Problem - Kevin Tafuro

4.3 Representing Binary Keys (or Other Raw
Data) as Hexadecimal
Problem
You want to print out keys in hexadecimal format, either for debugging or for easy
communication.
Solution
The easiest way is to use the “%X” specifier in the printf() family of functions. In
C++, you can set the ios::hex flag on a stream object before outputting a value, then
clear the flag afterward.
Discussion
Here is a function called spc_print_hex() that prints arbitrary data of a specified
length in formatted hexadecimal:
#include
#include
#define BYTES_PER_GROUP 4
#define GROUPS_PER_LINE 4
/* Don't change these */
#define BYTES_PER_LINE (BYTES_PER_GROUP * GROUPS_PER_LINE)
void spc_print_hex(char *prefix, unsigned char *str, int len) {
unsigned long i, j, preflen = 0;
if (prefix) {
printf("%s", prefix);
preflen = strlen(prefix);
}
for (i = 0; i < len; i++) {
printf("%02X ", str[i]);
if (((i % BYTES_PER_LINE) = = (BYTES_PER_LINE - 1)) && ((i + 1) != len)) {
putchar('\n');
for (j = 0; j < preflen; j++) putchar(' ');
}
else if ((i % BYTES_PER_GROUP) = = (BYTES_PER_GROUP - 1)) putchar(' ');
}
putchar('\n');
}
120 | Chapter 4: Symmetric Cryptography Fundamentals
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