android/libwvdrmengine/cdm/util/src/string_conversions.cpp

// Copyright 2018 Google LLC. All Rights Reserved. This file and proprietary
// source code may only be used and distributed under the Widevine License
// Agreement.

#include "string_conversions.h"

#include <ctype.h>
#include <stdint.h>
#include <stdio.h>
#include <string.h>

#include <iostream>

#include "log.h"
#include "platform.h"

namespace wvutil {
namespace {
// Base64 character set, indexed for their 6-bit mapping, plus '='.
const char kBase64Codes[] =
    "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/=";
// URL safe Base64 character set.
const char kBase64SafeCodes[] =
    "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789-_=";

// Gets the low |n| bits of |in|.
#define GET_LOW_BITS(in, n) ((in) & ((1 << (n)) - 1))
// Gets the given (zero-indexed) bits [a, b) of |in|.
#define GET_BITS(in, a, b) GET_LOW_BITS((in) >> (a), (b) - (a))
// Calculates a/b using round-up division (only works for positive numbers).
#define CEIL_DIVIDE(a, b) ((((a)-1) / (b)) + 1)

// Decodes a single Base64 encoded character into its 6-bit value.
// The provided |codes| must be a Base64 character map.
int DecodeBase64Char(char c, const char* codes) {
  const char* c_in_codes = strchr(codes, c);
  if (c_in_codes == nullptr) return -1;
  const uintptr_t c_in_codes_int = reinterpret_cast<uintptr_t>(c_in_codes);
  const uintptr_t codes_int = reinterpret_cast<uintptr_t>(codes);
  return static_cast<int>(c_in_codes_int - codes_int);
}

bool DecodeHexChar(char ch, uint8_t* digit) {
  if (ch >= '0' && ch <= '9') {
    *digit = ch - '0';
    return true;
  }
  ch = tolower(ch);
  if ((ch >= 'a') && (ch <= 'f')) {
    *digit = ch - 'a' + 10;
    return true;
  }
  return false;
}

// Encode for standard base64 encoding (RFC4648).
// https://en.wikipedia.org/wiki/Base64
// Text    |       M        |       a       |       n        |
// ASCI    |   77 (0x4d)    |   97 (0x61)   |   110 (0x6e)   |
// Bits    | 0 1 0 0 1 1 0 1 0 1 1 0 0 0 0 1 0 1 1 0 1 1 1 0 |
// Index   |     19     |     22    |      5    |     46     |
// Base64  |      T     |      W    |      F    |      u     |
//         | <-----------------  24-bits  -----------------> |

// The provided |codes| must be a Base64 character map.
std::string Base64EncodeInternal(const uint8_t* data, size_t length,
                                 const char* codes) {
  // |temp| stores a 24-bit block that is treated as an array where insertions
  // occur from high to low.
  uint32_t temp = 0;
  size_t out_index = 0;
  const size_t out_size = CEIL_DIVIDE(length, 3) * 4;
  std::string result(out_size, '\0');
  for (size_t i = 0; i < length; i++) {
    // "insert" 8-bits of data
    temp |= (data[i] << ((2 - (i % 3)) * 8));
    if (i % 3 == 2) {
      result[out_index++] = codes[GET_BITS(temp, 18, 24)];
      result[out_index++] = codes[GET_BITS(temp, 12, 18)];
      result[out_index++] = codes[GET_BITS(temp, 6, 12)];
      result[out_index++] = codes[GET_BITS(temp, 0, 6)];
      temp = 0;
    }
  }
  if (length % 3 == 1) {
    result[out_index++] = codes[GET_BITS(temp, 18, 24)];
    result[out_index++] = codes[GET_BITS(temp, 12, 18)];
    result[out_index++] = '=';
    result[out_index++] = '=';
  } else if (length % 3 == 2) {
    result[out_index++] = codes[GET_BITS(temp, 18, 24)];
    result[out_index++] = codes[GET_BITS(temp, 12, 18)];
    result[out_index++] = codes[GET_BITS(temp, 6, 12)];
    result[out_index++] = '=';
  }
  return result;
}

