P帧解码

app/src/main/cpp/PCode.c

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+
+#include "mbedtls/cipher.h"
+#include "mbedtls/entropy.h"
+#include "mbedtls/ctr_drbg.h"
+
+#include <stdio.h>
+#include <string.h>
+
+static void print_hex(const char *title, const unsigned char buf[], size_t len)
+{
+    printf("%s: ", title);
+    for (size_t i = 0; i < len; i++)
+        printf("%02x", buf[i]);
+
+    printf("\r\n");
+}
+
+/*
+ * The pre-shared key. Should be generated randomly and be unique to the
+ * device/channel/etc. Just used a fixed on here for simplicity.
+ */
+static const unsigned char secret_key[16] = {
+        0xf4, 0x82, 0xc6, 0x70, 0x3c, 0xc7, 0x61, 0x0a,
+        0xb9, 0xa0, 0xb8, 0xe9, 0x87, 0xb8, 0xc1, 0x72,
+};
+
+static int pcode(void)
+{
+    /* message that should be protected */
+    const char message[] = "Some things are better left unread";
+    /* metadata transmitted in the clear but authenticated */
+    const char metadata[] = "eg sequence number, routing info";
+    /* ciphertext buffer large enough to hold message + nonce + tag */
+    unsigned char ciphertext[128] = { 0 };
+    int ret;
+
+    printf("\r\n\r\n");
+    print_hex("plaintext message", (unsigned char *) message, sizeof message);
+
+    /*
+     * Setup random number generator
+     * (Note: later this might be done automatically.)
+     */
+    mbedtls_entropy_context entropy;    /* entropy pool for seeding PRNG */
+    mbedtls_ctr_drbg_context drbg;      /* pseudo-random generator */
+
+    mbedtls_entropy_init(&entropy);
+    mbedtls_ctr_drbg_init(&drbg);
+
+    /* Seed the PRNG using the entropy pool, and throw in our secret key as an
+     * additional source of randomness. */
+    ret = mbedtls_ctr_drbg_seed(&drbg, mbedtls_entropy_func, &entropy,
+                                secret_key, sizeof (secret_key));
+    if (ret != 0) {
+        printf("mbedtls_ctr_drbg_init() returned -0x%04X\r\n", -ret);
+        return 1;
+    }
+
+    /*
+     * Setup AES-CCM contex
+     */
+    mbedtls_cipher_context_t ctx;
+
+    mbedtls_cipher_init(&ctx);
+
+    ret = mbedtls_cipher_setup(&ctx, mbedtls_cipher_info_from_type(MBEDTLS_CIPHER_AES_128_CCM));
+    if (ret != 0) {
+        printf("mbedtls_cipher_setup() returned -0x%04X\r\n", -ret);
+        return 1;
+    }
+
+    ret = mbedtls_cipher_setkey(&ctx, secret_key, 8 * sizeof secret_key, MBEDTLS_ENCRYPT);
+    if (ret != 0) {
+        printf("mbedtls_cipher_setkey() returned -0x%04X\r\n", -ret);
+        return 1;
+    }
+
+    /*
+     * Encrypt-authenticate the message and authenticate additional data
+     *
+     * First generate a random 8-byte nonce.
+     * Put it directly in the output buffer as the recipient will need it.
+     *
+     * Warning: you must never re-use the same (key, nonce) pair. One of the
+     * best ways to ensure this to use a counter for the nonce. However this
+     * means you should save the counter accross rebots, if the key is a
+     * long-term one. The alternative we choose here is to generate the nonce
+     * randomly. However it only works if you have a good source of
+     * randomness.
+     */
+    const size_t nonce_len = 8;
+    mbedtls_ctr_drbg_random(&drbg, ciphertext, nonce_len);
+
+    size_t ciphertext_len = 0;
+    /* Go for a conservative 16-byte (128-bit) tag
+     * and append it to the ciphertext */
+    const size_t tag_len = 16;
+    ret = mbedtls_cipher_auth_encrypt(&ctx, ciphertext, nonce_len,
+                                      (const unsigned char *) metadata, sizeof metadata,
+                                      (const unsigned char *) message, sizeof message,
+                                      ciphertext + nonce_len, &ciphertext_len,
+                                      ciphertext + nonce_len + sizeof message, tag_len );
+    if (ret != 0) {
+        printf("mbedtls_cipher_auth_encrypt() returned -0x%04X\r\n", -ret);
+        return 1;
+    }
+    ciphertext_len += nonce_len + tag_len;
+
+    /*
+     * The following information should now be transmitted:
+     * - first ciphertext_len bytes of ciphertext buffer
+     * - metadata if not already transmitted elsewhere
+     */
+    print_hex("ciphertext", ciphertext, ciphertext_len);
+
+    /*
+     * Decrypt-authenticate
+     */
+    unsigned char decrypted[128] = { 0 };
+    size_t decrypted_len = 0;
+
+    ret = mbedtls_cipher_setkey(&ctx, secret_key, 8 * sizeof secret_key, MBEDTLS_DECRYPT);
+    if (ret != 0) {
+        printf("mbedtls_cipher_setkey() returned -0x%04X\r\n", -ret);
+        return 1;
+    }
+
+    ret = mbedtls_cipher_auth_decrypt(&ctx,
+                                      ciphertext, nonce_len,
+                                      (const unsigned char *) metadata, sizeof metadata,
+                                      ciphertext + nonce_len, ciphertext_len - nonce_len - tag_len,
+                                      decrypted, &decrypted_len,
+                                      ciphertext + ciphertext_len - tag_len, tag_len );
+    /* Checking the return code is CRITICAL for security here */
+    if (ret == MBEDTLS_ERR_CIPHER_AUTH_FAILED) {
+        printf("Something bad is happening! Data is not authentic!\r\n");
+        return 1;
+    }
+    if (ret != 0) {
+        printf("mbedtls_cipher_authdecrypt() returned -0x%04X\r\n", -ret);
+        return 1;
+    }
+
+    print_hex("decrypted", decrypted, decrypted_len);
+
+    printf("\r\nDONE\r\n");
+
+    return 0;
+}
+
+#if defined(TARGET_LIKE_MBED)
+
+#include "mbed-drivers/test_env.h"
+#include "minar/minar.h"
+
+static void run() {
+    MBED_HOSTTEST_TIMEOUT(10);
+    MBED_HOSTTEST_SELECT(default);
+    MBED_HOSTTEST_DESCRIPTION(mbed TLS example authcrypt);
+    MBED_HOSTTEST_START("MBEDTLS_EX_AUTHCRYPT");
+    MBED_HOSTTEST_RESULT(example() == 0);
+}
+
+void app_start(int, char*[]) {
+    /* Use 115200 bps for consistency with other examples */
+    get_stdio_serial().baud(115200);
+    minar::Scheduler::postCallback(mbed::util::FunctionPointer0<void>(run).bind());
+}
+
+#else
+
+int main() {
+    return example();
+}
+
+#endif