository specific trust information

We should store the following information to enable a trust relationship between a package consumer and a package repository.

• Repository source service index URI -
  Allows communication with the source to refresh certificate list and to match with the V3ServiceIndex attribute in a repository signature. This is needed when a trusted repository is not a source so there is no other way of finding out the certificate endpoint. If this property is present in a trusted signer entry, the entry is taken to be a repository.

If the user wants to only trust specific package owners for a repository, they should be able to specify a list of trusted owners that will be compared against the Package Owners field in the repository signature metadata.

Trust information location

Trust information should be stored in the nuget.config file.

Repository trust information schema

<trustedSigners>
  <NAME>
    <add key="type" value="TRUSTED_SIGNER_TYPE" />
    <add key="serviceIndex" value="SERVICE_INDEX_URI" /> <!-- If present then type should be Repository -->
    <add key="CERT_HASH" 
         value="FINGERPRINT_ALGORITHM" />
    <add key="untrustedRoot" value="UNTRUSTED_ROOT" /> <!-- Defaults to disallow -->
    <add key="owners" value="LIST_OF_TRUSTED_OWNERS" /> <!-- Can only be present if type is Repository -->
  </NAME>
</trustedSigners >

For example -

<?xml version="1.0" encoding="utf-8"?>
<configuration>
  <packageSources>
    <add key="NuGet.Org" value="https://api.nuget.org/v3/index.json" />
  </packageSources>
  <trustedSigners>
    <NuGet.Org>
      <add key="type" value="repository" />
      <add key="jQCosvMgBxcgQGNesKaHU1Axvgly73B6jkRXZsf9Y8w=" 
           value="SHA256" />
      <add key="vPv9/fx05OEc4atG7ny+5KXeLbV8xuZhp8ct1fgIhpfdP97ZQ2B801YBaBP61zd=" 
           value="SHA384" />
      <add key="owners" value="aspnet;microsoft" />
    </NuGet.Org>
    <vsts>
      <add key="type" value="repository" />
      <add key="serviceIndex"
           value="https://api.vsts.com/feed/index.json" />
      <add key="OdiswAGAy7da6Gs6sghKmg9e9r90wM385jRXZsf9Y5q="
           value="SHA256" />
      <add key="untrustedRoot" value="allow" />
    </vsts>
    <Microsoft>
      <add key="type" value="author" />
      <add key="jQCosvMgBxcgQGNesKaHU1Axvgly73B6jkRXZsf9Y8w=" 
           value="SHA256" />
    </Microsoft>
    <PatoBeltran>
      <add key="type" value="author" />
      <add key="jQCosvMgBxcgQGNesKaHU1Axvgly73B6jkRXZsf9Y8w=" 
           value="SHA256" />
      <add key="untrustedRoot" value="allow" />
    </PatoBeltran>
  </trustedSigners>
</configuration>

Trust information gesture

To enable the following user gestures we need to create a new nuget trusted-signers command.

Summary -

Operation	Signer Type	Command	Remarks
Add	Repository	nuget trusted-signers Add -Name <n> [-Owners <o>] [-UntrustedRoot <u>]	Only works if there exists a source with the same name
Add	Repository	nuget trusted-signers Add -Name <n> -ServiceIndex <s> [-Owners <o>] [-UntrustedRoot <u>]
Add	Author	nuget trusted-signers Add -Name <n> -CertificateFingerprint <f> -FingerprintAlgorithm <a> [-UntrustedRoot <u>]
Add	Repository	nuget trusted-signers Add <package_path> -Repository -Name <n> [-Owners <o>] [-UntrustedRoot <u>]	Only works if package is repository signed or repository countersigned
Add	Author	nuget trusted-signers Add <package_path> -Author -Name <n> [-UntrustedRoot <u>]	Only works if package is author signed
Remove	Any	nuget trusted-signers Remove -Name <n>
Update	Author	nuget trusted-signers Remove-Certificate -Name <n> -CertificateFingerprint <f>	Removes a specific certificate entry from an existing trusted signer entry
Update	Author	nuget trusted-signers Add-Certificate -Name <n> -CertificateFingerprint <f> -FingerprintAlgorithm <a>	Adds a certificate entry to an existing trusted signer
Sync	Repository	nuget trusted-signers Sync -Name <n>	Refreshes certificates entries with the ones announced by the repository. The entry has to exist and be a trusted repository with a service index or a corresponding package source.