DescripTor is a Java API that fetches Tor descriptors from a variety of sources like cached descriptors and directory authorities/mirrors. The DescripTor API is useful to support statistical analysis of the Tor network data and for building services and applications.
The descriptor types supported by DescripTor include relay and bridge descriptors which are part of Tor's directory protocol as well as Torperf data files and TorDNSEL's exit lists. Access to these descriptors is unified to facilitate access to publicly available data about the Tor network.
This API is designed for Java programs that process Tor descriptors in batches. A Java program using this API first sets up a descriptor source by defining where to find descriptors and which descriptors it considers relevant. The descriptor source then makes the descriptors available in a descriptor store. The program can then query the descriptor store for the contained descriptors. Changes to the descriptor sources after descriptors are made available in the descriptor store will not be noticed. This simple programming model was designed for periodically running, batch-processing applications and not for continuously running applications that rely on learning about changes to an underlying descriptor source.
The executable jar, source jar, and javadoc jar can be found in
generated/dist/
Before using them please verify the release (see below for instructions).
Releases can be cryptographically verified to get some more confidence that they were put together by a Tor developer. The following steps explain the verification process by example.
Download the release tarball and the separate signature file:
wget https://dist.torproject.org/metrics-lib/2.0.0/metrics-lib-2.0.0.tar.gz
wget https://dist.torproject.org/metrics-lib/2.0.0/metrics-lib-2.0.0.tar.gz.asc
(Note that earlier tarballs were named descriptor-VERSION.tar.gz and could be found in https://dist.torproject.org/descriptor/.)
Attempt to verify the signature on the tarball:
gpg --verify metrics-lib-2.0.0.tar.gz.asc
If the signature cannot be verified due to the public key of the signer not being locally available, download that public key from one of the key servers and retry:
gpg --keyserver pgp.mit.edu --recv-key 0x4EFD4FDC3F46D41E
gpg --verify metrics-lib-2.0.0.tar.gz.asc
If the signature still cannot be verified, something is wrong!
But note that even if it can be verified, you now only know that the signature was made by the person claiming to own this key, which could be anyone. You'll need a trust path to the owner of this key in order to trust this signature, but that's clearly out of scope here. In short, your best chance is to meet a Tor developer in real life and enter the web of trust.
If you want to go one step further in the verification game, you can verify the signature on the .jar files.
Print and then import the provided X.509 certificate:
keytool -printcert -file CERT
keytool -importcert -alias karsten -file CERT
Verify the signatures on the contained .jar files using Java's jarsigner tool:
jarsigner -verify metrics-lib-2.0.0.jar
jarsigner -verify metrics-lib-2.0.0-sources.jar
The Metrics website has a tutorial for getting started with metrics-lib:
https://metrics.torproject.org/metrics-lib.html
The examples explained in the tutorials are available as source code in
src/main/resources/examples/