LCOV - code coverage report
Current view: top level - src - bech32.cpp (source / functions) Hit Total Coverage
Test: total_coverage.info Lines: 67 67 100.0 %
Date: 2025-02-23 09:33:43 Functions: 6 6 100.0 %

          Line data    Source code
       1             : // Copyright (c) 2017 Pieter Wuille
       2             : // Distributed under the MIT software license, see the accompanying
       3             : // file COPYING or http://www.opensource.org/licenses/mit-license.php.
       4             : 
       5             : #include "bech32.h"
       6             : #include "util/vector.h"
       7             : 
       8             : #include <assert.h>
       9             : 
      10             : namespace
      11             : {
      12             : 
      13             : typedef std::vector<uint8_t> data;
      14             : 
      15             : /** The Bech32 character set for encoding. */
      16             : const char* CHARSET = "qpzry9x8gf2tvdw0s3jn54khce6mua7l";
      17             : 
      18             : /** The Bech32 character set for decoding. */
      19             : const int8_t CHARSET_REV[128] = {
      20             :     -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
      21             :     -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
      22             :     -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
      23             :     15, -1, 10, 17, 21, 20, 26, 30,  7,  5, -1, -1, -1, -1, -1, -1,
      24             :     -1, 29, -1, 24, 13, 25,  9,  8, 23, -1, 18, 22, 31, 27, 19, -1,
      25             :      1,  0,  3, 16, 11, 28, 12, 14,  6,  4,  2, -1, -1, -1, -1, -1,
      26             :     -1, 29, -1, 24, 13, 25,  9,  8, 23, -1, 18, 22, 31, 27, 19, -1,
      27             :      1,  0,  3, 16, 11, 28, 12, 14,  6,  4,  2, -1, -1, -1, -1, -1
      28             : };
      29             : 
      30             : /** This function will compute what 6 5-bit values to XOR into the last 6 input values, in order to
      31             :  *  make the checksum 0. These 6 values are packed together in a single 30-bit integer. The higher
      32             :  *  bits correspond to earlier values. */
      33       26686 : uint32_t PolyMod(const data& v)
      34             : {
      35             :     // The input is interpreted as a list of coefficients of a polynomial over F = GF(32), with an
      36             :     // implicit 1 in front. If the input is [v0,v1,v2,v3,v4], that polynomial is v(x) =
      37             :     // 1*x^5 + v0*x^4 + v1*x^3 + v2*x^2 + v3*x + v4. The implicit 1 guarantees that
      38             :     // [v0,v1,v2,...] has a distinct checksum from [0,v0,v1,v2,...].
      39             : 
      40             :     // The output is a 30-bit integer whose 5-bit groups are the coefficients of the remainder of
      41             :     // v(x) mod g(x), where g(x) is the Bech32 generator,
      42             :     // x^6 + {29}x^5 + {22}x^4 + {20}x^3 + {21}x^2 + {29}x + {18}. g(x) is chosen in such a way
      43             :     // that the resulting code is a BCH code, guaranteeing detection of up to 3 errors within a
      44             :     // window of 1023 characters. Among the various possible BCH codes, one was selected to in
      45             :     // fact guarantee detection of up to 4 errors within a window of 89 characters.
      46             : 
      47             :     // Note that the coefficients are elements of GF(32), here represented as decimal numbers
      48             :     // between {}. In this finite field, addition is just XOR of the corresponding numbers. For
      49             :     // example, {27} + {13} = {27 ^ 13} = {22}. Multiplication is more complicated, and requires
      50             :     // treating the bits of values themselves as coefficients of a polynomial over a smaller field,
      51             :     // GF(2), and multiplying those polynomials mod a^5 + a^3 + 1. For example, {5} * {26} =
      52             :     // (a^2 + 1) * (a^4 + a^3 + a) = (a^4 + a^3 + a) * a^2 + (a^4 + a^3 + a) = a^6 + a^5 + a^4 + a
      53             :     // = a^3 + 1 (mod a^5 + a^3 + 1) = {9}.
