gistfile1.m

#define KEY_LENGTH 2048

static const UInt8 publicKeyIdentifier[] = "com.apple.sample.publickey\0";
static const UInt8 privateKeyIdentifier[] = "com.apple.sample.privatekey\0";

NSData * publicTag;
NSData * privateTag;

+ (void)generateKeyPairPlease {
    OSStatus status = noErr;
    NSMutableDictionary *privateKeyAttr = [[NSMutableDictionary alloc] init];
    NSMutableDictionary *publicKeyAttr = [[NSMutableDictionary alloc] init];
    NSMutableDictionary *keyPairAttr = [[NSMutableDictionary alloc] init];
    // 2
    
    publicTag = [NSData dataWithBytes:publicKeyIdentifier
                               length:strlen((const char *)publicKeyIdentifier)];
    privateTag = [NSData dataWithBytes:privateKeyIdentifier
                                length:strlen((const char *)privateKeyIdentifier)];
    // 3
    
    SecKeyRef publicKey = NULL;
    SecKeyRef privateKey = NULL;                                // 4
    
    [keyPairAttr setObject:(__bridge id)kSecAttrKeyTypeRSA
                    forKey:(__bridge id)kSecAttrKeyType]; // 5
    [keyPairAttr setObject:[NSNumber numberWithInt:KEY_LENGTH]
                    forKey:(__bridge id)kSecAttrKeySizeInBits]; // 6
    
    [privateKeyAttr setObject:[NSNumber numberWithBool:YES]
                       forKey:(__bridge id)kSecAttrIsPermanent]; // 7
    [privateKeyAttr setObject:privateTag
                       forKey:(__bridge id)kSecAttrApplicationTag]; // 8
    
    [publicKeyAttr setObject:[NSNumber numberWithBool:YES]
                      forKey:(__bridge id)kSecAttrIsPermanent]; // 9
    [publicKeyAttr setObject:publicTag
                      forKey:(__bridge id)kSecAttrApplicationTag]; // 10
    
    [keyPairAttr setObject:privateKeyAttr
                    forKey:(__bridge id)kSecPrivateKeyAttrs]; // 11
    [keyPairAttr setObject:publicKeyAttr
                    forKey:(__bridge id)kSecPublicKeyAttrs]; // 12
    
    status = SecKeyGeneratePair((__bridge CFDictionaryRef)keyPairAttr,
                                &publicKey, &privateKey); // 13
    //    error handling...
    
    if(publicKey) CFRelease(publicKey);
    if(privateKey) CFRelease(privateKey);                       // 14
}

+ (NSData *)getPublicKeyBits {
    OSStatus sanityCheck = noErr;
    NSData * publicKeyBits = nil;
    
    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)kSecReturnData];
    
    CFDictionaryRef cfquery = (__bridge_retained CFDictionaryRef)queryPublicKey;
    CFTypeRef cfresult = (__bridge CFTypeRef)publicKeyBits;
    
    // Get the key bits.
    sanityCheck = SecItemCopyMatching(cfquery, (CFTypeRef *)&cfresult);
    CFRelease(cfquery);
    publicKeyBits = (__bridge NSData *)cfresult;
    
    if (sanityCheck != noErr) {
        publicKeyBits = nil;
    }
    
    
    return publicKeyBits;
}

+ (NSString *)getPublicKeyBase64 {
    return [[RSAKeys getPublicKeyBits] base64EncodedStringWithOptions:NSDataBase64Encoding64CharacterLineLength];
}