Converting NSString to char byte array - objective-c

In my program, I receive a NSString like this one : AA010158AA7D385002. And I need to pass it to a method which accept a char byte array, as below :
char[9] = {0xAA, 0x01, 0x01, 0x58, 0xAA, 0x7D, 0x38, 0x50, 0x02};
How to convert my NSString to char byte array like this one?
Thanks!

NSString *strCharData = #"AA010158AA7D385002";
const char *characterRes = [strCharData cStringUsingEncoding:NSUTF8StringEncoding];
or
NSString *strCharData = #"AA010158AA7D385002";
const char *characterRes = [strCharData UTF8String];

Use this answer if i am correct,i did little coding but might be there are possibilities of simpler solutions also like #user3182143
NSString * inputStr = #"AA010158AA7D385002";
NSMutableArray *charByteArray = [[NSMutableArray alloc]initWithCapacity:1];
int i = 0;
for (i = 0; i+2 <= inputStr.length; i+=2) {
NSRange range = NSMakeRange(i, 2);
NSString* charStr = [inputStr substringWithRange:range];
[charByteArray addObject:[NSString stringWithFormat:#"0x%#",charStr]];
}
Output :
char[9] = (
0xAA,
0x01,
0x01,
0x58,
0xAA,
0x7D,
0x38,
0x50,
0x02
)

Since your text is hex and you want actual bytes out (which each correspond to two hex characters), you'll have to manually convert each character into the corresponding number, and then add them together into the correct numerical value.
To do this, I'm taking advantage of the fact that, in ASCII characters, a...z are in a row, as are 0...9. I'm also taking advantage of the fact that hexadecimal is valid ASCII, and that Unicode characters from 0...127 are identical to their corresponding ASCII characters.
Below is a program that does this and prints out the original string's characters as well as the calculated bytes (as hex again):
#import <Foundation/Foundation.h>
int main(int argc, char *argv[])
{
#autoreleasepool
{
NSString *hexStr = #"1234567890abcdef12";
unsigned char theBytes[9] = {};
for( NSUInteger x = 0; x < sizeof(theBytes); x++ )
{
unsigned char digitOne = [hexStr characterAtIndex: x * 2];
if( digitOne >= 'a' )
digitOne -= 'a' -10;
else
digitOne -= '0';
unsigned char digitTwo = [hexStr characterAtIndex: (x * 2) +1];
if( digitTwo >= 'a' )
digitTwo -= 'a' -10;
else
digitTwo -= '0';
printf("%01x%01x",digitOne,digitTwo);
theBytes[x] = (digitOne << 4) | digitTwo;
}
printf("\n");
for( int x = 0; x < sizeof(theBytes); x++ )
printf("%02x",theBytes[x]);
printf("\n");
}
}
Note: This code naïvely assumes that you are providing a correct string. I.e. your input has to consist of lowercase characters and numbers only, and exactly 18 characters. Anything else and you get a wrong result or an exception.

I finally managed to find the answer to my own question. I am posting it here in case it helps someone else.
So I use a method to convert an NSString hex to bytes :
#implementation NSString (HexToBytes)
- (NSData *)hexToBytes
{
NSMutableData *data = [NSMutableData data];
int idx;
for (idx = 0; idx + 2 <= self.length; idx += 2) {
NSRange range = NSMakeRange(idx, 2);
NSString *hexStr = [self substringWithRange:range];
NSScanner *scanner = [NSScanner scannerWithString:hexStr];
unsigned int intValue;
[scanner scanHexInt:&intValue];
[data appendBytes:&intValue length:1];
}
return data;
}
#end
And then, I simply use it like that :
NSString *str = #"AA010158AA7D385002";
NSData *databytes = [str hexToBytes];
char *bytePtr = (char *)[databytes bytes];
And I finally get my char array. Hope it helps someone else.

