Unicode C

Create an Opaque (Attached) S/MIME Signature

Demonstrates the Chilkat Mime.ConvertToSigned method, which creates an opaque (attached) S/MIME signature. The only argument is the signing Cert. On success the entity is replaced by a CMS/PKCS #7 signed-data structure that wraps the content inside the signature.

Note: The file paths are relative to the application's current working directory. Absolute paths may also be used. Supply the paths appropriate to your own environment.

Background: An opaque signature bundles the content inside the CMS structure, so the message is a single application/pkcs7-mime blob that only S/MIME-aware software can read. It is more tamper-resistant in transit — nothing can alter the content without breaking the wrapper — at the cost of the backward compatibility a detached signature offers. Use it when every recipient is known to support S/MIME.

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Unicode C

#include <C_CkMimeW.h>
#include <C_CkCertW.h>

void ChilkatSample(void)
    {
    BOOL success;
    HCkMimeW mime;
    const wchar_t *pfxPassword;
    HCkCertW cert;

    success = FALSE;

    mime = CkMimeW_Create();
    success = CkMimeW_SetBodyFromPlainText(mime,L"This message will be signed.");
    if (success == FALSE) {
        wprintf(L"%s\n",CkMimeW_lastErrorText(mime));
        CkMimeW_Dispose(mime);
        return;
    }

    //  Load the signing certificate (which must have access to its private key) from a PFX file.
    //  The PFX password should come from a secure source rather than being hard-coded.
    pfxPassword = L"myPfxPassword";
    cert = CkCertW_Create();
    success = CkCertW_LoadPfxFile(cert,L"qa_data/signer.pfx",pfxPassword);
    if (success == FALSE) {
        wprintf(L"%s\n",CkCertW_lastErrorText(cert));
        CkMimeW_Dispose(mime);
        CkCertW_Dispose(cert);
        return;
    }

    //  Create an OPAQUE (attached) S/MIME signature.  The entity is replaced by a CMS/PKCS #7
    //  signed-data structure that wraps the content inside the signature.
    success = CkMimeW_ConvertToSigned(mime,cert);
    if (success == FALSE) {
        wprintf(L"%s\n",CkMimeW_lastErrorText(mime));
        CkMimeW_Dispose(mime);
        CkCertW_Dispose(cert);
        return;
    }

    success = CkMimeW_SaveMime(mime,L"qa_output/signed_opaque.eml");
    if (success == FALSE) {
        wprintf(L"%s\n",CkMimeW_lastErrorText(mime));
        CkMimeW_Dispose(mime);
        CkCertW_Dispose(cert);
        return;
    }

    wprintf(L"Message converted to an opaque signed message.\n");


    CkMimeW_Dispose(mime);
    CkCertW_Dispose(cert);

    }