(C#) Encrypt File to PKCS7 .p7m

C# example to public-key encrypt a file creating a PKCS#7 .p7m file as output. Also demonstrates how to decrypt the .p7m to recover the original file.

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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();

// Indicate the public-key encryption is to be used.
// Do this by setting the encryption algorithm equal 
// to "PKI" (an acroynm for public-key infrastructure).
crypt.CryptAlgorithm = "PKI";

// Indicate the inner symmetric encryption algorithm to be used.
// possible values are "aes", "des", "3des", and "rc2".
// For this example, we'll use 256-bit AES encryption.
crypt.Pkcs7CryptAlg = "aes";
crypt.KeyLength = 256;

// To encrypt, only a certificate w/ public key is needed.
// (The certificate w/ private key is required for decryption.)

// The LoadFromFile method can load virtually any certificate format:
// 1. DER encoded binary X.509 (.CER)
// 2. Base-64 encoded X.509 (.CER)
// 3. Cryptographic Message Syntax Standard - PKCS #7 Certificates (.P7B)
// 4. PEM format
Chilkat.Cert encryptCert = new Chilkat.Cert();
bool success = encryptCert.LoadFromFile("/Users/chilkat/testData/cer/acme.cer");
if (success != true) {
    Debug.WriteLine(encryptCert.LastErrorText);
    return;
}

// Tell the crypt object to use the certificate for encrypting:
crypt.AddEncryptCert(encryptCert);

// Encrypt a file, producing a .p7m as output.
// The input file is unchanged, the output .p7m contains the encrypted
// contents of the input file.
string inFile = "/Users/chilkat/testData/pdf/sample.pdf";
string outFile = "/Users/chilkat/testData/p7m/sample.pdf.p7m";
success = crypt.CkEncryptFile(inFile,outFile);
if (success != true) {
    Debug.WriteLine(crypt.LastErrorText);
    return;
}

// For demonstration purposes, a different instance of the object will be used
// for decryption.
Chilkat.Crypt2 decrypt = new Chilkat.Crypt2();

// To decrypt, the certificate w/ private key is required.  A PFX (also known
// as PKCS#12) is a common secure container for certs and private keys.
string pfxFilename = "/Users/chilkat/testData/pfx/acme.pfx";
string pfxPassword = "secret";

// Tell the component to look in the PFX file for certs and private keys.
success = decrypt.AddPfxSourceFile(pfxFilename,pfxPassword);
if (success != true) {
    Debug.WriteLine(decrypt.LastErrorText);
    return;
}

// Tell the decrypt object that PKI (public key encryption) is to be used
// for decryptiong.
decrypt.CryptAlgorithm = "PKI";
// There is no need to set the Pkcs7Alg or KeyLength because this information
// is contained within the .p7m

// Decrypt the .p7m
inFile = "/Users/chilkat/testData/p7m/sample.pdf.p7m";
outFile = "/Users/chilkat/testData/pdf/recovered.pdf";
success = decrypt.CkDecryptFile(inFile,outFile);
if (success == false) {
    Debug.WriteLine(decrypt.LastErrorText);
    return;
}

Debug.WriteLine("Success!");