3DES encryption using CFB8 and no padding in iOS? - ios

Question

I am developing an application which will send encrypted data to a server. The server uses 3des with CFB8 and no padding. I have read most of the related questions in stackoverflow but still unable to get it work. Been working on this for few days but still unable to get it to match with the server encryption. here is what i have tried-
+ (NSString*) doCipher:(NSString*)plainText operation:(CCOperation)encryptOrDecrypt {
const void *vplainText;
NSData* plainTextData;
size_t plainTextBufferSize;
if (encryptOrDecrypt == kCCDecrypt)
{
NSData *EncryptData =[NSData dataWithBase64EncodedString:plainText];
plainTextBufferSize = [EncryptData length];
vplainText = [EncryptData bytes];
}
else
{
plainTextData = [plainText dataUsingEncoding:NSUTF8StringEncoding];
plainTextBufferSize = [plainTextData length];
}
CCCryptorStatus ccStatus;
uint8_t *bufferPtr = NULL;
size_t bufferPtrSize = 0;
size_t movedBytes = 0;
uint8_t iv[kCCBlockSize3DES];
bufferPtrSize = (plainTextBufferSize + kCCBlockSize3DES) & ~(kCCBlockSize3DES - 1);
bufferPtr = malloc( bufferPtrSize * sizeof(uint8_t));
memset((void *)bufferPtr, 0x0, bufferPtrSize);
memset((void *) iv, 0x0, (size_t) sizeof(iv));
const void *vkey = kPrivateKey;
unsigned char IV[8]={0,0,0,0,0,0,0,0};
ccStatus = CCCrypt(encryptOrDecrypt,
kCCAlgorithm3DES,
0,
[keyData bytes],
[key length],
IV,
[plainTextData bytes],
plainTextBufferSize,
(void *)bufferPtr,
bufferPtrSize,
&movedBytes);
if (ccStatus == kCCSuccess) NSLog(#"SUCCESS");
else if (ccStatus == kCCParamError) return #"PARAM ERROR";
else if (ccStatus == kCCBufferTooSmall) return #"BUFFER TOO SMALL";
else if (ccStatus == kCCMemoryFailure) return #"MEMORY FAILURE";
else if (ccStatus == kCCAlignmentError) return #"ALIGNMENT";
else if (ccStatus == kCCDecodeError) return #"DECODE ERROR";
else if (ccStatus == kCCUnimplemented) return #"UNIMPLEMENTED";
NSString *result;
if (encryptOrDecrypt == kCCDecrypt)
{
result = [[NSString alloc] initWithData: [NSData dataWithBytes:(const void *)bufferPtr length:(NSUInteger)movedBytes] encoding:NSASCIIStringEncoding];
}
else
{
NSData *myData = [NSData dataWithBytes:(const void *)bufferPtr length:(NSUInteger)movedBytes];
result = [myData base64EncodedString];
}
return result;
}
It seems CCOptions currently supports kCCOptionPKCS7Padding and kCCOptionECBMode.How to achieve 3des with CFB8 and no padding.Any suggestion would be appreciated.

Answer 1

EDIT: Sorry; I overlooked a key point previously. You're never asking for CFB8 mode. The default is CBC mode.
You can't use CCCrypt() for this. You have to use CCCryptorCreateWithMode() so you can pass the mode. Then call CCCryptorUpdate() with the data and CCCryptorFinal() to finish.
If you don't want padding, why are you requesting padding? Remove kCCOptionPKCS7Padding. If you don't want any options (which you appear not to), just pass 0.
CFB-8 takes an initialization vector. You've set it to all 0's. Is this what the server is using? (This is a very poor IV; the IV for CFB should be random, not fixed.)
These lines are dangerous:
plainTextBufferSize = [plainText length];
vplainText = (const void *) [plainText UTF8String];
This will truncate any multi-byte strings. The better solution to this is to create an NSData:
plainTextData = [self.plainText dataUsingEncoding:NSUTF8StringEncoding];
You can then use bytes and length on plainTextData.