Objective-C

RSA Decrypt using Private Key on Smartcard or USB Token via Apple Keychain

See more Apple Keychain Examples

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.

Objective-C

#import <CkoBinData.h>
#import <CkoCert.h>
#import <CkoRsa.h>

BOOL success = NO;

// 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.
CkoBinData *bd = [[CkoBinData alloc] init];
// In all Chilkat methods expecting a path, you can pass either absolute or relative paths.
success = [bd LoadFile: @"rsaEncrypted/myAes.key"];
if (success == NO) {
    NSLog(@"%@",@"Failed to load the encrypted AES key.");
    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.
CkoCert *cert = [[CkoCert alloc] init];

// 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
// 
cert.SmartCardPin = @"123456";

success = [cert LoadByCommonName: @"Test 2048 bit RSA"];
if (success == NO) {
    NSLog(@"%@",cert.LastErrorText);
    return;
}

CkoRsa *rsa = [[CkoRsa alloc] init];

// Specify we wish to use the certificate's private key for decryption.
success = [rsa SetX509Cert: cert usePrivateKey: YES];
if (success == NO) {
    NSLog(@"%@",rsa.LastErrorText);
    return;
}

// RSA Decrypt
rsa.VerboseLogging = YES;
success = [rsa DecryptBd: bd usePrivateKey: YES];
if (success == NO) {
    NSLog(@"%@",rsa.LastErrorText);
    return;
}

// The contents of bd are now decrypted.
NSLog(@"%@%d",@"Num bytes after decryption: ",[bd.NumBytes intValue]);

// 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>)