Question

I am using rc4 algorithm to encrypt and decrypt a video. I am taking 64 bytes and encrypting. as the same way I am doing the decryption also but my video is not playing.Anyone have idea about this???

    - (void)encryptOnFly:(UInt8*)buffer bytesRead:(NSInteger)bytesRead
{
    for(long long i=0;i<bytesRead;i++)
    {

        [self push:buffer[i]];
        if([self isFull])
        {
            unsigned char *buf11=[self retrieveArray];
            unsigned char buf1[64];
            for(int j=0;j<64;j++)
            {
                buf1[j]=*buf11++;

            }

            NSData *data = [NSData dataWithBytes:buf1 length:sizeof(buf1)];
            aesCrypt = [data RC4EncryptDecryptWithKey:@"ABCD" operation:kCCEncrypt];
            //            aesCrypt=[data EncryptAES:@"akey"];
            const uint8_t *bytes = (const uint8_t*)[aesCrypt bytes];
            for(int j=0;j<63;j++)
            {
                buf1[j]=*bytes++;

            }
            [[self fileDownloadOutputStream] write:buf1 maxLength:64];
            [self empty];
        }

    }
}

this is the code to handle a file which is divisible by 64....

switch (type) {
        case kCFStreamEventHasBytesAvailable:
            [self handleBytesAvailable];
            break;

        case kCFStreamEventEndEncountered:
             NSLog(@"REACHED :: -- > kCFStreamEventEndEncountered");
            if (isEncryptionRequired)
            {
                if(pointer>-1)
                {
                    remBytes=pointer+1;
                    int tmp=64-remBytes;
                    for(int k=0;k<tmp;k++)
                    {
                        if (pointer!=62)
                        {
                            if(![self isFull])
                                [self push:0];
                        }
                        else
                            if(![self isFull])

                                [self push:remBytes];

                        if ([self isFull])
                        {
                            unsigned char *buf11= [self retrieveArray];
                            unsigned char buf1[64];
                            for(int j=0;j<64;j++)
                            {
                                buf1[j]=*buf11++;

                            }

                            NSData *data = [NSData dataWithBytes:buf1 length:sizeof(buf1)];
                            aesCrypt = [data RC4EncryptDecryptWithKey:@"ABCD" operation:kCCEncrypt];
                            //            aesCrypt=[data EncryptAES:@"akey"];
                            const uint8_t *bytes = (const uint8_t*)[aesCrypt bytes];
                            for(int j=0;j<63;j++)
                            {
                                buf1[j]=*bytes++;

                            }

                            [[self fileDownloadOutputStream] write:buf1 maxLength:16];
                            [self empty];

                        }}
                }

                else
                {

                    unsigned char extrabuf=0;
                    [[self fileDownloadOutputStream] write:extrabuf maxLength:1];
                    ///add
                }

            }
            else
            {
                [[self fileDownloadOutputStream] write:buf maxLength:16];
            }

            [self handleStreamComplete];
            break;

        case kCFStreamEventErrorOccurred:
            [self handleStreamError];
            break;

        default:
            break;
    }

this is the method to decrypt a file......

- (void)decryptFile:(NSString *)OMfileUrl
{
//    NSLog(@"omurl::%@",OMfileUrl);
    @try
    {
        __block NSURL *movieURL;
        isOffline = YES;
        {
            const char *srcfile = [OMfileUrl cStringUsingEncoding:NSUTF8StringEncoding];

            source = fopen(srcfile, "rb");

            filePath = [NSTemporaryDirectory() stringByAppendingPathComponent:@"assetforplay.mp4"];
            AppDelegate *delegate = (AppDelegate *) [[UIApplication sharedApplication] delegate];
            delegate.filePath = filePath;
            filePathCharArr = [filePath cStringUsingEncoding:NSUTF8StringEncoding];
            remove([filePath cStringUsingEncoding:NSUTF8StringEncoding]);
            if (source)
            {
                destination = fopen(filePathCharArr, "wb");
                cancelDecryption = NO;
                dispatch_queue_t concurrentQueue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
                dispatch_async(concurrentQueue, ^{

                    unsigned char temp[64];
                    long long totalBytes=0;
                    fseek(source, 0L, SEEK_END);
                    long long sz = ftell(source);
                    fseek(source, 0L, SEEK_SET);
                    int percentage=0,prevPercentage=0;
                    int xx=sz%64;
                    percentageLabel.hidden = NO;
                    if (xx==0)
                    {
                        NSData *data;
                        while (totalBytes<=(sz-64))
                        {
                            if(!cancelDecryption)
                            {

                                percentage =((double)totalBytes/(double)sz)*100;
                                if (percentage!=prevPercentage)
                                {
                                    prevPercentage=percentage;
                                    [[NSOperationQueue mainQueue] addOperationWithBlock:^{
                                        [percentageLabel setText:[NSString stringWithFormat:@"%i%%",percentage]];
                                    }];
                                }

                                fread(buffer,1, 64, source);
//                                memcpy( buf, buffer, 16);
//                                memcpy( keyoffline, [delegate secretKey], 16 + 0 * 8);
//                                aes_set_key( &ctx, keyoffline, 128 + 0 * 64);
//                                aes_decrypt( &ctx, buf, buf );
                                data = [NSData dataWithBytes:buffer length:64];
                                aesCrypt = [data RC4EncryptDecryptWithKey:@"ABCD" operation:kCCDecrypt];
                                //                                aesCrypt=[data DecryptAES:@"akey"];
                                const uint8_t *bytes = (const uint8_t*)[aesCrypt bytes];
                                for(int j=0;j<63;j++)
                                {
                                    buf[j]=*bytes++;

