Used OpenSSL correctly.

CMakeLists.txt

@@ -13,6 +13,11 @@ add_library(hdrbg SHARED ${sources})
 target_include_directories(hdrbg PRIVATE include)
 configure_file(hdrbg.pc.in hdrbg.pc @ONLY)
 
+find_package(OpenSSL 3.0.0)
+if(OpenSSL_FOUND)
+    target_compile_definitions(hdrbg PRIVATE TFPF_HASH_DRBG_OPENSSL_FOUND=1)
+endif()
+
 set_target_properties(hdrbg PROPERTIES
     PUBLIC_HEADER include/hdrbg.h
     SOVERSION 1

lib/sha256.c

@@ -1,10 +1,15 @@
 #include <inttypes.h>
+#include <limits.h>
 #include <stddef.h>
 #include <string.h>
 
 #include "extras.h"
 #include "sha.h"
 
+#ifdef TFPF_HASH_DRBG_OPENSSL_FOUND
+#include <openssl/sha.h>
+#endif
+
 #define ROTR32(x, n) ((x) >> (n) | (x) << (32 - (n)))
 
 // Hash initialiser.
@@ -46,6 +51,10 @@ sha256_bytes[32];
 uint8_t *
 sha256(uint8_t const *m_bytes_, size_t m_length_, uint8_t *h_bytes)
 {
+#if defined TFPF_HASH_DRBG_OPENSSL_FOUND && CHAR_BIT == 8
+    return SHA256(m_bytes_, m_length_, h_bytes);
+#endif
+
     // Initialise the hash.
     uint32_t h_words[8];
     memcpy(h_words, sha256_init, sizeof sha256_init);