We strongly recommend that users of DigiDoc4j library versions 5.1.0 to 6.0.1 update to version 6.1.0 as soon as possible. Starting from 4 February, signing with the aforementioned library versions using certificates issued by SK ID Solutions will no longer be possible.
Starting from 1 January 2026, errors occurred in information systems using DigiDoc4j library versions 5.1.0 to 6.0.1 or the national Digital Signature Gateway Service SiGa during digital signing, and the signing processes could not be completed. The reasons were related to technical limitations of the Digital Signature Service (DSS) base library used by DigiDoc4j, which no longer accepted RSA keys shorter than 3,000 bits for signing Online Certificate Status Protocol (OCSP) responses as of 1 January 2026. The Digidoc4j library version 6.1 utilises DSS version 6.2, where the validity of RSA key sizes from 1,900 to 3,000 bits is extended to 2029 in accordance with the standard ETSI TS 119 312 V1.5.1 (published in December 2024).
As the validity confirmation services offered by SK ID Solutions AS used 2,048-bit RSA keys for signing, signing in Digidoc4j libraries was no longer possible with Mobile-ID, Smart-ID, previous generation ID cards, and eSeal.
As a temporary solution, SK ID Solutions started using 4,096-bit RSA keys for signing validity confirmations. On 4 February 2026, SK ID Solutions will restore the key length to its previous level (2,048 bits) during the monthly certificate renewal process.
Here’s what will happen:
- On 4 February 2026, the signing flow will be interrupted in DigiDoc4j library versions 5.1.0 to 6.0.1, and signatures will not be completed.
Who will be affected:
- All information systems using DigiDoc4j library versions 5.1.0 (released on 24 March 2023) to 6.0.1 (released on 14 March 2025).
Who will not be affected:
- Users of the Digital Signature Gateway Service SiGa.
- Users of DigiDoc4j library version 6.1.0 (released on 15 December 2025) or versions 5.0.0 and earlier.
- Users of the DigiDoc client.
What to do:
- Implement the latest DigiDoc4j library, currently version 6.1.0. The update is also recommended in light of the upcoming TL version update in spring, which older versions will not automatically support. There is no workaround to get support.
- If it is necessary to support the affected library version, the integrator must overwrite the DSS default constraint file on the classpath with its own constraint file. More detailed instructions can be found here.
If you encounter insurmountable obstacles in implementing the solution, please feel free to contact [email protected].
