Question

I am trying to convert an NSData object that has been encrypted with AES256 encryption to base64 NSData object. I am under the impression that I can not directly convert a NSData object that has been encrypted with AES256 encryption to a NSString, and that I must first convert it to base64.

So how would I convert a NSData object to a base64 data object? And bonus I need to convert the base64 data object to a NSString.

I found this method, but I am not sure how I convert my NSData object to base64 using the method below.

 - (NSString*)base64forData:(NSData*)theData {

const uint8_t* input = (const uint8_t*)[theData bytes];
NSInteger length = [theData length];

static char table[] = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/=";

NSMutableData* data = [NSMutableData dataWithLength:((length + 2) / 3) * 4];
uint8_t* output = (uint8_t*)data.mutableBytes;

NSInteger i;
for (i=0; i < length; i += 3) {
    NSInteger value = 0;
    NSInteger j;
    for (j = i; j < (i + 3); j++) {
        value <<= 8;

        if (j < length) {
            value |= (0xFF & input[j]);
        }
    }

    NSInteger theIndex = (i / 3) * 4;
    output[theIndex + 0] =                    table[(value >> 18) & 0x3F];
    output[theIndex + 1] =                    table[(value >> 12) & 0x3F];
    output[theIndex + 2] = (i + 1) < length ? table[(value >> 6)  & 0x3F] : '=';
    output[theIndex + 3] = (i + 2) < length ? table[(value >> 0)  & 0x3F] : '=';
}

return [[NSString alloc] initWithData:data encoding:NSASCIIStringEncoding];
}

Answer 1

The method that you provided in your post should work (cocoadev has relevant discussion).

Here is how you use this method:

NSString *b64 = [self base64forData:myNsData];