# RSASSA-PSS p1v2.1 (rfc 4056) signing

I'm signing mails with the RSASSA-PSS (p1v2.1) certificate. When I click Details, it shows "Signature Algorithm: RSASSA-PSS". openssl x509 -text shows

    Signature Algorithm: rsassaPss
Hash Algorithm: sha256


certutil -dump shows:

1.2.840.113549.1.1.10 RSASSA-PSS


Now, whem I send my signed emails and click on Details in outlook, it shows "Signature Algorithm: RSA (2048)"

I'm using bouncycastle for signing and when I use "SHA256WithRSAEncryption" it works fine, but when I'm using "SHA256WithRSAAndMGF1" Signature, Outlook tells me "The digital signature on this item is Invalid or Not Trusted." and when I click details, I see "Signature Algorithm: RSA (2048)". Is p#1v2.1 still not supported by outlook/microsoft or am I just crazy?

• Why a program does not accept a signature format is off-topic here; I'm thus thinking of migrating to security-SE. That said, one possibility worth checking would be that the hash algorithm used in MGF1 is not the same on both sides: it's not specified by SHA256WithRSAAndMGF1. I have been hit (in encryption, not signature) by Java libraries where MGF1 is by default understood to use SHA-1 even when the algorithm's name mentions SHA-256, see this. – fgrieu Mar 14 at 8:33
• Note: as of 2020 this apparently wasn't supported, see the conversation here with an (initially helpful) Jenifer from Microsoft trying to fill the gaps, but getting wrong footed by her own engineers. – Maarten Bodewes Mar 16 at 13:17