sigsum-log-go

Sigsum logging brings transparency to signed checksums. What a checksum represents is up to you. For example, it could be the cryptographic hash of a provenance file, a Firefox binary, or a text document.

You can use sigsum logging to: 1. Discover which checksum signatures were produced by what secret signing keys. 2. Be sure that everyone observes the same signed checksums.

How it works

Suppose that you develop software and publish binaries. You sign those binaries and make them available to users in a package repository and on your website. You are committed to distribute the same signed binaries to every user. That is an easy claim to make. However, word is cheap and sometimes things go wrong. How would you even know if your signing infrastructure got compromised? A few select users might already receive maliciously signed binaries that include a backdoor. This is where we can help by adding transparency.

For each binary you can log a signed checksum that corresponds to that binary. If such a sigsum appears in the log that you did not expect: excellent, now you know that your signing infrastructure was compromised at some point. Similarly, you can also detect if a binary from your website or package repository misses a corresponding log entry by inspecting the log. The claim that the same binaries are published for everyone can be verified.

Starting to apply the pattern of transparent logging is already an improvement without any end-user enforcement. It becomes easier to detect honest mistakes and attacks against your website or package repository.

To make the most out of a sigsum log, end-users should start to enforce public logging in the future. This means that a binary in the above example would be rejected unless a corresponding sigsum is publicly logged.

Please refer to our design document and API specification for additional details.

Public prototype

We implemented sigsum logging as a Trillian personality. A public prototype is up and running with zero promises of uptime, stability, etc. The log's base URL is http://poc.sigsum.org:4780/st/v0. The log's public verification key is bc9308dab23781b8a13d59a9e67bc1b8c1585550e72956525a20e479b1f74404. The log's shard interval is [X, Y].

An experimental witness is also up and running with zero-promises of uptime, stability, etc. The public verification key is 777528f5fd96f95713b8c2bb48bce2c83628e39ad3bfbd95bc0045b143fe5c34.

You can talk to the log by passing ASCII key-value pairs. For example, fetch a tree head and a log entry:

$ curl http://poc.sigsum.org:4780/sigsum/v0/get-tree-head-latest
timestamp=1632956637
tree_size=17
root_hash=51ce7e8e7fa98d48ab84750ae9dcbabda268fbcca74ab907836a35a513396f9d
signature=c4bb2429410523d109540e0bd47e46b46bce6b233eb895fce4c761e60f15ac8a9d245153e3eaf30c7360b0f7bd49a6f7e4327bb1e7dc2396535726191b42c90b
$
$ printf "start_size=0\nend_size=0\n" | curl --data-binary @- http://poc.sigsum.org:4780/sigsum/v0/get-leaves
shard_hint=0
checksum=0000000000000000000000000000000000000000000000000000000000000000
signature=0e0424c7288dc8ebec6b2ebd45e14e7d7f86dd7b0abc03861976a1c0ad8ca6120d4efd58aeab167e5e84fcffd0fab5861ceae85dec7f4e244e7465e41c5d5207
key_hash=9d6c91319b27ff58043ff6e6e654438a4ca15ee11dd2780b63211058b274f1f6

We are currently working on tooling that makes it easier to interact with the log.