Add basic compatibility with OpenSSL 3.
https://github.com/frankmorgner/openpace/issues/53
https://github.com/frankmorgner/openpace/commit/2d94a152dd36543d2a713f1abe20717fdaafae0a
https://github.com/frankmorgner/openpace/commit/8b2c8a76873da4862dbf4240c901f3e6d4bc040a
https://github.com/frankmorgner/openpace/commit/4c22789d264bd249cfff1c3e69466991e58a76cf
--- src/eac/cv_cert.h.orig	2021-04-09 07:44:49.000000000 -0500
+++ src/eac/cv_cert.h	2021-12-20 05:31:17.000000000 -0600
@@ -341,7 +341,11 @@
  * @return Number of bytes successfully encoded or a negative value if an
  * error occured.
  */
-int i2d_CVC_CERT(CVC_CERT *a, unsigned char **out);
+int i2d_CVC_CERT(
+#if OPENSSL_VERSION_NUMBER >= 0x30000000L
+  const
+#endif
+  CVC_CERT *a, unsigned char **out);
 
 /**
  * @brief Duplicate a CV certificate
--- src/eac.c.orig	2021-04-09 07:42:03.000000000 -0500
+++ src/eac.c	2021-12-20 05:31:29.000000000 -0600
@@ -105,7 +105,9 @@
     if (!ctx)
         return 0;
 
-    return BN_zero(ctx->ssc);
+    BN_zero(ctx->ssc);
+
+    return 1;
 }
 
 int EAC_set_ssc(const EAC_CTX *ctx, unsigned long ssc)
--- src/eac_util.c.orig	2021-04-09 07:42:04.000000000 -0500
+++ src/eac_util.c	2021-12-20 05:31:31.000000000 -0600
@@ -321,6 +321,10 @@
     return NULL;
 }
 
+#if OPENSSL_VERSION_NUMBER >= 0x30000000L
+#include <openssl/provider.h>
+#endif
+
 BUF_MEM *
 retail_mac_des(const BUF_MEM * key, const BUF_MEM * in)
 {
@@ -331,6 +335,11 @@
 
     check(key, "Invalid arguments");
 
+#if OPENSSL_VERSION_NUMBER >= 0x30000000L
+    OSSL_PROVIDER *legacy;
+    legacy = OSSL_PROVIDER_load(NULL, "legacy");
+#endif
+
     len = EVP_CIPHER_block_size(EVP_des_cbc());
     check(key->length >= 2*len, "Key too short");
 
@@ -369,6 +378,9 @@
     BUF_MEM_free(c_tmp);
     BUF_MEM_free(d_tmp);
     EVP_CIPHER_CTX_free(ctx);
+#if OPENSSL_VERSION_NUMBER >= 0x30000000L
+    OSSL_PROVIDER_unload(legacy);
+#endif
 
     return mac;
 
@@ -381,6 +393,10 @@
         BUF_MEM_free(d_tmp);
     if (ctx)
         EVP_CIPHER_CTX_free(ctx);
+#if OPENSSL_VERSION_NUMBER >= 0x30000000L
+    if (legacy)
+        OSSL_PROVIDER_unload(legacy);
+#endif
 
     return NULL;
 }