diff --git a/src/ga_session.cpp b/src/ga_session.cpp
index 358109372..347cccd12 100644
--- a/src/ga_session.cpp
+++ b/src/ga_session.cpp
@@ -17,7 +17,6 @@
 #include <boost/algorithm/string/predicate.hpp>
 #include <boost/algorithm/string/split.hpp>
 #include <boost/lexical_cast.hpp>
-#include <boost/multiprecision/cpp_int.hpp>
 #include <nlohmann/json.hpp>
 
 #include "assertion.hpp"
@@ -66,20 +65,6 @@ namespace green {
         static const std::array<const std::string, 4> TX_NTFY_FIELDS
             = { "subaccounts", "txhash", "value", TXN_OPTIONAL };
 
-        // TODO: too slow. lacks validation.
-        static std::array<unsigned char, SHA256_LEN> uint256_to_base256(const std::string& input)
-        {
-            constexpr size_t base = 256;
-
-            std::array<unsigned char, SHA256_LEN> repr{};
-            size_t i = repr.size() - 1;
-            for (boost::multiprecision::checked_uint256_t num(input); num; num = num / base, --i) {
-                repr[i] = static_cast<unsigned char>(num % base);
-            }
-
-            return repr;
-        }
-
         static bool ignore_tx_notification(const nlohmann::json& details)
         {
             for (const auto& item : details.items()) {
@@ -351,19 +336,6 @@ namespace green {
         return m_nlocktimes;
     }
 
-    std::pair<std::string, std::string> ga_session::sign_challenge(
-        session_impl::locker_t& locker, const std::string& challenge)
-    {
-        GDK_RUNTIME_ASSERT(locker.owns_lock());
-        GDK_RUNTIME_ASSERT(m_signer);
-
-        const auto path_bytes = get_random_bytes<8>();
-        const auto path = bytes_to_bip32_path(path_bytes);
-        const auto challenge_hash = uint256_to_base256(challenge);
-
-        return { sig_only_to_der_hex(m_signer->ecdsa_sign(path, challenge_hash)), b2h(path_bytes) };
-    }
-
     void ga_session::set_fee_estimates(session_impl::locker_t& locker, const nlohmann::json& fee_estimates)
     {
         GDK_RUNTIME_ASSERT(locker.owns_lock());
diff --git a/src/ga_session.hpp b/src/ga_session.hpp
index d8667f439..6022a80c8 100644
--- a/src/ga_session.hpp
+++ b/src/ga_session.hpp
@@ -192,8 +192,6 @@ namespace green {
             const std::string& name, const std::string& receiving_id, const std::optional<xpub_hdkey>& recovery_key,
             uint32_t required_ca);
 
-        std::pair<std::string, std::string> sign_challenge(locker_t& locker, const std::string& challenge);
-
         void set_fee_estimates(locker_t& locker, const nlohmann::json& fee_estimates);
 
         nlohmann::json refresh_http_data(const std::string& page, const std::string& key, bool refresh);