std::vector<uint8_t> Base64DecodeInternal(const char* encoded, size_t length,
                                          const char* codes) {
  const size_t out_size_max = CEIL_DIVIDE(length * 3, 4);
  std::vector<uint8_t> result(out_size_max, '\0');
  // |temp| stores 24-bits of data that is treated as an array where insertions
  // occur from high to low.
  uint32_t temp = 0;
  size_t out_index = 0;
  size_t i;
  for (i = 0; i < length; i++) {
    if (encoded[i] == '=') {
      // Verify an '=' only appears at the end.  We want i to remain at the
      // first '=', so we need an inner loop.
      for (size_t j = i; j < length; j++) {
        if (encoded[j] != '=') {
          LOGE("base64Decode failed");
          return std::vector<uint8_t>();
        }
      }
      if (length % 4 != 0) {
        // If padded, then the length must be a multiple of 4.
        // Unpadded messages are OK.
        LOGE("base64Decode failed");
        return std::vector<uint8_t>();
      }
      break;
    }

    const int decoded = DecodeBase64Char(encoded[i], codes);
    if (decoded < 0) {
      LOGE("base64Decode failed");
      return std::vector<uint8_t>();
    }
    // "insert" 6-bits of data
    temp |= (decoded << ((3 - (i % 4)) * 6));

    if (i % 4 == 3) {
      result[out_index++] = GET_BITS(temp, 16, 24);
      result[out_index++] = GET_BITS(temp, 8, 16);
      result[out_index++] = GET_BITS(temp, 0, 8);
      temp = 0;
    }
  }

  switch (i % 4) {
    case 1:
      LOGE("base64Decode failed");
      return std::vector<uint8_t>();
    case 2:
      result[out_index++] = GET_BITS(temp, 16, 24);
      break;
    case 3:
      result[out_index++] = GET_BITS(temp, 16, 24);
      result[out_index++] = GET_BITS(temp, 8, 16);
      break;
  }
  result.resize(out_index);
  return result;
}
}  // namespace

// converts an ascii hex string(2 bytes per digit) into a decimal byte string
std::vector<uint8_t> a2b_hex(const std::string& byte) {
  std::vector<uint8_t> array;
  size_t count = byte.size();
  if (count == 0 || (count % 2) != 0) {
    LOGE("Invalid input size %zu for string %s", count, byte.c_str());
    return array;
  }

  for (size_t i = 0; i < count / 2; ++i) {
    unsigned char msb = 0;  // most significant 4 bits
    unsigned char lsb = 0;  // least significant 4 bits
    if (!DecodeHexChar(byte[i * 2], &msb) ||
        !DecodeHexChar(byte[i * 2 + 1], &lsb)) {
      LOGE("Invalid hex value %c%c at index %zu", byte[i * 2], byte[i * 2 + 1],
           i);
      return array;
    }
    array.push_back((msb << 4) | lsb);
  }
  return array;
}

// converts an ascii hex string(2 bytes per digit) into a decimal byte string
// dump the string with the label.
std::vector<uint8_t> a2b_hex(const std::string& label,
                             const std::string& byte) {
  std::cout << std::endl
            << "[[DUMP: " << label << " ]= \"" << byte << "\"]" << std::endl
            << std::endl;

  return a2b_hex(byte);
}

std::string a2bs_hex(const std::string& byte) {
  std::vector<uint8_t> array = a2b_hex(byte);
  return std::string(array.begin(), array.end());
}

std::string b2a_hex(const std::vector<uint8_t>& byte) {
  if (byte.empty()) return "";
  return HexEncode(byte.data(), byte.size());
}

std::string unlimited_b2a_hex(const std::vector<uint8_t>& byte) {
  if (byte.empty()) return "";
  return UnlimitedHexEncode(byte.data(), byte.size());
}

std::string b2a_hex(const std::string& byte) {
  if (byte.empty()) return "";
  return HexEncode(reinterpret_cast<const uint8_t*>(byte.data()),
                   byte.length());
}

std::string unlimited_b2a_hex(const std::string& byte) {
  if (byte.empty()) return "";
  return UnlimitedHexEncode(reinterpret_cast<const uint8_t*>(byte.data()),
                            byte.length());
}

std::string HexEncode(const uint8_t* in_buffer, size_t size) {
  constexpr unsigned int kMaxSafeSize = 2048;
  if (size > kMaxSafeSize) size = kMaxSafeSize;
  return UnlimitedHexEncode(in_buffer, size);
}

