My Objective-C app needs to do string encryption (specifically nsstring).
I've found that AES is the most secure encryption methodology available for consumer use. I also have an understanding of how to convert strings to NSData and back... (just a beginner). Unfortunately many webpages and Q&As about encryption with AES are unclear. None of them state how to use the code given.
This may be less of an "encryption" question, and more of a "how do I use these methods" question, so please bear with me.
I've found these example methods to encrypt and decrypt an NSString:
#import "<CommonCrypto/CommonCryptor.h>"
@implementation NSMutableData(AES)
For encryption:
- (NSMutableData *)encryptAES:(NSString *)key {
char keyPtr[kCCKeySizeAES256+1];
bzero(keyPtr, sizeof(keyPtr));
[key getCString: keyPtr maxLength: sizeof(keyPtr) encoding: NSUTF16StringEncoding];
size_t numBytesEncrypted = 0;
NSUInteger dataLength = [self length];
size_t bufferSize = dataLength + kCCBlockSizeAES128;
void *buffer = malloc(bufferSize);
NSMutableData *output = [[NSData alloc] init];
CCCryptorStatus result = CCCrypt(kCCEncrypt, kCCAlgorithmAES128, kCCOptionPKCS7Padding, keyPtr, kCCKeySizeAES256, NULL, [self mutableBytes], [self length], buffer, bufferSize, &numBytesEncrypted);
output = [NSMutableData dataWithBytesNoCopy:buffer length:numBytesEncrypted];
if (result == kCCSuccess) {
return output;
}
return NULL;
}
For decryption:
- (NSMutableData *)decryptAES:(NSString *)key andForData:(NSMutableData *)objEncryptedData {
char keyPtr[kCCKeySizeAES256+1];
bzero( keyPtr, sizeof(keyPtr) );
[key getCString:keyPtr maxLength:sizeof(keyPtr) encoding:NSUTF16StringEncoding];
size_t numBytesEncrypted = 0;
NSUInteger dataLength = [self length];
size_t bufferSize = dataLength + kCCBlockSizeAES128;
void *buffer_decrypt = malloc(bufferSize);
NSMutableData *output_decrypt = [[NSData alloc] init];
CCCryptorStatus result = CCCrypt(kCCDecrypt , kCCAlgorithmAES128, kCCOptionPKCS7Padding, keyPtr, kCCKeySizeAES256, NULL, [self mutableBytes], [self length], buffer_decrypt, bufferSize, &numBytesEncrypted);
output_decrypt = [NSMutableData dataWithBytesNoCopy:buffer_decrypt length:numBytesEncrypted];
if (result == kCCSuccess) {
return output_decrypt;
}
return NULL;
}
This is a method I wrote that I would like to use with the above methods:
- (void)encrypt {
// Convert NSString to NSData so that it can be used to encrypt the Input
NSString *input = [inputBox text];
NSData *inputData = [input dataUsingEncoding: NSUTF8StringEncoding];
// What to do here...?
}
How do I use the encryptAES and decryptAES methods? Where do they go in my implementation file?