Java-like hex digest generation in C using openssl / libssl

java-sha1.c

/*
 for mineserver ( https://github.com/fador/mineserver/ )
 fador@iki.fi
*/
#include <stdio.h>
#include <string.h>
#include <openssl/sha.h>

int main()
{
  unsigned char inbuf[] = "jeb_";
  SHA_CTX context;
  unsigned char md[20];
  char hexdigest[42];
  int i;
  int outpos = 0;
  const char hex[] = "0123456789abcdef";

  SHA1_Init(&context);
  SHA1_Update(&context, (unsigned char*)inbuf, strlen(inbuf));
  SHA1_Final(md, &context);

  if(md[0] & 0x80)
  {
    unsigned char carry = 1;
    hexdigest[outpos++] = '-';
    for (i = 19; i >= 0; i--)
    {
      unsigned short twocomp = (unsigned char)~md[i];
      twocomp+=carry;
      if(twocomp & 0xff00)
      {
        twocomp = twocomp&0xff;
      }
      else
      {
       carry = 0;
      }
      md[i] = twocomp;
    }
  }

  for (i = 0; i < 20; i++)
  {
   if(i || md[i]>>4)
   {
     hexdigest[outpos++] = hex[(md[i]>>4)];
   }
   if(i || md[i]>>4 || md[i]&0xf)
   {
    hexdigest[outpos++] = hex[(md[i]&0xf)];
   }
  }
  hexdigest[outpos] = '\0';

  printf("%s\n", hexdigest);

  return 0;
}

// Notch ->  4ed1f46bbe04bc756bcb17c0c7ce3e4632f06a48
// jeb_  -> -7c9d5b0044c130109a5d7b5fb5c317c02b4e28c1
// simon ->  88e16a1019277b15d58faf0541e11910eb756f6