Remove default ctors from SecretKey and PublicKey: (#4607)

* It is now an invariant that all constructed Public Keys are valid,
  non-empty and contain 33 bytes of data.
* Additionally, the memory footprint of the PublicKey class is reduced.
  The size_ data member is declared as static.
* Distinguish and identify the PublisherList retrieved from the local
  config file, versus the ones obtained from other validators.
* Fixes #2942

src/ripple/protocol/PublicKey.h

@@ -61,13 +61,17 @@ namespace ripple {
 class PublicKey
 {
 protected:
-    std::size_t size_ = 0;
-    std::uint8_t buf_[33];  // should be large enough
+    // All the constructed public keys are valid, non-empty and contain 33
+    // bytes of data.
+    static constexpr std::size_t size_ = 33;
+    std::uint8_t buf_[size_];  // should be large enough
 
 public:
     using const_iterator = std::uint8_t const*;
 
-    PublicKey() = default;
+public:
+    PublicKey() = delete;
+
     PublicKey(PublicKey const& other);
     PublicKey&
     operator=(PublicKey const& other);
@@ -115,12 +119,6 @@ public:
         return buf_ + size_;
     }
 
-    bool
-    empty() const noexcept
-    {
-        return size_ == 0;
-    }
-
     Slice
     slice() const noexcept
     {
@@ -141,8 +139,7 @@ operator<<(std::ostream& os, PublicKey const& pk);
 inline bool
 operator==(PublicKey const& lhs, PublicKey const& rhs)
 {
-    return lhs.size() == rhs.size() &&
-        std::memcmp(lhs.data(), rhs.data(), rhs.size()) == 0;
+    return std::memcmp(lhs.data(), rhs.data(), rhs.size()) == 0;
 }
 
 inline bool

src/ripple/protocol/SecretKey.h

@@ -41,7 +41,7 @@ private:
 public:
     using const_iterator = std::uint8_t const*;
 
-    SecretKey() = default;
+    SecretKey() = delete;
     SecretKey(SecretKey const&) = default;
     SecretKey&
     operator=(SecretKey const&) = default;

src/ripple/protocol/impl/PublicKey.cpp

@@ -24,7 +24,6 @@
 #include <ripple/protocol/impl/secp256k1.h>
 #include <boost/multiprecision/cpp_int.hpp>
 #include <ed25519.h>
-#include <type_traits>
 
 namespace ripple {
 
@@ -176,16 +175,19 @@ ed25519Canonical(Slice const& sig)
 
 PublicKey::PublicKey(Slice const& slice)
 {
+    if (slice.size() < size_)
+        LogicError(
+            "PublicKey::PublicKey - Input slice cannot be an undersized "
+            "buffer");
+
     if (!publicKeyType(slice))
         LogicError("PublicKey::PublicKey invalid type");
-    size_ = slice.size();
     std::memcpy(buf_, slice.data(), size_);
 }
 
-PublicKey::PublicKey(PublicKey const& other) : size_(other.size_)
+PublicKey::PublicKey(PublicKey const& other)
 {
-    if (size_)
-        std::memcpy(buf_, other.buf_, size_);
+    std::memcpy(buf_, other.buf_, size_);
 }
 
 PublicKey&
@@ -193,9 +195,7 @@ PublicKey::operator=(PublicKey const& other)
 {
     if (this != &other)
     {
-        size_ = other.size_;
-        if (size_)
-            std::memcpy(buf_, other.buf_, size_);
+        std::memcpy(buf_, other.buf_, size_);
     }
 
     return *this;