Question

EDIT: this is the corrected version of the converted code

int scrambBase20[] = {1,2,3};
- (NSString *) descramble:(NSString*) input{
    char *ret = [input UTF8String];
    int offset = -(sizeof scrambBase20);
    for(int i=0;i<[input length];i++){
        if(i%(sizeof scrambBase20)==0){
            offset+=(sizeof scrambBase20);
        }
        ret[scrambBase20[i%(sizeof scrambBase20)]+offset] = (char) ((Byte) [input characterAtIndex:i]^0x45);
    }
    NSString *realRet = [[NSString alloc] initWithUTF8String:ret];
    [realRet stringByTrimmingCharactersInSet:[NSCharacterSet whitespaceCharacterSet]];

    return realRet;
}

I have this block of Java which I am trying to convert to Objective-C.

I have an encrypted string which I am trying to decrypt.

[descramble: @"6&eee *eee1ee1e eee!"];

Should become

"testcode" (without quotes)

Instead, I get the output

"6&sec *ee 1ee1e  ee!" (without quotes)

The following code is my Java code [works]

String descramble(String input){
    Log.i("APP", "input length: " + input.length());
    char[] ret; //= new ArrayList<Character>();
    ret = input.toCharArray();
    int offset = -scrambBase20.length;
    for(int i=0;i<input.length();i++){
        if(i%scrambBase20.length==0)
            offset+=scrambBase20.length;
        ret[scrambBase20[i%scrambBase20.length]+offset]=(char) ((byte) (input.charAt(i))^0x45);
    }

    String realRet = "";
    for (char x : ret){
        realRet+=x;
    }
    realRet = realRet.trim();
    return realRet;
}

The following code is my converted code to Xcode [doesn’t work]

- (NSString *) descramble:(NSString*) input{
   char *ret = [input UTF8String];
   int offset = -(sizeof scrambBase20);
   for(int i=0;i<(sizeof input);i++){
        if(i%(sizeof scrambBase20)==0){
            offset+=(sizeof scrambBase20);
        }
        ret[scrambBase20[i%(sizeof scrambBase20)]+offset] = (char) ((Byte) [input characterAtIndex:i]^0x45);
    }
    NSString *realRet = [[NSString alloc] initWithUTF8String:ret];
    [realRet stringByTrimmingCharactersInSet:[NSCharacterSet whitespaceCharacterSet]];
    return realRet;
}

Does anyone see an error in the conversion from Java to Objective-C?

Answer 1

Since scrambBase20 is an array, you need to use count instead of sizeOf. Objective C equivalent of sizeOf() in Java is count.

- (NSString *) descramble:(NSString*) input{
   char *ret = [input UTF8String];
   int offset = (-1 * [scrambBase20 count]);
   for(int i=0;i<[input length];i++){
        if(i% [scrambBase20 count] == 0){
            offset+= [scrambBase20 count];
        }
        ret[scrambBase20[i%[scrambBase20 count]+offset] = (char) ((Byte) [input characterAtIndex:i]^0x45);
    }
    NSString *realRet = [[NSString alloc] initWithUTF8String:ret];
    [realRet stringByTrimmingCharactersInSet:[NSCharacterSet whitespaceCharacterSet]];
    return realRet;
}

For an NSString, equivalent of length() in java to objective c is [string length]. For cString, it is strlen().

Update:

As per your edit, it is a C array and not NSArray. In that case you need to use,

- (NSString *) descramble:(NSString*) input{
    char *ret = [input UTF8String];
    int offset = -1 * ((sizeof scrambBase20) / (sizeof int));
    for(int i=0;i < [input length];i++){
        if(i%((sizeof scrambBase20) / (sizeof int))==0){
            offset+=((sizeof scrambBase20) / (sizeof int));
        }
        ret[scrambBase20[i%((sizeof scrambBase20) / (sizeof int))]+offset] = (char) ((Byte) [input characterAtIndex:i]^0x45);
    }
    NSString *realRet = [[NSString alloc] initWithUTF8String:ret];
    [realRet stringByTrimmingCharactersInSet:[NSCharacterSet whitespaceCharacterSet]];

    return realRet;
}