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This includes a reformatted version of the Bech32 reference code (see https://github.com/sipa/bech32/tree/master/ref/c%2B%2B), with extra documentation.pull/4/head
Pieter Wuille
7 years ago
committed by
Jack Grigg
Jack Grigg
5 changed files with 286 additions and 0 deletions
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// Copyright (c) 2017 Pieter Wuille
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// Distributed under the MIT software license, see the accompanying
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// file COPYING or http://www.opensource.org/licenses/mit-license.php.
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#include "bech32.h" |
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namespace |
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{ |
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typedef std::vector<uint8_t> data; |
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/** The Bech32 character set for encoding. */ |
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const char* CHARSET = "qpzry9x8gf2tvdw0s3jn54khce6mua7l"; |
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/** The Bech32 character set for decoding. */ |
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const int8_t CHARSET_REV[128] = { |
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-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, |
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-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, |
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-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, |
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15, -1, 10, 17, 21, 20, 26, 30, 7, 5, -1, -1, -1, -1, -1, -1, |
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-1, 29, -1, 24, 13, 25, 9, 8, 23, -1, 18, 22, 31, 27, 19, -1, |
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1, 0, 3, 16, 11, 28, 12, 14, 6, 4, 2, -1, -1, -1, -1, -1, |
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-1, 29, -1, 24, 13, 25, 9, 8, 23, -1, 18, 22, 31, 27, 19, -1, |
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1, 0, 3, 16, 11, 28, 12, 14, 6, 4, 2, -1, -1, -1, -1, -1 |
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}; |
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/** Concatenate two byte arrays. */ |
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data Cat(data x, const data& y) |
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{ |
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x.insert(x.end(), y.begin(), y.end()); |
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return x; |
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} |
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/** This function will compute what 6 5-bit values to XOR into the last 6 input values, in order to
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* make the checksum 0. These 6 values are packed together in a single 30-bit integer. The higher |
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* bits correspond to earlier values. */ |
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uint32_t PolyMod(const data& v) |
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{ |
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// The input is interpreted as a list of coefficients of a polynomial over F = GF(32), with an
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// implicit 1 in front. If the input is [v0,v1,v2,v3,v4], that polynomial is v(x) =
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// 1*x^5 + v0*x^4 + v1*x^3 + v2*x^2 + v3*x + v4. The implicit 1 guarantees that
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// [v0,v1,v2,...] has a distinct checksum from [0,v0,v1,v2,...].
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// The output is a 30-bit integer whose 5-bit groups are the coefficients of the remainder of
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// v(x) mod g(x), where g(x) is the Bech32 generator,
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// 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
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// that the resulting code is a BCH code, guaranteeing detection of up to 3 errors within a
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// window of 1023 characters. Among the various possible BCH codes, one was selected to in
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// fact guarantee detection of up to 4 errors within a window of 89 characters.
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// Note that the coefficients are elements of GF(32), here represented as decimal numbers
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// between {}. In this finite field, addition is just XOR of the corresponding numbers. For
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// example, {27} + {13} = {27 ^ 13} = {22}. Multiplication is more complicated, and requires
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// treating the bits of values themselves as coefficients of a polynomial over a smaller field,
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// GF(2), and multiplying those polynomials mod a^5 + a^3 + 1. For example, {5} * {26} =
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// (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
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// = a^3 + 1 (mod a^5 + a^3 + 1) = {9}.
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// During the course of the loop below, `c` contains the bitpacked coefficients of the
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// polynomial constructed from just the values of v that were processed so far, mod g(x). In
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// the above example, `c` initially corresponds to 1 mod (x), and after processing 2 inputs of
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// v, it corresponds to x^2 + v0*x + v1 mod g(x). As 1 mod g(x) = 1, that is the starting value
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// for `c`.
