I am implementing AES decoder, for creating IV and key, the algorithm is such that
IV Key's 16 bytes：the first 16 bytes of ProductID.getBytes("UTF-8")
（If there are no enough bytes,
make up to 16 bytes at right by 0x32)
and my code for padding
- (char*)paddedStringFromString:(NSString *)string withLength:(NSUInteger)length{
const char *stringC = [string UTF8String];
char * output;
output = malloc(length+1);
for (NSInteger i = 0; i < length; i++) {
if (i < string.length) output[i] = stringC[i];
else output[i] = 0x32;
}
return output;
}
But I am not getting the right result. Is my approach for padding is right. Please help
I think the args length and string.length are not the same, right?
Related
I have a FixMessage and I want to calculate the checksum manually.
8=FIX.4.2|9=49|35=5|34=1|49=ARCA|52=20150916-04:14:05.306|56=TW|10=157|
The body length here is calculated:
8=FIX.4.2|9=49|35=5|34=1|49=ARCA|52=20150916-04:14:05.306|56=TW|10=157|
0 + 0 + 5 + 5 + 8 + 26 + 5 + 0 = 49(correct)
The checksum is 157 (10=157). How to calculate it in this case?
You need to sum every byte in the message up to but not including the checksum field. Then take this number modulo 256, and print it as a number of 3 characters with leading zeroes (e.g. checksum=13 would become 013).
Link from the FIX wiki: FIX checksum
An example implementation in C, taken from onixs.biz:
char *GenerateCheckSum( char *buf, long bufLen )
{
static char tmpBuf[ 4 ];
long idx;
unsigned int cks;
for( idx = 0L, cks = 0; idx < bufLen; cks += (unsigned int)buf[ idx++ ] );
sprintf( tmpBuf, "%03d", (unsigned int)( cks % 256 ) );
return( tmpBuf );
}
Ready-to-run C example adapted from here
8=FIX.4.2|9=49|35=5|34=1|49=ARCA|52=20150916-04:14:05.306|56=TW|10=157|
#include <stdio.h>
void GenerateCheckSum( char *buf, long bufLen )
{
unsigned sum = 0;
long i;
for( i = 0L; i < bufLen; i++ )
{
unsigned val = (unsigned)buf[i];
sum += val;
printf("Char: %02c Val: %3u\n", buf[i], val); // print value of each byte
}
printf("CheckSum = %03d\n", (unsigned)( sum % 256 ) ); // print result
}
int main()
{
char msg[] = "8=FIX.4.2\0019=49\00135=5\00134=1\00149=ARCA\00152=20150916-04:14:05.306\00156=TW\001";
int len = sizeof(msg) / sizeof(msg[0]);
GenerateCheckSum(msg, len);
}
Points to Note
GenerateCheckSum takes the entire FIX message except CheckSum field
Delimiter SOH is written as \001 which has ASCII value 1
static void Main(string[] args)
{
//10=157
string s = "8=FIX.4.2|9=49|35=5|34=1|49=ARCA|52=20150916-04:14:05.306|56=TW|";
byte[] bs = GetBytes(s);
int sum=0;
foreach (byte b in bs)
sum = sum + b;
int checksum = sum % 256;
}
//string to byte[]
static byte[] GetBytes(string str)
{
byte[] bytes = new byte[str.Length * sizeof(char)];
System.Buffer.BlockCopy(str.ToCharArray(), 0, bytes, 0, bytes.Length);
return bytes;
}
Using BodyLength[9] and CheckSum[10] fields.
BodyLength is calculated starting from field starting after BodyLenght and
before CheckSum field.
CheckSum is calculated from ‘8= upto SOH before the checksum field.
Binary value of each character is calculated and compared to the LSB of the calculated value to the checksum value.
If the checksum has been calculated to be 274 then the modulo 256 value is 18 (256 + 18 = 274). This value would be transmitted a 10=018 where
"10="is the tag for the checksum field.
In Java there is a method from QuickFixJ.
String fixStringMessage = "8=FIX.4.29=12535=81=6090706=011=014=017=020=322=837=038=4.39=054=155=ALFAA99=20220829150=0151=06020=06021=06022=F9014=Y";
int checkSum = quickfix.MessageUtils.checksum(fixStringMessage);
System.out.prinln(checkSum);
Output: 127
Hope it can help you.
I have this method to make a xor between 2 NSStrings, i´m printing the result on NSLog but it isn´t the expect.
Can´t figure out what i´m doing wrong.
(void)XorSecretKeyDeviceId
{
NSString* secretKey = #"123";//
NSString* deviceId = #"abcdef";//
NSData* stringKey = [secretKey dataUsingEncoding:NSUTF8StringEncoding];
NSData* stringDeviceId = [deviceId dataUsingEncoding:NSUTF8StringEncoding];
unsigned char* pBytesInput = (unsigned char*)[stringKey bytes]; //Bytes
unsigned char* pBytesKey = (unsigned char*)[stringDeviceId bytes];
unsigned int vlen = [secretKey length]; //Keys Length
unsigned int klen = [deviceId length];
unsigned int v;
unsigned int k = vlen % klen;
unsigned char c;
for(v = 0; v < vlen; v++)
{
c = pBytesInput[v] ^ pBytesKey[k];
pBytesInput[v] = c;
NSLog(#"%c", c);
k = (++k < klen ? k : 0);
}
}
Are you setting your pBytesInput and pBytesKey variables correctly? At the moment, you have unsigned char* pBytesInput = (unsigned char*)[stringKey bytes]; (i.e. the input is the "key"), and pBytesKey is the device ID. This seems odd.
