(Objective-C) Streaming Encryption by Encrypting in Chunks

Encrypt data in chunks.

Chilkat Objective-C Library Downloads MAC OS X (Cocoa) Libs iOS Libs

#import <CkoCrypt2.h>
#import <NSString.h>
#import <CkoStringBuilder.h>

// This example requires 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:128];

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

crypt.EncodingMode = @"hex";
NSString *txt1 = @"The quick brown fox jumped over the lazy dog.\r\n";
NSString *txt2 = @"-\r\n";
NSString *txt3 = @"Done.\r\n";

CkoStringBuilder *sbEncrypted = [[CkoStringBuilder alloc] init];

// Encrypt the 1st chunk:
// (don't worry about feeding the data to the encryptor in 
// exact multiples of the encryption algorithm's block size.
// Chilkat will buffer the data.)
crypt.FirstChunk = YES;
crypt.LastChunk = NO;
[sbEncrypted Append: [crypt EncryptStringENC: txt1]];

// Encrypt the 2nd chunk
crypt.FirstChunk = NO;
crypt.LastChunk = NO;
[sbEncrypted Append: [crypt EncryptStringENC: txt2]];

// Now encrypt N more chunks...
// Remember -- we're doing this in CBC mode, so each call
// to the encrypt method depends on the state from previous
// calls...
crypt.FirstChunk = NO;
crypt.LastChunk = NO;
int i;
for (i = 0; i <= 4; i++) {
    [sbEncrypted Append: [crypt EncryptStringENC: txt1]];
    [sbEncrypted Append: [crypt EncryptStringENC: txt2]];
}

// Now encrypt the last chunk:
crypt.FirstChunk = NO;
crypt.LastChunk = YES;
[sbEncrypted Append: [crypt EncryptStringENC: txt3]];

NSLog(@"%@",[sbEncrypted GetAsString]);

// Now decrypt in one call.
// (The data we're decrypting is both the first AND last chunk.)  
crypt.FirstChunk = YES;
crypt.LastChunk = YES;
NSString *decryptedText = [crypt DecryptStringENC: [sbEncrypted GetAsString]];

NSLog(@"%@",decryptedText);

// Note: You may decrypt in N chunks by setting the FirstChunk
// and LastChunk properties prior to calling the Decrypt* methods