PKCS12 sign a string

See more:

C++

C

C#

OpenSSL

I have a code written in C# to sign and envelop a string to be sent to a web service, this code receives a certificate in the format .pfx and the certificate password.

string myString = "Hello World";
X509Certificate2 cert = new X509Certificate2(@"<MY PFX FILE>", "<MY PASS>");
CmsSigner signer = new CmsSigner(SubjectIdentifierType.IssuerAndSerialNumber, cert);
signer.DigestAlgorithm = new Oid("<MY OID>");

ContentInfo content = new ContentInfo(new Oid("<MY OID>"), new System.Text.UTF8Encoding().GetBytes(myString));
SignedCms signedCms = new SignedCms(content, false);

signedCms.ComputeSignature(signer, false);

var asig = signedCms.Encode();

Now I need to write a code that does exactly the same thing, but in C, after performing several searches on google, I found some libs. that work with this type of information, and in this search I found OpenSSL.

But I did not find how I could sign and envelop the message, just like I am doing in C#. Thanks in advance if anyone can help me, how can I do the same thing I do in C# in C.

What I have tried:

I did some tests with lib "ChilKat", C RSA Sign Using Private Key from .pfx/.p12 to Base64 Signature[^], when I encrypted the same information with my C# program and with this C++ program, the output is complete different, and, I did not managed how to use the OID digest algorithm...

With OpenSSL, I didn't find how I can sign a message use PKCS#7 certification.