Related

Equivalent Hashing in C# and Objective-C using HMAC256

I'm working with a partner and we're not able to get C# and Objective-C to produce the same hashes using what we think are the same tools in the respective languages. In C#, I'm doing this:
byte[] noncebytes=new byte[32];
//We seed the hash generator with a new 32 position array. Each position is 0.
//In prod code this would be random, but for now it's all 0s.
HMACSHA256 hmac256 = new HMACSHA256(noncebytes);
string plaintext = "hello";
string UTFString = Convert.ToBase64String(
System.Text.Encoding.UTF8.GetBytes(plaintext));
string HashString = Convert.ToBase64String(
hmac256.ComputeHash(System.Text.Encoding.UTF8.GetBytes(plaintext))); //Convert that hash to a string.
This produces the following base64string hash:
Q1KybjP+DXaaiSKmuikAQQnwFojiasyebLNH5aWvxNo=
What is the equivalent Objective-C code to do this? We need the client and the server to be able to generate matching hashes for matching data.
Here is the Objective-C code we are currently using:
...
NSData *zeroNumber = [self zeroDataWithBytes:32]; //empty byte array
NSString *nonceTest = [zeroNumber base64String]; // using MF_Base64Additions.h here
NSData *hashTest = [self hmacForKeyAndData:nonceTest withData:#"hello"]; //creating hash
NSString *hashTestText = [hashTest base64String];
NSLog(#"hello hash is %#", hashTestText);
...
//functions for zeroing out the byte. I'm sure there's a better way
- (NSData *)zeroDataWithBytes: (NSUInteger)length {
NSMutableData *mutableData = [NSMutableData dataWithCapacity: length];
for (unsigned int i = 0; i < length; i++) {
NSInteger bits = 0;
[mutableData appendBytes: (void *) &bits length: 1];
} return mutableData;
}
//hash function
-(NSData *) hmacForKeyAndData:(NSString *)key withData:(NSString *) data {
const char *cKey = [key cStringUsingEncoding:NSASCIIStringEncoding];
const char *cData = [data cStringUsingEncoding:NSASCIIStringEncoding];
unsigned char cHMAC[CC_SHA256_DIGEST_LENGTH];
CCHmac(kCCHmacAlgSHA256, cKey, strlen(cKey), cData, strlen(cData), cHMAC);
return [[NSData alloc] initWithBytes:cHMAC length:sizeof(cHMAC)];
}
UPDATE:
There is a pretty good project on GitHub that seems to accomplish everything you want, plus a lot more encryption related options; includes unit tests.
NSData *hmacForKeyAndData(NSString *key, NSString *data)
{
const char *cKey = [key cStringUsingEncoding:NSASCIIStringEncoding];
const char *cData = [data cStringUsingEncoding:NSASCIIStringEncoding];
unsigned char cHMAC[CC_SHA256_DIGEST_LENGTH];
CCHmac(kCCHmacAlgSHA256, cKey, strlen(cKey), cData, strlen(cData), cHMAC);
return [[NSData alloc] initWithBytes:cHMAC length:sizeof(cHMAC)];
}
(Source)
With the above, I think you will have import <CommonCrypto/CommonHMAC.h>. The next step for encoding to Base64:
+ (NSString *)Base64Encode:(NSData *)data
{
//Point to start of the data and set buffer sizes
int inLength = [data length];
int outLength = ((((inLength * 4)/3)/4)*4) + (((inLength * 4)/3)%4 ? 4 : 0);
const char *inputBuffer = [data bytes];
char *outputBuffer = malloc(outLength);
outputBuffer[outLength] = 0;
//64 digit code
static char Encode[] = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
//start the count
int cycle = 0;
int inpos = 0;
int outpos = 0;
char temp;
//Pad the last to bytes, the outbuffer must always be a multiple of 4
outputBuffer[outLength-1] = '=';
outputBuffer[outLength-2] = '=';
/* http://en.wikipedia.org/wiki/Base64
Text content M a n
ASCII 77 97 110
8 Bit pattern 01001101 01100001 01101110
6 Bit pattern 010011 010110 000101 101110
Index 19 22 5 46
Base64-encoded T W F u
*/
while (inpos < inLength){
switch (cycle) {
case 0:
outputBuffer[outpos++] = Encode[(inputBuffer[inpos]&0xFC)>>2];
cycle = 1;
break;
case 1:
temp = (inputBuffer[inpos++]&0x03)<<4;
outputBuffer[outpos] = Encode[temp];
cycle = 2;
break;
case 2:
outputBuffer[outpos++] = Encode[temp|(inputBuffer[inpos]&0xF0)>> 4];
temp = (inputBuffer[inpos++]&0x0F)<<2;
outputBuffer[outpos] = Encode[temp];
cycle = 3;
break;
case 3:
outputBuffer[outpos++] = Encode[temp|(inputBuffer[inpos]&0xC0)>>6];
cycle = 4;
break;
case 4:
outputBuffer[outpos++] = Encode[inputBuffer[inpos++]&0x3f];
cycle = 0;
break;
default:
cycle = 0;
break;
}
}
NSString *pictemp = [NSString stringWithUTF8String:outputBuffer];
free(outputBuffer);
return pictemp;
}
Note the second line of code in the objective-c portion of the question.
NSString *nonceTest = [zeroNumber base64String];
but it should be this:
NSString *nonceTest = [[NSString alloc] initWithData:zeroNumber encoding:NSASCIIStringEncoding];
It was a case of converting the string to base64 when we didn't need to for the hmac seeeding.
We now get: Q1KybjP+DXaaiSKmuikAQQnwFojiasyebLNH5aWvxNo= as the hash on both platforms.

