AES Encryption and Decryption in iOS

Step 1: First you have to include these two files into your project.

#include <CommonCrypto/CommonCryptor.h>

@interface NSData(AES)
- (NSData*)AES128Decrypt;
- (NSData*)AES128Encrypt;
@end


#import "NSData+AES.h"

NSString *iv = @"fedcba9876543210";
NSString *key = @"0123456789abcdef";

@implementation NSData (AES)

-(NSData*)AES128Encrypt
{
    char ivPtr[kCCKeySizeAES128 + 1];
    bzero(ivPtr, sizeof(ivPtr));
    
    // fetch iv data
    [iv getCString:ivPtr maxLength:sizeof(ivPtr) encoding:NSUTF8StringEncoding];
    
    
    // 'key' should be 32 bytes for AES256, will be null-padded otherwise
    char keyPtr[kCCKeySizeAES128 + 1]; // room for terminator (unused)
    bzero(keyPtr, sizeof(keyPtr)); // fill with zeroes (for padding)
    
    // fetch key data
    [key getCString:keyPtr maxLength:sizeof(keyPtr) encoding:NSUTF8StringEncoding];
    
    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 numBytesEncrypted    = 0;
    CCCryptorStatus cryptStatus = CCCrypt(kCCEncrypt, kCCAlgorithmAES128, 0,
                                          keyPtr, kCCKeySizeAES128,
                                           ivPtr/* initialization vector (optional) */,
                                          [self bytes], dataLength, /* input */
                                          buffer, bufferSize, /* output */
                                          &numBytesEncrypted);
    

    if (cryptStatus == kCCSuccess)
    {
        //the returned NSData takes ownership of the buffer and will free it on deallocation
        return [NSData dataWithBytesNoCopy:buffer length:numBytesEncrypted];
    }
    
   free(buffer); //free the buffer;
    return nil;
}

- (NSData*)AES128Decrypt
{
    char ivPtr[kCCKeySizeAES128 + 1];
    bzero(ivPtr, sizeof(ivPtr)); 
    
    // fetch iv data
    [iv getCString:ivPtr maxLength:sizeof(ivPtr) encoding:NSUTF8StringEncoding];
    
    

    // 'key' should be 32 bytes for AES256, will be null-padded otherwise
    char keyPtr[kCCKeySizeAES128 + 1]; // room for terminator (unused)
    bzero(keyPtr, sizeof(keyPtr)); // fill with zeroes (for padding)
    
    // fetch key data
    [key getCString:keyPtr maxLength:sizeof(keyPtr) encoding:NSUTF8StringEncoding];
    
    
    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 cryptStatus = CCCrypt(kCCDecrypt, kCCAlgorithmAES128, 0,
                                          keyPtr, kCCKeySizeAES128,
                                          ivPtr /* initialization vector (optional) */,
                                          [self bytes], dataLength, /* input */
                                          buffer, bufferSize, /* output */
                                          &numBytesDecrypted);
    
    if (cryptStatus == kCCSuccess)
    {
        //the returned NSData takes ownership of the buffer and will free it on deallocation
        return [NSData dataWithBytes:buffer length:numBytesDecrypted] ;
    }
    
    free(buffer); //free the buffer;
    return nil;
}

@end

Step 2: You have to import "Security.framework" into your project.

Step 3: Now, you need to put below code into the class where you want to Encrypt or Decrypt a string and also need to import "NSData+AES.h" file.

- (void)testActuallyEncrypting:(NSString *)hexString
{
    NSLog(@"Encrypted HexString : %@",hexString);

    NSData *data = [self dataFromHexString:hexString];
    NSData *encryptedData =  [NSData dataWithBytes:[data bytes] length:[data length]];
    NSData *decryptedData = [encryptedData AES128Decrypt];
    NSString *decryptedString = [NSString stringWithUTF8String:[decryptedData bytes]];
    NSLog(@"Decrypted String : %@",decryptedString);

    decryptedString = [self addPaddingToString:decryptedString];
    decryptedData = [NSData dataWithBytes:[decryptedString UTF8String] length:[[decryptedString dataUsingEncoding:NSUTF8StringEncoding] length]];
    encryptedData = [decryptedData AES128Encrypt];
    if (encryptedData!=nil)
    {
        NSString *encryptedHexString = [self hexStringFromData:encryptedData];
        NSLog(@"Encrypted HexString : %@",encryptedHexString);

//        NSData *data1 = [self dataFromHexString:encryptedHexString];
//        NSData *encryptedData1 =  [NSData dataWithBytes:[data1 bytes] length:[data1 length]];
//        NSData *decryptedData1 = [encryptedData1 AES128Decrypt];
//        NSString *decryptedString1 = [NSString stringWithUTF8String:[decryptedData1 bytes]];
//        NSLog(@"Decrypted String Testing 123: %@",[decryptedString1 stringByTrimmingCharactersInSet:[NSCharacterSet characterSetWithCharactersInString:@" "]]);
    }
}
Step 4 : For step3 , you have to add these three methods into your code.

// For Converting incoming HexString into NSData
- (NSData *)dataFromHexString:(NSString *)string 
{   
    NSMutableData *stringData = [[[NSMutableData alloc] init] autorelease];
    unsigned char whole_byte;
    char byte_chars[3] = {'\0','\0','\0'};
    int i;
    for (i=0; i < [string length] / 2; i++) {
        byte_chars[0] = [string characterAtIndex:i*2];
        byte_chars[1] = [string characterAtIndex:i*2+1];
        whole_byte = strtol(byte_chars, NULL, 16);
        [stringData appendBytes:&whole_byte length:1]; 
    }
    return stringData;
}


// For converting Encrypted Data into NSString after the encryption 
- (NSString*)hexStringFromData:(NSData *)data 
{
    unichar* hexChars = (unichar*)malloc(sizeof(unichar) * (data.length*2));
    unsigned char* bytes = (unsigned char*)data.bytes;
    for (NSUInteger i = 0; i < data.length; i++) {
        unichar c = bytes[i] / 16;
        if (c < 10) c += '0';
        else c += 'a' - 10;
        hexChars[i*2] = c;
        c = bytes[i] % 16;
        if (c < 10) c += '0';
        else c += 'a' - 10;
        hexChars[i*2+1] = c;
    }
    NSString* retVal = [[NSString alloc] initWithCharactersNoCopy:hexChars
                                                           length:data.length*2 
                                                     freeWhenDone:YES];
    return [retVal autorelease];
}
// For padding into a string for required string length
-(NSString *)addPaddingToString:(NSString *)string
{
    NSInteger size = 16;
    NSInteger x = [string length]%size;
    NSInteger padLength = size - x;
    for (int i=0; i<padLength; i++)
    {
        string = [string stringByAppendingString:@" "];
    }
    return string;
}