Also, be careful using UTF-8 encoding. UTF-8 uses the high bit on any byte in the string to indicate a "continuation" of a multi-byte character into the next byte. Your encoding could plausibly generate invalid UTF-8 by giving the setting the high bit of the final byte in the encryption.
For more than that, you'll have to say what the "wrong result" is.
I have three CGLayers who's data I'd like to compare.
void *a = CGBitmapContextGetData(CGLayerGetContext(layerA));
void *b = CGBitmapContextGetData(CGLayerGetContext(layerB));
void *c = CGBitmapContextGetData(CGLayerGetContext(layerC));
I'd like to get a result like ((a OR b) AND c) where only bits that are on in layerA or layerB and also on in layerC end up in the result. These layers are kCGImageAlphaOnly so they are only 8 bits "deep", and I've only drawn into them with 1.0 alpha. I also don't need to know where the overlap lies, I just need to know whether there are any bits on in the result.
I'm really missing QuickDraw today, it had plenty of bit-oriented operations that were very speedy. Any thoughts on how to accomplish something like this?
Here's a naive implementation, assuming all three are the same size:
unsigned char *a = CGBitmapContextGetData(CGLayerGetContext(layerA));
unsigned char *b = CGBitmapContextGetData(CGLayerGetContext(layerB));
CGContextRef context = CGLayerGetContext(layerC);
unsigned char *c = CGBitmapContextGetData(context);
size_t bytesPerRow = CGBitmapContextGetBytesPerRow(context);
size_t height = CGBitmapContextGetHeight(context);
size_t len = bytesPerRow * height;
BOOL bitsFound = NO;
for (int i = 0; i < len; i++) {
if ((a[i] | b[i]) & c[i]) { bitsFound = YES; break; }
}
Since you're hankering for QuickDraw, I assume you could have written that yourself, and you know that will probably be slow.
If you can guarantee the bitmap sizes, you could use int instead of char and operate on four bytes at a time.
For more serious optimization, you should check out the Accelerate framework.
What about the CGBlendModes? kCGBlendModeDestinationOver acts as OR for A and B, and then you can use kCGBlendModeDestinationIn to AND that result with C.
I have used the following code for converting the bigint in decimal to bytearray (raw data), but I'm getting wrong result.
What is the mistake here?
I'm trying this in Apple Mac ( for Iphone app)
COMP_BYTE_SIZE is 4
Is there any bigendian/ little endian issue, please Help.
void bi_export(BI_CTX *ctx, bigint *x, uint8_t *data, int size)
{
int i, j, k = size-1;
check(x);
memset(data, 0, size); /* ensure all leading 0's are cleared */
for (i = 0; i < x->size; i++)
{
for (j = 0; j < COMP_BYTE_SIZE; j++)
{
comp mask = 0xff << (j*8);
int num = (x->comps[i] & mask) >> (j*8);
data[k--] = num;
if (k < 0)
{
break;
}
}
}
Thanks.
The argument size is at least x->size*4, ie. the target array is big enough? Also use
comp mask = (comp)0xff << (j*8);
num should be cast to uint8_t before copy
data[k--] = (uint8_t)num;
I'm looking for an Objective-C way of sorting characters in a string, as per the answer to this question.
Ideally a function that takes an NSString and returns the sorted equivalent.
Additionally I'd like to run length encode sequences of 3 or more repeats. So, for example "mississippi" first becomes "iiiimppssss", and then could be shortened by encoding as "4impp4s".
I'm not expert in Objective-C (more Java and C++ background) so I'd also like some clue as to what is the best practice for dealing with the memory management (retain counts etc - no GC on the iphone) for the return value of such a function. My source string is in an iPhone search bar control and so is an NSString *.
int char_compare(const char* a, const char* b) {
if(*a < *b) {
return -1;
} else if(*a > *b) {
return 1;
} else {
return 0;
}
}
NSString *sort_str(NSString *unsorted) {
int len = [unsorted length] + 1;
char *cstr = malloc(len);
[unsorted getCString:cstr maxLength:len encoding:NSISOLatin1StringEncoding];
qsort(cstr, len - 1, sizeof(char), char_compare);
NSString *sorted = [NSString stringWithCString:cstr encoding:NSISOLatin1StringEncoding];
free(cstr);
return sorted;
}
The return value is autoreleased so if you want to hold on to it in the caller you'll need to retain it. Not Unicode safe.
With a bounded code-set, radix sort is best:
NSString * sortString(NSString* word) {
int rads[128];
const char *cstr = [word UTF8String];
char *buff = calloc([word length]+1, sizeof(char));
int p = 0;
for(int c = 'a'; c <= 'z'; c++) {
rads[c] = 0;
}
for(int k = 0; k < [word length]; k++) {
int c = cstr[k];
rads[c]++;
}
for(int c = 'a'; c <= 'z'; c++) {
int n = rads[c];
while (n > 0) {
buff[p++] = c;
n--;
}
}
buff[p++] = 0;
return [NSString stringWithUTF8String: buff];
}
Note that the example above only works for lowercase letters (copied from a specific app which needs to sort lowercase strings). To expand it to handle all of the ASCII 127, just do for(c=0; c <= 127; c++).