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.

Download: Chilkat .NET Assemblies

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

//  Any string argument automatically begins the 30-day trial.
bool success;
success = crypt.UnlockComponent("30-day trial");
if (success != true) {
    textBox1.Text += crypt.LastErrorText + "\r\n";
    return;
}

//  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();
success = encryptCert.LoadFromFile("/Users/chilkat/testData/cer/acme.cer");
if (success != true) {
    textBox1.Text += encryptCert.LastErrorText + "\r\n";
    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;
inFile = "/Users/chilkat/testData/pdf/sample.pdf";
string outFile;
outFile = "/Users/chilkat/testData/p7m/sample.pdf.p7m";
success = crypt.CkEncryptFile(inFile,outFile);
if (success != true) {
    textBox1.Text += crypt.LastErrorText + "\r\n";
    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;
pfxFilename = "/Users/chilkat/testData/pfx/acme.pfx";
string pfxPassword;
pfxPassword = "secret";

//  Tell the component to look in the PFX file for certs and private keys.
success = decrypt.AddPfxSourceFile(pfxFilename,pfxPassword);
if (success != true) {
    textBox1.Text += decrypt.LastErrorText + "\r\n";
    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) {
    textBox1.Text += decrypt.LastErrorText + "\r\n";
    return;
}

MessageBox.Show("Success!");