mbedtls: Add AES-CBC performance test

Hardware AES engine gets 11.0MB/sec on Release config
Software AES is around 2.3MB/sec on Release config

components/idf_test/include/idf_performance.h

@@ -25,3 +25,6 @@
 // esp_sha() time to process 32KB of input data from RAM
 #define IDF_PERFORMANCE_MAX_ESP32_TIME_SHA1_32KB                                5000
 #define IDF_PERFORMANCE_MAX_ESP32_TIME_SHA512_32KB                              4500
+// AES-CBC hardware throughput (accounts for worst-case performance with PSRAM workaround)
+#define IDF_PERFORMANCE_MIN_AES_CBC_THROUGHPUT_MBSEC                            8.5
+

components/mbedtls/test/test_aes_perf.c

@@ -0,0 +1,71 @@
+/* mbedTLS AES performance test
+*/
+#include <string.h>
+#include <stdio.h>
+#include <stdbool.h>
+#include <esp_system.h>
+#include "mbedtls/aes.h"
+#include "unity.h"
+#include "sdkconfig.h"
+#include "esp_timer.h"
+#include "esp_heap_caps.h"
+#include "test_utils.h"
+
+TEST_CASE("mbedtls AES performance", "[aes]")
+{
+    const unsigned CALLS = 256;
+    const unsigned CALL_SZ = 32*1024;
+    mbedtls_aes_context ctx;
+    int64_t start, end;
+    uint8_t iv[16];
+    uint8_t key[16];
+
+    memset(iv, 0xEE, 16);
+    memset(key, 0x44, 16);
+
+    // allocate internal memory
+    uint8_t *buf = heap_caps_malloc(CALL_SZ, MALLOC_CAP_8BIT|MALLOC_CAP_INTERNAL);
+    TEST_ASSERT_NOT_NULL(buf);
+    mbedtls_aes_init(&ctx);
+    mbedtls_aes_setkey_enc(&ctx, key, 128);
+
+    start = esp_timer_get_time();
+    for (int c = 0; c < CALLS; c++) {
+        memset(buf, 0xAA, CALL_SZ);
+        mbedtls_aes_crypt_cbc(&ctx, MBEDTLS_AES_ENCRYPT, CALL_SZ, iv, buf, buf);
+    }
+    end = esp_timer_get_time();
+
+    /* Sanity check: make sure the last ciphertext block matches
+       what we expect to see.
+
+       Last block produced via this Python:
+       import os, binascii
+       from cryptography.hazmat.primitives.ciphers import Cipher, algorithms, modes
+       from cryptography.hazmat.backends import default_backend
+       key = b'\x44' * 16
+       iv = b'\xee' * 16
+       cipher = Cipher(algorithms.AES(key), modes.CBC(iv), backend=default_backend())
+       encryptor = cipher.encryptor()
+       ct = encryptor.update(b'\xaa' * 256 * 32 * 1024) + encryptor.finalize()
+       print(binascii.hexlify(ct[-16:]))
+    */
+    const uint8_t expected_last_block[] = {
+        0x50, 0x81, 0xe0, 0xe1, 0x15, 0x2f, 0x14, 0xe9,
+        0x97, 0xa0, 0xc6, 0xe6, 0x36, 0xf3, 0x5c, 0x25,
+    };
+    TEST_ASSERT_EQUAL_HEX8_ARRAY(expected_last_block, buf + CALL_SZ - 16, 16);
+
+    free(buf);
+
+    float usecs = end - start;
+    // bytes/usec = MB/sec
+    float mb_sec = (CALL_SZ * CALLS) / usecs;
+    printf("Encryption rate %.3fMB/sec\n", mb_sec);
+#ifdef CONFIG_MBEDTLS_HARDWARE_AES
+    // Don't put a hard limit on software AES performance (software is approx 2.3MB/sec on Release config)
+    TEST_PERFORMANCE_GREATER_THAN(AES_CBC_THROUGHPUT_MBSEC, "%.3fMB/sec", mb_sec);
+#endif
+}
+
+