diff --git a/tests/CMakeLists.txt b/tests/CMakeLists.txt
index 208d62dd..44d4f201 100644
--- a/tests/CMakeLists.txt
+++ b/tests/CMakeLists.txt
@@ -12,6 +12,7 @@ include_directories(${OPENSSL_INCLUDE_DIR}
                     ${libssh_BINARY_DIR}/include
                     ${libssh_BINARY_DIR}
                     ${libssh_SOURCE_DIR}/src
+                    ${CMAKE_SOURCE_DIR}/include
                     ${CMAKE_CURRENT_SOURCE_DIR}
                     ${CMAKE_BINARY_DIR}/tests)
 
@@ -32,6 +33,50 @@ target_compile_options(${TORTURE_LIBRARY} PRIVATE
                        -DSSH_PING_EXECUTABLE="${CMAKE_CURRENT_BINARY_DIR}/ssh_ping"
 )
 
+# The shared version of the library is only useful when client testing is
+# enabled
+if (CLIENT_TESTING)
+    # create shared test library
+    set(TORTURE_SHARED_LIBRARY torture_shared)
+
+    if (MINGW)
+        set(USE_ATTRIBUTE_WEAK "-DUSE_ATTRIBUTE_WEAK")
+    endif ()
+
+    # Create a list of symbols that should be wrapped for override test
+    set(WRAP_SYMBOLS "")
+    list(APPEND WRAP_SYMBOLS
+         "-Wl,--wrap=chacha_keysetup"
+         "-Wl,--wrap=chacha_ivsetup"
+         "-Wl,--wrap=chacha_encrypt_bytes")
+    list(APPEND WRAP_SYMBOLS "-Wl,--wrap=poly1305_auth")
+    list(APPEND WRAP_SYMBOLS
+         "-Wl,--wrap=crypto_sign_ed25519_keypair"
+         "-Wl,--wrap=crypto_sign_ed25519"
+         "-Wl,--wrap=crypto_sign_ed25519_open")
+    list(APPEND WRAP_SYMBOLS
+         "-Wl,--wrap=crypto_scalarmult_base"
+         "-Wl,--wrap=crypto_scalarmult")
+
+    add_library(${TORTURE_SHARED_LIBRARY}
+                SHARED
+                    cmdline.c
+                    torture.c
+                    torture_key.c
+                    torture_pki.c
+                    torture_cmocka.c
+               )
+    target_link_libraries(${TORTURE_SHARED_LIBRARY}
+                          ${CMOCKA_LIBRARY}
+                          ssh::static
+                          ${WRAP_SYMBOLS}
+                         )
+    target_compile_options(${TORTURE_SHARED_LIBRARY} PRIVATE
+                           -DSSH_PING_EXECUTABLE="${CMAKE_CURRENT_BINARY_DIR}/ssh_ping"
+                           ${USE_ATTRIBUTE_WEAK}
+    )
+endif ()
+
 if (ARGP_LIBRARY)
     target_link_libraries(${TORTURE_LIBRARY}
         ${ARGP_LIBRARY}
@@ -259,6 +304,9 @@ endif ()
 
 if (CLIENT_TESTING)
     add_subdirectory(client)
+
+    # Only add override testing if testing the client
+    add_subdirectory(external_override)
 endif ()
 
 if (WITH_SERVER AND SERVER_TESTING)
diff --git a/tests/external_override/CMakeLists.txt b/tests/external_override/CMakeLists.txt
new file mode 100644
index 00000000..a0d584e3
--- /dev/null
+++ b/tests/external_override/CMakeLists.txt
@@ -0,0 +1,133 @@
+project(external-override C)
+
+include_directories(${CMAKE_SOURCE_DIR}/include)
+
+set(LIBSSH_OVERRIDE_TESTS
+    torture_override
+)
+
+# chacha20_override
+add_library(chacha20_override SHARED
+            chacha20_override.c
+            ${libssh_SOURCE_DIR}/src/external/chacha.c
+           )
+set(CHACHA20_OVERRIDE_LIBRARY
+    ${libssh_BINARY_DIR}/lib/${CMAKE_SHARED_LIBRARY_PREFIX}chacha20_override${CMAKE_SHARED_LIBRARY_SUFFIX})
+
+# poly1305_override
+add_library(poly1305_override SHARED
+            poly1305_override.c
+            ${libssh_SOURCE_DIR}/src/external/poly1305.c
+           )
+set(POLY1305_OVERRIDE_LIBRARY
+${libssh_BINARY_DIR}/lib/${CMAKE_SHARED_LIBRARY_PREFIX}poly1305_override${CMAKE_SHARED_LIBRARY_SUFFIX})