      54             : 
      55             :     // During the course of the loop below, `c` contains the bitpacked coefficients of the
      56             :     // polynomial constructed from just the values of v that were processed so far, mod g(x). In
      57             :     // the above example, `c` initially corresponds to 1 mod (x), and after processing 2 inputs of
      58             :     // v, it corresponds to x^2 + v0*x + v1 mod g(x). As 1 mod g(x) = 1, that is the starting value
      59             :     // for `c`.
      60       26686 :     uint32_t c = 1;
      61     4473144 :     for (auto v_i : v) {
      62             :         // We want to update `c` to correspond to a polynomial with one extra term. If the initial
      63             :         // value of `c` consists of the coefficients of c(x) = f(x) mod g(x), we modify it to
      64             :         // correspond to c'(x) = (f(x) * x + v_i) mod g(x), where v_i is the next input to
      65             :         // process. Simplifying:
      66             :         // c'(x) = (f(x) * x + v_i) mod g(x)
      67             :         //         ((f(x) mod g(x)) * x + v_i) mod g(x)
      68             :         //         (c(x) * x + v_i) mod g(x)
      69             :         // If c(x) = c0*x^5 + c1*x^4 + c2*x^3 + c3*x^2 + c4*x + c5, we want to compute
      70             :         // c'(x) = (c0*x^5 + c1*x^4 + c2*x^3 + c3*x^2 + c4*x + c5) * x + v_i mod g(x)
      71             :         //       = c0*x^6 + c1*x^5 + c2*x^4 + c3*x^3 + c4*x^2 + c5*x + v_i mod g(x)
      72             :         //       = c0*(x^6 mod g(x)) + c1*x^5 + c2*x^4 + c3*x^3 + c4*x^2 + c5*x + v_i
      73             :         // If we call (x^6 mod g(x)) = k(x), this can be written as
      74             :         // c'(x) = (c1*x^5 + c2*x^4 + c3*x^3 + c4*x^2 + c5*x + v_i) + c0*k(x)
      75             : 
      76             :         // First, determine the value of c0:
      77     4446451 :         uint8_t c0 = c >> 25;
      78             : 
      79             :         // Then compute c1*x^5 + c2*x^4 + c3*x^3 + c4*x^2 + c5*x + v_i:
      80     4446451 :         c = ((c & 0x1ffffff) << 5) ^ v_i;
      81             : 
      82             :         // Finally, for each set bit n in c0, conditionally add {2^n}k(x):
      83     4446451 :         if (c0 & 1)  c ^= 0x3b6a57b2; //     k(x) = {29}x^5 + {22}x^4 + {20}x^3 + {21}x^2 + {29}x + {18}
      84     4446451 :         if (c0 & 2)  c ^= 0x26508e6d; //  {2}k(x) = {19}x^5 +  {5}x^4 +     x^3 +  {3}x^2 + {19}x + {13}
      85     4446451 :         if (c0 & 4)  c ^= 0x1ea119fa; //  {4}k(x) = {15}x^5 + {10}x^4 +  {2}x^3 +  {6}x^2 + {15}x + {26}
      86     4446451 :         if (c0 & 8)  c ^= 0x3d4233dd; //  {8}k(x) = {30}x^5 + {20}x^4 +  {4}x^3 + {12}x^2 + {30}x + {29}
      87     4446451 :         if (c0 & 16) c ^= 0x2a1462b3; // {16}k(x) = {21}x^5 +     x^4 +  {8}x^3 + {24}x^2 + {21}x + {19}
      88             :     }
      89       26686 :     return c;
      90             : }
      91             : 
      92             : /** Convert to lower case. */
      93      119360 : inline unsigned char LowerCase(unsigned char c)
      94             : {
      95      119360 :     return (c >= 'A' && c <= 'Z') ? (c - 'A') + 'a' : c;
      96             : }
      97             : 
      98             : /** Expand a HRP for use in checksum computation. */
      99       26686 : data ExpandHRP(const std::string& hrp)
     100             : {
     101       26686 :     data ret;
     102       26686 :     ret.reserve(hrp.size() + 90);
     103       26686 :     ret.resize(hrp.size() * 2 + 1);
     104      326119 :     for (size_t i = 0; i < hrp.size(); ++i) {
     105      299433 :         unsigned char c = hrp[i];
     106      299433 :         ret[i] = c >> 5;
     107      299433 :         ret[i + hrp.size() + 1] = c & 0x1f;
     108             :     }
     109       26686 :     ret[hrp.size()] = 0;
     110       26686 :     return ret;
     111             : }
     112             : 
     113             : /** Verify a checksum. */
     114        8601 : bool VerifyChecksum(const std::string& hrp, const data& values)
     115             : {
     116             :     // PolyMod computes what value to xor into the final values to make the checksum 0. However,
     117             :     // if we required that the checksum was 0, it would be the case that appending a 0 to a valid
     118             :     // list of values would result in a new valid list. For that reason, Bech32 requires the
     119             :     // resulting checksum to be 1 instead.
