After upgrading to a new computer with Ubuntu 20.04, I encountered the following error:
1 signature is unknown!
Error details:
SignatureXAdES_LTA.cpp:198 Signature validation
SignatureXAdES_B.cpp:738 Unable to verify signing certificate
X509CertStore.cpp:351 unable to get local issuer certificate:0
OCSP.cpp:308 Certificate status: unknown
Root Cause
This issue is caused by the OpenSSL 1.1.1f version included in Ubuntu 20.04 LTS.
More information: Open-eID issue #341
The bundled OpenSSL version has known problems with certificate validation, especially when using OCSP and complex certificate chains.
Solution
Building and installing a newer OpenSSL version (1.1.1g or higher) from source helped resolve the error.
Note: Even with OpenSSL 1.1.1g, some minor certificate validation issues might still remain.
How to Build OpenSSL from Source
A detailed guide for compiling OpenSSL on Linux is available here: → HowtoForge: How to Install OpenSSL from Source
