digital signature with php on excel

Question

I'm trying to add a digital sign to an excel document with the function openssl_pkcs7_sign. The problem is that the output file has wrong format and excel open it with wrong characters.

Somebody knows how to keep the format on the signed file?

Thanks

Answer 1

The function you used creates a wrapping PKCS#7/CMS signature. Office files are signed in a very different way (using their own format, where the signature is embedded into the document) and you can't sign office files with OpenSSL.

I don't know if there exist any libraries for signing office documents from PHP. You might need to create a native or .NET/Mono executable to sign a file and call it from your PHP script. Our SecureBlackbox offers components and classes that let you do signing of Office documents.