From ae6019b3a5f99e63b5f23e48fd430147b8500877 Mon Sep 17 00:00:00 2001
From: josibake <josibake@protonmail.com>
Date: Tue, 18 Jul 2023 22:26:04 +0200
Subject: [PATCH] Add functions for decoding SP addresses

Add a function for decoding the string address and a second
function for decoding the data part of the silent payment address.
---
 src/key_io.cpp | 32 ++++++++++++++++++++++++++++++++
 src/key_io.h   |  4 ++++
 2 files changed, 36 insertions(+)

diff --git a/src/key_io.cpp b/src/key_io.cpp
index 454a96df5e5bc..46e2559077102 100644
--- a/src/key_io.cpp
+++ b/src/key_io.cpp
@@ -15,6 +15,8 @@
 /// Maximum witness length for Bech32 addresses.
 static constexpr std::size_t BECH32_WITNESS_PROG_MAX_LEN = 40;
 
+/// Data size for decoded Bech32m silent payment addresses (33 byte pubkey + 33 byte pubkey)
+static constexpr std::size_t SILENT_PAYMENT_V0_DATA_SIZE = 66;
 namespace {
 class DestinationEncoder
 {
@@ -309,3 +311,33 @@ bool IsValidDestinationString(const std::string& str)
 {
     return IsValidDestinationString(str, Params());
 }
+
+std::pair<CPubKey, CPubKey> DecodeSilentData(const std::vector<unsigned char>& data)
+{
+
+    std::vector<unsigned char> scan_pubkey_data(data.begin(), data.begin() + 33);
+    CPubKey scan_pubkey{scan_pubkey_data};
+
+    std::vector<unsigned char> spend_pubkey_data(data.begin() + 33, data.end());
+    CPubKey spend_pubkey{spend_pubkey_data};
+
+    return {scan_pubkey, spend_pubkey};
+}
+
+std::vector<unsigned char> DecodeSilentAddress(const std::string& str)
+{
+    const auto& params{Params()};
+    const auto& silent_payment_hrp = params.SilentPaymentHRP();
+    const auto dec = bech32::Decode(str, /*silent=*/true);
+    if (dec.encoding != bech32::Encoding::BECH32M || dec.hrp != silent_payment_hrp) {
+        return {};
+    }
+    auto version = dec.data.front();  // retrieve the version
+    std::vector<unsigned char> silent_payment_data;
+    silent_payment_data.reserve(((dec.data.size() - 1) * 5) / 8);
+    if (!ConvertBits<5, 8, false>([&](unsigned char c) { silent_payment_data.push_back(c); }, dec.data.begin() + 1, dec.data.end())) {
+        return {};
+    }
+    if ((version == 0 && silent_payment_data.size() != SILENT_PAYMENT_V0_DATA_SIZE) || silent_payment_data.size() < SILENT_PAYMENT_V0_DATA_SIZE) return {};
+    return silent_payment_data;
+}
diff --git a/src/key_io.h b/src/key_io.h
index 07b80c4b859fe..9c67d819141d1 100644
--- a/src/key_io.h
+++ b/src/key_io.h
@@ -24,6 +24,10 @@ std::string EncodeExtPubKey(const CExtPubKey& extpubkey);
 std::string EncodeDestination(const CTxDestination& dest);
 CTxDestination DecodeDestination(const std::string& str);
 CTxDestination DecodeDestination(const std::string& str, std::string& error_msg, std::vector<int>* error_locations = nullptr);
+
+std::pair<CPubKey, CPubKey> DecodeSilentData(const std::vector<unsigned char>& data);
+std::vector<unsigned char> DecodeSilentAddress(const std::string& str);
+
 bool IsValidDestinationString(const std::string& str);
 bool IsValidDestinationString(const std::string& str, const CChainParams& params);