diff --git a/src/span.h b/src/span.h
index dba6a2133..9e101deb3 100644
--- a/src/span.h
+++ b/src/span.h
@@ -1,198 +1,228 @@
 // Copyright (c) 2018 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_SPAN_H
 #define BITCOIN_SPAN_H
 
 #include <algorithm>
 #include <cassert>
 #include <cstddef>
+#include <cstdint>
 #include <type_traits>
 
 #ifdef DEBUG
 #define CONSTEXPR_IF_NOT_DEBUG
 #define ASSERT_IF_DEBUG(x) assert((x))
 #else
 #define CONSTEXPR_IF_NOT_DEBUG constexpr
 #define ASSERT_IF_DEBUG(x)
 #endif
 
 /**
  * A Span is an object that can refer to a contiguous sequence of objects.
  *
  * It implements a subset of C++20's std::span.
  */
 template <typename C> class Span {
     C *m_data;
     std::size_t m_size;
 
 public:
     constexpr Span() noexcept : m_data(nullptr), m_size(0) {}
 
     /**
      * Construct a span from a begin pointer and a size.
      *
      * This implements a subset of the iterator-based std::span constructor in
      * C++20, which is hard to implement without std::address_of.
      */
     template <typename T,
               typename std::enable_if<
                   std::is_convertible<T (*)[], C (*)[]>::value, int>::type = 0>
     constexpr Span(T *begin, std::size_t size) noexcept
         : m_data(begin), m_size(size) {}
 
     /**
      * Construct a span from a begin and end pointer.
      *
      * This implements a subset of the iterator-based std::span constructor in
      * C++20, which is hard to implement without std::address_of.
      */
     template <typename T,
               typename std::enable_if<
                   std::is_convertible<T (*)[], C (*)[]>::value, int>::type = 0>
     CONSTEXPR_IF_NOT_DEBUG Span(T *begin, T *end) noexcept
         : m_data(begin), m_size(end - begin) {
         ASSERT_IF_DEBUG(end >= begin);
     }
 
     /**
      * Implicit conversion of spans between compatible types.
      *
      *  Specifically, if a pointer to an array of type O can be implicitly
      * converted to a pointer to an array of type C, then permit implicit
      * conversion of Span<O> to Span<C>. This matches the behavior of the
      * corresponding C++20 std::span constructor.
      *
      *  For example this means that a Span<T> can be converted into a Span<const
      * T>.
      */
     template <typename O,
               typename std::enable_if<
                   std::is_convertible<O (*)[], C (*)[]>::value, int>::type = 0>
     constexpr Span(const Span<O> &other) noexcept
         : m_data(other.m_data), m_size(other.m_size) {}
 
     /** Default copy constructor. */
     constexpr Span(const Span &) noexcept = default;
 
     /** Default assignment operator. */
     Span &operator=(const Span &other) noexcept = default;
 
     /** Construct a Span from an array. This matches the corresponding C++20
      * std::span constructor. */
     template <int N>
     constexpr Span(C (&a)[N]) noexcept : m_data(a), m_size(N) {}
 
     /**
      * Construct a Span for objects with .data() and .size() (std::string,
      * std::array, std::vector, ...).
      *
      * This implements a subset of the functionality provided by the C++20
      * std::span range-based constructor.
      *
      * To prevent surprises, only Spans for constant value types are supported
      * when passing in temporaries. Note that this restriction does not exist
      * when converting arrays or other Spans (see above).
      */
     template <
         typename V,
         typename std::enable_if<
             (std::is_const<C>::value || std::is_lvalue_reference<V>::value) &&
                 std::is_convertible<
                     typename std::remove_pointer<
                         decltype(std::declval<V &>().data())>::type (*)[],
                     C (*)[]>::value &&
                 std::is_convertible<decltype(std::declval<V &>().size()),
                                     std::size_t>::value,
             int>::type = 0>
     constexpr Span(V &&v) noexcept : m_data(v.data()), m_size(v.size()) {}
 
