How do I base64 encode (decode) in C?

Question

I have binary data in an unsigned char variable. I need to convert them to PEM base64 in c. I looked in openssl library but i could not find any function. Does any body have any idea?

Answer 1

glib has functions for base64 encoding: http://library.gnome.org/devel/glib/2.18/glib-Base64-Encoding.html

Answer 2

But you can also do it in openssl (openssl enc command does it....), look at the BIO_f_base64() function

Answer 3

GNU coreutils has it in lib/base64. It's a little bloated but deals with stuff like EBCDIC. You can also play around on your own, e.g.,

char base64_digit (n) unsigned n; {
  if (n < 10) return n - '0';
  else if (n < 10 + 26) return n - 'a';
  else if (n < 10 + 26 + 26) return n - 'A';
  else assert(0);
  return 0;
}

unsigned char base64_decode_digit(char c) {
  switch (c) {
    case '=' : return 62;
    case '.' : return 63;
    default  :
      if (isdigit(c)) return c - '0';
      else if (islower(c)) return c - 'a' + 10;
      else if (isupper(c)) return c - 'A' + 10 + 26;
      else assert(0);
  }
  return 0xff;
}

unsigned base64_decode(char *s) {
  char *p;
  unsigned n = 0;

  for (p = s; *p; p++)
    n = 64 * n + base64_decode_digit(*p);

  return n;
}

Answer 4

Here's the decoder I've been using for years...

    static const char  table[] = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
    static const int   BASE64_INPUT_SIZE = 57;

    BOOL isbase64(char c)
    {
       return c && strchr(table, c) != NULL;
    }

    inline char value(char c)
    {
       const char *p = strchr(table, c);
       if(p) {
          return p-table;
       } else {
          return 0;
       }
    }

    int UnBase64(unsigned char *dest, const unsigned char *src, int srclen)
    {
       *dest = 0;
       if(*src == 0) 
       {
          return 0;
       }
       unsigned char *p = dest;
       do
       {

          char a = value(src[0]);
          char b = value(src[1]);
          char c = value(src[2]);
          char d = value(src[3]);
          *p++ = (a << 2) | (b >> 4);
          *p++ = (b << 4) | (c >> 2);
          *p++ = (c << 6) | d;
          if(!isbase64(src[1])) 
          {
             p -= 2;
             break;
          } 
          else if(!isbase64(src[2])) 
          {
             p -= 2;
             break;
          } 
          else if(!isbase64(src[3])) 
          {
             p--;
             break;
          }
          src += 4;
          while(*src && (*src == 13 || *src == 10)) src++;
       }
       while(srclen-= 4);
       *p = 0;
       return p-dest;
    }

Answer 5

BASE64 Source Code in C

http://base64.sourceforge.net/

Answer 6

Larry - could you explain what the "value" function is in your UnBase64 code sample? A C lib function I hope?

Thanks! :)