+
+# ed25519_override
+add_library(ed25519_override SHARED
+            ed25519_override.c
+            ${libssh_SOURCE_DIR}/src/external/fe25519.c
+            ${libssh_SOURCE_DIR}/src/external/ge25519.c
+            ${libssh_SOURCE_DIR}/src/external/sc25519.c
+            ${libssh_SOURCE_DIR}/src/external/ed25519.c
+           )
+set(ED25519_OVERRIDE_LIBRARY
+${libssh_BINARY_DIR}/lib/${CMAKE_SHARED_LIBRARY_PREFIX}ed25519_override${CMAKE_SHARED_LIBRARY_SUFFIX})
+
+# curve25519_override
+add_library(curve25519_override SHARED
+            curve25519_override.c
+            ${libssh_SOURCE_DIR}/src/external/curve25519_ref.c
+            ${libssh_SOURCE_DIR}/src/external/fe25519.c
+            ${libssh_SOURCE_DIR}/src/external/ge25519.c
+            ${libssh_SOURCE_DIR}/src/external/sc25519.c
+            ${libssh_SOURCE_DIR}/src/external/ed25519.c
+           )
+set(CURVE25519_OVERRIDE_LIBRARY
+${libssh_BINARY_DIR}/lib/${CMAKE_SHARED_LIBRARY_PREFIX}curve25519_override${CMAKE_SHARED_LIBRARY_SUFFIX})
+
+set(OVERRIDE_LIBRARIES
+    ${CHACHA20_OVERRIDE_LIBRARY}:${POLY1305_OVERRIDE_LIBRARY}:${ED25519_OVERRIDE_LIBRARY}:${CURVE25519_OVERRIDE_LIBRARY}
+)
+
+if (WITH_MBEDTLS)
+    if (HAVE_MBEDTLS_CHACHA20_H AND HAVE_MBEDTLS_POLY1305_H)
+        list(APPEND OVERRIDE_RESULTS "-DSHOULD_CALL_INTERNAL_CHACHAPOLY=0")
+    else ()
+        list(APPEND OVERRIDE_RESULTS "-DSHOULD_CALL_INTERNAL_CHACHAPOLY=1")
+    endif ()
+    list(APPEND OVERRIDE_RESULTS "-DSHOULD_CALL_INTERNAL_ED25519=1")
+    list(APPEND OVERRIDE_RESULTS "-DSHOULD_CALL_INTERNAL_CURVE25519=1")
+elseif (WITH_GCRYPT)
+    if (HAVE_GCRYPT_CHACHA_POLY)
+        list(APPEND OVERRIDE_RESULTS "-DSHOULD_CALL_INTERNAL_CHACHAPOLY=0")
+    else ()
+        list(APPEND OVERRIDE_RESULTS "-DSHOULD_CALL_INTERNAL_CHACHAPOLY=1")
+    endif ()
+    list(APPEND OVERRIDE_RESULTS "-DSHOULD_CALL_INTERNAL_ED25519=1")
+    list(APPEND OVERRIDE_RESULTS "-DSHOULD_CALL_INTERNAL_CURVE25519=1")
+else ()
+    if (HAVE_OPENSSL_EVP_CHACHA20 AND HAVE_OPENSSL_EVP_POLY1305)
+        list(APPEND OVERRIDE_RESULTS "-DSHOULD_CALL_INTERNAL_CHACHAPOLY=0")
+    else ()
+        list(APPEND OVERRIDE_RESULTS "-DSHOULD_CALL_INTERNAL_CHACHAPOLY=1")
+    endif ()
+
+    if (HAVE_OPENSSL_ED25519)
+        list(APPEND OVERRIDE_RESULTS "-DSHOULD_CALL_INTERNAL_ED25519=0")
+    else ()
+        list(APPEND OVERRIDE_RESULTS "-DSHOULD_CALL_INTERNAL_ED25519=1")
+    endif ()
+
+    if (HAVE_OPENSSL_X25519)
+        list(APPEND OVERRIDE_RESULTS "-DSHOULD_CALL_INTERNAL_CURVE25519=0")
+    else ()
+        list(APPEND OVERRIDE_RESULTS "-DSHOULD_CALL_INTERNAL_CURVE25519=1")
+    endif ()
+endif ()
+
+if (NOT OSX)
+    # Remove any preload string from the environment variables list
+    foreach(env_string ${TORTURE_ENVIRONMENT})
+        if (${env_string} MATCHES "^LD_PRELOAD=*")
+            list(REMOVE_ITEM TORTURE_ENVIRONMENT ${env_string})
+            set(PRELOAD_STRING "${env_string}:")
+        endif ()
+    endforeach ()
+
+    if ("${PRELOAD_STRING}" STREQUAL "")
+        set(PRELOAD_STRING "LD_PRELOAD=")
+    endif ()
+
+    list(APPEND TORTURE_ENVIRONMENT
+         "${PRELOAD_STRING}${OVERRIDE_LIBRARIES}")
+endif()
+
+foreach(_OVERRIDE_TEST ${LIBSSH_OVERRIDE_TESTS})
+    add_cmocka_test(${_OVERRIDE_TEST}
+                    SOURCES ${_OVERRIDE_TEST}.c
+                    COMPILE_OPTIONS ${DEFAULT_C_COMPILE_FLAGS}
+                        ${OVERRIDE_RESULTS}
+                    LINK_LIBRARIES
