Index: lang/dotnet/Makefile
===================================================================
--- lang/dotnet/Makefile
+++ lang/dotnet/Makefile
@@ -60,10 +60,16 @@
 				SDKVERSION=${SDKVERSION} SDKVERSIONSUFFIX=${SDKVERSIONSUFFIX} \
 				DOTNET_NETVERSION=net${DOTNETVERSION}
 
-OPTIONS_DEFINE=		NUPKG
+OPTIONS_DEFINE=		LIBRESSL NUPKG
 OPTIONS_DEFAULT=	NUPKG
 OPTIONS_SUB=		yes
+LIBRESSL_DESC=		Add experimental LibreSSL support (see pkg-descr)
 NUPKG_DESC=		Install FreeBSD runtime NuGet packages
+
+LIBRESSL_EXTRA_PATCHES=	${PATCHDIR}/extra-patch-libressl
+LIBRESSL_VARS_OFF=	BROKEN_SSL=libressl \
+			BROKEN_SSL_REASON="Not supported upstream"
+
 NUPKG_SUB_FILES=	post-install-register-nuget
 NUPKG_VARS=		PKGPOSTINSTALL+=${WRKDIR}/post-install-register-nuget
 
Index: lang/dotnet/files/extra-patch-libressl
===================================================================
--- /dev/null
+++ lang/dotnet/files/extra-patch-libressl
@@ -0,0 +1,167 @@
+--- src/runtime/src/native/libs/System.Security.Cryptography.Native/openssl.c.orig	2024-03-27 20:02:53 UTC
++++ src/runtime/src/native/libs/System.Security.Cryptography.Native/openssl.c
+@@ -21,7 +21,11 @@
+ #include <unistd.h>
+ 
+ #if OPENSSL_VERSION_NUMBER >= OPENSSL_VERSION_1_1_0_RTM
++#  ifdef LIBRESSL_VERSION_NUMBER
++c_static_assert(CRYPTO_EX_INDEX_X509 == 12);
++#  else
+ c_static_assert(CRYPTO_EX_INDEX_X509 == 3);
++#  endif
+ #else
+ c_static_assert(CRYPTO_EX_INDEX_X509 == 10);
+ #endif
+@@ -1206,7 +1210,7 @@ static void ExDataFree(
+ // In the OpenSSL 3 headers, `from_d` changed from (void*) to (void**).
+ static int ExDataDup(
+     CRYPTO_EX_DATA* to,
+-#if OPENSSL_VERSION_NUMBER >= OPENSSL_VERSION_1_1_0_RTM
++#if OPENSSL_VERSION_NUMBER >= OPENSSL_VERSION_1_1_0_RTM && !defined LIBRESSL_VERSION_NUMBER
+     const CRYPTO_EX_DATA* from,
+ #else
+     CRYPTO_EX_DATA* from,
+@@ -1444,7 +1448,11 @@ static int32_t EnsureOpenSsl11Initialized(void)
+     atexit(HandleShutdown);
+ 
+     // In OpenSSL 1.1.0+, CRYPTO_EX_INDEX_X509 is 3.
++#ifdef LIBRESSL_VERSION_NUMBER
++    g_x509_ocsp_index = CRYPTO_get_ex_new_index(12, 0, NULL, NULL, ExDataDup, ExDataFree);
++#else
+     g_x509_ocsp_index = CRYPTO_get_ex_new_index(3, 0, NULL, NULL, ExDataDup, ExDataFree);
++#endif
+     return 0;
+ }
+ 
+--- src/runtime/src/native/libs/System.Security.Cryptography.Native/pal_dsa.c.orig	2024-03-28 09:01:52 UTC
++++ src/runtime/src/native/libs/System.Security.Cryptography.Native/pal_dsa.c
+@@ -100,6 +100,7 @@ int32_t CryptoNative_DsaSign(
+ 
+     ERR_clear_error();
+ 
++#ifndef LIBRESSL_VERSION_NUMBER
+     // DSA_OpenSSL() returns a shared pointer, no need to free/cache.
