Rsa Implementations in Objective C

RSA implementations in Objective C

I have tried RSA Encryption and Decryption for NSString. Here is the code:

Add Security.Framework to your project bundle.

ViewController.h code is as follows:

#import 
#import 

@interface ViewController : UIViewController
{
SecKeyRef publicKey;
SecKeyRef privateKey;
    NSData *publicTag;
    NSData *privateTag;
}
- (void)encryptWithPublicKey:(uint8_t *)plainBuffer cipherBuffer:(uint8_t *)cipherBuffer;
- (void)decryptWithPrivateKey:(uint8_t *)cipherBuffer plainBuffer:(uint8_t *)plainBuffer;
- (SecKeyRef)getPublicKeyRef;
- (SecKeyRef)getPrivateKeyRef;
- (void)testAsymmetricEncryptionAndDecryption;
- (void)generateKeyPair:(NSUInteger)keySize;
@end

ViewController.m file code is as follows:

#import "ViewController.h"

const size_t BUFFER_SIZE = 64;
const size_t CIPHER_BUFFER_SIZE = 1024;
const uint32_t PADDING = kSecPaddingNone;
static const UInt8 publicKeyIdentifier[] = "com.apple.sample.publickey";
static const UInt8 privateKeyIdentifier[] = "com.apple.sample.privatekey";

@implementation ViewController

-(SecKeyRef)getPublicKeyRef { 

    OSStatus sanityCheck = noErr; 
    SecKeyRef publicKeyReference = NULL;

    if (publicKeyReference == NULL) { 
        [self generateKeyPair:512];
                NSMutableDictionary *queryPublicKey = [[NSMutableDictionary alloc] init];

        // Set the public key query dictionary.
        [queryPublicKey setObject:(__bridge id)kSecClassKey forKey:(__bridge id)kSecClass];
        [queryPublicKey setObject:publicTag forKey:(__bridge id)kSecAttrApplicationTag];
        [queryPublicKey setObject:(__bridge id)kSecAttrKeyTypeRSA forKey:(__bridge id)kSecAttrKeyType];
        [queryPublicKey setObject:[NSNumber numberWithBool:YES] forKey:(__bridge id)kSecReturnRef];


        // Get the key.
        sanityCheck = SecItemCopyMatching((__bridge CFDictionaryRef)queryPublicKey, (CFTypeRef *)&publicKeyReference);


        if (sanityCheck != noErr)
        {
            publicKeyReference = NULL;
        }


//        [queryPublicKey release];

    } else { publicKeyReference = publicKey; }

    return publicKeyReference; }

- (void)didReceiveMemoryWarning
{
    [super didReceiveMemoryWarning];
    // Release any cached data, images, etc that aren't in use.
}




- (void)testAsymmetricEncryptionAndDecryption {

    uint8_t *plainBuffer;
    uint8_t *cipherBuffer;
    uint8_t *decryptedBuffer;



    const char inputString[] = "This is a test demo for RSA Implementation in Objective C";
    int len = strlen(inputString);
    // TODO: this is a hack since i know inputString length will be less than BUFFER_SIZE
    if (len > BUFFER_SIZE) len = BUFFER_SIZE-1;

    plainBuffer = (uint8_t *)calloc(BUFFER_SIZE, sizeof(uint8_t));
    cipherBuffer = (uint8_t *)calloc(CIPHER_BUFFER_SIZE, sizeof(uint8_t));
    decryptedBuffer = (uint8_t *)calloc(BUFFER_SIZE, sizeof(uint8_t));

    strncpy( (char *)plainBuffer, inputString, len);

    NSLog(@"init() plainBuffer: %s", plainBuffer);
    //NSLog(@"init(): sizeof(plainBuffer): %d", sizeof(plainBuffer));
    [self encryptWithPublicKey:(UInt8 *)plainBuffer cipherBuffer:cipherBuffer];
    NSLog(@"encrypted data: %s", cipherBuffer);
    //NSLog(@"init(): sizeof(cipherBuffer): %d", sizeof(cipherBuffer));
    [self decryptWithPrivateKey:cipherBuffer plainBuffer:decryptedBuffer];
    NSLog(@"decrypted data: %s", decryptedBuffer);
    //NSLog(@"init(): sizeof(decryptedBuffer): %d", sizeof(decryptedBuffer));
    NSLog(@"====== /second test =======================================");

    free(plainBuffer);
    free(cipherBuffer);
    free(decryptedBuffer);
}

/* Borrowed from:
 * https://developer.apple.com/library/mac/#documentation/security/conceptual/CertKeyTrustProgGuide/iPhone_Tasks/iPhone_Tasks.html
 */
- (void)encryptWithPublicKey:(uint8_t *)plainBuffer cipherBuffer:(uint8_t *)cipherBuffer
{