+                        ${TORTURE_SHARED_LIBRARY}
+                        chacha20_override
+                        poly1305_override
+                        ed25519_override
+                        curve25519_override
+    )
+
+    if (OSX)
+        set_property(
+            TEST
+                ${_OVERRIDE_TEST}
+            PROPERTY
+            ENVIRONMENT DYLD_FORCE_FLAT_NAMESPACE=1;DYLD_INSERT_LIBRARIES=${OVERRIDE_LIBRARIES})
+
+    else ()
+        set_property(
+            TEST
+                ${_OVERRIDE_TEST}
+            PROPERTY
+                ENVIRONMENT ${TORTURE_ENVIRONMENT})
+
+    endif()
+endforeach()
diff --git a/tests/external_override/chacha20_override.c b/tests/external_override/chacha20_override.c
new file mode 100644
index 00000000..7e166e7c
--- /dev/null
+++ b/tests/external_override/chacha20_override.c
@@ -0,0 +1,80 @@
+/*
+ * This file is part of the SSH Library
+ *
+ * Copyright (c) 2021 by Anderson Toshiyuki Sasaki - Red Hat, Inc.
+ *
+ * The SSH Library is free software: you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation, either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * The SSH Library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with the SSH Library; see the file COPYING. If not,
+ * see <https://www.gnu.org/licenses/>.
+ */
+
+#include "config.h"
+
+#include <stdlib.h>
+#include <stdint.h>
+#include <stdio.h>
+#include <libssh/chacha.h>
+#include <libssh/priv.h>
+
+#include "chacha20_override.h"
+
+static bool internal_function_called = false;
+
+void __wrap_chacha_keysetup(struct chacha_ctx *x,
+                            const uint8_t *k,
+                            uint32_t kbits)
+#ifdef HAVE_GCC_BOUNDED_ATTRIBUTE
+    __attribute__((__bounded__(__minbytes__, 2, CHACHA_MINKEYLEN)))
+#endif
+{
+    fprintf(stderr, "%s: Internal implementation was called\n", __func__);
+    internal_function_called = true;
+    chacha_keysetup(x, k, kbits);
+}
+
+void __wrap_chacha_ivsetup(struct chacha_ctx *x,
+                           const uint8_t *iv,
+                           const uint8_t *ctr)
+#ifdef HAVE_GCC_BOUNDED_ATTRIBUTE
+    __attribute__((__bounded__(__minbytes__, 2, CHACHA_NONCELEN)))
+    __attribute__((__bounded__(__minbytes__, 3, CHACHA_CTRLEN)))
+#endif
+{
+    fprintf(stderr, "%s: Internal implementation was called\n", __func__);
+    internal_function_called = true;
+    chacha_ivsetup(x, iv, ctr);
+}
+
+void __wrap_chacha_encrypt_bytes(struct chacha_ctx *x,
+                                 const uint8_t *m,
+                                 uint8_t *c,
+                                 uint32_t bytes)
+#ifdef HAVE_GCC_BOUNDED_ATTRIBUTE
+    __attribute__((__bounded__(__buffer__, 2, 4)))
+    __attribute__((__bounded__(__buffer__, 3, 4)))
+#endif
+{
+    fprintf(stderr, "%s: Internal implementation was called\n", __func__);
+    internal_function_called = true;
+    chacha_encrypt_bytes(x, m, c, bytes);
+}
+
+bool internal_chacha20_function_called(void)
+{
+    return internal_function_called;
+}
+
+void reset_chacha20_function_called(void)
+{
+    internal_function_called = false;
+}
diff --git a/tests/external_override/chacha20_override.h b/tests/external_override/chacha20_override.h
new file mode 100644
index 00000000..58f8f211
--- /dev/null
+++ b/tests/external_override/chacha20_override.h
@@ -0,0 +1,51 @@
+/*
+ * This file is part of the SSH Library
+ *
+ * Copyright (c) 2021 by Anderson Toshiyuki Sasaki - Red Hat, Inc.
