I am trying to convert a hexadecimal character array to a binary string (unsigned char) that I can use in crypto functions using Cryptlib or OpenSSL. Basically I have a Hex representation of a key like (02726d40f378e716981c4321d60ba3a3) which as a character string is 32 characters but as a binary string should be 16 bytes.
The character string is being read in from a file, how can I convert it to its binary representation as an unsigned char array?
Thanks.
If it's being read in as characters, read in two at a time and write one byte.
How?
The string is being read from a file with fgets() and being stored in a char*
Then go through the stored string in your char* two at a time and write out one byte at a time.
I don't think that will work. I'm reading in characters from a file and I need to convert them to binary. I need one character in an unsigned char array to represent one byte (two characters) from a char array.
Of course it's possible; in fact, it's trivial. If you need it spelled out, well, let's spell it out:Originally Posted by maxhavoc
- Decide the numerical value of the first character in a byte pair (0-15).
- Shift this value over four bits to the left.
- Add the numerical value of the second character in a byte pair (0-15).
- Lather, rinse, repeat.
If you can come up with a way to only give strtoul two characters at a time, it becomes even more trivial.
Or do repeated
every 2 bytes.Code:sscanf(&input_string[i], "%02x", &number); byte_string[j] = (unsigned char)number
Ok, sorry guys, I'm a bit slow. Here's the function I've put together based on nonoob's answer:
I'm getting a runtime error about stack corruption on uChar. What am I doing wrong?Code:void stringToHex(unsigned char* hexString, char* string, int stringLength) { unsigned char uChar = 0; for (int x = 0; x < stringLength; x++) { sscanf_s(&string[x], "%02x", &uChar); hexString[x] = uChar; } }
You need to put the result into an int first. Then cast it and assign to char like in my example. Your x should go up by 2 indexing string[]. But where your destination is into hexString the index should go up by 1s.
sscanf is really the best option here, of course - this is just an example of doing it 'by hand':
[edit]Code:int hex_char_to_binary( char ch, char* ret ) { ch = tolower( ch ); if( isdigit( ch ) ) *ret = ch - '0'; else if( ch >= 'a' && ch <= 'f' ) *ret = ( ch - 'a' ) + 10; else return *ret = 0; return 1; } char* hex_to_binary_copy( const char* str, char* ret ) { char * cpy = ret, low, high; if( strlen( str ) % 2 ) { *ret = 0; return 0; } for( const char* ptr = str; *ptr; ptr += 2 ) { if ( !hex_char_to_binary( *ptr, &high ) || !hex_char_to_binary( *( ptr + 1 ), &low ) ) { *ret = 0; return 0; } *cpy++ = low | ( high << 4 ); } *cpy = 0; return ret; }
Or perhaps better yet:
[/edit]
Code:int hex_to_binary( const char* str, void* buf, int* siz ) { char * cpy = ( char* )buf, low, high; const char * ptr = str; int unused, len = strlen( str ), half = len / 2, odd = len % 2; if( siz == 0 ) siz = &unused; if( odd ) { /* a bit of a hack... */ --ptr; ++half; high = 0; goto skip; } for( ; *ptr; ptr += 2 ) { if( !hex_char_to_binary( *ptr, &high ) ) return *siz = 0; skip: if( !hex_char_to_binary( *( ptr + 1 ), &low ) ) return *siz = 0; *cpy++ = low | ( high << 4 ); } return *siz = half; }
Last edited by Sebastiani; 10-04-2008 at 12:52 PM. Reason: additions, corrections
Code:#include <cmath> #include <complex> bool euler_flip(bool value) { return std::pow ( std::complex<float>(std::exp(1.0)), std::complex<float>(0, 1) * std::complex<float>(std::atan(1.0) *(1 << (value + 2))) ).real() < 0; }
I know this post was a while ago but thanks for your answers! Specially to nonoob...
Saved me time and effort...
Click the "like" link then, instead of digging up dead threads, as mentioned in the rules as something NOT to do.
If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
If at first you don't succeed, try writing your phone number on the exam paper.
