diff --git a/tests/scripts/all.sh b/tests/scripts/all.sh
index d0bd1eb..127f424 100755
--- a/tests/scripts/all.sh
+++ b/tests/scripts/all.sh
@@ -2716,6 +2716,15 @@
     make test
 }
 
+component_test_alt_timing() {
+    msg "build: alternate timing implementation"
+    scripts/config.py set MBEDTLS_TIMING_ALT
+    make lib TEST_TIMING_ALT_IMPL=1 CFLAGS="-I../tests/src/external_timing"
+
+    msg "test: MBEDTLS_TIMING_ALT - test suites"
+    make test TEST_TIMING_ALT_IMPL=1 CFLAGS="-I../tests/src/external_timing"
+}
+
 component_test_platform_calloc_macro () {
     msg "build: MBEDTLS_PLATFORM_{CALLOC/FREE}_MACRO enabled (ASan build)"
     scripts/config.py set MBEDTLS_PLATFORM_MEMORY
diff --git a/tests/src/external_timing/external_timing_for_test.c b/tests/src/external_timing/external_timing_for_test.c
new file mode 100644
index 0000000..454ebbe
--- /dev/null
+++ b/tests/src/external_timing/external_timing_for_test.c
@@ -0,0 +1,351 @@
+/** \file external_timing_for_test.c
+ *
+ * \brief Helper functions to test an alternate timing implementation.
+ */
+
+/*
+ *  Copyright The Mbed TLS Contributors
+ *  SPDX-License-Identifier: Apache-2.0
+ *
+ *  Licensed under the Apache License, Version 2.0 (the "License"); you may
+ *  not use this file except in compliance with the License.
+ *  You may obtain a copy of the License at
+ *
+ *  http://www.apache.org/licenses/LICENSE-2.0
+ *
+ *  Unless required by applicable law or agreed to in writing, software
+ *  distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+ *  WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ *  See the License for the specific language governing permissions and
+ *  limitations under the License.
+ */
+
+#include <timing_alt.h>
+#if defined(MBEDTLS_TIMING_ALT)
+
+#if !defined(unix) && !defined(__unix__) && !defined(__unix) && \
+    !defined(__APPLE__) && !defined(_WIN32) && !defined(__QNXNTO__) && \
+    !defined(__HAIKU__) && !defined(__midipix__)
+#error "This module only works on Unix and Windows, see MBEDTLS_TIMING_C in config.h"
+#endif
+
+/* *INDENT-OFF* */
+#ifndef asm
+#define asm __asm
+#endif
+/* *INDENT-ON* */
+
+#if defined(_WIN32) && !defined(EFIX64) && !defined(EFI32)
+
+#include <windows.h>
+#include <process.h>
+
+struct _hr_time {
+    LARGE_INTEGER start;
+};
+
+#else
+
+#include <unistd.h>
+#include <sys/types.h>
+#include <signal.h>
+/* time.h should be included independently of MBEDTLS_HAVE_TIME. If the
+ * platform matches the ifdefs above, it will be used. */
+#include <time.h>
+#include <sys/time.h>
+struct _hr_time {
+    struct timeval start;
+};
+#endif /* _WIN32 && !EFIX64 && !EFI32 */
+
+#if !defined(HAVE_HARDCLOCK) && defined(MBEDTLS_HAVE_ASM) &&  \
+    (defined(_MSC_VER) && defined(_M_IX86)) || defined(__WATCOMC__)
+
+#define HAVE_HARDCLOCK
+
+unsigned long mbedtls_timing_hardclock(void)
+{
+    unsigned long tsc;
+    __asm   rdtsc
+    __asm   mov[tsc], eax
+    return tsc;
+}
+#endif /* !HAVE_HARDCLOCK && MBEDTLS_HAVE_ASM &&
+          ( _MSC_VER && _M_IX86 ) || __WATCOMC__ */
+
+/* some versions of mingw-64 have 32-bit longs even on x84_64 */
+#if !defined(HAVE_HARDCLOCK) && defined(MBEDTLS_HAVE_ASM) &&  \
+    defined(__GNUC__) && (defined(__i386__) || (                       \
+    (defined(__amd64__) || defined(__x86_64__)) && __SIZEOF_LONG__ == 4))
+
+#define HAVE_HARDCLOCK
+
+unsigned long mbedtls_timing_hardclock(void)
+{
+    unsigned long lo, hi;
+    asm volatile ("rdtsc" : "=a" (lo), "=d" (hi));
+    return lo;
+}
+#endif /* !HAVE_HARDCLOCK && MBEDTLS_HAVE_ASM &&
+          __GNUC__ && __i386__ */
