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WebID

WebID Creation and Validation (Tutorial, Tools, Best practices)

Authors

Jan Forberg and Sebastian Hellmann, DBpedia and KILT Competence Center @ InfAI License CC-BY © 2018 All feedback welcome (Issue tracker).

Why WebID?

WebID is a novel way to identify and authenticate users and organisations on the Web with established methods. The main advantages are:

  • people and organisations become the main authority for their data with full control
  • No need for passwords any more. Authentication is done with your own secure key

In comparison to any other services like Facebook, LinkedIn or OpenID you are the owner of the data and of the secure key and therefore your own authority. The WebID workflow uses public/private key cryptography and client certificate authorization to establish secure, authenticated HTTPS connections. We compiled a list of background reading at the end.

Terminology

WebID or WebID URI - The WebID itself is an identifier that represents a person or an organisation. In simple terms it is a self-chosen URI that can be used to retrieve additional information in form of the WebID profile document via the browser or with software (e.g. curl). Note the duplicate in WebID(entifier) and Uniform Resource Identifier (URI).
Examples:

WebID profile document or WebID file - The WebID profile document is the file that is downloaded when you execute a HTTP(S) request and contains the identifier and all relevant information about the person and organisation, in particular the RSA Public Key used to verify authentication. The file is normally written in Turtle Syntax (RDF).

# fragment - In website URLs the # is used to jump to certain parts of a HTML page, usually a paragraph. In WebID, the URL of the WebID profile document is appended by a fragment #this or #me to distinguish between the URL of the WebID profile document (the whole file) and the identifier and data in the document (part of the file).

Client Certificate or PKCS12 File (.pfx;.p12) - The file that contains an X.509 certificate along with the private key to establish the secure connection and authentication.

Example 1

This is Jan's WebID: http://holycrab13.github.io/webid.ttl#this If you open it in a browser or curl it the #this is ignored and the full turtle file is retrieved. In the turtle file you can find a section with additional information about Jan as well as his public key:

  • HTTP retrieval: curl -H "Accept: text/turtle" "http://holycrab13.github.io/webid.ttl#this"
  • Retrieval and RDF parsing : rapper -i turtle http://holycrab13.github.io/webid.ttl#this
# Note that <#this> is a relative path for the webid resolving to the full URI once the RDF is parsed.
<#this> a foaf:Person ;
   foaf:name "Jan Forberg";
   cert:key [ 
       a cert:RSAPublicKey;
       rdfs:label "made on 23 November 2011 on my laptop";
       cert:modulus "978CD24[...]3F29B"^^xsd:hexBinary;
       cert:exponent "65537"^^xsd:nonNegativeInteger
      ] .

Example 2

We prepared a full example in the example folder in this repository: https://github.com/dbpedia/webid/tree/master/example Note that this also contains the files private_key.pem and certificate.pfx , which are normally not public.

The Rules of WebID

  1. The WebID profile document is editable only by its owner or the owning organisation.
  2. The WebID profile document is retrievable as Turtle file via HTTP(S) request on the WebID URI. Use of Accept: text/turtle header is mandatory for the request.
  3. The WebID profile document must contain:
  • A foaf:primaryTopic from the WebID profile URI to the WebID.
  • A statement whether the WebID is a foaf:Person, foaf:Organisation or foaf:Agent
  • The modulus and of the RSAPublicKey
  1. The WebID profile document should be public as in open access like the majority of websites.
  2. The private key as well as the PKCS12 (.pfx,.p12) file must be kept in a secure location (normally password protected file or entrusted to a web browser).
  3. The X.509 Certificate, which is part of the PKCS12 file must contain the WebID in the subject alternative name (SAN) field

Note: The WebID profile document can contain any amount of additional information and extensions in the document. Some applications may require additional information.

Setup

WebID and WebID profile document

Choose the URI

Before publishing your WebID, think about the URI and the hosting space. Different options are documented below. Basically, you will need some webspace to put a file there. The URL of this file will make up the first part of your WebID (plus #this). There are actually many, many, many ways to do it. The main benefit of using just a Turtle/RDF file are that you just need to publish one file (file publishing is supported by many web services). Turtle allows to use the file URL as @base for all the relative URIs described, see https://www.w3.org/TR/turtle/#sec-intro . The three general ways to choose an URI are:

  • deploy file in a provided environment (e.g. Github pages)
  • deploy file on a webserver with own domain or subdomain on your own server (See)
  • use of more sophisticated Semantic Web tools (see list at end)

Note that querying the URI with #this or without should return the same result with HTTP as anything behind # is not sent to the server. However, the URI with #this at the end is your WebID and without the .ttl file.