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uint32_t c = 1; |
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for (auto v_i : v) { |
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// We want to update `c` to correspond to a polynomial with one extra term. If the initial
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// value of `c` consists of the coefficients of c(x) = f(x) mod g(x), we modify it to
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// correspond to c'(x) = (f(x) * x + v_i) mod g(x), where v_i is the next input to
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// process. Simplifying:
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// c'(x) = (f(x) * x + v_i) mod g(x)
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// ((f(x) mod g(x)) * x + v_i) mod g(x)
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// (c(x) * x + v_i) mod g(x)
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// If c(x) = c0*x^5 + c1*x^4 + c2*x^3 + c3*x^2 + c4*x + c5, we want to compute
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// c'(x) = (c0*x^5 + c1*x^4 + c2*x^3 + c3*x^2 + c4*x + c5) * x + v_i mod g(x)
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// = c0*x^6 + c1*x^5 + c2*x^4 + c3*x^3 + c4*x^2 + c5*x + v_i mod g(x)
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// = c0*(x^6 mod g(x)) + c1*x^5 + c2*x^4 + c3*x^3 + c4*x^2 + c5*x + v_i
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// If we call (x^6 mod g(x)) = k(x), this can be written as
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// c'(x) = (c1*x^5 + c2*x^4 + c3*x^3 + c4*x^2 + c5*x + v_i) + c0*k(x)
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// First, determine the value of c0:
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uint8_t c0 = c >> 25; |
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// Then compute c1*x^5 + c2*x^4 + c3*x^3 + c4*x^2 + c5*x + v_i:
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c = ((c & 0x1ffffff) << 5) ^ v_i; |
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// Finally, for each set bit n in c0, conditionally add {2^n}k(x):
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if (c0 & 1) c ^= 0x3b6a57b2; // k(x) = {29}x^5 + {22}x^4 + {20}x^3 + {21}x^2 + {29}x + {18}
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if (c0 & 2) c ^= 0x26508e6d; // {2}k(x) = {19}x^5 + {5}x^4 + x^3 + {3}x^2 + {19}x + {13}
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if (c0 & 4) c ^= 0x1ea119fa; // {4}k(x) = {15}x^5 + {10}x^4 + {2}x^3 + {6}x^2 + {15}x + {26}
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if (c0 & 8) c ^= 0x3d4233dd; // {8}k(x) = {30}x^5 + {20}x^4 + {4}x^3 + {12}x^2 + {30}x + {29}
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if (c0 & 16) c ^= 0x2a1462b3; // {16}k(x) = {21}x^5 + x^4 + {8}x^3 + {24}x^2 + {21}x + {19}
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} |
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return c; |
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} |
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/** Convert to lower case. */ |
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inline unsigned char LowerCase(unsigned char c) |
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{ |
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return (c >= 'A' && c <= 'Z') ? (c - 'A') + 'a' : c; |
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} |
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/** Expand a HRP for use in checksum computation. */ |
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data ExpandHRP(const std::string& hrp) |
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{ |
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data ret; |
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ret.reserve(hrp.size() + 90); |
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ret.resize(hrp.size() * 2 + 1); |
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for (size_t i = 0; i < hrp.size(); ++i) { |
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unsigned char c = hrp[i]; |
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ret[i] = c >> 5; |
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ret[i + hrp.size() + 1] = c & 0x1f; |
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} |
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ret[hrp.size()] = 0; |
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return ret; |
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} |
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/** Verify a checksum. */ |
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bool VerifyChecksum(const std::string& hrp, const data& values) |
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{ |
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// PolyMod computes what value to xor into the final values to make the checksum 0. However,
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// if we required that the checksum was 0, it would be the case that appending a 0 to a valid
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// list of values would result in a new valid list. For that reason, Bech32 requires the
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// resulting checksum to be 1 instead.
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return PolyMod(Cat(ExpandHRP(hrp), values)) == 1; |
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} |
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/** Create a checksum. */ |
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data CreateChecksum(const std::string& hrp, const data& values) |
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{ |
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data enc = Cat(ExpandHRP(hrp), values); |
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enc.resize(enc.size() + 6); // Append 6 zeroes
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uint32_t mod = PolyMod(enc) ^ 1; // Determine what to XOR into those 6 zeroes.
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data ret(6); |
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for (size_t i = 0; i < 6; ++i) { |
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// Convert the 5-bit groups in mod to checksum values.
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ret[i] = (mod >> (5 * (5 - i))) & 31; |
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} |
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return ret; |
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} |
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} // namespace
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namespace bech32 |
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{ |
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/** Encode a Bech32 string. */ |
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std::string Encode(const std::string& hrp, const data& values) { |
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data checksum = CreateChecksum(hrp, values); |
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data combined = Cat(values, checksum); |
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std::string ret = hrp + '1'; |
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ret.reserve(ret.size() + combined.size()); |
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for (auto c : combined) { |
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ret += CHARSET[c]; |
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} |
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return ret; |
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} |
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/** Decode a Bech32 string. */ |
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std::pair<std::string, data> Decode(const std::string& str) { |
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bool lower = false, upper = false; |
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for (size_t i = 0; i < str.size(); ++i) { |
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unsigned char c = str[i]; |
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if (c < 33 || c > 126) return {}; |
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if (c >= 'a' && c <= 'z') lower = true; |
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if (c >= 'A' && c <= 'Z') upper = true; |
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} |
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if (lower && upper) return {}; |
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size_t pos = str.rfind('1'); |
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if (str.size() > 90 || pos == str.npos || pos == 0 || pos + 7 > str.size()) { |
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return {}; |
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} |
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data values(str.size() - 1 - pos); |
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for (size_t i = 0; i < str.size() - 1 - pos; ++i) { |
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unsigned char c = str[i + pos + 1]; |
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int8_t rev = (c < 33 || c > 126) ? -1 : CHARSET_REV[c]; |
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if (rev == -1) { |
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return {}; |
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} |
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values[i] = rev; |
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} |
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std::string hrp; |
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for (size_t i = 0; i < pos; ++i) { |
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hrp += LowerCase(str[i]); |
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} |
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if (!VerifyChecksum(hrp, values)) { |
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return {}; |
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} |
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return {hrp, data(values.begin(), values.end() - 6)}; |
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} |
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} // namespace bech32
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@ -0,0 +1,25 @@ |
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// Copyright (c) 2017 Pieter Wuille
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// Distributed under the MIT software license, see the accompanying
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// file COPYING or http://www.opensource.org/licenses/mit-license.php.