+
+#if !defined(HAVE_HARDCLOCK) && defined(MBEDTLS_HAVE_ASM) &&  \
+    defined(__GNUC__) && (defined(__amd64__) || defined(__x86_64__))
+
+#define HAVE_HARDCLOCK
+
+unsigned long mbedtls_timing_hardclock(void)
+{
+    unsigned long lo, hi;
+    asm volatile ("rdtsc" : "=a" (lo), "=d" (hi));
+    return lo | (hi << 32);
+}
+#endif /* !HAVE_HARDCLOCK && MBEDTLS_HAVE_ASM &&
+          __GNUC__ && ( __amd64__ || __x86_64__ ) */
+
+#if !defined(HAVE_HARDCLOCK) && defined(MBEDTLS_HAVE_ASM) &&  \
+    defined(__GNUC__) && (defined(__powerpc__) || defined(__ppc__))
+
+#define HAVE_HARDCLOCK
+
+unsigned long mbedtls_timing_hardclock(void)
+{
+    unsigned long tbl, tbu0, tbu1;
+
+    do {
+        asm volatile ("mftbu %0" : "=r" (tbu0));
+        asm volatile ("mftb  %0" : "=r" (tbl));
+        asm volatile ("mftbu %0" : "=r" (tbu1));
+    } while (tbu0 != tbu1);
+
+    return tbl;
+}
+#endif /* !HAVE_HARDCLOCK && MBEDTLS_HAVE_ASM &&
+          __GNUC__ && ( __powerpc__ || __ppc__ ) */
+
+#if !defined(HAVE_HARDCLOCK) && defined(MBEDTLS_HAVE_ASM) &&  \
+    defined(__GNUC__) && defined(__sparc64__)
+
+#if defined(__OpenBSD__)
+#warning OpenBSD does not allow access to tick register using software version instead
+#else
+#define HAVE_HARDCLOCK
+
+unsigned long mbedtls_timing_hardclock(void)
+{
+    unsigned long tick;
+    asm volatile ("rdpr %%tick, %0;" : "=&r" (tick));
+    return tick;
+}
+#endif /* __OpenBSD__ */
+#endif /* !HAVE_HARDCLOCK && MBEDTLS_HAVE_ASM &&
+          __GNUC__ && __sparc64__ */
+
+#if !defined(HAVE_HARDCLOCK) && defined(MBEDTLS_HAVE_ASM) &&  \
+    defined(__GNUC__) && defined(__sparc__) && !defined(__sparc64__)
+
+#define HAVE_HARDCLOCK
+
+unsigned long mbedtls_timing_hardclock(void)
+{
+    unsigned long tick;
+    asm volatile (".byte 0x83, 0x41, 0x00, 0x00");
+    asm volatile ("mov   %%g1, %0" : "=r" (tick));
+    return tick;
+}
+#endif /* !HAVE_HARDCLOCK && MBEDTLS_HAVE_ASM &&
+          __GNUC__ && __sparc__ && !__sparc64__ */
+
+#if !defined(HAVE_HARDCLOCK) && defined(MBEDTLS_HAVE_ASM) &&      \
+    defined(__GNUC__) && defined(__alpha__)
+
+#define HAVE_HARDCLOCK
+
+unsigned long mbedtls_timing_hardclock(void)
+{
+    unsigned long cc;
+    asm volatile ("rpcc %0" : "=r" (cc));
+    return cc & 0xFFFFFFFF;
+}
+#endif /* !HAVE_HARDCLOCK && MBEDTLS_HAVE_ASM &&
+          __GNUC__ && __alpha__ */
+
+#if !defined(HAVE_HARDCLOCK) && defined(MBEDTLS_HAVE_ASM) &&      \
+    defined(__GNUC__) && defined(__ia64__)
+
+#define HAVE_HARDCLOCK
+
+unsigned long mbedtls_timing_hardclock(void)
+{
+    unsigned long itc;
+    asm volatile ("mov %0 = ar.itc" : "=r" (itc));
+    return itc;
+}
+#endif /* !HAVE_HARDCLOCK && MBEDTLS_HAVE_ASM &&
+          __GNUC__ && __ia64__ */
+
+#if !defined(HAVE_HARDCLOCK) && defined(_MSC_VER) && \
+    !defined(EFIX64) && !defined(EFI32)
+
+#define HAVE_HARDCLOCK
+
+unsigned long mbedtls_timing_hardclock(void)
+{
+    LARGE_INTEGER offset;
+
+    QueryPerformanceCounter(&offset);
+
+    return (unsigned long) (offset.QuadPart);
+}
+#endif /* !HAVE_HARDCLOCK && _MSC_VER && !EFIX64 && !EFI32 */
+
+#if !defined(HAVE_HARDCLOCK)
+
+#define HAVE_HARDCLOCK
+
+static int hardclock_init = 0;
+static struct timeval tv_init;
+
+unsigned long mbedtls_timing_hardclock(void)
+{
+    struct timeval tv_cur;
+
+    if (hardclock_init == 0) {
+        gettimeofday(&tv_init, NULL);
+        hardclock_init = 1;
+    }
+
+    gettimeofday(&tv_cur, NULL);
+    return (tv_cur.tv_sec  - tv_init.tv_sec) * 1000000U
+           + (tv_cur.tv_usec - tv_init.tv_usec);
+}
