text: //  --------------------------------------------------------------------------
  //  Reference implementation for rfc.zeromq.org/spec:32/Z85
  //
  //  This implementation provides a Z85 codec as an easy-to-reuse C class 
  //  designed to be easy to port into other languages.
  
  //  --------------------------------------------------------------------------
  //  Copyright (c) 2010-2013 iMatix Corporation and Contributors
  //  
  //  Permission is hereby granted, free of charge, to any person obtaining a 
  //  copy of this software and associated documentation files (the "Software"),
  //  to deal in the Software without restriction, including without limitation 
  //  the rights to use, copy, modify, merge, publish, distribute, sublicense, 
  //  and/or sell copies of the Software, and to permit persons to whom the 
  //  Software is furnished to do so, subject to the following conditions:
  //  
  //  The above copyright notice and this permission notice shall be included in 
  //  all copies or substantial portions of the Software.
  //  
  //  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR 
  //  IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, 
  //  FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL 
  //  THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
  //  LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING 
  //  FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER 
  //  DEALINGS IN THE SOFTWARE.
  //  --------------------------------------------------------------------------
  
  #include <stdlib.h>
  #include <stdint.h>
  #include <stdio.h>
  #include <string.h>
  #include <assert.h>
  
  //  Basic language taken from CZMQ's prelude
  typedef unsigned char byte;
  #define streq(s1,s2) (!strcmp ((s1), (s2)))
  
  //  Maps base 256 to base 85
  static char encoder [85 + 1] = {
      "0123456789" 
      "abcdefghij" 
      "klmnopqrst" 
      "uvwxyzABCD"
      "EFGHIJKLMN" 
      "OPQRSTUVWX" 
      "YZ.-:+=^!/" 
      "*?&<>()[]{" 
      "}@%$#"
  };
  
  //  Maps base 85 to base 256
  //  We chop off lower 32 and higher 128 ranges
  static byte decoder [96] = {
      0x00, 0x44, 0x00, 0x54, 0x53, 0x52, 0x48, 0x00, 
      0x4B, 0x4C, 0x46, 0x41, 0x00, 0x3F, 0x3E, 0x45, 
      0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 
      0x08, 0x09, 0x40, 0x00, 0x49, 0x42, 0x4A, 0x47, 
      0x51, 0x24, 0x25, 0x26, 0x27, 0x28, 0x29, 0x2A, 
      0x2B, 0x2C, 0x2D, 0x2E, 0x2F, 0x30, 0x31, 0x32, 
      0x33, 0x34, 0x35, 0x36, 0x37, 0x38, 0x39, 0x3A, 
      0x3B, 0x3C, 0x3D, 0x4D, 0x00, 0x4E, 0x43, 0x00, 
      0x00, 0x0A, 0x0B, 0x0C, 0x0D, 0x0E, 0x0F, 0x10, 
      0x11, 0x12, 0x13, 0x14, 0x15, 0x16, 0x17, 0x18, 
      0x19, 0x1A, 0x1B, 0x1C, 0x1D, 0x1E, 0x1F, 0x20, 
      0x21, 0x22, 0x23, 0x4F, 0x00, 0x50, 0x00, 0x00
  };
  
  //  --------------------------------------------------------------------------
  //  Encode a byte array as a string
  
  char *
  Z85_encode (byte *data, size_t size)
  {
      //  Accepts only byte arrays bounded to 4 bytes
      if (size % 4)
          return NULL;
      
      size_t encoded_size = size * 5 / 4;
      char *encoded = malloc (encoded_size + 1);
      uint char_nbr = 0;
      uint byte_nbr = 0;
      uint32_t value = 0;
      while (byte_nbr < size) {
          //  Accumulate value in base 256 (binary)
          value = value * 256 + data [byte_nbr++];
          if (byte_nbr % 4 == 0) {
              //  Output value in base 85
              uint divisor = 85 * 85 * 85 * 85;
              while (divisor) {
                  encoded [char_nbr++] = encoder [value / divisor % 85];
                  divisor /= 85;
              }
              value = 0;
          }
      }
      assert (char_nbr == encoded_size);
      encoded [char_nbr] = 0;
      return encoded;
  }
  
      
  //  --------------------------------------------------------------------------
  //  Decode an encoded string into a byte array; size of array will be
  //  strlen (string) * 4 / 5.
  
