Objective-C Raw MD5-hash - objective-c

Question

In Objective-C, I generate a simple MD5-hash of 'HelloKey', which returns 0FD16658AEE3C52060A39F4EDFB11437. Unfortunately, I could not get a raw return, so I have to work with this string to get a raw MD5-hash (or do you know how I can get a raw result from the start?)
Anyway, in order to convert it to raw, I split it into chunks of 2 chars each, calculate the hex value, and append a char with that value to a string.
Here's the function:
- (NSString *)hex2bin:(NSString *)input{
NSString *output = #"";
for (int i = 0; i < input.length; i+=2){
NSString *component = [input substringWithRange:NSMakeRange(i, 2)];
unsigned int outVal;
NSScanner* scanner = [NSScanner scannerWithString:component];
[scanner scanHexInt:&outVal];
/* if(outVal > 127){
outVal -= 256;
} */
// unsigned char appendage = (char)outVal;
output = [NSString stringWithFormat:#"%#%c", output, outVal];
NSLog(#"component: %# = %d", component, outVal);
}
return output;
}
When I print each outval, I get:
0F = 15
D1 = 209
66 = 102
58 = 88
AE = 174
E3 = 227
C5 = 197
20 = 32
60 = 96
A3 = 163
9F = 159
4E = 78
DF = 223
B1 = 177
14 = 20
37 = 55
However, when I print the string that I get with a special function that tells me the integer values of each character (a function which is shown here):
- (NSString *)str2bin:(NSString *)input{
NSString *output = #"";
for (NSInteger charIdx=0; charIdx < input.length; charIdx++){
char currentChar = [input characterAtIndex:charIdx];
int charNum = [NSNumber numberWithChar:currentChar].intValue;
output = [NSString stringWithFormat:#"%# %d", output, charNum];
}
return output;
}
I get: 15 20 102 88 -58 30 72 32 96 -93 -4 78 2 -79 20 55. You will notice that there are significant differences, like 209 -> 20, 174 -> -58, 227 -> 30. In some cases, the difference is 256, so no harm done. But in other cases, it's not, and I would really like to know what's going wrong. Any tips?

Answer 1

You are doing it wrong, since you are trying to store binary data in NSString, which is UTF8 string.
You should use NSData (or C string) to store binary hash representation.