Changeset View
Changeset View
Standalone View
Standalone View
src/bech32.cpp
- This file was added.
// Copyright (c) 2017 Pieter Wuille | |||||
// Distributed under the MIT software license, see the accompanying | |||||
// file COPYING or http://www.opensource.org/licenses/mit-license.php. | |||||
#include "bech32.h" | |||||
namespace { | |||||
typedef std::vector<uint8_t> data; | |||||
/** The Bech32 character set for encoding. */ | |||||
const char *CHARSET = "qpzry9x8gf2tvdw0s3jn54khce6mua7l"; | |||||
/** The Bech32 character set for decoding. */ | |||||
const int8_t CHARSET_REV[128] = { | |||||
-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, | |||||
-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, | |||||
-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, 15, -1, 10, 17, 21, 20, 26, 30, 7, | |||||
5, -1, -1, -1, -1, -1, -1, -1, 29, -1, 24, 13, 25, 9, 8, 23, -1, 18, 22, | |||||
31, 27, 19, -1, 1, 0, 3, 16, 11, 28, 12, 14, 6, 4, 2, -1, -1, -1, -1, | |||||
-1, -1, 29, -1, 24, 13, 25, 9, 8, 23, -1, 18, 22, 31, 27, 19, -1, 1, 0, | |||||
3, 16, 11, 28, 12, 14, 6, 4, 2, -1, -1, -1, -1, -1}; | |||||
/** Concatenate two byte arrays. */ | |||||
data Cat(data x, const data &y) { | |||||
x.insert(x.end(), y.begin(), y.end()); | |||||
return x; | |||||
} | |||||
/** This function will compute what 6 5-bit values to XOR into the last 6 input | |||||
* values, in order to | |||||
* make the checksum 0. These 6 values are packed together in a single 30-bit | |||||
* integer. The higher | |||||
* bits correspond to earlier values. */ | |||||
deadalnix: Please format like:
/**
* blablabla
*/
You can put the comment on one line and let… | |||||
uint32_t PolyMod(const data &v) { | |||||
// The input is interpreted as a list of coefficients of a polynomial over F | |||||
// = GF(32), with an | |||||
// implicit 1 in front. If the input is [v0,v1,v2,v3,v4], that polynomial is | |||||
// v(x) = | |||||
// 1*x^5 + v0*x^4 + v1*x^3 + v2*x^2 + v3*x + v4. The implicit 1 guarantees | |||||
// that | |||||
// [v0,v1,v2,...] has a distinct checksum from [0,v0,v1,v2,...]. | |||||
deadalnixUnsubmitted Done Inline Actionsdito deadalnix: dito | |||||
// The output is a 30-bit integer whose 5-bit groups are the coefficients of | |||||
// the remainder of | |||||
// v(x) mod g(x), where g(x) is the Bech32 generator, | |||||
// 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 | |||||
// that the resulting code is a BCH code, guaranteeing detection of up to 3 | |||||
// errors within a | |||||
// window of 1023 characters. Among the various possible BCH codes, one was | |||||
// selected to in | |||||
// fact guarantee detection of up to 4 errors within a window of 89 | |||||
// characters. | |||||
deadalnixUnsubmitted Done Inline Actionsdito deadalnix: dito | |||||
// Note that the coefficients are elements of GF(32), here represented as | |||||
// decimal numbers | |||||
// between {}. In this finite field, addition is just XOR of the | |||||
// corresponding numbers. For | |||||
// example, {27} + {13} = {27 ^ 13} = {22}. Multiplication is more | |||||
// complicated, and requires | |||||
// treating the bits of values themselves as coefficients of a polynomial | |||||
// over a smaller field, | |||||
// GF(2), and multiplying those polynomials mod a^5 + a^3 + 1. For example, | |||||
// {5} * {26} = | |||||
// (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 | |||||
