Hi Elva,
PKCS 2.2 has been supported in Mbed TLS for a long time (way before Mbed TLS 2.28.2). We reference the RFC variant of the document https://www.rfc-editor.org/rfc/rfc8017.html (The
original standard was issued by RSA Labs, the above RFC is the IETF adoption of it, which as far as I know a verbatim equivalent of the original.) This standard describes PKCS#1 versions 1.5 and 2.2 and Mbed TLS implements both. The standard describes RSA
encryption, signature and key formats. We are planning to retire PKCS#1 encryption v1.5 in Mbed TLS 4.0 (both versions of signature and v2.2 encryption will remain).
Best regards,
Janos