(Objective-C) RSA SHA256 Signature using Private Key from Java Keystore

Signs plaintext using RSA SHA256 using a key from a Java keystore.

Duplicatest this code:

KeyStore keystore; // key repository for keys containing signature certificate
String alias; // alias for the certificate in the key repository
String password; // password for the certificate's private key
String plaintext; // text being signed


Signature signature = Signature.getInstance("SHA256withRSA");
signature.initSign((PrivateKey) keystore.getKey(alias, password.toCharArray()));
signature.update(plaintext.getBytes("UTF-8"));
byte[] rsa_text= signature.sign();

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#import <CkoJavaKeyStore.h>
#import <NSString.h>
#import <CkoPrivateKey.h>
#import <CkoRsa.h>

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

CkoJavaKeyStore *jks = [[CkoJavaKeyStore alloc] init];

NSString *jksPassword = @"secret";

// Load the Java keystore from a file.  The JKS file password is used
// to verify the keyed digest that is found at the very end of the keystore.
// It verifies that the keystore has not been modified.
BOOL success = [jks LoadFile: jksPassword path: @"qa_data/jks/sample_secret.jks"];
if (success != YES) {
    NSLog(@"%@",jks.LastErrorText);
    return;
}

// Get the private key from the JKS.
// The private key password may be different than the file password.
NSString *privKeyPassword = @"secret";
BOOL caseSensitive = NO;
CkoPrivateKey *privKey = [jks FindPrivateKey: privKeyPassword alias: @"some.alias" caseSensitive: caseSensitive];
if (jks.LastMethodSuccess != YES) {
    NSLog(@"%@",jks.LastErrorText);
    return;
}

// Establish the RSA object and tell it to use the private key..
CkoRsa *rsa = [[CkoRsa alloc] init];

success = [rsa ImportPrivateKeyObj: privKey];

if (success != YES) {
    NSLog(@"%@",rsa.LastErrorText);
    return;
}

// Indicate we'll be signing the utf-8 byte representation of the string..
rsa.Charset = @"utf-8";

// Sign some plaintext using RSA-SHA256
NSData binarySignature;
NSString *plaintext = @"this is the text to be signed";
binarySignature = [rsa SignString: plaintext hashAlg: @"SHA256"];
if (rsa.LastMethodSuccess != YES) {
    NSLog(@"%@",rsa.LastErrorText);
    return;
}

// Alternatively, if the signature is desired in some encoded string form,
// such as base64, base64-url, hex, etc.
rsa.EncodingMode = @"base64-url";
NSString *signatureStr = [rsa SignStringENC: plaintext hashAlg: @"SHA256"];
NSLog(@"%@%@",@"base64-url RSA signature: ",signatureStr);