Github.io

A simple way to get a WebID is using Github.io Pages as a free hosting service. GitHub page setup is explained here: https://pages.github.com/ (Basically it is creating a repository with the name ${username}.github.io and creating a webid.ttl there, your WebId will then be <YOUR_GITHUB_NAME>.github.io/webid.ttl#this (see example above). Here is the repo of Jan: https://github.com/holycrab13/holycrab13.github.io leading to https://holycrab13.github.io/webid.ttl

Note that Github pages sets the Content-Type HTTP response header correctly to text/turtle, but needs 3-5 minutes to update on commit/push. See the header here: curl -I "https://holycrab13.github.io/webid.ttl#this"

Apache2

Create a regular virtualhost for the domain and put the file there. since text/turtle is normally registered as mimetype under /etc/mime.types Apache2 will automatically recognise it. Otherwise you will need to add AddType text/turtle .ttl to the .htaccess file or the virtual host config.

Example: curl -I http://kurzum.net/webid.ttl

Create the WebID profile document in Turtle syntax

Create a new file and name it webid.ttl. Make sure to replace YOUR_NAME, PUBLIC_KEY_MODULUS and PUBLIC_KEY_EXPONENT with your respective information. Generation of the public key modulus and exponent is described in the next section. You can generate them using openssl or the provided create_certs.sh bash script.

@prefix foaf: <http://xmlns.com/foaf/0.1/> .
@prefix xsd: <http://www.w3.org/2001/XMLSchema#> .
@prefix cert: <http://www.w3.org/ns/auth/cert#> .
@prefix rdfs: <http://www.w3.org/1999/02/22-rdf-syntax-ns#> .

<> a foaf:PersonalProfileDocument ;
   foaf:maker <#this> ;
   foaf:primaryTopic <#this> .

<#this> a foaf:Person ;
   foaf:name "YOUR_NAME";
   cert:key [ 
       a cert:RSAPublicKey;
       rdfs:label "THIS FIELD IS FOR YOUR LABEL, SO YOU CAN NAME DIFFERENT KEYS";
       cert:modulus "PUBLIC_KEY_MODULUS(NO WHITSPACE, REMOVE 'modulus=`)"^^xsd:hexBinary;
       cert:exponent "PUBLIC_KEY_EXPONENT(NO  WHITESPACE)"^^xsd:nonNegativeInteger 
      ] . 

A complete WebId Document can look like this:

@prefix foaf: <http://xmlns.com/foaf/0.1/> .
@prefix xsd: <http://www.w3.org/2001/XMLSchema#> .
@prefix cert: <http://www.w3.org/ns/auth/cert#> .
@prefix rdfs: <http://www.w3.org/1999/02/22-rdf-syntax-ns#> .

<> a foaf:PersonalProfileDocument ;
   foaf:maker <#this> ;
   foaf:primaryTopic <#this> .

<#this> a foaf:Person ;
   foaf:name "Jan Forberg";
   cert:key [ 
       a cert:RSAPublicKey;
       rdfs:label "made on 23 November 2011 on my laptop";
       cert:modulus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xsd:hexBinary;
       cert:exponent "65537"^^xsd:nonNegativeInteger 
      ] .

Publish properly and check

NOTE: publishing means uploading the webid.ttl file to the web space as described before.

Check HTTP header

curl -I -L -H "Accept: text/turtle" "webid-uri" should return either:

  • HTTP/*.* 200 OK and Content-Type: text/turtle ,
  • HTTP/*.* 30X (a redirect) and give a Location: with the actual file (HTTP redirect)

Check Turtle syntax

Using the Helper Script

You can either download and run the create_certs.sh script or skip this section and do the Private/Public key generation yourself using openssl. To execute the script, simply download and run it using

mkdir certs
cd certs
bash ../create_certs.sh

The script will ask you for the relevant information for your certificate and WebId document. After running the script, the folder certs will contain the private and public key files, a x509 certificate, a PKCS12 signed certificate and a text file containing the exponent and modulus information for your WebId document. Replace the certificate information in your published webid.ttl file with the content of the generated text file.

You can upload the PKCS12 certificate (.pfx) to your browser by using the password you entered when running the script. That's it, you're all set to use your WebId.

Security Notice: the PKCS12 file contains the private key. Keep it a secret and entrust it only to reliable applications such as your browser, curl or other software that should act on your behalf (like your browser logging in for you).

Public/Private Key

Generation

Ubuntu (openssl)

# This will create two files in PEM format, private_key_webid.pem and public_key_webid.pem
openssl genpkey -algorithm RSA -out private_key_webid.pem -pkeyopt rsa_keygen_bits:2048
openssl rsa -pubout -in private_key_webid.pem -out public_key_webid.pem

Modulus and exponent

For the WebID, you will need the modulus and exponent of your public_key.

