(Mono C#) Duplicate OpensSSL to Encrypt a Signed File

This example duplicates the following:

openssl smime -encrypt –in SIGNED.P7M –outform der –binary –des3 -out ENCRYPTED.ENC OTHERPARTYCERTIFICATE.PEM

Note: Although "smime" is the OpenSSL command, it's not actually producing S/MIME. The arguments "-outform der -binary" indicates that the output is binary DER (i.e. the PKCS7 binary signature). The input file (in this case) is a .p7m opaque signature, but it can be any type of file. There is nothing special about the fact that the input is .p7m. It is treated exactly the same as any other type of file. From the standpoint of encryption, the input file is just a bunch of bytes that needs to be encrypted and emitted to a PKCS7 binary DER output.

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

Chilkat.Crypt2 crypt = new Chilkat.Crypt2();

// PKCS7 encryption only requires the certificate (which contains the public key).
// Load the certificate..

// The cert.LoadFromFile method detects the file format.  You may load any type of file
// containing a certificate..
Chilkat.Cert cert = new Chilkat.Cert();
bool success = cert.LoadFromFile("qa_data/certs/otherPartyCert.pem");
if (success != true) {
    Debug.WriteLine(cert.LastErrorText);
    return;
}

// Indicate that we want Public Key Infrastructure (PKI) encryption.
crypt.CryptAlgorithm = "pki";

// The desired encryption is "-des3", so choose "3des" for the underlying PKCS7 symmetric encryption:
crypt.Pkcs7CryptAlg = "3des";

// Indicate the cert/public key to use for encryption:
success = crypt.SetEncryptCert(cert);
if (success != true) {
    Debug.WriteLine(crypt.LastErrorText);
    return;
}

// Call a crypt.Encrypt* methods to encrypt to/from memory sources (i.e. strings or bytes)
// or.. call CkEncryptFile to do file-to-file encryption.
// In this case the file to be encrypted is "signed.p7m", but it could be any type of file..
success = crypt.CkEncryptFile("somedir/signed.p7m","qa_output/encrypted.enc");
if (success != true) {
    Debug.WriteLine(crypt.LastErrorText);
    return;
}

Debug.WriteLine("Success.");