    NSLog(@"== encryptWithPublicKey()");

    OSStatus status = noErr;

    NSLog(@"** original plain text 0: %s", plainBuffer);

    size_t plainBufferSize = strlen((char *)plainBuffer);
    size_t cipherBufferSize = CIPHER_BUFFER_SIZE;

    NSLog(@"SecKeyGetBlockSize() public = %lu", SecKeyGetBlockSize([self getPublicKeyRef]));
    //  Error handling
    // Encrypt using the public.
    status = SecKeyEncrypt([self getPublicKeyRef],
                           PADDING,
                           plainBuffer,
                           plainBufferSize,
                           &cipherBuffer[0],
                           &cipherBufferSize
                           );
    NSLog(@"encryption result code: %ld (size: %lu)", status, cipherBufferSize);
    NSLog(@"encrypted text: %s", cipherBuffer);
}

- (void)decryptWithPrivateKey:(uint8_t *)cipherBuffer plainBuffer:(uint8_t *)plainBuffer
{
    OSStatus status = noErr;

    size_t cipherBufferSize = strlen((char *)cipherBuffer);

    NSLog(@"decryptWithPrivateKey: length of buffer: %lu", BUFFER_SIZE);
    NSLog(@"decryptWithPrivateKey: length of input: %lu", cipherBufferSize);

    // DECRYPTION
    size_t plainBufferSize = BUFFER_SIZE;

    //  Error handling
    status = SecKeyDecrypt([self getPrivateKeyRef],
                           PADDING,
                           &cipherBuffer[0],
                           cipherBufferSize,
                           &plainBuffer[0],
                           &plainBufferSize
                           );
    NSLog(@"decryption result code: %ld (size: %lu)", status, plainBufferSize);
    NSLog(@"FINAL decrypted text: %s", plainBuffer);

}



- (SecKeyRef)getPrivateKeyRef {
    OSStatus resultCode = noErr;
    SecKeyRef privateKeyReference = NULL;
//    NSData *privateTag = [NSData dataWithBytes:@"ABCD" length:strlen((const char *)@"ABCD")];
//    if(privateKey == NULL) {
        [self generateKeyPair:512];
        NSMutableDictionary * queryPrivateKey = [[NSMutableDictionary alloc] init];

        // Set the private key query dictionary.
        [queryPrivateKey setObject:(__bridge id)kSecClassKey forKey:(__bridge id)kSecClass];
        [queryPrivateKey setObject:privateTag forKey:(__bridge id)kSecAttrApplicationTag];
        [queryPrivateKey setObject:(__bridge id)kSecAttrKeyTypeRSA forKey:(__bridge id)kSecAttrKeyType];
        [queryPrivateKey setObject:[NSNumber numberWithBool:YES] forKey:(__bridge id)kSecReturnRef];

        // Get the key.
        resultCode = SecItemCopyMatching((__bridge CFDictionaryRef)queryPrivateKey, (CFTypeRef *)&privateKeyReference);
        NSLog(@"getPrivateKey: result code: %ld", resultCode);

        if(resultCode != noErr)
        {
            privateKeyReference = NULL;
        }

//        [queryPrivateKey release];
//    } else {
//        privateKeyReference = privateKey;
//    }

    return privateKeyReference;
}


#pragma mark - View lifecycle



- (void)viewDidLoad
{
    [super viewDidLoad];
    // Do any additional setup after loading the view, typically from a nib.
}

- (void)viewDidUnload
{
    [super viewDidUnload];
    // Release any retained subviews of the main view.
    // e.g. self.myOutlet = nil;
}

- (void)viewWillAppear:(BOOL)animated
{
    [super viewWillAppear:animated];
    privateTag = [[NSData alloc] initWithBytes:privateKeyIdentifier length:sizeof(privateKeyIdentifier)];
    publicTag = [[NSData alloc] initWithBytes:publicKeyIdentifier length:sizeof(publicKeyIdentifier)];
    [self testAsymmetricEncryptionAndDecryption];

}

- (void)viewDidAppear:(BOOL)animated
{
    [super viewDidAppear:animated];
}

- (void)viewWillDisappear:(BOOL)animated
{
    [super viewWillDisappear:animated];
}

- (void)viewDidDisappear:(BOOL)animated
{
    [super viewDidDisappear:animated];
}

- (BOOL)shouldAutorotateToInterfaceOrientation:(UIInterfaceOrientation)interfaceOrientation
{
    // Return YES for supported orientations
    if ([[UIDevice currentDevice] userInterfaceIdiom] == UIUserInterfaceIdiomPhone) {
        return (interfaceOrientation != UIInterfaceOrientationPortraitUpsideDown);
    } else {
        return YES;
    }
}

