Security¶

What is a security issue?¶

Anytime it’s possible to write code using cryptography‘s public API which does not provide the guarantees that a reasonable developer would expect it to based on our documentation.

That’s a bit academic, but basically it means the scope of what we consider a vulnerability is broad, and we do not require a proof of concept or even a specific exploit, merely a reasonable threat model under which cryptography could be attacked.

To give a few examples of things we would consider security issues:

• If a recipe, such as Fernet, made it easy for a user to bypass confidentiality or integrity with the public API (e.g. if the API let a user reuse nonces).
• If, under any circumstances, we used a CSPRNG which wasn’t fork-safe.
• If cryptography used an API in an underlying C library and failed to handle error conditions safely.

Examples of things we wouldn’t consider security issues:

• Offering ECB mode for symmetric encryption in the Hazmat layer. Though ECB is critically weak, it is documented as being weak in our documentation.
• Using a variable time comparison somewhere, if it’s not possible to articulate any particular program in which this would result in problematic information disclosure.

In general, if you’re unsure, we request that you to default to treating things as security issues and handling them sensitively, the worst thing that can happen is that we’ll ask you to file a bug issue.

Reporting a security issue¶

We ask that you do not report security issues to our normal GitHub issue tracker.

If you believe you’ve identified a security issue with cryptography, please report it to alex.gaynor@gmail.com. Messages may be optionally encrypted with PGP using key fingerprint F7FC 698F AAE2 D2EF BECD  E98E D1B3 ADC0 E023 8CA6 (this public key is available from most commonly-used key servers).

Once you’ve submitted an issue via email, you should receive an acknowledgment within 48 hours, and depending on the action to be taken, you may receive further follow-up emails.

Supported Versions¶

At any given time, we will provide security support for the master branch as well as the most recent release.

New releases for OpenSSL updates¶

As of version 0.5, cryptography statically links OpenSSL on Windows, and as of version 1.0.1 on OS X, to ease installation. Due to this, cryptography will release a new version whenever OpenSSL has a security or bug fix release to avoid shipping insecure software.

Like all our other releases, this will be announced on the mailing list and we strongly recommend that you upgrade as soon as possible.

Disclosure Process¶

Our process for taking a security issue from private discussion to public disclosure involves multiple steps.

Approximately one week before full public disclosure, we will send advance notification of the issue to a list of people and organizations, primarily composed of operating-system vendors and other distributors of cryptography. This notification will consist of an email message containing:

• A full description of the issue and the affected versions of cryptography.
• The steps we will be taking to remedy the issue.
• The patches, if any, that will be applied to cryptography.
• The date on which the cryptography team will apply these patches, issue new releases, and publicly disclose the issue.

Simultaneously, the reporter of the issue will receive notification of the date on which we plan to take the issue public.

On the day of disclosure, we will take the following steps:

• Apply the relevant patches to the cryptography repository. The commit messages for these patches will indicate that they are for security issues, but will not describe the issue in any detail; instead, they will warn of upcoming disclosure.
• Issue the relevant releases.
• Post a notice to the cryptography mailing list that describes the issue in detail, point to the new release and crediting the reporter of the issue.

If a reported issue is believed to be particularly time-sensitive – due to a known exploit in the wild, for example – the time between advance notification and public disclosure may be shortened considerably.

The list of people and organizations who receives advanced notification of security issues is not and will not be made public. This list generally consists of high profile downstream distributors and is entirely at the discretion of the cryptography team.