Sigsum is a transparency system that makes signatures discoverable [1]. In other words: everytime a signature is created that an end-user accepts as valid, then that signature also becomes discoverable in a global append-only log.
Since dubbing the stable version of Sigsum in 2023 [2], many of the bits and pieces have been made available as independent specifications at C2SP.org [3]. The next major version of Sigsum (v2.0.0) is therefore expected to be mostly composed of multiple C2SP.org specifications: tlog-witness, tlog-cosignature, tlog-tiles, tlog-proof, https-bastion, and so forth. One important piece that’s still missing is the upcoming v2 leaf format. We’re currently working with people from Sigstore to define a single leaf format that could work for both Sigsum and Sigstore [4], thereby taking us in the direction of interoperability.
This talk provides a primer of what we’re planning to change from sigsum/v1 to sigsum/v2. We will also cover the work-in-progress leaf format, which among other things brings PQ resistance and separate signing contexts [5, 6, 7].
1: https://www.sigsum.org/
2: https://lists.sigsum.org/mailman3/hyperkitty/list/sigsum-general@lists.sigsum.org/thread/LX42ONBGWO4JMSMCDGS5Z7ORKJHFHQOO/
3: https://git.glasklar.is/sigsum/project/documentation/-/blob/main/proposals/2024-01-on-specifications-and-governance.md
4: https://github.com/C2SP/C2SP/pull/244
5: https://git.glasklar.is/sigsum/project/documentation/-/blob/main/archive/2024-11-04-sigsum-v2-ideas
6: https://git.glasklar.is/sigsum/project/documentation/-/blob/main/archive/2025-09-03-leaf-context-for-sigsum-v2.md
7: https://git.glasklar.is/sigsum/project/documentation/-/blob/main/archive/2026-05-12-sigsum-next-meetup-notes
Speaker
Rasmus Dahlberg is a computer scientist and software engineer based in Stockholm, Sweden. He has contributed to transparency log research and development since 2016. Examples of recent contributions include his involvement in the Sigsum project and C2SP community specifications related to witness cosigning.
