[−][src]Module cargo_crev::doc::user::trust

Trust and Web of Trust

The goal of this document is to help users understand trust in crev (and cargo-crev).

Web of Trust

Trust proofs

Any identity can generate and sign a trust proof to express direct trust in another identity.

Example.

-----BEGIN CREV TRUST -----
version: -1
date: "2019-04-28T22:05:05.147481998-07:00"
from:
  id-type: crev
  id: FYlr8YoYGVvDwHQxqEIs89reKKDy-oWisoO0qXXEfHE
  url: "https://github.com/dpc/crev-proofs"
ids:
  - id-type: crev
    id: YWfa4SGgcW87fIT88uCkkrsRgIbWiGOOYmBbA1AtnKA
    url: "https://github.com/oherrala/crev-proofs"
trust: low
-----BEGIN CREV TRUST SIGNATURE-----
02BF0i1K0O7uR8T5UHzymqTo65P9R7JDuvfowZuHb3ubW8kd2-Fbl4jSv0n08ZdSU9P_E2YLWvEJrVQDYfjVCg
-----END CREV TRUST-----

Identity FYlr8YoYGVvDwHQxqEIs89reKKDy-oWisoO0qXXEfHE trusts identity YWfa4SGgcW87fIT88uCkkrsRgIbWiGOOYmBbA1AtnKA. Notably, trust proofs include trust level information (trust field).

cargo-crev builds WoT from from all the available trust proofs, and calculates a personal trust set from it.

When calculating the trust set, crev recursively traverses the graph from the given root identity. This makes trust transitive.

The root identity is typically the current identity of the user, but can be specified arbitrarily with the --for-id argument.

effective trust level

While traversing the graph crev keeps track of an effective trust level of each trusted identity. In simple terms: if R is the root identity, and R trust X with a low trust level, and X trusts Y with high trust level, R will have a low effective trust level for Y, because effective trust level for Y can't exceed the effective trust level in X.

More precisely: effective trust level of R for Y is equal to:

  • maximum of:
    • direct trust level of R for Y (if available), or
    • for any already trusted identity Xi that also trusts Y, the maximum value of the lowest of:
      • direct trust level of Xi for Y
      • the effective trust level of R for Y

Or in other words: for R to have a given effective trust for Y, there has to exist at least on path from R and Y, where every previous node directly trusts the next one at the level at least as high.

That's because any effective trust level can only be as high as the higest effective trust level

Depth of the WoT

While traversing the trust graph to calculate the WoT, cargo-crev keeps track of the distance from the root ID. The exact details how far from it it will reach can be controlled by the following command line options:

--depth <depth>
--high-cost <high_cost>
--medium-cost <medium_cost>
--low-cost <low_cost>

This allows flexible control over transitive trust. For example:

--high-cost 1 --medium-cost 1 --low-cost 1 --depth 1

would effectively make cargo-crev use only directly trusted identities.

Filtering reviews

In addition to control over how the WoT is calculated, it is possible to filter package reviews used by other criteria.

--trust options allows verification of packages only by reviews created by identities of a given trust level (or higher).

The following options:

--thoroughness <thoroughness>
--understanding <understanding>

control filtering of the reviews by their qualities.

Finally:

--redundancy <redundancy>          Number of reviews required [default: 1]

control how many trusted reviews is required to consider each package as trustworthy.