                                }
                                fwrite(buf, 1, 64, destination);
                                totalBytes=totalBytes+64;
                            }
                            else
                            {
                                percentageLabel.text=@"";
                                NSFileManager *fileManager = [NSFileManager defaultManager];
                                NSError *err;
                                if (![fileManager removeItemAtPath:filePath error:&err])
                                {
                                    NSLog(@"Unable to delete the essence. Reason:%@",[err description]);
                                }
                                break;
                            }
                        }
                        fseek(source, -64, SEEK_END);
                        sz = ftell(source);
//                        fread(buffer, 1, 16, source);
//                        memcpy( buf, buffer, 16);
//                        memcpy( keyoffline, [delegate secretKey], 16 + 0 * 8);
//                        aes_set_key( &ctx, keyoffline, 128 + 0 * 64);
//                        aes_decrypt( &ctx, buf, buf );
                        data = [NSData dataWithBytes:buffer length:64];
                        aesCrypt = [data RC4EncryptDecryptWithKey:@"ABCD" operation:kCCDecrypt];
                        //                                aesCrypt=[data DecryptAES:@"akey"];
                        const uint8_t *bytes = (const uint8_t*)[aesCrypt bytes];
                        for(int j=0;j<63;j++)
                        {
                            buf[j]=*bytes++;

                        }
                        int buf1 = buf[63];
                        for(int j=0;j<buf1;j++)
                        {
                            temp[j] = buf[j];
                        }
                        fwrite(temp, 1, buf1, destination);

                    }
                    else
                    {
                        NSData *data;
                        while (totalBytes<=(sz-1))
                        {
                            if(!cancelDecryption)
                            {
                                percentage =((double)totalBytes/(double)sz)*100;
                                if (percentage!=prevPercentage)
                                {
                                    prevPercentage=percentage;
                                    [[NSOperationQueue mainQueue] addOperationWithBlock:^{
                                        [percentageLabel setText:[NSString stringWithFormat:@"%i%%",percentage]];
                                    }];
                                }

                                fread(buffer,1, 64, source);
//                                memcpy( buf, buffer, 16);
//                                memcpy( keyoffline, [delegate secretKey], 16 + 0 * 8);
//                                aes_set_key( &ctx, keyoffline, 128 + 0 * 64);
//                                aes_decrypt( &ctx, buf, buf );
                                data = [NSData dataWithBytes:buffer length:64];
                                aesCrypt = [data RC4EncryptDecryptWithKey:@"ABCD" operation:kCCDecrypt];
                                //                                aesCrypt=[data DecryptAES:@"akey"];
                                const uint8_t *bytes = (const uint8_t*)[aesCrypt bytes];
                                for(int j=0;j<63;j++)
                                {
                                    buf[j]=*bytes++;

                                }
                                fwrite(buf, 1, 64, destination);
                                totalBytes=totalBytes+64;
                            }
                            else
                            {
                                percentageLabel.text=@"";
                                NSFileManager *fileManager = [NSFileManager defaultManager];
                                NSError *err;
                                if (![fileManager removeItemAtPath:filePath error:&err])
                                {
                                    NSLog(@"Unable to delete the essence. Reason:%@",[err description]);
                                }
                                break;
                            }

                     }

                    }

                    dispatch_async(dispatch_get_main_queue(), ^{
                        percentageLabel.text=@"";
                        if (!cancelDecryption)
                        {
                            percentageLabel.hidden = YES;
                            movieURL = [NSURL fileURLWithPath:filePath];
                            [self.mediaPanelViewCtrl setURL:movieURL];
                        }

                    });

                });

            }
        }

    }
    @catch (NSException *exception)
    {
        NSLog(@"Exception in decrypt file::%@",[exception description]);
    }

}

this is the method to do encryption and decryption using RC4....

  - (NSData*)RC4EncryptDecryptWithKey:(NSString *)key operation:(CCOperation)operation
{
    // convert to C string..
    int keySize = [key length];
    char keyPtr[keySize];
    bzero(keyPtr, sizeof(keyPtr));
    [key getCString:keyPtr
          maxLength:sizeof(keyPtr)
           encoding:NSUTF8StringEncoding];

    // encode/decode
    NSUInteger dataLength = [self length];
    size_t bufferSize = dataLength;
    void *buffer = malloc(bufferSize);

    size_t numBytesOut = 0;
    CCCryptorStatus cryptStatus = CCCrypt(operation,
                                          kCCAlgorithmRC4,
                                          kCCOptionECBMode,
                                          keyPtr,
                                          kCCKeySizeMinRC4,
                                          NULL,
                                          [self bytes],
                                          dataLength,
                                          buffer,
                                          bufferSize,
                                          &numBytesOut);
    if (cryptStatus == kCCSuccess) {
        return [NSData dataWithBytesNoCopy:buffer
                                    length:numBytesOut
                              freeWhenDone:YES];
    }

    free(buffer);
    return nil;
}

No correct solution

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