+     if (DSA_get_method(dsa) == DSA_OpenSSL())
+     {
+@@ -114,6 +115,7 @@ int32_t CryptoNative_DsaSign(
+             return 0;
+         }
+     }
++#endif
+ 
+     unsigned int unsignedSigLen = 0;
+     int32_t success = DSA_sign(0, hash, hashLength, refsignature, &unsignedSigLen, dsa);
+--- src/runtime/src/native/libs/System.Security.Cryptography.Native/pal_evp.c.orig	2024-03-27 20:33:36 UTC
++++ src/runtime/src/native/libs/System.Security.Cryptography.Native/pal_evp.c
+@@ -69,7 +69,7 @@ int32_t CryptoNative_EvpDigestFinalEx(EVP_MD_CTX* ctx,
+ 
+ int32_t CryptoNative_EvpDigestFinalXOF(EVP_MD_CTX* ctx, uint8_t* md, uint32_t len)
+ {
+-    #if HAVE_OPENSSL_SHA3
++    #if HAVE_OPENSSL_SHA3 && !defined(LIBRESSL_VERSION_NUMBER)
+         if (API_EXISTS(EVP_DigestFinalXOF))
+         {
+             ERR_clear_error();
+@@ -300,7 +300,7 @@ const EVP_MD* CryptoNative_EvpSha3_512(void)
+ const EVP_MD* CryptoNative_EvpShake128(void)
+ {
+     // No error queue impact.
+-#if HAVE_OPENSSL_SHA3
++#if HAVE_OPENSSL_SHA3 && !defined(LIBRESSL_VERSION_NUMBER)
+     if (API_EXISTS(EVP_shake128))
+     {
+         return EVP_shake128();
+@@ -313,7 +313,7 @@ const EVP_MD* CryptoNative_EvpShake128(void)
+ const EVP_MD* CryptoNative_EvpShake256(void)
+ {
+     // No error queue impact.
+-#if HAVE_OPENSSL_SHA3
++#if HAVE_OPENSSL_SHA3 && !defined(LIBRESSL_VERSION_NUMBER)
+     if (API_EXISTS(EVP_shake256))
+     {
+         return EVP_shake256();
+--- src/runtime/src/native/libs/System.Security.Cryptography.Native/pal_evp_pkey.c.orig	2024-03-27 20:49:40 UTC
++++ src/runtime/src/native/libs/System.Security.Cryptography.Native/pal_evp_pkey.c
+@@ -276,9 +276,18 @@ int32_t CryptoNative_EncodeSubjectPublicKeyInfo(EVP_PK
+     return i2d_PUBKEY(pkey, &buf);
+ }
+ 
++#ifdef LIBRESSL_VERSION_NUMBER
+ static EVP_PKEY* LoadKeyFromEngine(
+     const char* engineName,
+     const char* keyName,
++    EVP_PKEY * (*load_func)(ENGINE *, const char *, UI_METHOD *, void *))
++{
++    return NULL;
++}
++#else
++static EVP_PKEY* LoadKeyFromEngine(
++    const char* engineName,
++    const char* keyName,
+     ENGINE_LOAD_KEY_PTR load_func)
+ {
+     ERR_clear_error();
+@@ -304,6 +313,7 @@ static EVP_PKEY* LoadKeyFromEngine(
+ 
+     return ret;
+ }
++#endif
+ 
+ EVP_PKEY* CryptoNative_LoadPrivateKeyFromEngine(const char* engineName, const char* keyName)
+ {
+--- src/runtime/src/native/libs/System.Security.Cryptography.Native/pal_ssl.c.orig	2024-03-28 07:25:55 UTC
++++ src/runtime/src/native/libs/System.Security.Cryptography.Native/pal_ssl.c
+@@ -111,7 +111,7 @@ static void DetectCiphersuiteConfiguration(void)
+     //
+     // The method uses OpenSSL 1.0.x API, except for the fallback function SSL_CTX_config, to
+     // make the portable version easier.
+-#if defined NEED_OPENSSL_1_1 || defined NEED_OPENSSL_3_0
++#if (defined NEED_OPENSSL_1_1 || defined NEED_OPENSSL_3_0) && !defined(LIBRESSL_VERSION_NUMBER)
+ 
+     // Check to see if there's a registered default CipherString. If not, we will use our own.
