diff --git a/src/test/fuzz/CMakeLists.txt b/src/test/fuzz/CMakeLists.txt
--- a/src/test/fuzz/CMakeLists.txt
+++ b/src/test/fuzz/CMakeLists.txt
@@ -70,12 +70,14 @@
 
 add_regular_fuzz_targets(
 	addrdb
+	base_encode_decode
 	block
 	bloom_filter
 	rolling_bloom_filter
 	cashaddr
 	descriptor_parse
 	eval_script
+	hex
 	integer
 	net_permissions
 	parse_hd_keypath
diff --git a/src/test/fuzz/base_encode_decode.cpp b/src/test/fuzz/base_encode_decode.cpp
new file mode 100644
--- /dev/null
+++ b/src/test/fuzz/base_encode_decode.cpp
@@ -0,0 +1,51 @@
+// Copyright (c) 2019 The Bitcoin Core developers
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+#include <base58.h>
+#include <util/strencodings.h>
+#include <util/string.h>
+
+#include <test/fuzz/fuzz.h>
+
+#include <cassert>
+#include <cstdint>
+#include <string>
+#include <vector>
+
+void test_one_input(const std::vector<uint8_t> &buffer) {
+    const std::string random_encoded_string(buffer.begin(), buffer.end());
+
+    std::vector<uint8_t> decoded;
+    if (DecodeBase58(random_encoded_string, decoded, 100)) {
+        const std::string encoded_string = EncodeBase58(decoded);
+        assert(encoded_string == TrimString(encoded_string));
+        assert(ToLower(encoded_string) ==
+               ToLower(TrimString(random_encoded_string)));
+    }
+
+    if (DecodeBase58Check(random_encoded_string, decoded, 100)) {
+        const std::string encoded_string = EncodeBase58Check(decoded);
+        assert(encoded_string == TrimString(encoded_string));
+        assert(ToLower(encoded_string) ==
+               ToLower(TrimString(random_encoded_string)));
+    }
+
+    bool pf_invalid;
+    std::string decoded_string =
+        DecodeBase32(random_encoded_string, &pf_invalid);
+    if (!pf_invalid) {
+        const std::string encoded_string = EncodeBase32(decoded_string);
+        assert(encoded_string == TrimString(encoded_string));
+        assert(ToLower(encoded_string) ==
+               ToLower(TrimString(random_encoded_string)));
+    }
+
+    decoded_string = DecodeBase64(random_encoded_string, &pf_invalid);
+    if (!pf_invalid) {
+        const std::string encoded_string = EncodeBase64(decoded_string);
+        assert(encoded_string == TrimString(encoded_string));
+        assert(ToLower(encoded_string) ==
+               ToLower(TrimString(random_encoded_string)));
+    }
+}
diff --git a/src/test/fuzz/hex.cpp b/src/test/fuzz/hex.cpp
new file mode 100644
--- /dev/null
+++ b/src/test/fuzz/hex.cpp
@@ -0,0 +1,21 @@
+// Copyright (c) 2019 The Bitcoin Core developers
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+#include <util/strencodings.h>
+
+#include <test/fuzz/fuzz.h>
+
+#include <cassert>
+#include <cstdint>
+#include <string>
+#include <vector>
+
+void test_one_input(const std::vector<uint8_t> &buffer) {
+    const std::string random_hex_string(buffer.begin(), buffer.end());
+    const std::vector<uint8_t> data = ParseHex(random_hex_string);
+    const std::string hex_data = HexStr(data);
+    if (IsHex(random_hex_string)) {
+        assert(ToLower(random_hex_string) == hex_data);
+    }
+}
diff --git a/src/util/string.h b/src/util/string.h
--- a/src/util/string.h
+++ b/src/util/string.h
@@ -11,6 +11,16 @@
 #include <string>
 #include <vector>
 
+NODISCARD inline std::string
+TrimString(const std::string &str, const std::string &pattern = " \f\n\r\t\v") {
+    std::string::size_type front = str.find_first_not_of(pattern);
+    if (front == std::string::npos) {
+        return std::string();
+    }
+    std::string::size_type end = str.find_last_not_of(pattern);
+    return str.substr(front, end - front + 1);
+}
+
 /**
  * Join a list of items
  *
diff --git a/src/util/system.cpp b/src/util/system.cpp
--- a/src/util/system.cpp
+++ b/src/util/system.cpp
@@ -812,16 +812,6 @@
     return AbsPathForConfigVal(fs::path(confPath), false);
 }
 
-static std::string TrimString(const std::string &str,
-                              const std::string &pattern) {
-    std::string::size_type front = str.find_first_not_of(pattern);
-    if (front == std::string::npos) {
-        return std::string();
-    }
-    std::string::size_type end = str.find_last_not_of(pattern);
-    return str.substr(front, end - front + 1);
-}
-
 static bool
 GetConfigOptions(std::istream &stream, const std::string &filepath,
                  std::string &error,