If it is your first time using your Singpass app to sign documents or authorise transactions, you will be prompted to request for a signing certificate. This certificate, issued by the National Certificate Authority (NCA), contains information about your identity and will be used to create and verify digital signatures. 

When you use your Singpass app to perform digital signing by scanning the QR code, the signing certificate within your app generates a digital signature on the document to be signed, which will be embedded within the final document to prove its authenticity.

Similarly for authorising transactions, by scanning the QR code, you can authorise a transaction to proceed. This transaction will be "signed" with a digital signature generated with your signing certificate.

The signing certificate is valid for 1 year in the Singpass app. Once it expires, you will be prompted to renew the signing certificate. You can proceed to renew the certificate, in order to continue using the Singpass app to sign documents or authorise transactions. 

The signing certificate is different from your authentication certificate, which will be used when you Login with Singpass.