How to encrypt with AES 256 CBC in Objective C - objective-c

Question

I am building an iPhone app which gets a encrypt string and sent it to backend.
In PHP I am encrypting the string like this:
$encrypt_method = "AES-256-CBC";
$secret_key = 'This is my secret key';
$secret_iv = 'This is my secret iv';
// hash
$key = hash('sha256', $secret_key);
// iv - encrypt method AES-256-CBC expects 16 bytes - else you will get a warning
$iv = substr(hash('sha256', $secret_iv), 0, 16);
if( $action == 'encrypt' ) {
$output = openssl_encrypt($string, $encrypt_method, $key, 0, $iv);
$output = base64_encode($output);
}
How I do the same like that but in Objective C

Answer 1

#import <CommonCrypto/CommonCryptor.h>
#define key #"YOUR_KEY"
#define iv #"YOUR_IV"
- (NSData *) cryptOperation:(CCOperation)operation
{
// 'key' should be 32 bytes for AES256, will be null-padded otherwise
char keys[kCCKeySizeAES256 + 1];
[key getCString:keys maxLength:sizeof(keys) encoding:NSUTF8StringEncoding];
// Perform PKCS7Padding on the key.
unsigned long bytes_to_pad = sizeof(keys) - [key length];
if (bytes_to_pad > 0)
{
char byte = bytes_to_pad;
for (unsigned long i = sizeof(keys) - bytes_to_pad; i < sizeof(keys); i++)
keys[i] = byte;
}
NSUInteger dataLength = [self length];
//See the doc: For block ciphers, the output size will always be less than or
//equal to the input size plus the size of one block.
//That's why we need to add the size of one block here
size_t bufferSize = dataLength + kCCBlockSizeAES128;
void *buffer = malloc(bufferSize);
size_t numBytesDecrypted = 0;
CCCryptorStatus status = CCCrypt(operation, kCCAlgorithmAES128,
kCCOptionPKCS7Padding,
keys, kCCKeySizeAES256,
[iv UTF8String],
[self bytes], dataLength, /* input */
buffer, bufferSize, /* output */
&numBytesDecrypted);
if (status == kCCSuccess)
{
//the returned NSData takes ownership of buffer and will free it on dealloc
return [NSData dataWithBytesNoCopy:buffer length:numBytesDecrypted];
}
free(buffer); //free the buffer;
return nil;
}
- (NSData *)AES256Encrypt
{
return [self cryptOperation:kCCEncrypt];
}
- (NSData *)AES256Decrypt
{
return [self cryptOperation:kCCDecrypt];
}
you can use this method by following way..
NSString *receivedDataDecryptString = [self decrypt:#"YOUR_STRING"];
NSString *receivedDataEncryptString = [self encrypt:#"YOUR_STRING"];
-(NSString *)encrypt:(NSString *)string
{
NSData *data = [string dataUsingEncoding:NSUTF8StringEncoding];
NSData *dataEncrypted = [data AES256Encrypt];
NSString *strRecordEncrypted = [dataEncrypted base64EncodedStringWithOptions:0];
return strRecordEncrypted;
}
-(NSString *)decrypt:(NSString *)string
{
if([string containsString:#"\n"] || [string containsString:#"\t"])
{
string = [[string componentsSeparatedByCharactersInSet:[NSCharacterSet newlineCharacterSet]] componentsJoinedByString:#""];
string = [string stringByReplacingOccurrencesOfString:#"\t" withString:#""];
}
NSData *keyData = [[NSData alloc] initWithBase64EncodedString:string options:0];
NSData *dataDecrypted = [keyData AES256Decrypt];
NSString *receivedDataDecryptString = [[NSString alloc]initWithData:dataDecrypted encoding:NSUTF8StringEncoding];
return receivedDataDecryptString;
}

Answer 2

Thanks Nirav Kotecha for your answer.
I ended up using CrytoSwift and Add Extension class NSString and String to call it.