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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.

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const std = @import("std");
const chilkat = @import("chilkat");

pub fn main(init: std.process.Init) !void {
    const alloc = init.arena.allocator();

    // 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.
    const bd = try chilkat.BinData.init();
    defer bd.deinit();
    // In all Chilkat methods expecting a path, you can pass either absolute or relative paths.
    bd.loadFile("rsaEncrypted/myAes.key") catch {
        std.debug.print("Failed to load the encrypted AES key.\n", .{});
        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.
    const cert = try chilkat.Cert.init();
    defer cert.deinit();

    // 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.setSmartCardPin("123456");

    cert.loadByCommonName("Test 2048 bit RSA") catch {
        std.debug.print("{s}\n", .{try cert.getLastErrorText(alloc)});
        return;
    };

    const rsa = try chilkat.Rsa.init();
    defer rsa.deinit();

    // Specify we wish to use the certificate's private key for decryption.
    rsa.setX509Cert(cert, true) catch {
        std.debug.print("{s}\n", .{try rsa.getLastErrorText(alloc)});
        return;
    };

    // RSA Decrypt
    rsa.setVerboseLogging(true);
    rsa.decryptBd(bd, true) catch {
        std.debug.print("{s}\n", .{try rsa.getLastErrorText(alloc)});
        return;
    };

    // The contents of bd are now decrypted.
    std.debug.print("Num bytes after decryption: {d}\n", .{bd.getNumBytes()});

    // 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>)
}