(Unicode C) RSA Decrypt using Private Key on Smartcard or USB Token via Apple Keychain

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RSA decryption using a certificate's private key located on a hardware token or smartcard via the Apple Keychain.

Note: This example requires Chilkat v10.1.2 or greater.

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#include <C_CkBinDataW.h>
#include <C_CkCertW.h>
#include <C_CkRsaW.h>

void ChilkatSample(void)
    {
    HCkBinDataW bd;
    BOOL success;
    HCkCertW cert;
    HCkRsaW rsa;

    // Beforehand, we generated a 256-bit AES key, RSA encrypted, and saved to a file as in this example:
    // Generate a Random 256-bit AES Key and RSA Encrypt

    // The RSA public key used to encrypt in the above example was obtained from the Apple Keychain
    // like this:
    // Export a Public Key from USB Token or Smartcard using the Apple Keychain

    // This example will load the encrypted data and will RSA decrypt using the 
    // private key of a certificate on a USB token (or smart card) via the Keychain.
    // You can list the Keychain certificates on hardware tokens using the following example:
    // Apple Keychain - List Certs on Smartcards and USB Tokens

    // Get the RSA encrypted data to be decrypted.
    bd = CkBinDataW_Create();
    // In all Chilkat methods expecting a path, you can pass either absolute or relative paths.
    success = CkBinDataW_LoadFile(bd,L"rsaEncrypted/myAes.key");
    if (success == FALSE) {
        wprintf(L"Failed to load the encrypted AES key.\n");
        CkBinDataW_Dispose(bd);
        return;
    }

    // Load the certificate having the private key from the Apple Keychain
    // On MacOS and iOS, the LoadByCommonName function will search the Apple Keychain for the matching certificate.
    cert = CkCertW_Create();

    // To potentially prevent the PIN dialog from being displayed,
    // we'll need to provide the USB token (or smart card) PIN
    // Note: It might not be possible to prevent the PIN dialog from being displayed
    // 
    CkCertW_putSmartCardPin(cert,L"123456");

    success = CkCertW_LoadByCommonName(cert,L"Test 2048 bit RSA");
    if (success == FALSE) {
        wprintf(L"%s\n",CkCertW_lastErrorText(cert));
        CkBinDataW_Dispose(bd);
        CkCertW_Dispose(cert);
        return;
    }

    rsa = CkRsaW_Create();

    // Specify we wish to use the certificate's private key for decryption.
    success = CkRsaW_SetX509Cert(rsa,cert,TRUE);
    if (success == FALSE) {
        wprintf(L"%s\n",CkRsaW_lastErrorText(rsa));
        CkBinDataW_Dispose(bd);
        CkCertW_Dispose(cert);
        CkRsaW_Dispose(rsa);
        return;
    }

    // RSA Decrypt
    CkRsaW_putVerboseLogging(rsa,TRUE);
    success = CkRsaW_DecryptBd(rsa,bd,TRUE);
    if (success == FALSE) {
        wprintf(L"%s\n",CkRsaW_lastErrorText(rsa));
        CkBinDataW_Dispose(bd);
        CkCertW_Dispose(cert);
        CkRsaW_Dispose(rsa);
        return;
    }

    // The contents of bd are now decrypted.
    wprintf(L"Num bytes after decryption: %d\n",CkBinDataW_getNumBytes(bd));

    // Some additional notes:
    // 
    // If using a Yubikey token, the certificate must be installed in the Key Management slot.
    // The Digital Signature slot is for RSA keys to be used for signing, 
    // and the Key Management slot is for RSA keys to be used for decrypting.
    // 

    // If you try to use the RSA key from the Digital Signature slot, you'll get an error such as this:

    // The operation couldn't be completed. 
    // (OSStatus error -50 - algid:encrypt:RSA:PKCS1: algorithm not supported by the key 
    // <SecKeyRef:('com.apple.pivtoken:AF7172EB60DDCBF1D28459AE24398E11') 0x600001ecca90>)


    CkBinDataW_Dispose(bd);
    CkCertW_Dispose(cert);
    CkRsaW_Dispose(rsa);

    }