- (void)generateKeyPair:(NSUInteger)keySize {
    OSStatus sanityCheck = noErr;
    publicKey = NULL;
    privateKey = NULL;

//  LOGGING_FACILITY1( keySize == 512 || keySize == 1024 || keySize == 2048, @"%d is an invalid and unsupported key size.", keySize );

    // First delete current keys.
//  [self deleteAsymmetricKeys];

    // Container dictionaries.
    NSMutableDictionary * privateKeyAttr = [[NSMutableDictionary alloc] init];
    NSMutableDictionary * publicKeyAttr = [[NSMutableDictionary alloc] init];
    NSMutableDictionary * keyPairAttr = [[NSMutableDictionary alloc] init];

    // Set top level dictionary for the keypair.
    [keyPairAttr setObject:(__bridge id)kSecAttrKeyTypeRSA forKey:(__bridge id)kSecAttrKeyType];
    [keyPairAttr setObject:[NSNumber numberWithUnsignedInteger:keySize] forKey:(__bridge id)kSecAttrKeySizeInBits];

    // Set the private key dictionary.
    [privateKeyAttr setObject:[NSNumber numberWithBool:YES] forKey:(__bridge id)kSecAttrIsPermanent];
    [privateKeyAttr setObject:privateTag forKey:(__bridge id)kSecAttrApplicationTag];
    // See SecKey.h to set other flag values.

    // Set the public key dictionary.
    [publicKeyAttr setObject:[NSNumber numberWithBool:YES] forKey:(__bridge id)kSecAttrIsPermanent];
    [publicKeyAttr setObject:publicTag forKey:(__bridge id)kSecAttrApplicationTag];
    // See SecKey.h to set other flag values.

    // Set attributes to top level dictionary.
    [keyPairAttr setObject:privateKeyAttr forKey:(__bridge id)kSecPrivateKeyAttrs];
    [keyPairAttr setObject:publicKeyAttr forKey:(__bridge id)kSecPublicKeyAttrs];

    // SecKeyGeneratePair returns the SecKeyRefs just for educational purposes.
    sanityCheck = SecKeyGeneratePair((__bridge CFDictionaryRef)keyPairAttr, &publicKey, &privateKey);
//  LOGGING_FACILITY( sanityCheck == noErr && publicKey != NULL && privateKey != NULL, @"Something really bad went wrong with generating the key pair." );
    if(sanityCheck == noErr  && publicKey != NULL && privateKey != NULL)
    {
        NSLog(@"Successful");
    }
//  [privateKeyAttr release];
//  [publicKeyAttr release];
//  [keyPairAttr release];
}


@end

Here is where I originally posted my answer : Iphone - How to encrypt NSData with public key and decrypt with private key?

Let me know if you need more help.

Hope this helps.

Objective-c / Is it possible to encrypt rsa using modulus and exponent without external library?

Yes of course it is possible. To implement you'd have the following.

1. A stream of bytes you need to encrypt.
2. The RSA modulus and exponent. Suppose the modulus is n bytes long.

Now to encrypt the stream you'd do it as follows.

1. Use a chunk of bytes that is n bytes long. If not, pad (postfix) with zero.
2. Raise the chunk to the power of the exponent (e.g. using successive squares) and calculate modulus the modulus.
3. If the result is not n bytes long then zero pad again (this time prefix).

That is it, you have an encrypted stream.

Java to Objective-C RSA Implementation

As I explained in my other answer, it is very tricky to generate the same key pair using the same value of the PRNG. But that does not seem to be what you are after. It seems that you want to use your own seeded PRNG to generate the key pair.

---

In general, the default SecureRandom in Java is seeded by the operating system. The idea that you can supply your own random number generator is that you may get "better" results using for instance your own entropy pool (e.g. from a a hardware random number generator). Normally the default Java PRNG seeded by the operating system would however provide enough random.

As you are using the SecureRandom class, you supplant the operating system provided seed with your own relatively weakly seeded PRNG. currentTimeMilis certainly does not give you much entropy, and the password seems to be static. This is generally not thought to be enough for generating RSA key pairs.

If you really want to you can add some entropy to the pool instead:

// create runtime default PRNG
SecureRandom rng = new SecureRandom();
// make sure that the rng is seeded by the operating system
rng.nextInt();
// add secret to the pool
rng.setSeed("SOME_SECRET".getBytes(StandardCharsets.UTF_8));
// add time information to the pool
rng.setSeed(System.currentTimeMillis());
// use for e.g. RSA key pair generation

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There seems to be no method of injecting your own random number generator in Apple's OS X libraries. As indicated, usually the OS provided random number generator is good enough. If you really want to you can write your additional seeds to /dev/random though.

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