Convert one NSArray filled with NSStrings to a UTF8String vector

So I was wondering, is there some quick way of converting one NSArray filled with NSStrings to the equivalent UTF8string values?
I want to store some parameter configuration in a NSArray and then use them in a function that takes (int argv, const char *argv[]) as arguments.
I implemented this in a convoluted way
int argc = [gameParameters count];
const char **argv = (const char **)malloc(sizeof(const char*)*argc);
for (int i = 0; i < argc; i++) {
argv[i] = (const char *)malloc(sizeof(char)*[[gameParameters objectAtIndex:i] length]+1);
strncpy((void *)argv[i], [[gameParameters objectAtIndex:i] UTF8String], [[gameParameters objectAtIndex:i] length]+1);
}
but I'm not really happy with and cleaning up memory is tedious.
Do you know a better way to achieve this result?
Your current implementation is not correct if the string contains non-ASCII characters. For example, the string #"é" (SMALL LETTER E WITH ACUTE) has length 1, but the UTF-8 sequence "C3 A9" has 2 bytes. Your code would not allocate enough memory for that string.
(In other words: [string length] returns the number of Unicode characters in the string, not the number of bytes of the UTF-8 representation.)
Using strdup(), as suggested by Kevin Ballard, would solve this problem:
argv[i] = strdup([[gameParameters objectAtIndex:i] UTF8String]);
But you should also check if duplicating the strings is necessary at all. If you call the function in the current autorelease context, the following would be sufficient:
int argc = [gameParameters count];
const char **argv = (const char **)malloc(sizeof(const char*)*argc);
for (int i = 0; i < argc; i++) {
argv[i] = [[gameParameters objectAtIndex:i] UTF8String];
}
yourFunction(argc, argv);
free(argv);

