Thumper

Thumper is a secure time stamp client/server system that implements RFC-3161. It allows clients to obtain cryptographic time stamps that can be used to later verify that certain documents existed on or before the time mentioned in the time stamp. Thumper is written in a combination of Ada 2012 and SPARK 2014 and makes use of external C libraries for database access and cryptographic operations. Thumper is used as a SPARK technology demonstration.

The system is intended to satisfy two major goals.

1. To serve as an educational vehicle for secure, high integrity programming, along with related topics.

2. To allow students to obtain strong time stamps of their work that can be used to prove it was completed on time.

Thumper requires manipulating ASN.1 data and includes a library called Hermes written in SPARK 2014 for doing this. The library is not organized as a separate project but is simply a collection of files in the hermes folder beneath src. Tests and documentation for Hermes are also provided and integrated into the other Thumper tests and documentation. However, Hermes does enjoy some level of independence, at least conceptually, and could potentially be separated into its own project in the future.

Quick Start

Thumper was developed and tested primarily on Windows. However, the project file, thumper.gpr, is intended to be cross-platform. The Thumper client uses GtkAda, which is not available on macOS, so users of that platform will not be able to build the client. See Additional Notes below for more information.

To build Thumper you'll need the following software installed:

• GNAT Community 2021 (or its equivalent). This can be downloaded from AdaCore. GNAT Community contains a suitable version of SPARK and some other supporting libraries (such as AUnit).

• GtkAda. This can be downloaded from AdaCore. You may need to select the "additional packages" option to find the installer on the web site. GtkAda is used for the client side graphical user interface.

• AWS. The Ada Web Server can be downloaded from the GitHub page. We recommend downloading an official release rather than using the latest revision in the Git repository. Note, however, that (at the time of this writing) the release archive does not include the templates_parser subproject. Thus you must go to the GitHub repository for that project and clone it into the proper folder before you try to build AWS. There is a link on the code page for AWS that points at the appropriate version in the templates_parser history. On Windows, be sure the GNAT tools are in the path and then do win32\build.cmd C:\GNAT\2021 to compile and install AWS to your GNAT installation folder (replace the target path as appropriate). For Linux and macOS do make setup build install.

• PostgreSQL 14. The exact version is not necessarily critical but if you use a different version, or if you install it in a non-standard location, you'll need to modify the thumper.gpr project file to specify an appropriate path to PostgreSQL's lib folder. You should also be sure the PostgreSQL bin folder is in your PATH or otherwise make an arrangement so the needed shared libraries can be found during execution.

Be sure you match the bit size of the compiler target (e.g., 64 bits) with the bit size of GtkAda and PostgreSQL.

You will also need to set up a database in the PostgreSQL server for use by Thumper. In what follows, the $ character is the console prompt and not part of the commands. Proceed as follows:

$ psql -U postgres
postgres=> CREATE ROLE thumper WITH CREATEDB LOGIN PASSWORD 'rabbitsfoot';
postgres=> \q
$ createdb -U thumper ThumperDB

The above commands log into PostgreSQL as the server superuser, creates a thumper user on the server with the ability to create databases, and then uses createdb to create the (empty) database needed by the Thumper server.

After setting up the software above, you should be able to load the thumper.gpr project file into GNATstudio or a similar IDE (Visual Studio Code, etc.) and build the Thumper client, server, and test programs (for Thumper and Hermes). Note that the Hermes library will be automatically built when Thumper is built.

See the documentation in the doc folder for more information.

Additional Notes

The macOS platform does not support GtkAda and developers on other platforms may choose not to install it (GtkAda is only needed for the client). In that case, create a file gtkada.gpr in the root of the project containing the following:

project GtkAda is
end GtkAda;

This dummy file will be loaded by thumper.gpr thus allowing development to proceed without editing the main project file (which should be avoided if possible).

On Linux systems, you will of course need to have the PostgreSQL server package installed. You may also need to install a PostgreSQL development package in order to have the necessary libraries on your system. On Ubuntu 20.04 do:

sudo apt install libpq-dev

PostgreSQL on Linux systems may be configured by default in a way that makes it awkward to log into the server as the thumper user from the system running the server. Consider modifying the file /etc/postgresql/[VERSION]/main/pg_hba.conf to contain the following lines (order is significant):

# "local" is for Unix domain socket connections only
local   ThumperDB       thumper        md5
local   all             all            peer

This allows the user thumper to attach to the ThumperDB database via md5-style passwords, even when connecting from the local system. Peer authentication won't work because there is (probably) no thumper user on the overall Linux system. The order of the lines matter because if they were in the opposite order, the "all all" will match every database and every user before the specific information is reached. After making this change you will need to restart the server:

# systemctl restart postgresql

The default port used for communication between the client and server is 318. On Unix-like systems (macOS and Linux), the server will not be able to bind to that port when run under an ordinary user account ("permission denied"). Use the -p option when running the server to specify an available port address greater than 1024:

$ ./thumper_server -p 9000

Of course, a similar option will need to be provided to the client in order for the two programs to connect successfully.

Contributors

Several of my students have assisted in the development of Thumper. Specifically:

• Luke Alden: Unit testing.
• Nathan Brown: Interfacing to OpenSSL.
• Andrew Clark: Setting up digital signatures using OpenSSL.
• Tim Cross: Primitive encoding/decoding subprograms in Hermes.
• Michael Green: Implementation of SHA-256 in Ada/SPARK.
• Nicole Hurley: Interfacing to OpenSSL.
• Nancy Mai: Client side GUI.
• Elizabeth Nittler: Database access.
• Carter Ransom: Primitive encoding/decoding subprograms in Hermes.
• Ian Schulze: Providing AWS support for remote access to the server.
• Falit Sehgal: Providing AWS support for remote access to the server.
• Stirling Sidaway: Client file hashing.

Peter C. Chapin
[email protected]