     120       17202 :     return PolyMod(Cat(ExpandHRP(hrp), values)) == 1;
     121             : }
     122             : 
     123             : /** Create a checksum. */
     124       18085 : data CreateChecksum(const std::string& hrp, const data& values)
     125             : {
     126       18085 :     data enc = Cat(ExpandHRP(hrp), values);
     127       18085 :     enc.resize(enc.size() + 6); // Append 6 zeroes
     128       18085 :     uint32_t mod = PolyMod(enc) ^ 1; // Determine what to XOR into those 6 zeroes.
     129       18085 :     data ret(6);
     130      126595 :     for (size_t i = 0; i < 6; ++i) {
     131             :         // Convert the 5-bit groups in mod to checksum values.
     132      108510 :         ret[i] = (mod >> (5 * (5 - i))) & 31;
     133             :     }
     134       36170 :     return ret;
     135             : }
     136             : 
     137             : } // namespace
     138             : 
     139             : namespace bech32
     140             : {
     141             : 
     142             : /** Encode a Bech32 string. */
     143       18085 : std::string Encode(const std::string& hrp, const data& values) {
     144       36170 :     data checksum = CreateChecksum(hrp, values);
     145       36170 :     data combined = Cat(values, checksum);
     146       36170 :     std::string ret = hrp + '1';
     147       18085 :     ret.reserve(ret.size() + combined.size());
     148     2367257 :     for (auto c : combined) {
     149     2349616 :         if (c >= 32) {
     150         446 :             return "";
     151             :         }
     152     2349166 :         ret += CHARSET[c];
     153             :     }
     154       35724 :     return ret;
     155             : }
     156             : 
     157             : /** Decode a Bech32 string. */
     158        9554 : std::pair<std::string, data> Decode(const std::string& str) {
     159        9554 :     bool lower = false, upper = false;
     160     1638811 :     for (size_t i = 0; i < str.size(); ++i) {
     161     1629261 :         unsigned char c = str[i];
     162     1629261 :         if (c < 33 || c > 126) return {};
     163     1629261 :         if (c >= 'a' && c <= 'z') lower = true;
     164     1629261 :         if (c >= 'A' && c <= 'Z') upper = true;
     165             :     }
     166        9550 :     if (lower && upper) return {};
     167        8608 :     size_t pos = str.rfind('1');
     168        8608 :     if (str.size() > 1023 || pos == str.npos || pos == 0 || pos + 7 > str.size()) {
     169           6 :         return {};
     170             :     }
     171       18156 :     data values(str.size() - 1 - pos);
     172     1460930 :     for (size_t i = 0; i < str.size() - 1 - pos; ++i) {
     173     1452338 :         unsigned char c = str[i + pos + 1];
     174     1452338 :         int8_t rev = (c < 33 || c > 126) ? -1 : CHARSET_REV[c];
     175     1452338 :         if (rev == -1) {
     176           1 :             return {};
     177             :         }
     178     1452328 :         values[i] = rev;
     179             :     }
     180       17203 :     std::string hrp;
     181      127961 :     for (size_t i = 0; i < pos; ++i) {
     182      119362 :         hrp += LowerCase(str[i]);
     183             :     }
     184        8601 :     if (!VerifyChecksum(hrp, values)) {
     185        8601 :         return {};
     186             :     }
     187       17192 :     return {hrp, data(values.begin(), values.end() - 6)};
     188             : }
     189             : 
     190             : } // namespace bech32

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