How to convert an array to a hash?

Question

What am i trying to do

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The MD5 function from the OpenSSL cryptographic library (as well as many of its other hash functions) returns an array unsigned char. I am trying to get a hash string from this array.

Example:

Array:

{126, 113, 177, 57, 8, 169, 240, 118, 60, 10, 229, 74, 249, 6, 32, 128}

Hash:

7e71b13908a9f0763c0ae54af9062080

Each number in the array is represented as two hexadecimal digits. And the hash string is twice the length of the array.

What I have

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Please view the full code here . Here is a part of it.

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#define nu 0

typedef struct {
   int len;
   unsigned char *Hash;
}Type;

Type test[6];


int main(void) {

    unsigned char XUzQ[16]={
    126, 113, 177, 57, 8, 169, 240, 118, 60, 10, 229, 74, 249, 6, 32, 128
    };
    test[0].len=16; test[0].Hash=XUzQ;

    int h; 
    const char *hex="0123456789abcdef";
    char *Ha=calloc(test[nu].len*2+1,sizeof(char));

    for (h=0;h<test[nu].len;++h) {
        *(++Ha)=hex[(test[nu].Hash[h]/16)%16];
        *(++Ha)=hex[test[nu].Hash[h]%16];
    }

    Ha-=(test[nu].len*2-1);

    if (strlen(Ha)==(test[nu].len*2))
    printf("'%s'\n",Ha);
    else puts("Failed!");

    Ha--;

    free(Ha);

    return 0;
}

This prints out the value that I expect ( 7e71b13908a9f0763c0ae54af9062080), but, in my opinion, the same thing could be implemented better and faster.

Notes

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The names of the arrays I'm working with are so strange that they were automatically generated by my Python script using random characters.

test (. , ).

---

? , , OpenSSL.

Answer 1

snprintf, , , :

char* to_hex_string(const unsigned char h[16]) {
  char* out = malloc(33);
  size_t l =
    snprintf(out, 33,
      "%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x",
      h[0], h[1], h[2], h[3], h[4], h[5], h[6], h[7],
      h[8], h[9], h[10], h[11], h[12], h[13], h[14], h[15]);
  assert(l == 32);
  return out;
}

, sprintf:

void byte_to_02x(char out[3], unsigned char byte) {
  assert(snprintf(out, 3, "%02x", byte) == 2);
}
char* bytevector_to_hexstring(unsigned char* bytes, size_t n) {
  char* out = malloc(2*n + 1);
  for (int i = 0; i < n; ++i)
    assert(snprintf(&out[2*i], 3, "%02x", bytes[i]);
  return out;
}