hex.cpp

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/*
* Hex Encoding and Decoding
* (C) 2010,2020 Jack Lloyd
*
* Botan is released under the Simplified BSD License (see license.txt)
*/
 
#include <botan/hex.h>
 
#include <botan/exceptn.h>
#include <botan/mem_ops.h>
#include <botan/internal/charset.h>
#include <botan/internal/fmt.h>
#include <botan/internal/int_utils.h>
#include <botan/internal/loadstor.h>
 
namespace Botan {
 
namespace {
 
uint16_t hex_encode_2nibble(uint8_t n8, bool uppercase) {
   // Offset for upper or lower case 'a' resp
   const uint16_t a_mask = uppercase ? 0x0707 : 0x2727;
 
   const uint16_t n = (static_cast<uint16_t>(n8 & 0xF0) << 4) | (n8 & 0x0F);
   // n >= 10? If so add offset
   const uint16_t diff = swar_lt<uint16_t>(0x0909, n) & a_mask;
   // Can't overflow between bytes, so don't need explicit SWAR addition:
   return n + 0x3030 + diff;
}
 
}  // namespace
 
void hex_encode(char output[], const uint8_t input[], size_t input_length, bool uppercase) {
   for(size_t i = 0; i != input_length; ++i) {
      const uint16_t h = hex_encode_2nibble(input[i], uppercase);
      output[2 * i] = get_byte<0>(h);
      output[2 * i + 1] = get_byte<1>(h);
   }
}
 
std::string hex_encode(const uint8_t input[], size_t input_length, bool uppercase) {
   const size_t output_length = mul_or_throw<size_t>(2, input_length, "Input too large to hex encode");
   std::string output(output_length, 0);
 
   if(input_length > 0) {
      hex_encode(&output.front(), input, input_length, uppercase);
   }
 
   return output;
}
 
namespace {
 
uint8_t hex_char_to_bin(char input) {
   // Starts of valid value ranges (v_lo) and their lengths (v_range)
   constexpr uint64_t v_lo = make_uint64(0, '0', 'a', 'A', ' ', '\n', '\t', '\r');
   constexpr uint64_t v_range = make_uint64(0, 10, 6, 6, 1, 1, 1, 1);
   constexpr uint64_t expand8 = 0x0101010101010101;
   constexpr uint64_t top64 = 0x8000000000000000;
 
   const uint8_t x = static_cast<uint8_t>(input);
   const uint64_t x8 = x * expand8;
 
   const uint64_t v_mask = swar_in_range<uint64_t>(x8, v_lo, v_range) ^ top64;
 
   // This is the offset added to x to get the value we need
   const uint64_t val_v = 0xd0a9c960767773 ^ static_cast<uint64_t>(0xFF - x) << 56;
 
   return x + static_cast<uint8_t>(val_v >> (8 * index_of_first_set_byte(v_mask)));
}
 
}  // namespace
 
size_t hex_decode(uint8_t output[], const char input[], size_t input_length, size_t& input_consumed, bool ignore_ws) {
   uint8_t* out_ptr = output;
   bool top_nibble = true;
   uint8_t next = 0;
 
   input_consumed = 0;
 
   clear_mem(output, input_length / 2);
 
   for(size_t i = 0; i != input_length; ++i) {
      const uint8_t bin = hex_char_to_bin(input[i]);
 
      if(bin >= 0x10) {
         if(bin == 0x80 && ignore_ws) {
            continue;
         }
 
         throw Invalid_Argument(fmt("hex_decode: invalid character '{}'", format_char_for_display(input[i])));
      }
 
      if(top_nibble) {
         next = bin << 4;
      } else {
         next |= bin;
         *out_ptr = next;
      }
 
      top_nibble = !top_nibble;
      if(top_nibble) {
         ++out_ptr;
         input_consumed = i + 1;
      }
   }
 
   /*
   * Consume trailing whitespace following the last full byte; a leftover
   * unpaired nibble (if any) stops the scan and is left unconsumed.
   */
   while(input_consumed < input_length && hex_char_to_bin(input[input_consumed]) == 0x80) {
      ++input_consumed;
   }
 
   return (out_ptr - output);
}
 
size_t hex_decode(uint8_t output[], const char input[], size_t input_length, bool ignore_ws) {
   size_t consumed = 0;
   const size_t written = hex_decode(output, input, input_length, consumed, ignore_ws);
 
   if(consumed != input_length) {
      throw Invalid_Argument("hex_decode: input did not have full bytes");
   }
 
   return written;
}
 
size_t hex_decode(uint8_t output[], std::string_view input, bool ignore_ws) {
   return hex_decode(output, input.data(), input.length(), ignore_ws);
}
 
size_t hex_decode(std::span<uint8_t> output, std::string_view input, bool ignore_ws) {
   if(output.size() < input.length() / 2) {
      throw Invalid_Argument("hex_decode: output buffer too small");
   }
   return hex_decode(output.data(), input.data(), input.length(), ignore_ws);
}
 
secure_vector<uint8_t> hex_decode_locked(const char input[], size_t input_length, bool ignore_ws) {
   secure_vector<uint8_t> bin(1 + input_length / 2);
 
   const size_t written = hex_decode(bin.data(), input, input_length, ignore_ws);
 
   bin.resize(written);
   return bin;
}
 
secure_vector<uint8_t> hex_decode_locked(std::string_view input, bool ignore_ws) {
   return hex_decode_locked(input.data(), input.size(), ignore_ws);
}
 
std::vector<uint8_t> hex_decode(const char input[], size_t input_length, bool ignore_ws) {
   std::vector<uint8_t> bin(1 + input_length / 2);
 
   const size_t written = hex_decode(bin.data(), input, input_length, ignore_ws);
 
   bin.resize(written);
   return bin;
}
 
std::vector<uint8_t> hex_decode(std::string_view input, bool ignore_ws) {
   return hex_decode(input.data(), input.size(), ignore_ws);
}
 
}  // namespace Botan