Random: Add seeded PRNG

2 files changed, 62 insertions, 5 deletions

diff --git a/Source/Core/Common/Random.cpp b/Source/Core/Common/Random.cpp
index c512e7695d..754cea397f 100644
--- a/Source/Core/Common/Random.cpp
+++ b/Source/Core/Common/Random.cpp
@@ -11,10 +11,42 @@
 
 namespace Common::Random
 {
-class CSPRNG final
+struct PRNG::Impl
+{
+  Impl(void* seed, std::size_t size)
+  {
+    mbedtls_hmac_drbg_init(&m_context);
+    const int ret = mbedtls_hmac_drbg_seed_buf(
+        &m_context, mbedtls_md_info_from_type(MBEDTLS_MD_SHA256), static_cast<u8*>(seed), size);
+    ASSERT(ret == 0);
+  }
+
+  ~Impl() { mbedtls_hmac_drbg_free(&m_context); }
+
+  void Generate(void* buffer, std::size_t size)
+  {
+    const int ret = mbedtls_hmac_drbg_random(&m_context, static_cast<u8*>(buffer), size);
+    ASSERT(ret == 0);
+  }
+
+  mbedtls_hmac_drbg_context m_context;
+};
+
+PRNG::PRNG(void* seed, std::size_t size) : m_impl(std::make_unique<Impl>(seed, size))
+{
+}
+
+PRNG::~PRNG() = default;
+
+void PRNG::Generate(void* buffer, std::size_t size)
+{
+  m_impl->Generate(buffer, size);
+}
+
+class EntropySeededPRNG final
 {
 public:
-  CSPRNG()
+  EntropySeededPRNG()
   {
     mbedtls_entropy_init(&m_entropy);
     mbedtls_hmac_drbg_init(&m_context);
@@ -23,7 +55,7 @@ public:
     ASSERT(ret == 0);
   }
 
-  ~CSPRNG()
+  ~EntropySeededPRNG()
   {
     mbedtls_hmac_drbg_free(&m_context);
     mbedtls_entropy_free(&m_entropy);
@@ -40,10 +72,10 @@ private:
   mbedtls_hmac_drbg_context m_context;
 };
 
-static thread_local CSPRNG s_csprng;
+static thread_local EntropySeededPRNG s_esprng;
 
 void Generate(void* buffer, std::size_t size)
 {
-  s_csprng.Generate(buffer, size);
+  s_esprng.Generate(buffer, size);
 }
 }  // namespace Common::Random
diff --git a/Source/Core/Common/Random.h b/Source/Core/Common/Random.h
index 1f234f8ac3..789f62d9c1 100644
--- a/Source/Core/Common/Random.h
+++ b/Source/Core/Common/Random.h
@@ -5,12 +5,37 @@
 #pragma once
 
 #include <cstddef>
+#include <memory>
 #include <type_traits>
 
 #include "Common/CommonTypes.h"
 
 namespace Common::Random
 {
+/// Cryptographically secure pseudo-random number generator, with explicit seed.
+class PRNG final
+{
+public:
+  explicit PRNG(u64 seed) : PRNG(&seed, sizeof(u64)) {}
+  PRNG(void* seed, std::size_t size);
+  ~PRNG();
+
+  void Generate(void* buffer, std::size_t size);
+
+  template <typename T>
+  T GenerateValue()
+  {
+    static_assert(std::is_arithmetic<T>(), "T must be an arithmetic type in GenerateValue.");
+    T value;
+    Generate(&value, sizeof(value));
+    return value;
+  }
+
+private:
+  struct Impl;
+  std::unique_ptr<Impl> m_impl;
+};
+
 /// Fill `buffer` with random bytes using a cryptographically secure pseudo-random number generator.
 void Generate(void* buffer, std::size_t size);