Securing Freedom, Defending Privacy

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LibrePGP is an alternative, updated specification of the OpenPGP encryption standard. It was developed as a response to changes made to the OpenPGP specification by a subgroup within the IETF OpenPGP working group. These changes were perceived as disruptive to the existing implementations, raising concerns about interoperability and security.

LibrePGP wants to preserve the core principles of openness and compatibility:

  • Long-term Stability: LibrePGP ensures reliable encryption with decades in mind.
  • Critical Deployment: LibrePGP is designed for KRITIS, GDPR, NGOs, journalist, public administration, …
  • Compatibilty: LibrePGP stands for a stable protocol where implementors can rely upon.
  • Real-world Focus: Everyday security concerns over academic ones.

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Software with LibrePGP support

Given that the majority of email clients and related software rely on GnuPG or RNP we anticipate no compatibility issues for users.

A Critique on the OpenPGP Updates

The IETF OpenPGP Working Group (WG) at some point decided to give up on its charter to produce an updated specification and instead started to re-invent that standard. Whether this is in line with IETF rules is questionable.

Considering that new features and discussions for larger updates of the specification delayed a new RFC for many years and were the reason for closing the WG in 2017 and re-opening in 2020, we proposed to go back to the last commonly agreed upon draft or to conclude the WG on the grounds that no rough consensus could be found.

01 Symmetric Mode

It seems that this new scheme was introduced for the benefit of allowing GCM as yet another encryption mode. GCM is a counter mode and, as can be seen by the large changes required, is hard to get right. Meanwhile we have GCM in CMS (the core of S/MIME) because Microsoft decided to go this way. However, OpenPGP has made its decisions based on technical soundness and not based on larger vendor, government, or committee decision.

The WG once decided to go with OCB and EAX. EAX was only added to avoid possible patent problems. However, in the 4.5 years since the introduction of EAX, the OCB patent expired. Thus, there is no more reason to reject OCB, and it should be declared as a RECOMMENDED mode with the intention to make it a MUST mode in some future OpenPGP. It can also be expected that FIPS-140 will eventually allow OCB.

Our suggestion was: Drop all the new AEAD ideas and use what has been deployed and agreed upon in the OpenPGP WG a long time ago. Further, turn OCB into MUST WG a long time ago. Further, turn OCB into MUST and EAX into MAY (only for backward compatibility with deployed implementations).

02 Padding Packet

A padding packet is introduced with the idea to mitigate traffic analysis. However, it is suggested to use random data for the content of this packet and thus this packet opens a huge covert channel. This is especially concerning for institutional users efforts regarding Data Leak Prevention (DLP). Suggestions to use padding based on a verifiable seed, were rejected despite that this is the standard method to do padding.

This padding idea has come up in discussion every once in a while over the last 25 years and has always been rejected because it does not belong into the encryption layer but into the application (plaintext) layer.

03 Changes to the ECDH Encryption

ECDH is the standard way to do encryption with elliptic curves. For OpenPGP ECDH has been specified in RFC-6637 from 2012 and been implemented by PGP and GnuPG even a year earlier. Instead of keeping this solid specification some details have been changed without a sound reason.

04 Proliferation for Algorithms

The new draft not only allow the use of GCM as a third encryption mode but adds a couple of other required algorithms:

  • HKDF
  • Argon2
  • Optional modes (EAX, OCB, GCM, and a way to define even more)

Werner Koch joined the AES conference in 2000 on Phil Zimmermann's wish to talk about algorithm proliferation. They agreed on pushing the forthcoming AES along with their MDC extension, get Twofish and so out of the focus, and in general resist to add new algorithms. That is for the simple reason that neither PGP nor GnuPG wanted to maintain all new algorithms until eternity.

Later, they had to do a political compromise to allow Camellia for the use in Japan and Brainpool curves for European use. We should really stick to this and not support algorithms which are just a substitute for existing crypto building blocks. Since added complexity makes a review harder and the larger codebase has to be maintained indefinitely for backwards compatibility.

05 Removal of Useful Real-world Features

For example, in 2016 an m flag was introduced to indicate that the plaintext shall be interpreted as MIME data. This has been removed along with deprecating the traditional t flag to distinguish between binary and text data. Having the ability to easily detect MIME data is for example required to process attachments from web mail clients or in air-gaped environments.