+#endif /* !HAVE_HARDCLOCK */
+
+volatile int mbedtls_timing_alarmed = 0;
+
+#if defined(_WIN32) && !defined(EFIX64) && !defined(EFI32)
+
+unsigned long mbedtls_timing_get_timer(struct mbedtls_timing_hr_time *val, int reset)
+{
+    struct _hr_time *t = (struct _hr_time *) val;
+
+    if (reset) {
+        QueryPerformanceCounter(&t->start);
+        return 0;
+    } else {
+        unsigned long delta;
+        LARGE_INTEGER now, hfreq;
+        QueryPerformanceCounter(&now);
+        QueryPerformanceFrequency(&hfreq);
+        delta = (unsigned long) ((now.QuadPart - t->start.QuadPart) * 1000ul
+                                 / hfreq.QuadPart);
+        return delta;
+    }
+}
+
+/* It's OK to use a global because alarm() is supposed to be global anyway */
+static DWORD alarmMs;
+
+static void TimerProc(void *TimerContext)
+{
+    (void) TimerContext;
+    Sleep(alarmMs);
+    mbedtls_timing_alarmed = 1;
+    /* _endthread will be called implicitly on return
+     * That ensures execution of thread function's epilogue */
+}
+
+void mbedtls_set_alarm(int seconds)
+{
+    if (seconds == 0) {
+        /* No need to create a thread for this simple case.
+         * Also, this shorcut is more reliable at least on MinGW32 */
+        mbedtls_timing_alarmed = 1;
+        return;
+    }
+
+    mbedtls_timing_alarmed = 0;
+    alarmMs = seconds * 1000;
+    (void) _beginthread(TimerProc, 0, NULL);
+}
+
+#else /* _WIN32 && !EFIX64 && !EFI32 */
+
+unsigned long mbedtls_timing_get_timer(struct mbedtls_timing_hr_time *val, int reset)
+{
+    struct _hr_time *t = (struct _hr_time *) val;
+
+    if (reset) {
+        gettimeofday(&t->start, NULL);
+        return 0;
+    } else {
+        unsigned long delta;
+        struct timeval now;
+        gettimeofday(&now, NULL);
+        delta = (now.tv_sec  - t->start.tv_sec) * 1000ul
+                + (now.tv_usec - t->start.tv_usec) / 1000;
+        return delta;
+    }
+}
+
+static void sighandler(int signum)
+{
+    mbedtls_timing_alarmed = 1;
+    signal(signum, sighandler);
+}
+
+void mbedtls_set_alarm(int seconds)
+{
+    mbedtls_timing_alarmed = 0;
+    signal(SIGALRM, sighandler);
+    alarm(seconds);
+    if (seconds == 0) {
+        /* alarm(0) cancelled any previous pending alarm, but the
+           handler won't fire, so raise the flag straight away. */
+        mbedtls_timing_alarmed = 1;
+    }
+}
+
+#endif /* _WIN32 && !EFIX64 && !EFI32 */
+
+/*
+ * Set delays to watch
+ */
+void mbedtls_timing_set_delay(void *data, uint32_t int_ms, uint32_t fin_ms)
+{
+    mbedtls_timing_delay_context *ctx = (mbedtls_timing_delay_context *) data;
+
+    ctx->int_ms = int_ms;
+    ctx->fin_ms = fin_ms;
+
+    if (fin_ms != 0) {
+        (void) mbedtls_timing_get_timer(&ctx->timer, 1);
+    }
+}
+
+/*
+ * Get number of delays expired
+ */
+int mbedtls_timing_get_delay(void *data)
+{
+    mbedtls_timing_delay_context *ctx = (mbedtls_timing_delay_context *) data;
+    unsigned long elapsed_ms;
+
+    if (ctx->fin_ms == 0) {
+        return -1;
+    }
+
+    elapsed_ms = mbedtls_timing_get_timer(&ctx->timer, 0);
+
+    if (elapsed_ms >= ctx->fin_ms) {
+        return 2;
+    }
+
+    if (elapsed_ms >= ctx->int_ms) {
+        return 1;
+    }
+
+    return 0;
+}
+
+#endif /* MBEDTLS_TIMING_ALT */
diff --git a/tests/src/external_timing/timing_alt.h b/tests/src/external_timing/timing_alt.h
new file mode 100644
index 0000000..204dbe8
--- /dev/null
+++ b/tests/src/external_timing/timing_alt.h
@@ -0,0 +1,130 @@
+/*
+ * Copy of the internal MbedTLS timing implementation, to be used in tests.