// = a^3 + 1 (mod a^5 + a^3 + 1) = {9}. | |||||
deadalnixUnsubmitted Done Inline Actionsdito deadalnix: dito | |||||
// During the course of the loop below, `c` contains the bitpacked | |||||
// coefficients of the | |||||
// polynomial constructed from just the values of v that were processed so | |||||
// far, mod g(x). In | |||||
// the above example, `c` initially corresponds to 1 mod (x), and after | |||||
// processing 2 inputs of | |||||
// v, it corresponds to x^2 + v0*x + v1 mod g(x). As 1 mod g(x) = 1, that is | |||||
// the starting value | |||||
// for `c`. | |||||
deadalnixUnsubmitted Done Inline Actionsdito deadalnix: dito | |||||
uint32_t c = 1; | |||||
for (size_t i = 0; i < v.size(); ++i) { | |||||
// We want to update `c` to correspond to a polynomial with one extra | |||||
// term. If the initial | |||||
// value of `c` consists of the coefficients of c(x) = f(x) mod g(x), we | |||||
// modify it to | |||||
// correspond to c'(x) = (f(x) * x + v[i]) mod g(x), where v[i] is the | |||||
// next input to | |||||
// process. Simplifying: | |||||
// c'(x) = (f(x) * x + v[i]) mod g(x) | |||||
// ((f(x) mod g(x)) * x + v[i]) mod g(x) | |||||
// (c(x) * x + v[i]) mod g(x) | |||||
// If c(x) = c0*x^5 + c1*x^4 + c2*x^3 + c3*x^2 + c4*x + c5, we want to | |||||
// compute | |||||
// c'(x) = (c0*x^5 + c1*x^4 + c2*x^3 + c3*x^2 + c4*x + c5) * x + v[i] | |||||
// mod g(x) | |||||
// = c0*x^6 + c1*x^5 + c2*x^4 + c3*x^3 + c4*x^2 + c5*x + v[i] mod | |||||
// g(x) | |||||
// = c0*(x^6 mod g(x)) + c1*x^5 + c2*x^4 + c3*x^3 + c4*x^2 + c5*x | |||||
// + v[i] | |||||
// If we call (x^6 mod g(x)) = k(x), this can be written as | |||||
// c'(x) = (c1*x^5 + c2*x^4 + c3*x^3 + c4*x^2 + c5*x + v[i]) + c0*k(x) | |||||
// First, determine the value of c0: | |||||
uint8_t c0 = c >> 25; | |||||
// Then compute c1*x^5 + c2*x^4 + c3*x^3 + c4*x^2 + c5*x + v[i]: | |||||
c = ((c & 0x1ffffff) << 5) ^ v[i]; | |||||
// Finally, for each set bit n in c0, conditionally add {2^n}k(x): | |||||
if (c0 & 1) | |||||
c ^= 0x3b6a57b2; // k(x) = {29}x^5 + {22}x^4 + {20}x^3 + {21}x^2 | |||||
// + {29}x + {18} | |||||
deadalnixUnsubmitted Done Inline Actionsif (c0 & 1) { // k(x) = {29}x^5 + {22}x^4 + {20}x^3 + {21}x^2 + {29}x + {18} c ^= 0x3b6a57b2; } deadalnix: if (c0 & 1) {
// k(x) = {29}x^5 + {22}x^4 + {20}x^3 + {21}x^2 + {29}x + {18}
c ^=… | |||||
if (c0 & 2) | |||||
c ^= 0x26508e6d; // {2}k(x) = {19}x^5 + {5}x^4 + x^3 + {3}x^2 | |||||
// + {19}x + {13} | |||||
if (c0 & 4) | |||||
c ^= 0x1ea119fa; // {4}k(x) = {15}x^5 + {10}x^4 + {2}x^3 + {6}x^2 | |||||
// + {15}x + {26} | |||||
if (c0 & 8) | |||||
c ^= 0x3d4233dd; // {8}k(x) = {30}x^5 + {20}x^4 + {4}x^3 + {12}x^2 | |||||
// + {30}x + {29} | |||||
if (c0 & 16) | |||||
c ^= 0x2a1462b3; // {16}k(x) = {21}x^5 + x^4 + {8}x^3 + {24}x^2 | |||||
// + {21}x + {19} | |||||
} | |||||
return c; | |||||
} | |||||
/** Convert to lower case. */ | |||||
inline unsigned char LowerCase(unsigned char c) { | |||||
return (c >= 'A' && c <= 'Z') ? (c - 'A') + 'a' : c; | |||||
} | |||||
/** Expand a HRP for use in checksum computation. */ | |||||
data ExpandHRP(const std::string &hrp) { | |||||
data ret; | |||||
ret.resize(hrp.size() * 2 + 1); | |||||
for (size_t i = 0; i < hrp.size(); ++i) { | |||||
unsigned char c = hrp[i]; | |||||
ret[i] = c >> 5; | |||||
ret[i + hrp.size() + 1] = c & 0x1f; | |||||
} | |||||
ret[hrp.size()] = 0; | |||||
