In Swift, I need to create a CMS to input a web service. In Android we used 'spongycastle' https://www.bouncycastle.org/docs/pkixdocs1.4/org/bouncycastle/cms/CMSSignedData.html But I did not find a sample or solution for Swift or objective C. I also read Apple related documents https://developer.apple.com/documentation/security/cryptographic_message_syntax_services#1677736 , but still nothing special. Does anyone have experience working with a specific solution for Swift or objective C code to do this? thank you.

I'm currently working on a project in Swift where I need to digitally sign a PDF file. I have the following resources available: Private Key stored in the iOS Keychain with a tag. Public Key also stored in the iOS Keychain with a tag. A valid certificate stored as a PEM string. I need to digitally sign a PDF file with the above keys and certificate, but I'm struggling to find a clear and straightforward example or guidance on how to achieve this in Swift. Specifically, I’m looking for help with: Creating the digital signature using the private key and certificate. Embedding this signature into the PDF file. Any considerations I should be aware of regarding the format of the signed PDF (e.g., CMS, PKCS7, etc.). If anyone has experience with digitally signing PDFs in Swift, I would greatly appreciate your guidance or code examples. Thank you in advance!