Sovereign Tech Agency invests over €1m in Let's Encrypt post-quantum certificates

The Sovereign Tech Agency, the German agency funding critical open source infrastructure, has signed a contract with the Internet Security Research Group (ISRG) to develop a Certificate Authority based on Merkle Tree Certificates at Let's Encrypt. The contract covers development until the end of 2027 for a total exceeding €1 million. According to Let's Encrypt, this is the largest single investment received to date for post-quantum preparation.

Server administrators running HTTPS will eventually need to grapple with this transition: every TLS certificate signed with classical algorithms (RSA, ECDSA) becomes vulnerable once a sufficiently powerful quantum computer is available. The practical problem is that replacing current signatures with their post-quantum equivalents—one signature per certificate—balloons the TLS handshake beyond 10 kilobytes, resulting in slower connections and some destined to fail.

What are Merkle Tree Certificates

MTCs solve the problem by signing not individual certificates but an entire batch: instead of one signature per certificate, the CA signs a tree structure covering many together, keeping the handshake small even with post-quantum algorithms.

The funding covers three fronts through 2027: standardisation work at the IETF, in the C2SP community project and with browser root programmes; transitioning the infrastructure from staging to fully compliant production; and documentation and adoption by subscribers.

This is not the Sovereign Tech Agency's first intervention at Let's Encrypt. In 2025 the agency had already commissioned work for €402,800, aimed at preparing the infrastructure database for short-lived certificates, adding Encrypted Client Hello support and deploying Hickory DNS. The new contract arrives as Let's Encrypt has already announced it will reduce maximum certificate lifetime to 64 days by February 2027 and to 45 days by February 2028: a system that signs in bulk adapts better to more frequent renewals than one signing certificate-by-certificate.

For infrastructure administrators, nothing changes in day-to-day issuance via ACME for now: MTCs are still in development, there are no commands to update and no operational deadlines announced in this announcement.

Those wishing to support ISRG as a funder can write to donate@abetterinternet.org.