+ *
+ * The SSH Library is free software: you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation, either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * The SSH Library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with the SSH Library; see the file COPYING. If not,
+ * see <https://www.gnu.org/licenses/>.
+ */
+
+#include "libssh/chacha.h"
+
+void __wrap_chacha_keysetup(struct chacha_ctx *x,
+                            const uint8_t *k,
+                            uint32_t kbits)
+#ifdef HAVE_GCC_BOUNDED_ATTRIBUTE
+    __attribute__((__bounded__(__minbytes__, 2, CHACHA_MINKEYLEN)))
+#endif
+;
+
+void __wrap_chacha_ivsetup(struct chacha_ctx *x,
+                           const uint8_t *iv,
+                           const uint8_t *ctr)
+#ifdef HAVE_GCC_BOUNDED_ATTRIBUTE
+    __attribute__((__bounded__(__minbytes__, 2, CHACHA_NONCELEN)))
+    __attribute__((__bounded__(__minbytes__, 3, CHACHA_CTRLEN)))
+#endif
+;
+
+void __wrap_chacha_encrypt_bytes(struct chacha_ctx *x,
+                                 const uint8_t *m,
+                                 uint8_t *c,
+                                 uint32_t bytes)
+#ifdef HAVE_GCC_BOUNDED_ATTRIBUTE
+    __attribute__((__bounded__(__buffer__, 2, 4)))
+    __attribute__((__bounded__(__buffer__, 3, 4)))
+#endif
+;
+
+bool internal_chacha20_function_called(void);
+void reset_chacha20_function_called(void);
diff --git a/tests/external_override/curve25519_override.c b/tests/external_override/curve25519_override.c
new file mode 100644
index 00000000..983d57cd
--- /dev/null
+++ b/tests/external_override/curve25519_override.c
@@ -0,0 +1,58 @@
+/*
+ * This file is part of the SSH Library
+ *
+ * Copyright (c) 2021 by Anderson Toshiyuki Sasaki - Red Hat, Inc.
+ *
+ * The SSH Library is free software: you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation, either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * The SSH Library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with the SSH Library; see the file COPYING. If not,
+ * see <https://www.gnu.org/licenses/>.
+ */
+
+#include "config.h"
+
+#include <stdlib.h>
+#include <stdint.h>
+#include <stdio.h>
+#include <libssh/curve25519.h>
+#include <libssh/priv.h>
+
+#include "curve25519_override.h"
+
+static bool internal_function_called = false;
+
+int __wrap_crypto_scalarmult_base(unsigned char *q,
+                                  const unsigned char *n)
+{
+    fprintf(stderr, "%s: Internal implementation was called\n", __func__);
+    internal_function_called = true;
+    return crypto_scalarmult_base(q, n);
+}
+
+int __wrap_crypto_scalarmult(unsigned char *q,
+                             const unsigned char *n,
+                             const unsigned char *p)
+{
+    fprintf(stderr, "%s: Internal implementation was called\n", __func__);
+    internal_function_called = true;
+    return crypto_scalarmult(q, n, p);
+}
+
+bool internal_curve25519_function_called(void)
+{
+    return internal_function_called;
+}
+
+void reset_curve25519_function_called(void)
+{
+    internal_function_called = false;
+}
diff --git a/tests/external_override/curve25519_override.h b/tests/external_override/curve25519_override.h
new file mode 100644
index 00000000..634c1c40
--- /dev/null
+++ b/tests/external_override/curve25519_override.h
@@ -0,0 +1,31 @@
+/*
+ * This file is part of the SSH Library
+ *
+ * Copyright (c) 2021 by Anderson Toshiyuki Sasaki - Red Hat, Inc.
+ *
+ * The SSH Library is free software: you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation, either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * The SSH Library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with the SSH Library; see the file COPYING. If not,
+ * see <https://www.gnu.org/licenses/>.
+ */
+
+#include "libssh/curve25519.h"
+
+int __wrap_crypto_scalarmult_base(unsigned char *q,
+                                  const unsigned char *n);
+
+int __wrap_crypto_scalarmult(unsigned char *q,
+                             const unsigned char *n,
+                             const unsigned char *p);
+
+bool internal_curve25519_function_called(void);
+void reset_curve25519_function_called(void);
diff --git a/tests/external_override/ed25519_override.c b/tests/external_override/ed25519_override.c
new file mode 100644
index 00000000..439a5dab
--- /dev/null
+++ b/tests/external_override/ed25519_override.c
@@ -0,0 +1,71 @@
+/*
+ * This file is part of the SSH Library
+ *
+ * Copyright (c) 2021 by Anderson Toshiyuki Sasaki - Red Hat, Inc.