return ret; | |||||
} | |||||
deadalnixUnsubmitted Not Done Inline ActionsHash the lower 5 bits of all characters + a zero. deadalnix: Hash the lower 5 bits of all characters + a zero. | |||||
/** Verify a checksum. */ | |||||
bool VerifyChecksum(const std::string &hrp, const data &values) { | |||||
// PolyMod computes what value to xor into the final values to make the | |||||
// checksum 0. However, | |||||
// if we required that the checksum was 0, it would be the case that | |||||
// appending a 0 to a valid | |||||
// list of values would result in a new valid list. For that reason, Bech32 | |||||
// requires the | |||||
// resulting checksum to be 1 instead. | |||||
return PolyMod(Cat(ExpandHRP(hrp), values)) == 1; | |||||
} | |||||
/** Create a checksum. */ | |||||
data CreateChecksum(const std::string &hrp, const data &values) { | |||||
data enc = Cat(ExpandHRP(hrp), values); | |||||
enc.resize(enc.size() + 6); // Append 6 zeroes | |||||
uint32_t mod = | |||||
PolyMod(enc) ^ 1; // Determine what to XOR into those 6 zeroes. | |||||
deadalnixUnsubmitted Done Inline ActionsComment on the previous line. deadalnix: Comment on the previous line. | |||||
data ret; | |||||
ret.resize(6); | |||||
for (size_t i = 0; i < 6; ++i) { | |||||
// Convert the 5-bit groups in mod to checksum values. | |||||
ret[i] = (mod >> (5 * (5 - i))) & 31; | |||||
} | |||||
return ret; | |||||
} | |||||
} // namespace | |||||
namespace bech32 { | |||||
/** Encode a Bech32 string. */ | |||||
std::string Encode(const std::string &hrp, const data &values) { | |||||
data checksum = CreateChecksum(hrp, values); | |||||
data combined = Cat(values, checksum); | |||||
std::string ret = hrp + '1'; | |||||
ret.reserve(ret.size() + combined.size()); | |||||
for (size_t i = 0; i < combined.size(); ++i) { | |||||
ret += CHARSET[combined[i]]; | |||||
} | |||||
return ret; | |||||
} | |||||
/** Decode a Bech32 string. */ | |||||
std::pair<std::string, data> Decode(const std::string &str) { | |||||
bool lower = false, upper = false; | |||||
for (size_t i = 0; i < str.size(); ++i) { | |||||
unsigned char c = str[i]; | |||||
if (c < 33 || c > 126) return std::make_pair(std::string(), data()); | |||||
if (c >= 'a' && c <= 'z') lower = true; | |||||
if (c >= 'A' && c <= 'Z') upper = true; | |||||
} | |||||
if (lower && upper) return std::make_pair(std::string(), data()); | |||||
size_t pos = str.rfind('1'); | |||||
deadalnixUnsubmitted Not Done Inline ActionsUse ':' as a separator. deadalnix: Use ':' as a separator. | |||||
if (str.size() > 90 || pos == str.npos || pos == 0 || | |||||
pos + 7 > str.size()) { | |||||
return std::make_pair(std::string(), data()); | |||||
} | |||||
data values; | |||||
values.resize(str.size() - 1 - pos); | |||||
for (size_t i = 0; i < str.size() - 1 - pos; ++i) { | |||||
unsigned char c = str[i + pos + 1]; | |||||
if (CHARSET_REV[c] == -1) { | |||||
return std::make_pair(std::string(), data()); | |||||
} | |||||
values[i] = CHARSET_REV[c]; | |||||
} | |||||
std::string hrp; | |||||
for (size_t i = 0; i < pos; ++i) { | |||||
hrp += LowerCase(str[i]); | |||||
} | |||||
if (!VerifyChecksum(hrp, values)) { | |||||
return std::make_pair(std::string(), data()); | |||||
} | |||||
return std::make_pair(hrp, data(values.begin(), values.end() - 6)); | |||||
} | |||||
} // namespace bech32 |
Please format like:
You can put the comment on one line and let clang-format do its magic.