Add compile-time key length check

1 files changed, 33 insertions, 24 deletions

diff --git a/blowfish.hpp b/blowfish.hpp
index 9a6e0fe..3637335 100644
--- a/blowfish.hpp
+++ b/blowfish.hpp
@@ -5,32 +5,39 @@
 #include "blowfish_init.hpp"
 #include <algorithm>
 
-class Blowfish {
-public:
-  struct Block {
-    constexpr Block(uint64_t x) {
-      L = x >> 32;
-      R = x & 0xffffffff;
-    }
-    constexpr Block(uint32_t l, uint32_t r) : L(l), R(r) {}
+namespace Blowfish {
+template <std::size_t sz> concept is_valid_key_length = (sz < KEYLEN);
 
-    constexpr operator uint64_t() const {
-      return (static_cast<uint64_t>(L) << 32) + R;
-    }
-    uint32_t L;
-    uint32_t R;
-  };
+struct Block {
+  constexpr Block(uint64_t x) {
+    static_assert(sizeof(Block) == sizeof(uint64_t));
+    L = x >> 32;
+    R = x & 0xffffffff;
+  }
+  constexpr Block(uint32_t l, uint32_t r) : L(l), R(r) {
+    static_assert(sizeof(Block) == sizeof(uint64_t));
+  }
 
-  constexpr Blowfish(const uint8_t key[], size_t keylen) {
-    for (size_t i = 0; i < BOXES; ++i) {
+  constexpr operator uint64_t() const {
+    return (static_cast<uint64_t>(L) << 32) + R;
+  }
+  uint32_t L;
+  uint32_t R;
+};
+
+template <std::size_t keylen>
+requires is_valid_key_length<keylen> class Context {
+public:
+  constexpr Context(const std::array<uint8_t, keylen> &key) {
+    for (std::size_t i = 0; i < BOXES; ++i) {
       std::copy(S_INIT[i].begin(), S_INIT[i].end(), S[i].begin());
     }
 
     //
-    size_t k = 0;
-    for (size_t i = 0; i < SUBKEYS; ++i) {
+    std::size_t k = 0;
+    for (std::size_t i = 0; i < SUBKEYS; ++i) {
       uint32_t qk = 0;
-      for (size_t j = 0; j < 4; ++j) {
+      for (std::size_t j = 0; j < 4; ++j) {
         qk = (qk << 8) | key[k];
         ++k;
         if (k >= keylen) {
@@ -42,13 +49,13 @@ public:
 
     Block x(0, 0);
 
-    for (size_t i = 0; i < SUBKEYS; i += 2) {
+    for (std::size_t i = 0; i < SUBKEYS; i += 2) {
       x = encrypt(x);
       P[i] = x.L;
       P[i + 1] = x.R;
     }
-    for (size_t i = 0; i < BOXES; ++i) {
-      for (size_t j = 0; j < ENTRIES; j += 2) {
+    for (std::size_t i = 0; i < BOXES; ++i) {
+      for (std::size_t j = 0; j < ENTRIES; j += 2) {
         x = encrypt(x);
         S[i][j] = x.L;
         S[i][j + 1] = x.R;
@@ -58,7 +65,7 @@ public:
 
   constexpr Block encrypt(const Block &x) const {
     Block y(x);
-    for (size_t i = 0; i < ROUNDS; ++i) {
+    for (std::size_t i = 0; i < ROUNDS; ++i) {
       y.L = y.L ^ P[i];
       y.R = F(y.L) ^ y.R;
       std::swap(y.L, y.R);
@@ -72,7 +79,7 @@ public:
 
   constexpr Block decrypt(const Block &x) const {
     Block y(x);
-    for (size_t i = ROUNDS + 1; i > 1; --i) {
+    for (std::size_t i = ROUNDS + 1; i > 1; --i) {
       y.L = y.L ^ P[i];
       y.R = F(y.L) ^ y.R;
       std::swap(y.L, y.R);
@@ -99,3 +106,5 @@ private:
   std::array<uint32_t, SUBKEYS> P;
   std::array<std::array<uint32_t, ENTRIES>, BOXES> S;
 };
+
+} // namespace Blowfish