Ubuntu (openssl)

# Note that the public key was generated from the private key in the first place. 
# To print the modulus without separators for copy/paste into your WebId document, run
openssl rsa -noout -modulus -in private_key_webid.pem
# This command will print out the exponent of your public key. 
# The modulus printed out here is essentially the same, but in a different format (remove whitespace, newlines, : and 00 at the front). 
openssl rsa -pubin -inform PEM -text -noout < public_key_webid.pem

PKCS12 file

In cryptography, PKCS #12 defines an archive file format for storing many cryptography objects as a single file. It is commonly used to bundle a private key with its X.509 certificate (Source: https://en.wikipedia.org/wiki/PKCS_12).

Private key and X.509 together are required for Client Certificate Authorization, whereas the private key allows you to establish a secure connection (in this case TLS) and the X.509 certificate allows to authenticate your identity. The connection between these two is promed by signing the X.509 certificate with the private key.

X.509 certificate with WebID in Subject Alternative Name

The certificate file (.cer) file is created using your private key and a config file. Below is a sample config file (copy and paste to cert.config) and adapt each line. The most important part is the URI in alt_names

[req]
default_bits = 2048
prompt = no
default_md = sha256
req_extensions = v3_req
distinguished_name = dn

[ dn ]
# Country Code
C=DE
# State
ST=Saxonia
# City
L=Dresden    
# Organization
O=DBpedia
# Organizational Unit
OU=.
# Email Address
emailAddress=jan.forberg@hotmail.de
# Name
CN = Jan Forberg

[ v3_req ]
basicConstraints = CA:FALSE
keyUsage = nonRepudiation, digitalSignature, keyEncipherment
subjectAltName = @alt_names

[ alt_names ]
# Web Id
# Make sure to put your Web Id between quotes, otherwise the fragment identifier will be cropped automatically.
URI = "https://holycrab13.github.io/webid.ttl#this"

Run the following command to use your private key private_key_webid.pem and cert.config to generate a new file cert.cer.

openssl req -x509 -new -nodes -key private_key_webid.pem -days 3650 -out cert.cer -config cert.config -extensions v3_req

You can validate the contents of cert.cer by running

openssl x509 -in cert.cer -text

PKCS 12 file (.pfx, .pem or .p12)

PKCS 12 is an archive file format that serves as a container for several cryptographic parts. Bundle your new cert.cer to a PKCS12 file including your private_key_webid.pem by running the following command:

# Bundling
openssl pkcs12 -export -out certificate.pfx -inkey private_key_webid.pem -in cert.cer
# Conversion to .pem
openssl pkcs12 -in certificate.pfx -out certificate.pem

This generates a new file certificate.pfx. Security Notice: the file contains the private key. Keep it a secret and entrust it only to reliable applications such as your browser, curl or other software that should act on your behalf (like your browser logging in for you).

Browser installation

You can upload your certificate.pfx to your browser via the settings

  • Google Chrome: go to Settings > Advanced > Manage Certificates and Import your certificate file.
  • Firefox: go to Preferences > Privacy & Security > Certificates (at bottom) > View Certificates

Note: some browsers need a restart. There are plugins that let you switch between webids

Validation

We assume that HTTP Header and Turtle syntax have been checked before (see above). This part outlines additional validation to see whether everything is working.

Certificate and WebId Validation using curl

To verify your certificate, you can run

 curl -v -L --cert certificate.pem:yourpassword https://webid.dbpedia.org/verify.php

If everything is configured correctly, this will return your WebId and Public Key along with a SUCCESS message

You can try out your WebId by sending us a message by running

 curl -v -L --cert certificate.pem:yourpassword --data-urlencode "message=Thanks for the Tutorial!" https://webid.dbpedia.org/app/thanks.php

Applications using WebId Authentication

We have set up two example applications to verify your browser installation. You can leave us a message on the messageboard at https://webid.dbpedia.org/messageboard. Also feel free to register for the WebId Community Viewer at https://webid.dbpedia.org/viewer.

Content validation of WebID

TODO shacl

Testing of client certificate and secure connection

http://id.myopenlink.net/ods/webid_demo.html

Testing of authentication

http://ods-qa.openlinksw.com/youid http://linkeddata.uriburner.com/sparql

TODO

openssl dgst -sha256 -sign ~/.ssh/$private_key  anyFile.txt  | openssl base64 -out anyFile.signed

Background reading

If you are interested in the basic technologies behind WebID and TLS, we recommend to read these documents as a starting point.

Linked Data and RDF

Cryptography and Handshake