  byte *
  Z85_decode (char *string)
  {
      //  Accepts only strings bounded to 5 bytes
      if (strlen (string) % 5)
          return NULL;
      
      size_t decoded_size = strlen (string) * 4 / 5;
      byte *decoded = malloc (decoded_size);
  
      uint byte_nbr = 0;
      uint char_nbr = 0;
      uint32_t value = 0;
      while (char_nbr < strlen (string)) {
          //  Accumulate value in base 85
          value = value * 85 + decoder [(byte) string [char_nbr++] - 32];
          if (char_nbr % 5 == 0) {
              //  Output value in base 256
              uint divisor = 256 * 256 * 256;
              while (divisor) {
                  decoded [byte_nbr++] = value / divisor % 256;
                  divisor /= 256;
              }
              value = 0;
          }
      }
      assert (byte_nbr == decoded_size);
      return decoded;
  }
  
  int main (void)
  {
      byte test_data_1 [8] = {
          0x86, 0x4F, 0xD2, 0x6F, 0xB5, 0x59, 0xF7, 0x5B
      };
      byte test_data_2 [32] = {
          0x8E, 0x0B, 0xDD, 0x69, 0x76, 0x28, 0xB9, 0x1D, 
          0x8F, 0x24, 0x55, 0x87, 0xEE, 0x95, 0xC5, 0xB0, 
          0x4D, 0x48, 0x96, 0x3F, 0x79, 0x25, 0x98, 0x77, 
          0xB4, 0x9C, 0xD9, 0x06, 0x3A, 0xEA, 0xD3, 0xB7  
      };
      char *encoded;
      byte *decoded;
  
      encoded = Z85_encode (NULL, 0);
      decoded = Z85_decode (encoded);
      assert (streq (encoded, ""));
      free (decoded);
      free (encoded);
      
      encoded = Z85_encode (test_data_1, 3);
      assert (encoded == NULL);
      
      encoded = Z85_encode (test_data_1, sizeof (test_data_1));
      assert (strlen (encoded) == 10);
      assert (streq (encoded, "HelloWorld"));
      decoded = Z85_decode (encoded);
      assert (memcmp (test_data_1, decoded, sizeof (test_data_1)) == 0);
      free (decoded);
      free (encoded);
      
      encoded = Z85_encode (test_data_2, sizeof (test_data_2));
      assert (strlen (encoded) == 40);
      assert (streq (encoded, "JTKVSB%%)wK0E.X)V>+}o?pNmC{O&4W4b!Ni{Lh6"));
      decoded = Z85_decode (encoded);
      assert (memcmp (test_data_2, decoded, sizeof (test_data_2)) == 0);
      free (decoded);
      free (encoded);
  
      //  Standard test keys defined by zmq_curve man page
      byte client_public [32] = { 
          0xBB, 0x88, 0x47, 0x1D, 0x65, 0xE2, 0x65, 0x9B, 
          0x30, 0xC5, 0x5A, 0x53, 0x21, 0xCE, 0xBB, 0x5A, 
          0xAB, 0x2B, 0x70, 0xA3, 0x98, 0x64, 0x5C, 0x26, 
          0xDC, 0xA2, 0xB2, 0xFC, 0xB4, 0x3F, 0xC5, 0x18
      };
      byte client_secret [32] = { 
          0x7B, 0xB8, 0x64, 0xB4, 0x89, 0xAF, 0xA3, 0x67, 
          0x1F, 0xBE, 0x69, 0x10, 0x1F, 0x94, 0xB3, 0x89, 
          0x72, 0xF2, 0x48, 0x16, 0xDF, 0xB0, 0x1B, 0x51, 
          0x65, 0x6B, 0x3F, 0xEC, 0x8D, 0xFD, 0x08, 0x88
      };
      encoded = Z85_encode (client_public, 32);
  //     puts (encoded);
      free (encoded);
      encoded = Z85_encode (client_secret, 32);
  //     puts (encoded);
      free (encoded);
  
      byte server_public [32] = { 
          0x54, 0xFC, 0xBA, 0x24, 0xE9, 0x32, 0x49, 0x96, 
          0x93, 0x16, 0xFB, 0x61, 0x7C, 0x87, 0x2B, 0xB0, 
          0xC1, 0xD1, 0xFF, 0x14, 0x80, 0x04, 0x27, 0xC5, 
          0x94, 0xCB, 0xFA, 0xCF, 0x1B, 0xC2, 0xD6, 0x52
      };
      byte server_secret [32] = { 
          0x8E, 0x0B, 0xDD, 0x69, 0x76, 0x28, 0xB9, 0x1D, 
          0x8F, 0x24, 0x55, 0x87, 0xEE, 0x95, 0xC5, 0xB0, 
          0x4D, 0x48, 0x96, 0x3F, 0x79, 0x25, 0x98, 0x77, 
          0xB4, 0x9C, 0xD9, 0x06, 0x3A, 0xEA, 0xD3, 0xB7
      };
      encoded = Z85_encode (server_public, 32);
  //     puts (encoded);
      free (encoded);
      encoded = Z85_encode (server_secret, 32);
  //     puts (encoded);
      free (encoded);
      
      exit (0);
  }
  