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Prove a file currently exists without disclosing it's content.

Project description


Cotary allows you to prove that you have a document without releasing it.


The following scenario describes the motivation for this simple tool: Alice as an idea that she wants to use; either by publishing it in an article or paper or using it in a product. But she needs help; so she asks Bob to collaborate with her. Alice's idea is so good, though, that she is afraid that Bob will steal the idea from her and not involve her.

To counter this, she needs proof that she had the idea first; but without releasing the idea to the public yet. So she writes a simple draft of her ideas including all important ingredients, calculates a cryptographic hash H(d) of this document d and stores the document it in a safe place. Before talking to Bob, she publishes the hash. Since H is one-way, her ideas are still safe.

In case Bob tries to use Alice's ideas without her approval, she can at a later stage release the document d to the world. Since everyone can check that her previously published hash H(d) belongs to the document, she now proved that she had the ideas in the document before talking to Bob.

Cotary (code notary) makes this process for Alice very easy. Simply execute cotary on a file and it will publish a cryptographically secure hash on your Twitter account. This tweet with a timestamp and the hash proves you had the file at time of publishing.

This shows a very simple use case of hash functions and how to use them in practice.


cotary currently only support python3. python2 is not supported. Thus, make sure you use pip for your python3 environment; sometime it is called pip3. On some systems, the python3 executable is called python3 instead of python. In those cases, you can use python3 -m pip instead of just calling pip to make sure you have the right version.

Installation from PyPI

cotary is available on PyPI so installation is very easy using pip:

Make sure you have pip installed for your python3 environment.

$ python3 -m pip install --user cotary

Omit --user to install it system-wide.

Now, the cotary executable should be in your PATH and ready to use.

Installation from source

Pip can be used to install from source, as well. The file contains everything pip needs to know, so you can install your local copy of the source easily:

Make sure you have pip installed for your python3 environment.

$ python3 -m pip install --user .

Omit --user to install it system-wide.

Now, the cotary executable should be in your PATH and ready to use.


Configuration of Twitter APIs is done using a yaml config file. At the moment, these are the options. Default config file is in ~/.config/cotary/config.yaml.

    message: 'I own a file with checksum {checksum} (cotary)'
    # The following are twitter API keys. Get them from
        key: null
        secret: null
        key: null
        secret: null


usage: cotary [-h] [-c] [--config [CONFIG]] [-q] [file]

Publish the checksum of a file on Twitter.

positional arguments:
  file               File for which to publish checksum. If none is given,
                     read from stdin

optional arguments:
  -h, --help         show this help message and exit
  -c, --calc_only    Only calculate and print the checksum, do not publish it
  --config [CONFIG]  Use given config instead of ~/.local/cotary/config.yaml
  -q, --quiet        Do not print any messages


$ cotary 
checksum: openssl_sha256:66ca5ae6f1f3760ad7258cc1d1e906ec8853a0e4da2b2de42f55036cffe8f8a2
Status published at 2019-01-16 15:18:38

Leads to this Twitter message:

I own a file with checksum openssl_sha256:66ca5ae6f1f3760ad7258cc1d1e906ec8853a0e4da2b2de42f55036cffe8f8a2 (cotary)

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