Convert NSString to C string, increment and come back to NSString

I'm trying to develop a simple application where i can encrypt a message. The algorithm is Caesar's algorithm and for example, for 'Hello World' it prints 'KHOOR ZRUOG' if the increment is 3 (standard).
My problem is how to take each single character and increment it...
I've tried this:
NSString *text = #"hello";
int q, increment = 3;
NSString *string;
for (q = 0; q < [text length]; q++) {
string = [text substringWithRange:NSMakeRange(q, 1)];
const char *c = [string UTF8String] + increment;
NSLog(#"%#", [NSString stringWithUTF8String:c]);
}
very simple but it doesn't work.. My theory was: take each single character, transform into c string and increment it, then return to NSString and print it, but xcode print nothing, also if i print the char 'c' i can't see the result in console. Where is the problem?
First of all, incrementing byte by byte only works for ASCII strings. If you use UTF-8, you will get garbage for glyphs that have multi-byte representations.
With that in mind, this should work (and work faster than characterAtIndex: and similar methods):
NSString *foo = #"FOOBAR";
int increment = 3;
NSUInteger bufferSize = [foo length] + 1;
char *buffer = (char *)calloc(bufferSize, sizeof(char));
if ([foo getCString:buffer maxLength:bufferSize encoding:NSASCIIStringEncoding]) {
int bufferLen = strlen(buffer);
for (int i = 0; i < bufferLen; i++) {
buffer[i] += increment;
if (buffer[i] > 'Z') {
buffer[i] -= 26;
}
}
NSString *encoded = [NSString stringWithCString:buffer
encoding:NSASCIIStringEncoding];
}
free(buffer);
first of all replace your code with this:
for (q = 0; q < [text length]; q++) {
string = [text substringWithRange:NSMakeRange(q, 1)];
const char *c = [string UTF8String];
NSLog(#"Addr: 0x%X", c);
c = c + increment;
NSLog(#"Addr: 0x%X", c);
NSLog(#"%#", [NSString stringWithUTF8String:c]);
}
Now you can figure out your problem. const char *c is a pointer. A pointer saves a memory address.
When I run this code the first log output is this:
Addr: 0x711DD10
that means the char 'h' from the NSString named string with the value #"h" is saved at address 0x711DD10 in memory.
Now we increment this address by 3. Next output is this:
Addr: 0x711DD13
In my case at this address there is a '0x00'. But it doesn't matter what is actually there because a 'k' won't be there (unless you are very lucky).
If you are happy there is a 0x00 too. Because then nothing bad will happen. If you are unlucky there is something else. If there is something other than 0x00 (or the string delimiter or "end of string") NSString will try to convert it. It might crash while trying this, or it might open a huge security hole.
so instead of manipulating pointers you have to manipulate the values where they point to.
You can do this like this:
for (q = 0; q < [text length]; q++) {
string = [text substringWithRange:NSMakeRange(q, 1)];
const char *c = [string UTF8String]; // get the pointer
char character = *c; // get the character from this pointer address
character = character + 3; // add 3 to the letter
char cString[2] = {0, 0}; // create a cstring with length of 1. The second char is \0, the delimiter (the "end marker") of the string
cString[0] = character; // assign our changed character to the first character of the cstring
NSLog(#"%#", [NSString stringWithUTF8String:cString]); // profit...
}