+     SSL_CTX* ctx = SSL_CTX_new(TLS_method());
+@@ -718,7 +718,7 @@ void CryptoNative_SslSessionFree(SSL_SESSION* session)
+ 
+ const char* CryptoNative_SslSessionGetHostname(SSL_SESSION* session)
+ {
+-#if defined NEED_OPENSSL_1_1 || defined NEED_OPENSSL_3_0
++#if (defined NEED_OPENSSL_1_1 || defined NEED_OPENSSL_3_0) && !defined(LIBRESSL_VERSION_NUMBER)
+     if (API_EXISTS(SSL_SESSION_get0_hostname))
+     {
+         return SSL_SESSION_get0_hostname(session);
+@@ -731,7 +731,7 @@ const char* CryptoNative_SslSessionGetHostname(SSL_SES
+ 
+ int CryptoNative_SslSessionSetHostname(SSL_SESSION* session, const char* hostname)
+ {
+-#if defined NEED_OPENSSL_1_1 || defined NEED_OPENSSL_3_0
++#if (defined NEED_OPENSSL_1_1 || defined NEED_OPENSSL_3_0) && !defined(LIBRESSL_VERSION_NUMBER)
+     if (API_EXISTS(SSL_SESSION_set1_hostname))
+     {
+         SSL_SESSION_set1_hostname(session, hostname);
+@@ -1002,7 +1002,9 @@ void CryptoNative_SslSetClientCertCallback(SSL* ssl, i
+ {
+     // void shim functions don't lead to exceptions, so skip the unconditional error clearing.
+ 
++#ifndef LIBRESSL_VERSION_NUMBER
+     SSL_set_cert_cb(ssl, set ? client_certificate_cb : NULL, NULL);
++#endif
+ }
+ 
+ void CryptoNative_SslCtxSetKeylogCallback(SSL_CTX* ctx, SslCtxSetKeylogCallback cb)
+--- src/runtime/src/native/libs/System.Security.Cryptography.Native/pal_x509.c.orig	2024-03-28 07:59:11 UTC
++++ src/runtime/src/native/libs/System.Security.Cryptography.Native/pal_x509.c
+@@ -57,12 +57,14 @@ c_static_assert(PAL_X509_V_ERR_UNSUPPORTED_CONSTRAINT_
+ c_static_assert(PAL_X509_V_ERR_UNSUPPORTED_CONSTRAINT_SYNTAX == X509_V_ERR_UNSUPPORTED_CONSTRAINT_SYNTAX);
+ c_static_assert(PAL_X509_V_ERR_UNSUPPORTED_NAME_SYNTAX == X509_V_ERR_UNSUPPORTED_NAME_SYNTAX);
+ c_static_assert(PAL_X509_V_ERR_CRL_PATH_VALIDATION_ERROR == X509_V_ERR_CRL_PATH_VALIDATION_ERROR);
++#ifndef LIBRESSL_VERSION_NUMBER
+ c_static_assert(PAL_X509_V_ERR_SUITE_B_INVALID_VERSION == X509_V_ERR_SUITE_B_INVALID_VERSION);
+ c_static_assert(PAL_X509_V_ERR_SUITE_B_INVALID_ALGORITHM == X509_V_ERR_SUITE_B_INVALID_ALGORITHM);
+ c_static_assert(PAL_X509_V_ERR_SUITE_B_INVALID_CURVE == X509_V_ERR_SUITE_B_INVALID_CURVE);
+ c_static_assert(PAL_X509_V_ERR_SUITE_B_INVALID_SIGNATURE_ALGORITHM == X509_V_ERR_SUITE_B_INVALID_SIGNATURE_ALGORITHM);
+ c_static_assert(PAL_X509_V_ERR_SUITE_B_LOS_NOT_ALLOWED == X509_V_ERR_SUITE_B_LOS_NOT_ALLOWED);
+ c_static_assert(PAL_X509_V_ERR_SUITE_B_CANNOT_SIGN_P_384_WITH_P_256 == X509_V_ERR_SUITE_B_CANNOT_SIGN_P_384_WITH_P_256);
++#endif
+ c_static_assert(PAL_X509_V_ERR_HOSTNAME_MISMATCH == X509_V_ERR_HOSTNAME_MISMATCH);
+ c_static_assert(PAL_X509_V_ERR_EMAIL_MISMATCH == X509_V_ERR_EMAIL_MISMATCH);
+ c_static_assert(PAL_X509_V_ERR_IP_ADDRESS_MISMATCH == X509_V_ERR_IP_ADDRESS_MISMATCH);
Index: lang/dotnet/pkg-descr
===================================================================
--- lang/dotnet/pkg-descr
+++ lang/dotnet/pkg-descr
@@ -2,3 +2,9 @@
 many different types of applications. It provides a standard set of base class
 libraries and APIs that are common to all .NET applications. .NET apps can be
 written in such languages as C#, F#, or Visual Basic.
+
+Using LibreSSL is not supported. Enabling the LIBRESSL port option will patch
+the sources, so building with LibreSSL works, but this will just disable some
+functionality and also interfere with runtime detection of OpenSSL APIs. .NET
+projects built with this option set might fail to work correctly and are likely
+to fail on machines using OpenSSL.