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diff --git a/src/test/fuzz/util/descriptor.h b/src/test/fuzz/util/descriptor.h
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+++ b/src/test/fuzz/util/descriptor.h
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+// Copyright (c) 2023-present The Bitcoin Core developers
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+#ifndef BITCOIN_TEST_FUZZ_UTIL_DESCRIPTOR_H
+#define BITCOIN_TEST_FUZZ_UTIL_DESCRIPTOR_H
+
+#include <key_io.h>
+#include <util/strencodings.h>
+#include <script/descriptor.h>
+
+#include <functional>
+
+/**
+ * Converts a mocked descriptor string to a valid one. Every key in a mocked descriptor key is
+ * represented by 2 hex characters preceded by the '%' character. We parse the two hex characters
+ * as an index in a list of pre-generated keys. This list contains keys of the various types
+ * accepted in descriptor keys expressions.
+ */
+class MockedDescriptorConverter {
+private:
+    //! Types are raw (un)compressed pubkeys, raw xonly pubkeys, raw privkeys (WIF), xpubs, xprvs.
+    static constexpr uint8_t KEY_TYPES_COUNT{6};
+    //! How many keys we'll generate in total.
+    static constexpr size_t TOTAL_KEYS_GENERATED{std::numeric_limits<uint8_t>::max() + 1};
+    //! 256 keys of various types.
+    std::array<std::string, TOTAL_KEYS_GENERATED> keys_str;
+
+public:
+    // We derive the type of key to generate from the 1-byte id parsed from hex.
+    bool IdIsCompPubKey(uint8_t idx) const { return idx % KEY_TYPES_COUNT == 0; }
+    bool IdIsUnCompPubKey(uint8_t idx) const { return idx % KEY_TYPES_COUNT == 1; }
+    bool IdIsXOnlyPubKey(uint8_t idx) const { return idx % KEY_TYPES_COUNT == 2; }
+    bool IdIsConstPrivKey(uint8_t idx) const { return idx % KEY_TYPES_COUNT == 3; }
+    bool IdIsXpub(uint8_t idx) const { return idx % KEY_TYPES_COUNT == 4; }
+    bool IdIsXprv(uint8_t idx) const { return idx % KEY_TYPES_COUNT == 5; }
+
+    //! When initializing the target, populate the list of keys.
+    void Init();
+
+    //! Parse an id in the keys vectors from a 2-characters hex string.
+    std::optional<uint8_t> IdxFromHex(std::string_view hex_characters) const;
+
+    //! Get an actual descriptor string from a descriptor string whose keys were mocked.
+    std::optional<std::string> GetDescriptor(std::string_view mocked_desc) const;
+};
+
+#endif // BITCOIN_TEST_FUZZ_UTIL_DESCRIPTOR_H