(MFC) Encrypt a file to a PKCS7 encrypted message using multiple certificates from different users

Demonstrates how to encrypt a file to a PKCS7 encrypted message using multiple certificates from different users. Any one of the users can decrypt using his/her own certificate + private key.

Note: When doing public key encryption, it is the public key that is used to encrypt. The private key is required for decryption.

Chilkat C/C++ Library Downloads MS Visual C/C++ Libs

See Also: Using MFC CString in Chilkat

#include <CkCrypt2.h>
#include <CkCert.h>
#include <CkBinData.h>

void ChilkatSample(void)
    {
    CkString strOut;

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

    CkCrypt2 crypt;

    //  Tell the crypt object to use 3 certificates.
    //  Do this by calling AddEncryptCert for each certificate.

    //  Load a digital certificate.
    //  We don't need the private key for encryption.
    //  Only the public key is needed (which is included in a certificate).
    CkCert cert1;
    bool success = cert1.LoadFromFile("qa_data/user1/cert_user1.pem");
    //  Assume success for the example, but make sure your application checks for success/failure...
    crypt.AddEncryptCert(cert1);

    CkCert cert2;
    success = cert2.LoadFromFile("qa_data/user2/cert_user2.pem");
    crypt.AddEncryptCert(cert2);

    CkCert cert3;
    success = cert3.LoadFromFile("qa_data/user3/cert_user3.pem");
    crypt.AddEncryptCert(cert3);

    //  Indicate that we want PKI encryption (i.e. public-key infrastructure)
    //  to produce a CMS message (Cryptographic Message Syntax/PKCS7),
    //  that is be created with RSAES-OAEP padding, SHA256, and AES-128 for the
    //  bulk encryption.
    crypt.put_CryptAlgorithm("pki");
    crypt.put_Pkcs7CryptAlg("aes");
    crypt.put_KeyLength(128);
    crypt.put_OaepHash("sha256");
    crypt.put_OaepPadding(true);

    //  Load the file to be encrypted...
    CkBinData fileData;
    success = fileData.LoadFile("qa_data/jpg/penguins.jpg");
    //  Your app should check for success/failure..

    //  Encrypt the data.  The contents of the fileData object are replaced with the PKCS7 encrypted message.
    success = crypt.EncryptBd(fileData);
    if (success != true) {
        strOut.append(crypt.lastErrorText());
        strOut.append("\r\n");
        SetDlgItemText(IDC_EDIT1,strOut.getUnicode());
        return;
    }

    //  Save the PKCS7 encrypted message to a file..
    success = fileData.WriteFile("qa_output/pkcs7_encrypted.p7");

    //  Now indicate that the PKCS7 output is to be returned in the base64 encoding.
    crypt.put_EncodingMode("base64");

    strOut.append("OK.");
    strOut.append("\r\n");


    SetDlgItemText(IDC_EDIT1,strOut.getUnicode());

    }