The designated revoker feature has also been deprecated with the rationale that a better method is to achieve this with an "escrowed" revocation, pre-created by the user. In fact, GnuPG creates such a revocation certificate since version 2.1 (released in 2014), to mitigate the common problem of a forgotten password. But this is not a replacement for corporate needs: the designated revoker is an important feature to manage a large scale deployments of OpenPGP keys and acts as a CRL (certificate revocation list) replacement.

06 Removal of Security Fixes

Due to an implementation bug in PGP 5, the metadata of a signed file was not covered by the signatures. RFC-4880 didn't fix that for backward compatibility. However, users were often surprised when they learned that the shown filename and file data could be changed while keeping the signature intact. With the introduction of the new v5 signature packet format, the opportunity to fix that was taken.

However, the crypto-refresh group then introduced v6 signatures and removed the fix (see this commit) with the flimsy explanation that the way to populate that the field is not clear in a theoretical encrypt-then-sign scenario and that signatures could not be detached and reattached (which is obvioulsy wrong). A later proposed fix for v4 signature packets (Meta Hash subpacket, see discussion) was not considered.

07 Salted Signature Issue

Salted signature were introduced with the idea that they might mitigate a chosen prefix attack in the same way as they will do for a certain SHA-1 based Web-of-Trust attack. No research for that statement has been cited just an assumption and a concern related to fault attacks on EdDSA which is about the development of Wireguard-like protocol. However, such fault attacks can be more securely detected by checking the signature after verification in the same way as the mitigation to Lenstra's attack on RSA's CRT.

Anyway, the major concern here is that this adds another 32 octet covert channel to each message (and also blow the signature up by 64 octets) In this case it is not an optional feature as with the padding packet. This is a clear violation of best current practices in sensitive areas where signed mails are mandatory and encryption is not enforced (or monitored by a gateway).

08 Regression from Deployed Formats and Standard Behavior

In general the crypto-refresh draft tends to ignore the requirements of long term storage needs and considers online communication and software deployment pattern as the major OpenPGP usage. Data and software life-cycle management has not been adequately taken in consideration and thus the draft regresses heavily from 30 years of PGP history.


Development Timeline

  • 1996-08
    The preceding "PGP Message Exchange Formats" RFC 1991, specifies the V3 key format.
  • 1997-11
    Work begins on OpenPGP RFC 2440, with the V4 key format.
  • 1997-12
    First release of GnuPG, compatible to PGP
  • 2007-11
    OpenPGP RFC 4880 with minor updates published.
  • 2015
    Work on rfc4880bis with V5 key format and OCB mode starts.
  • 2018-01
    Working code in RNP.
  • 2018-02
    Working code in GnuPG 2.3.
  • 2020-07
    GnuPG 2.2 has been released, featuring a backported version of the V5 key format.
  • 2021-09
    Consensus on RFC 4880bis draft, only editorial things needed to be finalized.
  • 2021-10 to present
    A small group initiated a significant revision of the RFC, setting aside previous efforts. This included the introduction of a new key format, removal of the V5 key format, and incompatible changes to OCB.
  • 2023-11
    LibrePGP: based on the latest consensus, working code, and the V5 format in use.


LibrePGP is supported by the following Open Source projects/organizations:


GnuPG allows you to encrypt and sign your data and communications; it features a versatile key management system, along with access modules for all kinds of public key directories. GnuPG, also known as GPG, is a command line tool with features for easy integration with other applications.

Since 1998 GnuPG provides end-to-end encryption on a wide range of platforms. It is the workhorse of the internet for data and mail encryption, as well as for signing software repositories. Select versions of GnuPG are also sanctioned and extensively utilized for EU/NATO-Restricted communication.


RNP is a set of openly-licensed OpenPGP tools that works on all major platforms, including Windows, macOS, Linux and *BSD. This includes the executables rnp for handling OpenPGP data and rnpkeys for key management. librnp is the core library used for all OpenPGP functions.

Since 2019 RNP provides the OpenPGP functionality for the Mozilla Thunderbird mail client. Thunderbird is available for all common computing platforms like macOS, Linux, *BSD, and Windows.


Gpg4win (GNU Privacy Guard for Windows) enables users to securely transport emails and files with the help of encryption and digital signatures through an easy to use user interface. Encryption protects the contents against an unwanted party reading it. Digital signatures make sure that it was not modified and comes from a specific sender.

Since its inception more than 18 years ago Gpg4win is the de-facto standard to use LibrePGP on Windows. It used by journalists, activists and companies all over the world.

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