Add base58 decoding

include/mtxclient/crypto/utils.hpp

@@ -106,5 +106,8 @@ bin2base64_urlsafe_unpadded(const std::string &bin);
 
 std::string
 bin2base58(const std::string &bin);
+
+std::string
+base582bin(const std::string &bin);
 } // namespace crypto
 } // namespace mtx

lib/crypto/client.cpp

@@ -641,4 +641,3 @@ mtx::crypto::decrypt_exported_sessions(const std::string &data, std::string pass
         std::string plaintext(decrypted.begin(), decrypted.end());
         return json::parse(plaintext);
 }
-

lib/crypto/encoding.cpp

+#include <algorithm>
 #include <array>
 #include <string>
 #include <vector>
@@ -87,6 +88,43 @@ encode_base58(const std::array<char, 58> &alphabet, const std::string &input)
         return result;
 }
 
+inline std::string
+decode_base58(const std::array<uint8_t, 256> &reverse_alphabet, const std::string &input)
+{
+        std::string result;
+        if (input.empty())
+                return result;
+
+        result.reserve(input.size() * 733 / 1000 + 1);
+
+        // result.push_back(0);
+
+        for (uint8_t b : input) {
+                if (b == ' ')
+                        continue;
+
+                if (b == 0xff)
+                        return "";
+
+                uint32_t carry = reverse_alphabet[b];
+                for (std::size_t j = 0; j < result.size(); j++) {
+                        carry += static_cast<uint8_t>(result[j]) * 58;
+                        result[j] = static_cast<uint8_t>(carry % 0x100);
+                        carry /= 0x100;
+                }
+                while (carry > 0) {
+                        result.push_back(static_cast<uint8_t>(carry % 0x100));
+                        carry /= 0x100;
+                }
+        }
+
+        for (size_t i = 0; i < input.length() && input[i] == '1'; i++)
+                result.push_back(0);
+
+        std::reverse(result.begin(), result.end());
+        return result;
+}
+
 template<bool pad>
 inline std::string
 encode_base64(const std::array<char, 64> &alphabet, std::string input)
@@ -210,5 +248,11 @@ bin2base58(const std::string &bin)
 {
         return encode_base58(base58_alphabet, bin);
 }
+
+std::string
+base582bin(const std::string &bin)
+{
+        return decode_base58(base58_to_int, bin);
+}
 }
 }

tests/crypto.cpp

@@ -184,6 +184,14 @@ TEST(Base58, EncodingDecoding)
         EXPECT_EQ(bin2base58("foob"), "3csAg9");
         EXPECT_EQ(bin2base58("fooba"), "CZJRhmz");
         EXPECT_EQ(bin2base58("foobar"), "t1Zv2yaZ");
+
+        EXPECT_EQ("", base582bin(""));
+        EXPECT_EQ("f", base582bin("2m"));
+        EXPECT_EQ("fo", base582bin("8o8"));
+        EXPECT_EQ("foo", base582bin("bQbp"));
+        EXPECT_EQ("foob", base582bin("3csAg9"));
+        EXPECT_EQ("fooba", base582bin("CZJRhmz"));
+        EXPECT_EQ("foobar", base582bin("t1Zv2yaZ"));
 }
 
 TEST(ExportSessions, EncryptDecrypt)