(C#) Decrypt S/MIME and Verify S/MIME Signatures

C# example to decrypt S/MIME and verify S/MIME signatures. The S/MIME is unwrapped to get the original MIME prior to signing/encrypting.

Note: This example requires Chilkat v11.0.0 or greater.

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bool success = false;

// This example requires the Chilkat API to have been previously unlocked.
// See Global Unlock Sample for sample code.

Chilkat.Mime mime = new Chilkat.Mime();

// Load an S/MIME message from a file:
success = mime.LoadMimeFile("signedMime.txt");
if (success == false) {
    Debug.WriteLine(mime.LastErrorText);
    return;
}

// The ContainsEncryptedParts/ContainsSignedParts methods
// can be called to determine if the MIME is encrypted and/or signed:
bool isEncrypted = mime.ContainsEncryptedParts();
bool isSigned = mime.ContainsSignedParts();

// We don't want the "unwrap extras".  You'll see what those
// are in a few moments...
mime.UnwrapExtras = false;

// To verify the signature, call UnwrapSecurity.  This will
// verify the signature(s) and decrypt the S/MIME and restore
// the MIME to the unsigned/unencrypted state.
// The results of what was found are present in the MIME object's
// properties, as well as extra header fields that are added
// to the unwrapped MIME.
success = mime.UnwrapSecurity();
if (success != true) {
    // UnwrapSecurity returns true if all signatures were
    // verified and all parts decrypted.
    Debug.WriteLine(mime.LastErrorText);
    return;
}

// The mime.UnwrapExtras property controls whether or not
// these additional fields are added to the unwrapped MIME:
// 
// X-NumPartsSigned: 1
// X-SignaturesValid: yes
// X-NumPartsEncrypted: 1
// X-Decrypted: no
// 
// The X-NumPartsSigned/X-SignaturesValid headers are added
// if the MIME was signed.  
// 
// The X-NumPartsEncrypted/X-Decrypted headers are added
// if the MIME was encrypted.
// 

// If the MIME was signed, get the certificate used for signing.
if (isSigned == true) {
    Chilkat.Cert signerCert = new Chilkat.Cert();

    // The NumSignerCerts property indicates how many certificates
    // were used for signing.  This example will assume the value is 1.
    // To get the 1st signer cert, call LastSignerCert with an index of 0:
    success = mime.LastSignerCert(0,signerCert);
    if (success == true) {
        Debug.WriteLine("**** Signer Cert: " + signerCert.SubjectCN);
    }

}

// If the MIME was encrypted, get the certificate used for decryption
if (isEncrypted == true) {
    // The NumDecryptCerts property indicates how many certificates
    // were used for decrypting.  This example will assume the value is 1.
    // To get the 1st decrypt cert, call LastDecryptCert with an index of 0:
    Chilkat.Cert decryptCert = new Chilkat.Cert();
    success = mime.LastDecryptCert(0,decryptCert);
    if (success == true) {
        Debug.WriteLine("**** Decrypt Cert: " + decryptCert.SubjectCN);
    }

}

// Display the unwrapped MIME:
Debug.WriteLine(mime.GetMime());

// Save the unwrapped MIME to a file:
success = mime.SaveMime("unwrappedMime.txt");