+ *
+ * The SSH Library is free software: you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation, either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * The SSH Library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with the SSH Library; see the file COPYING. If not,
+ * see <https://www.gnu.org/licenses/>.
+ */
+
+#include "config.h"
+
+#include <stdlib.h>
+#include <stdint.h>
+#include <stdio.h>
+#include <libssh/ed25519.h>
+#include <libssh/priv.h>
+
+#include "ed25519_override.h"
+
+static bool internal_function_called = false;
+
+int __wrap_crypto_sign_ed25519_keypair(ed25519_pubkey pk,
+                                       ed25519_privkey sk)
+{
+    fprintf(stderr, "%s: Internal implementation was called\n", __func__);
+    internal_function_called = true;
+    return crypto_sign_ed25519_keypair(pk, sk);
+}
+
+int __wrap_crypto_sign_ed25519(unsigned char *sm,
+                               uint64_t *smlen,
+                               const unsigned char *m,
+                               uint64_t mlen,
+                               const ed25519_privkey sk)
+{
+    fprintf(stderr, "%s: Internal implementation was called\n", __func__);
+    internal_function_called = true;
+    return crypto_sign_ed25519(sm, smlen, m, mlen, sk);
+}
+
+int __wrap_crypto_sign_ed25519_open(unsigned char *m,
+                                    uint64_t *mlen,
+                                    const unsigned char *sm,
+                                    uint64_t smlen,
+                                    const ed25519_pubkey pk)
+{
+    fprintf(stderr, "%s: Internal implementation was called\n", __func__);
+    internal_function_called = true;
+    return crypto_sign_ed25519_open(m, mlen, sm, smlen, pk);
+}
+
+bool internal_ed25519_function_called(void)
+{
+    return internal_function_called;
+}
+
+void reset_ed25519_function_called(void)
+{
+    internal_function_called = false;
+}
diff --git a/tests/external_override/ed25519_override.h b/tests/external_override/ed25519_override.h
new file mode 100644
index 00000000..0abe2e24
--- /dev/null
+++ b/tests/external_override/ed25519_override.h
@@ -0,0 +1,39 @@
+/*
+ * This file is part of the SSH Library
+ *
+ * Copyright (c) 2021 by Anderson Toshiyuki Sasaki - Red Hat, Inc.
+ *
+ * The SSH Library is free software: you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation, either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * The SSH Library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with the SSH Library; see the file COPYING. If not,
+ * see <https://www.gnu.org/licenses/>.
+ */
+
+#include "libssh/ed25519.h"
+
+int __wrap_crypto_sign_ed25519_keypair(ed25519_pubkey pk,
+                                       ed25519_privkey sk);
+
+int __wrap_crypto_sign_ed25519(unsigned char *sm,
+                               uint64_t *smlen,
+                               const unsigned char *m,
+                               uint64_t mlen,
+                               const ed25519_privkey sk);
+
+int __wrap_crypto_sign_ed25519_open(unsigned char *m,
+                                    uint64_t *mlen,
+                                    const unsigned char *sm,
+                                    uint64_t smlen,
+                                    const ed25519_pubkey pk);
+
+bool internal_ed25519_function_called(void);
+void reset_ed25519_function_called(void);
diff --git a/tests/external_override/poly1305_override.c b/tests/external_override/poly1305_override.c
new file mode 100644
index 00000000..4d78272f
--- /dev/null
+++ b/tests/external_override/poly1305_override.c
@@ -0,0 +1,54 @@
+/*
+ * This file is part of the SSH Library
+ *
+ * Copyright (c) 2021 by Anderson Toshiyuki Sasaki - Red Hat, Inc.
+ *
+ * The SSH Library is free software: you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation, either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * The SSH Library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with the SSH Library; see the file COPYING. If not,
+ * see <https://www.gnu.org/licenses/>.
