Send an Email with a Digital Signature

See more Email Object Examples

Demonstrates the Chilkat Email.SendSigned property. Set it to true to have the email sent with a digital signature (the default is false). Signing also requires a certificate with access to its private key. This example loads that certificate (and its private key) from a PFX file with Cert.LoadPfxFile, supplies it via SetSigningCert, and enables signed sending.

Background: Signing is the mirror image of encrypting. To encrypt for a recipient you use their public certificate; to sign you use your own private key, and recipients verify with your public certificate. A signature does not hide the message — a signed email is still readable by anyone — but it proves who sent it and guarantees the content was not tampered with. A PFX (also called PKCS#12, .pfx or .p12) is a password-protected file that bundles a certificate together with its private key, making it a convenient single-file source for signing credentials.

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#include <C_CkEmail.h>
#include <C_CkCert.h>

void ChilkatSample(void)
    {
    BOOL success;
    HCkEmail email;
    HCkCert cert;

    success = FALSE;

    //  Demonstrates the Email.SendSigned property with a full signing setup.  Set SendSigned
    //  to true to have the email sent with a digital signature.  Signing requires a certificate
    //  with access to its private key, which we load here from a PFX (.pfx / .p12) file.

    email = CkEmail_Create();
    CkEmail_putSubject(email,"Signed email");
    CkEmail_putBody(email,"This message will be sent with a digital signature.");
    CkEmail_putFrom(email,"alice@example.com");
    CkEmail_AddTo(email,"Bob","bob@example.com");

    //  Load the signing certificate (including its private key) from a PFX file.
    //  The 2nd argument is the PFX password.
    cert = CkCert_Create();
    success = CkCert_LoadPfxFile(cert,"qa_data/certs/signer.pfx","pfx_password");
    if (success == FALSE) {
        printf("%s\n",CkCert_lastErrorText(cert));
        CkEmail_Dispose(email);
        CkCert_Dispose(cert);
        return;
    }

    //  Provide the signing certificate.
    success = CkEmail_SetSigningCert(email,cert);
    if (success == FALSE) {
        printf("%s\n",CkEmail_lastErrorText(email));
        CkEmail_Dispose(email);
        CkCert_Dispose(cert);
        return;
    }

    //  Request that the email be sent with a digital signature.
    CkEmail_putSendSigned(email,TRUE);

    printf("SendSigned = %d\n",CkEmail_getSendSigned(email));

    //  Note: The path "qa_data/certs/signer.pfx" is a relative local filesystem path,
    //  relative to the current working directory of the running application.


    CkEmail_Dispose(email);
    CkCert_Dispose(cert);

    }