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// Bech32 is a string encoding format used in newer address types.
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// The output consists of a human-readable part (alphanumeric), a
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// separator character (1), and a base32 data section, the last
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// 6 characters of which are a checksum.
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//
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// For more information, see BIP 173.
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#include <stdint.h> |
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#include <string> |
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#include <vector> |
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namespace bech32 |
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{ |
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/** Encode a Bech32 string. Returns the empty string in case of failure. */ |
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std::string Encode(const std::string& hrp, const std::vector<uint8_t>& values); |
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/** Decode a Bech32 string. Returns (hrp, data). Empty hrp means failure. */ |
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std::pair<std::string, std::vector<uint8_t>> Decode(const std::string& str); |
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} // namespace bech32
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@ -0,0 +1,67 @@ |
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// Copyright (c) 2017 Pieter Wuille
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// Distributed under the MIT software license, see the accompanying
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// file COPYING or http://www.opensource.org/licenses/mit-license.php.
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#include "bech32.h" |
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#include "test/test_bitcoin.h" |
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#include <boost/test/unit_test.hpp> |
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BOOST_FIXTURE_TEST_SUITE(bech32_tests, BasicTestingSetup) |
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bool CaseInsensitiveEqual(const std::string &s1, const std::string &s2) |
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{ |
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if (s1.size() != s2.size()) return false; |
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for (size_t i = 0; i < s1.size(); ++i) { |
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char c1 = s1[i]; |
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if (c1 >= 'A' && c1 <= 'Z') c1 -= ('A' - 'a'); |
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char c2 = s2[i]; |
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if (c2 >= 'A' && c2 <= 'Z') c2 -= ('A' - 'a'); |
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if (c1 != c2) return false; |
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} |
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return true; |
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} |
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BOOST_AUTO_TEST_CASE(bip173_testvectors_valid) |
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{ |
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static const std::string CASES[] = { |
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"A12UEL5L", |
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"a12uel5l", |
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"an83characterlonghumanreadablepartthatcontainsthenumber1andtheexcludedcharactersbio1tt5tgs", |
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"abcdef1qpzry9x8gf2tvdw0s3jn54khce6mua7lmqqqxw", |
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"11qqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqc8247j", |
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"split1checkupstagehandshakeupstreamerranterredcaperred2y9e3w", |
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"?1ezyfcl", |
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}; |
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for (const std::string& str : CASES) { |
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auto ret = bech32::Decode(str); |
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BOOST_CHECK(!ret.first.empty()); |
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std::string recode = bech32::Encode(ret.first, ret.second); |
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BOOST_CHECK(!recode.empty()); |
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BOOST_CHECK(CaseInsensitiveEqual(str, recode)); |
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} |
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} |
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BOOST_AUTO_TEST_CASE(bip173_testvectors_invalid) |
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{ |
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static const std::string CASES[] = { |
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" 1nwldj5", |
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"\x7f""1axkwrx", |
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"\x80""1eym55h", |
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"an84characterslonghumanreadablepartthatcontainsthenumber1andtheexcludedcharactersbio1569pvx", |
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"pzry9x0s0muk", |
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"1pzry9x0s0muk", |
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"x1b4n0q5v", |
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"li1dgmt3", |
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"de1lg7wt\xff", |
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"A1G7SGD8", |
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"10a06t8", |
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"1qzzfhee", |
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}; |
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for (const std::string& str : CASES) { |
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auto ret = bech32::Decode(str); |
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BOOST_CHECK(ret.first.empty()); |
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} |
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} |
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BOOST_AUTO_TEST_SUITE_END() |
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