+ */
+/*
+ *  Copyright The Mbed TLS Contributors
+ *  SPDX-License-Identifier: Apache-2.0
+ *
+ *  Licensed under the Apache License, Version 2.0 (the "License"); you may
+ *  not use this file except in compliance with the License.
+ *  You may obtain a copy of the License at
+ *
+ *  http://www.apache.org/licenses/LICENSE-2.0
+ *
+ *  Unless required by applicable law or agreed to in writing, software
+ *  distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+ *  WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ *  See the License for the specific language governing permissions and
+ *  limitations under the License.
+ */
+
+#ifndef EXTERNAL_TIMING_FOR_TEST_H
+#define EXTERNAL_TIMING_FOR_TEST_H
+
+#if !defined(MBEDTLS_CONFIG_FILE)
+#include "mbedtls/config.h"
+#else
+#include MBEDTLS_CONFIG_FILE
+#endif
+
+#include <stdint.h>
+
+/**
+ * \brief          timer structure
+ */
+struct mbedtls_timing_hr_time {
+    unsigned char opaque[32];
+};
+
+/**
+ * \brief          Context for mbedtls_timing_set/get_delay()
+ */
+typedef struct mbedtls_timing_delay_context {
+    struct mbedtls_timing_hr_time   timer;
+    uint32_t                        int_ms;
+    uint32_t                        fin_ms;
+} mbedtls_timing_delay_context;
+
+#else  /* MBEDTLS_TIMING_ALT */
+#include "timing_alt.h"
+#endif /* MBEDTLS_TIMING_ALT */
+
+extern volatile int mbedtls_timing_alarmed;
+
+/**
+ * \brief          Return the CPU cycle counter value
+ *
+ * \warning        This is only a best effort! Do not rely on this!
+ *                 In particular, it is known to be unreliable on virtual
+ *                 machines.
+ *
+ * \note           This value starts at an unspecified origin and
+ *                 may wrap around.
+ */
+unsigned long mbedtls_timing_hardclock(void);
+
+/**
+ * \brief          Return the elapsed time in milliseconds
+ *
+ * \param val      points to a timer structure
+ * \param reset    If 0, query the elapsed time. Otherwise (re)start the timer.
+ *
+ * \return         Elapsed time since the previous reset in ms. When
+ *                 restarting, this is always 0.
+ *
+ * \note           To initialize a timer, call this function with reset=1.
+ *
+ *                 Determining the elapsed time and resetting the timer is not
+ *                 atomic on all platforms, so after the sequence
+ *                 `{ get_timer(1); ...; time1 = get_timer(1); ...; time2 =
+ *                 get_timer(0) }` the value time1+time2 is only approximately
+ *                 the delay since the first reset.
+ */
+unsigned long mbedtls_timing_get_timer(struct mbedtls_timing_hr_time *val, int reset);
+
+/**
+ * \brief          Setup an alarm clock
+ *
+ * \param seconds  delay before the "mbedtls_timing_alarmed" flag is set
+ *                 (must be >=0)
+ *
+ * \warning        Only one alarm at a time  is supported. In a threaded
+ *                 context, this means one for the whole process, not one per
+ *                 thread.
+ */
+void mbedtls_set_alarm(int seconds);
+
+/**
+ * \brief          Set a pair of delays to watch
+ *                 (See \c mbedtls_timing_get_delay().)
+ *
+ * \param data     Pointer to timing data.
+ *                 Must point to a valid \c mbedtls_timing_delay_context struct.
+ * \param int_ms   First (intermediate) delay in milliseconds.
+ *                 The effect if int_ms > fin_ms is unspecified.
+ * \param fin_ms   Second (final) delay in milliseconds.
+ *                 Pass 0 to cancel the current delay.
+ *
+ * \note           To set a single delay, either use \c mbedtls_timing_set_timer
+ *                 directly or use this function with int_ms == fin_ms.
+ */
+void mbedtls_timing_set_delay(void *data, uint32_t int_ms, uint32_t fin_ms);
+
+/**
+ * \brief          Get the status of delays
+ *                 (Memory helper: number of delays passed.)
+ *
+ * \param data     Pointer to timing data
+ *                 Must point to a valid \c mbedtls_timing_delay_context struct.
+ *
+ * \return         -1 if cancelled (fin_ms = 0),
+ *                  0 if none of the delays are passed,
+ *                  1 if only the intermediate delay is passed,
+ *                  2 if the final delay is passed.
+ */
+int mbedtls_timing_get_delay(void *data);
+
+#ifdef __cplusplus
+}
+
+#endif /* FAKE_EXTERNAL_RNG_FOR_TEST_H */