std::string UnlimitedHexEncode(const uint8_t* in_buffer, size_t size) {
  static const char kHexChars[] = "0123456789ABCDEF";
  if (size == 0) return "";
  // Each input byte creates two output hex characters.
  std::string out_buffer(size * 2, '\0');
  for (unsigned int i = 0; i < size; ++i) {
    char byte = in_buffer[i];
    out_buffer[(i << 1)] = kHexChars[(byte >> 4) & 0xf];
    out_buffer[(i << 1) + 1] = kHexChars[byte & 0xf];
  }
  return out_buffer;
}

// Standard Base64 encoding and decoding.

std::string Base64Encode(const std::vector<uint8_t>& bin_input) {
  if (bin_input.empty()) {
    return std::string();
  }
  return Base64EncodeInternal(bin_input.data(), bin_input.size(), kBase64Codes);
}

std::string Base64Encode(const std::string& bin_input) {
  if (bin_input.empty()) {
    return std::string();
  }
  return Base64EncodeInternal(
      reinterpret_cast<const uint8_t*>(bin_input.data()), bin_input.size(),
      kBase64Codes);
}

// Decode for standard base64 encoding (RFC4648).
std::vector<uint8_t> Base64Decode(const std::string& b64_input) {
  if (b64_input.empty()) {
    return std::vector<uint8_t>();
  }
  return Base64DecodeInternal(b64_input.data(), b64_input.size(), kBase64Codes);
}

// URL/Filename Safe Base64 encoding and decoding.

// This is the encoding required to interface with the provisioning server, as
// well as for certain license server transactions.  It is also used for logging
// certain strings. The difference between web safe encoding vs regular encoding
// is that the web safe version replaces '+' with '-' and '/' with '_'.
std::string Base64SafeEncode(const std::vector<uint8_t>& bin_input) {
  if (bin_input.empty()) {
    return std::string();
  }
  return Base64EncodeInternal(bin_input.data(), bin_input.size(),
                              kBase64SafeCodes);
}

std::string Base64SafeEncode(const std::string& bin_input) {
  if (bin_input.empty()) {
    return std::string();
  }
  return Base64EncodeInternal(
      reinterpret_cast<const uint8_t*>(bin_input.data()), bin_input.size(),
      kBase64SafeCodes);
}

std::vector<uint8_t> Base64SafeDecode(const std::string& b64_input) {
  if (b64_input.empty()) {
    return std::vector<uint8_t>();
  }
  return Base64DecodeInternal(b64_input.data(), b64_input.size(),
                              kBase64SafeCodes);
}

// URL/Filename Safe Base64 encoding without padding.

std::string Base64SafeEncodeNoPad(const std::vector<uint8_t>& bin_input) {
  std::string b64_output = Base64SafeEncode(bin_input);
  // Output size: ceiling [ bin_input.size() * 4 / 3 ].
  b64_output.resize((bin_input.size() * 4 + 2) / 3);
  return b64_output;
}

std::string Base64SafeEncodeNoPad(const std::string& bin_input) {
  std::string b64_output = Base64SafeEncode(bin_input);
  // Output size: ceiling [ bin_input.size() * 4 / 3 ].
  b64_output.resize((bin_input.size() * 4 + 2) / 3);
  return b64_output;
}

// Host to Network/Network to Host conversion.

// Convert to big endian (network-byte-order)
int64_t htonll64(int64_t x) {
  union {
    uint32_t array[2];
    int64_t number;
  } mixed;
  mixed.number = 1;
  if (mixed.array[0] == 1) {  // Little Endian.
    mixed.number = x;
    uint32_t temp = mixed.array[0];
    mixed.array[0] = htonl(mixed.array[1]);
    mixed.array[1] = htonl(temp);
    return mixed.number;
  } else {  // Big Endian.
    return x;
  }
}

// Encode unsigned integer into a big endian formatted string
std::string EncodeUint32(unsigned int u) {
  std::string s;
  s.push_back((u >> 24) & 0xFF);
  s.push_back((u >> 16) & 0xFF);
  s.push_back((u >> 8) & 0xFF);
  s.push_back(u & 0xFF);
  return s;
}

}  // namespace wvutil