Converting NSString to Hex

I've been doing a lot of reading on how to convert a string to a hex value. Here is what I found to accomplish this:
NSString * hexString = [NSString stringWithFormat:#"%x", midiValue];
This returned some "interesting" results and upon reading a little further I found a post that mentioned this
"You're passing a pointer to an object representing a numeric value, not the numeric value proper."
So I substituted 192 instead of "midiValue" and it did what I expected.
How would I pass the string value and not the pointer?
Decleration of midiValue:
NSString *dMidiInfo = [object valueForKey:#"midiInformation"];
int midiValue = dMidiInfo;
You probably need to do something like this:
NSNumberFormatter *numberFormatter= [[NSNumberFormatter alloc] init];
int anInt= [[numberFormatter numberFromString:string ] intValue];
also, I think there is some example code in the xcode documentation for converting to and from a hex value, in the QTMetadataEditor sample. in the MyValueFormatter class.
+ (NSString *)hexStringFromData:(NSData*) dataValue{
UInt32 byteLength = [dataValue length], byteCounter = 0;
UInt32 stringLength = (byteLength*2) + 1, stringCounter = 0;
unsigned char dstBuffer[stringLength];
unsigned char srcBuffer[byteLength];
unsigned char *srcPtr = srcBuffer;
[dataValue getBytes:srcBuffer];
const unsigned char t[16] = "0123456789ABCDEF";
for (; byteCounter < byteLength; byteCounter++){
unsigned src = *srcPtr;
dstBuffer[stringCounter++] = t[src>>4];
dstBuffer[stringCounter++] = t[src & 15];
srcPtr++;
}
dstBuffer[stringCounter] = '\0';
return [NSString stringWithUTF8String:(char*)dstBuffer];
}
+ (NSData *)dataFromHexString:(NSString*) dataValue{
UInt32 stringLength = [dataValue length];
UInt32 byteLength = stringLength/2;
UInt32 byteCounter = 0;
unsigned char srcBuffer[stringLength];
[dataValue getCString:(char *)srcBuffer];
unsigned char *srcPtr = srcBuffer;
Byte dstBuffer[byteLength];
Byte *dst = dstBuffer;
for(; byteCounter < byteLength;){
unsigned char c = *srcPtr++;
unsigned char d = *srcPtr++;
unsigned hi = 0, lo = 0;
hi = charTo4Bits(c);
lo = charTo4Bits(d);
if (hi== 255 || lo == 255){
//errorCase
return nil;
}
dstBuffer[byteCounter++] = ((hi << 4) | lo);
}
return [NSData dataWithBytes:dst length:byteLength];
}
Hopefully this helps.
if you are messing with a simple iPhone app in Xcode using the iPhone 5.1 Simulator then this is useful:
//========================================================
// This action is executed whenever the hex button is
// tapped by the user.
//========================================================
- (IBAction)hexPressed:(UIButton *)sender
{
// Change the current base to hex.
self.currentBase = #"hex";
// Aquire string object from text feild and store in a NSString object
NSString *temp = self.labelDisplay.text;
// Cast NSString object into an Int and the using NSString method StringWithFormat
// which is similar to c's printf format then output into hexidecimal then return
// this NSString object with the hexidecimal value back to the text field for display
self.labelDisplay.text=[NSString stringWithFormat:#"%x",[temp intValue]];
}

How do I convert NSString with Hexvalue to binary char*?

I have a long hex value stored as a NSString, something like:
c12761787e93534f6c443be73be31312cbe343816c062a278f3818cb8363c701
How do I convert it back into a binary value stored as a char*
This is a little sloppy, but should get you on the right track:
NSString *hexString = #"c12761787e93534f6c443be73be31312cbe343816c062a278f3818cb8363c701";
char binChars[128]; // I'm being sloppy and just making some room
const char *hexChars = [hexString UTF8String];
NSUInteger hexLen = strlen(hexChars);
const char *nextHex = hexChars;
char *nextChar = binChars;
for (NSUInteger i = 0; i < hexLen - 1; i++)
{
sscanf(nextHex, "%2x", nextChar);
nextHex += 2;
nextChar++;
}
There was a thread on this (or on a very similar) hexadecimal conversion topic a couple of weeks back over on one of the Cocoa mailing lists.
I can't reasonably reproduce the full discussion here (long thread), but the message that starts off the thread is here:
http://www.cocoabuilder.com/archive/message/cocoa/2009/5/9/236391
I do wish there were a Cocoa method for this task, but (pending finding that or pending its implementation) the code (by Mr Gecko, posted at http://www.cocoabuilder.com/archive/message/cocoa/2009/5/10/236424) looks like it would work here.
static NSString* hexval(NSData *data) {
NSMutableString *hex = [NSMutableString string];
unsigned char *bytes = (unsigned char *)[data bytes];
char temp[3];
int i = 0;
for (i = 0; i < [data length]; i++) {
temp[0] = temp[1] = temp[2] = 0;
(void)sprintf(temp, "%02x", bytes[i]);
[hex appendString:[NSString stringWithUTF8String: temp]];
}
return hex;
}