+ */
+
+#include "config.h"
+
+#include <stdlib.h>
+#include <stdint.h>
+#include <stdio.h>
+#include <libssh/poly1305.h>
+#include <libssh/priv.h>
+
+static bool internal_function_called = false;
+
+void __wrap_poly1305_auth(uint8_t out[POLY1305_TAGLEN],
+                          const uint8_t *m,
+                          size_t inlen,
+                          const uint8_t key[POLY1305_KEYLEN])
+#ifdef HAVE_GCC_BOUNDED_ATTRIBUTE
+    __attribute__((__bounded__(__minbytes__, 1, POLY1305_TAGLEN)))
+    __attribute__((__bounded__(__buffer__, 2, 3)))
+    __attribute__((__bounded__(__minbytes__, 4, POLY1305_KEYLEN)))
+#endif
+{
+    fprintf(stderr, "%s: Internal implementation was called\n", __func__);
+    internal_function_called = true;
+    poly1305_auth(out, m, inlen, key);
+}
+
+bool internal_poly1305_function_called(void)
+{
+    return internal_function_called;
+}
+
+void reset_poly1305_function_called(void)
+{
+    internal_function_called = false;
+}
diff --git a/tests/external_override/poly1305_override.h b/tests/external_override/poly1305_override.h
new file mode 100644
index 00000000..87717800
--- /dev/null
+++ b/tests/external_override/poly1305_override.h
@@ -0,0 +1,35 @@
+/*
+ * This file is part of the SSH Library
+ *
+ * Copyright (c) 2021 by Anderson Toshiyuki Sasaki - Red Hat, Inc.
+ *
+ * The SSH Library is free software: you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation, either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * The SSH Library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with the SSH Library; see the file COPYING. If not,
+ * see <https://www.gnu.org/licenses/>.
+ */
+
+#include "libssh/poly1305.h"
+
+void __wrap_poly1305_auth(uint8_t out[POLY1305_TAGLEN],
+                          const uint8_t *m,
+                          size_t inlen,
+                          const uint8_t key[POLY1305_KEYLEN])
+#ifdef HAVE_GCC_BOUNDED_ATTRIBUTE
+    __attribute__((__bounded__(__minbytes__, 1, POLY1305_TAGLEN)))
+    __attribute__((__bounded__(__buffer__, 2, 3)))
+    __attribute__((__bounded__(__minbytes__, 4, POLY1305_KEYLEN)))
+#endif
+;
+
+bool internal_poly1305_function_called(void);
+void reset_poly1305_function_called(void);
diff --git a/tests/external_override/torture_override.c b/tests/external_override/torture_override.c
new file mode 100644
index 00000000..f351d52e
--- /dev/null
+++ b/tests/external_override/torture_override.c
@@ -0,0 +1,320 @@
+/*
+ * This file is part of the SSH Library
+ *
+ * Copyright (c) 2021 by Anderson Toshiyuki Sasaki - Red Hat, Inc.
+ *
+ * The SSH Library is free software: you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation, either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * The SSH Library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with the SSH Library; see the file COPYING. If not,
+ * see <https://www.gnu.org/licenses/>.
+ */
+
+#include "config.h"
+
+#include "torture.h"
+#include "libssh/libssh.h"
+#include "libssh/priv.h"
+#include "libssh/session.h"
+
+#include <errno.h>
+#include <sys/types.h>
+#include <pwd.h>
+
+#include "chacha20_override.h"
+#include "poly1305_override.h"
+#include "curve25519_override.h"
+#include "ed25519_override.h"
+
+const char template[] = "temp_dir_XXXXXX";
+
+struct test_st {
+    char *temp_dir;
+    char *orig_dir;
+};
+
+static int sshd_setup(void **state)
+{
+    struct torture_state *s;
+    struct test_st *test_state = NULL;
+    char *temp_dir;
+    int rc;
+
+    torture_setup_sshd_server(state, false);
+
+    test_state = malloc(sizeof(struct test_st));
+    assert_non_null(test_state);
+
+    s = *((struct torture_state **)state);
+    s->private_data = test_state;
+
+    test_state->orig_dir = strdup(torture_get_current_working_dir());
+    assert_non_null(test_state->orig_dir);
+
+    temp_dir = torture_make_temp_dir(template);
+    assert_non_null(temp_dir);
+
+    rc = torture_change_dir(temp_dir);
+    assert_int_equal(rc, 0);
+
+    test_state->temp_dir = temp_dir;
+
+    return 0;
+}
+
+static int sshd_teardown(void **state)
+{