     constexpr C *data() const noexcept { return m_data; }
     constexpr C *begin() const noexcept { return m_data; }
     constexpr C *end() const noexcept { return m_data + m_size; }
     CONSTEXPR_IF_NOT_DEBUG C &front() const noexcept {
         ASSERT_IF_DEBUG(size() > 0);
         return m_data[0];
     }
     CONSTEXPR_IF_NOT_DEBUG C &back() const noexcept {
         ASSERT_IF_DEBUG(size() > 0);
         return m_data[m_size - 1];
     }
     constexpr std::size_t size() const noexcept { return m_size; }
     CONSTEXPR_IF_NOT_DEBUG C &operator[](std::size_t pos) const noexcept {
         ASSERT_IF_DEBUG(size() > pos);
         return m_data[pos];
     }
     CONSTEXPR_IF_NOT_DEBUG Span<C> subspan(std::size_t offset) const noexcept {
         ASSERT_IF_DEBUG(size() >= offset);
         return Span<C>(m_data + offset, m_size - offset);
     }
     CONSTEXPR_IF_NOT_DEBUG Span<C> subspan(std::size_t offset,
                                            std::size_t count) const noexcept {
         ASSERT_IF_DEBUG(size() >= offset + count);
         return Span<C>(m_data + offset, count);
     }
     CONSTEXPR_IF_NOT_DEBUG Span<C> first(std::size_t count) const noexcept {
         ASSERT_IF_DEBUG(size() >= count);
         return Span<C>(m_data, count);
     }
     CONSTEXPR_IF_NOT_DEBUG Span<C> last(std::size_t count) const noexcept {
         ASSERT_IF_DEBUG(size() >= count);
         return Span<C>(m_data + m_size - count, count);
     }
 
     friend constexpr bool operator==(const Span &a, const Span &b) noexcept {
         return a.size() == b.size() &&
                std::equal(a.begin(), a.end(), b.begin());
     }
     friend constexpr bool operator!=(const Span &a, const Span &b) noexcept {
         return !(a == b);
     }
     friend constexpr bool operator<(const Span &a, const Span &b) noexcept {
         return std::lexicographical_compare(a.begin(), a.end(), b.begin(),
                                             b.end());
     }
     friend constexpr bool operator<=(const Span &a, const Span &b) noexcept {
         return !(b < a);
     }
     friend constexpr bool operator>(const Span &a, const Span &b) noexcept {
         return (b < a);
     }
     friend constexpr bool operator>=(const Span &a, const Span &b) noexcept {
         return !(a < b);
     }
 
     template <typename O> friend class Span;
 };
 
 // MakeSpan helps constructing a Span of the right type automatically.
 /** MakeSpan for arrays: */
 template <typename A, int N> Span<A> constexpr MakeSpan(A (&a)[N]) {
     return Span<A>(a, N);
 }
 /** MakeSpan for temporaries / rvalue references, only supporting const output.
  */
 template <typename V>
 constexpr auto MakeSpan(V &&v) -> typename std::enable_if<
     !std::is_lvalue_reference<V>::value,
     Span<const typename std::remove_pointer<decltype(v.data())>::type>>::type {
     return std::forward<V>(v);
 }
 /** MakeSpan for (lvalue) references, supporting mutable output. */
 template <typename V>
 constexpr auto MakeSpan(V &v)
     -> Span<typename std::remove_pointer<decltype(v.data())>::type> {
     return v;
 }
 
 /** Pop the last element off a span, and return a reference to that element. */
 template <typename T> T &SpanPopBack(Span<T> &span) {
     size_t size = span.size();
     ASSERT_IF_DEBUG(size > 0);
     T &back = span[size - 1];
     span = Span<T>(span.data(), size - 1);
     return back;
 }
 
+// Helper functions to safely cast to uint8_t pointers.
+inline uint8_t *UCharCast(char *c) {
+    return (uint8_t *)c;
+}
+inline uint8_t *UCharCast(uint8_t *c) {
+    return c;
+}
+inline const uint8_t *UCharCast(const char *c) {
+    return (uint8_t *)c;
+}
+inline const uint8_t *UCharCast(const uint8_t *c) {
+    return c;
+}
+
+// Helper function to safely convert a Span to a Span<[const] uint8_t>.
+template <typename T>
+constexpr auto UCharSpanCast(Span<T> s)
+    -> Span<typename std::remove_pointer<decltype(UCharCast(s.data()))>::type> {
+    return {UCharCast(s.data()), s.size()};
+}
+
+/** Like MakeSpan, but for (const) uint8_t member types only. Only works
+ * for (un)signed char containers. */
+template <typename V>
+constexpr auto MakeUCharSpan(V &&v)
+    -> decltype(UCharSpanCast(MakeSpan(std::forward<V>(v)))) {
+    return UCharSpanCast(MakeSpan(std::forward<V>(v)));
+}
+
 #endif // BITCOIN_SPAN_H