Objective-C

Encrypt File in Chunks using AES CBC

See more Encryption Examples

Demonstrates how to use the FirstChunk/LastChunk properties to encrypt a file chunk-by-chunk. Objective-C

#import <CkoCrypt2.h>
#import <NSString.h>
#import <CkoFileAccess.h>
#import <CkoBinData.h>

BOOL success = NO;

//  This example assumes the Chilkat API to have been previously unlocked.
//  See Global Unlock Sample for sample code.

CkoCrypt2 *crypt = [[CkoCrypt2 alloc] init];

crypt.CryptAlgorithm = @"aes";
crypt.CipherMode = @"cbc";
crypt.KeyLength = [NSNumber numberWithInt:256];

[crypt SetEncodedKey: @"000102030405060708090A0B0C0D0E0F000102030405060708090A0B0C0D0E0F" encoding: @"hex"];
[crypt SetEncodedIV: @"000102030405060708090A0B0C0D0E0F" encoding: @"hex"];

NSString *fileToEncrypt = @"qa_data/hamlet.xml";
CkoFileAccess *facIn = [[CkoFileAccess alloc] init];
success = [facIn OpenForRead: fileToEncrypt];
if (success != YES) {
    NSLog(@"%@",@"Failed to open file that is to be encrytped.");
    return;
}

NSString *outputEncryptedFile = @"c:/temp/qa_output/hamlet.enc";
CkoFileAccess *facOutEnc = [[CkoFileAccess alloc] init];
success = [facOutEnc OpenForWrite: outputEncryptedFile];
if (success != YES) {
    NSLog(@"%@",@"Failed to encrypted output file.");
    return;
}

//  Let's encrypt in 10000 byte chunks.
int chunkSize = 10000;
int numChunks = [[facIn GetNumBlocks: [NSNumber numberWithInt: chunkSize]] intValue];

crypt.FirstChunk = YES;
crypt.LastChunk = NO;

CkoBinData *bd = [[CkoBinData alloc] init];

int i = 0;
while (i < numChunks) {
    i = i + 1;
    if (i == numChunks) {
        crypt.LastChunk = YES;
    }

    //  Read the next chunk from the file.
    //  The last chunk will be whatever amount remains in the file..
    [bd Clear];
    [facIn FileReadBd: [NSNumber numberWithInt: chunkSize] binData: bd];

    //  Encrypt.
    [crypt EncryptBd: bd];

    //  Write the encrypted chunk to the output file.
    [facOutEnc FileWriteBd: bd offset: [NSNumber numberWithInt: 0] numBytes: [NSNumber numberWithInt: 0]];

    crypt.FirstChunk = NO;
}

//  Make sure both FirstChunk and LastChunk are restored to true after
//  encrypting or decrypting in chunks.  Otherwise subsequent encryptions/decryptions
//  will produce unexpected results.
crypt.FirstChunk = YES;
crypt.LastChunk = YES;

[facIn FileClose];
[facOutEnc FileClose];

//  Decrypt the encrypted output file in a single call using CBC mode:
NSString *decryptedFile = @"qa_output/hamlet_dec.xml";
success = [crypt CkDecryptFile: outputEncryptedFile destFile: decryptedFile];
//  Assume success for the example..

//  Compare the contents of the decrypted file with the original file:
BOOL bSame = [facIn FileContentsEqual: fileToEncrypt path2: decryptedFile];
NSLog(@"%@%d",@"bSame = ",bSame);