+    struct torture_state *s = *state;
+    struct test_st *test_state = s->private_data;
+    int rc;
+
+    rc = torture_change_dir(test_state->orig_dir);
+    assert_int_equal(rc, 0);
+
+    rc = torture_rmdirs(test_state->temp_dir);
+    assert_int_equal(rc, 0);
+
+    SAFE_FREE(test_state->temp_dir);
+    SAFE_FREE(test_state->orig_dir);
+    SAFE_FREE(test_state);
+
+    torture_teardown_sshd_server(state);
+
+    return 0;
+}
+
+static int session_setup(void **state)
+{
+    struct torture_state *s = *state;
+    int verbosity = torture_libssh_verbosity();
+    struct passwd *pwd;
+    bool false_v = false;
+    int rc;
+
+    pwd = getpwnam("bob");
+    assert_non_null(pwd);
+
+    rc = setuid(pwd->pw_uid);
+    assert_return_code(rc, errno);
+
+    s->ssh.session = ssh_new();
+    assert_non_null(s->ssh.session);
+
+    ssh_options_set(s->ssh.session, SSH_OPTIONS_LOG_VERBOSITY, &verbosity);
+    ssh_options_set(s->ssh.session, SSH_OPTIONS_HOST, TORTURE_SSH_SERVER);
+    /* Prevent parsing configuration files that can introduce different
+     * algorithms then we want to test */
+    ssh_options_set(s->ssh.session, SSH_OPTIONS_PROCESS_CONFIG, &false_v);
+
+    reset_chacha20_function_called();
+    reset_poly1305_function_called();
+    reset_curve25519_function_called();
+    reset_ed25519_function_called();
+
+    return 0;
+}
+
+static int session_teardown(void **state)
+{
+    struct torture_state *s = *state;
+
+    ssh_disconnect(s->ssh.session);
+    ssh_free(s->ssh.session);
+
+    return 0;
+}
+
+static void test_algorithm(ssh_session session,
+                           const char *kex,
+                           const char *cipher,
+                           const char *hostkey)
+{
+    char data[256];
+    int rc;
+
+    if (kex != NULL) {
+        rc = ssh_options_set(session, SSH_OPTIONS_KEY_EXCHANGE, kex);
+        assert_ssh_return_code(session, rc);
+    }
+
+    if (cipher != NULL) {
+        rc = ssh_options_set(session, SSH_OPTIONS_CIPHERS_C_S, cipher);
+        assert_ssh_return_code(session, rc);
+        rc = ssh_options_set(session, SSH_OPTIONS_CIPHERS_S_C, cipher);
+        assert_ssh_return_code(session, rc);
+    }
+
+    if (hostkey != NULL) {
+        rc = ssh_options_set(session, SSH_OPTIONS_HOSTKEYS, hostkey);
+        assert_ssh_return_code(session, rc);
+    }
+
+    rc = ssh_connect(session);
+    assert_ssh_return_code(session, rc);
+
+    /* send ignore packets of all sizes */
+    memset(data, 'A', sizeof(data));
+    ssh_send_ignore(session, data);
+    ssh_handle_packets(session, 50);
+
+    rc = ssh_userauth_none(session, NULL);
+    if (rc != SSH_OK) {
+        rc = ssh_get_error_code(session);
+        assert_int_equal(rc, SSH_REQUEST_DENIED);
+    }
+
+    ssh_disconnect(session);
+}
+
+#ifdef OPENSSH_CHACHA20_POLY1305_OPENSSH_COM
+static void torture_override_chacha20_poly1305(void **state)
+{
+    struct torture_state *s = *state;
+
+    bool internal_chacha20_called;
+    bool internal_poly1305_called;
+
+    if (ssh_fips_mode()) {
+        skip();
+    }
+
+    test_algorithm(s->ssh.session,
+                   NULL, /* kex */
+                   "chacha20-poly1305@openssh.com",
+                   NULL  /* hostkey */);
+
+    internal_chacha20_called = internal_chacha20_function_called();
+    internal_poly1305_called = internal_poly1305_function_called();
+
+#if SHOULD_CALL_INTERNAL_CHACHAPOLY
+    assert_true(internal_chacha20_called ||
+                internal_poly1305_called);
+#else
+    assert_false(internal_chacha20_called ||
+                 internal_poly1305_called);
+#endif
+
+}
+#endif /* OPENSSH_CHACHA20_POLY1305_OPENSSH_COM */
+
+#ifdef OPENSSH_CURVE25519_SHA256
+static void torture_override_ecdh_curve25519_sha256(void **state)
+{
+    struct torture_state *s = *state;
+    bool internal_curve25519_called;
+
+    if (ssh_fips_mode()) {
+        skip();
+    }
+
+    test_algorithm(s->ssh.session,
+                   "curve25519-sha256",
+                   NULL, /* cipher */
+                   NULL  /* hostkey */);
+
+    internal_curve25519_called = internal_curve25519_function_called();
+
+#if SHOULD_CALL_INTERNAL_CURVE25519
+    assert_true(internal_curve25519_called);
+#else
+    assert_false(internal_curve25519_called);
+#endif
+}
+#endif /* OPENSSH_CURVE25519_SHA256 */
+
+#ifdef OPENSSH_CURVE25519_SHA256_LIBSSH_ORG
+static void torture_override_ecdh_curve25519_sha256_libssh_org(void **state)
+{
+    struct torture_state *s = *state;
+    bool internal_curve25519_called;
+
+    if (ssh_fips_mode()) {
+        skip();
+    }
+
+    test_algorithm(s->ssh.session,
+                   "curve25519-sha256@libssh.org",
+                   NULL, /* cipher */
+                   NULL  /* hostkey */);
+
+    internal_curve25519_called = internal_curve25519_function_called();
+
+#if SHOULD_CALL_INTERNAL_CURVE25519
+    assert_true(internal_curve25519_called);
+#else
+    assert_false(internal_curve25519_called);
+#endif
+}
+#endif /* OPENSSH_CURVE25519_SHA256_LIBSSH_ORG */
+
+#ifdef OPENSSH_SSH_ED25519
+static void torture_override_ed25519(void **state)
+{
+    struct torture_state *s = *state;
+    bool internal_ed25519_called;
+
+    if (ssh_fips_mode()) {
+        skip();
+    }
+
+    test_algorithm(s->ssh.session,
+                   NULL, /* kex */
+                   NULL, /* cipher */
+                   "ssh-ed25519");
+
+    internal_ed25519_called = internal_ed25519_function_called();
+
+#if SHOULD_CALL_INTERNAL_ED25519
+    assert_true(internal_ed25519_called);
+#else
+    assert_false(internal_ed25519_called);
+#endif
+}
+#endif /* OPENSSH_SSH_ED25519 */
+
+int torture_run_tests(void)
+{
+    int rc;
+    struct CMUnitTest tests[] = {
+#ifdef OPENSSH_CHACHA20_POLY1305_OPENSSH_COM
+        cmocka_unit_test_setup_teardown(torture_override_chacha20_poly1305,
+                                        session_setup,
+                                        session_teardown),
+#endif /* OPENSSH_CHACHA20_POLY1305_OPENSSH_COM */
+#ifdef OPENSSH_CURVE25519_SHA256
+        cmocka_unit_test_setup_teardown(torture_override_ecdh_curve25519_sha256,
+                                        session_setup,
+                                        session_teardown),
+#endif /* OPENSSH_CURVE25519_SHA256 */
+#ifdef OPENSSH_CURVE25519_SHA256_LIBSSH_ORG
+        cmocka_unit_test_setup_teardown(torture_override_ecdh_curve25519_sha256_libssh_org,
+                                        session_setup,
+                                        session_teardown),
+#endif /* OPENSSH_CURVE25519_SHA256_LIBSSH_ORG */
+#ifdef OPENSSH_SSH_ED25519
+        cmocka_unit_test_setup_teardown(torture_override_ed25519,
+                                        session_setup,
+                                        session_teardown),
+#endif /* OPENSSH_SSH_ED25519 */
+    };
+
+    ssh_init();
+
+    torture_filter_tests(tests);
+    rc = cmocka_run_group_tests(tests, sshd_setup, sshd_teardown);
+    if (rc != 0) {
+        return rc;
+    }
+
+    ssh_finalize();
+
+    return rc;
+}
diff --git a/tests/torture.c b/tests/torture.c
index 7d26b013..4ac1ec66 100644
--- a/tests/torture.c
+++ b/tests/torture.c
@@ -1606,6 +1606,13 @@ void torture_reset_config(ssh_session session)
     memset(session->opts.options_seen, 0, sizeof(session->opts.options_seen));
 }
 
+#if ((defined _WIN32) || (defined _WIN64)) && (defined USE_ATTRIBUTE_WEAK)
+__attribute__((weak)) int torture_run_tests(void)
+{
+    fail();
+}
+#endif
+
 int main(int argc, char **argv) {
     struct argument_s arguments;
     char *env = getenv("LIBSSH_VERBOSITY");
diff --git a/tests/torture.h b/tests/torture.h
index dc211443..b9b87b6a 100644
--- a/tests/torture.h
+++ b/tests/torture.h
@@ -144,7 +144,11 @@ void torture_setup_libssh_server(void **state, const char *server_path);
 /*
  * This function must be defined in every unit test file.
  */
+#if ((defined _WIN32) || (defined _WIN64)) && (defined USE_ATTRIBUTE_WEAK)
+__attribute__((weak)) int torture_run_tests(void);
+#else
 int torture_run_tests(void);
+#endif
 
 char *torture_make_temp_dir(const char *template);
 char *torture_create_temp_file(const char *template);