aes_mbedtls_adapter.c

00001 /*
00002  * Copyright (c) 2015-2019, Arm Limited and affiliates.
00003  * SPDX-License-Identifier: Apache-2.0
00004  *
00005  * Licensed under the Apache License, Version 2.0 (the "License");
00006  * you may not use this file except in compliance with the License.
00007  * You may obtain a copy of the License at
00008  *
00009  *     http://www.apache.org/licenses/LICENSE-2.0
00010  *
00011  * Unless required by applicable law or agreed to in writing, software
00012  * distributed under the License is distributed on an "AS IS" BASIS,
00013  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
00014  * See the License for the specific language governing permissions and
00015  * limitations under the License.
00016  */
00017 /*
00018  * Implementation of platform/arm_hal_aes.h using mbed TLS.
00019  *
00020  * Possible scenarios:
00021  *
00022  * 1) Platform with no hardware AES assist, mbed TLS not in use:
00023  *     Use this source file, and let it pull in the minimal mbed TLS code
00024  *     contained in aes_mbedtls.c to implement software AES.
00025  *
00026  * 2) Platform with hardware AES assist, mbed TLS not in use:
00027  *     Do not use this source file - implement arm_hal_aes.h yourself using
00028  *     your AES hardware. Note that you must be able to provide
00029  *     ARM_AES_MBEDTLS_CONTEXT_MIN contexts. This may or may not be 1, depending
00030  *     on Nanostack config.
00031  *
00032  * 3) Platform without hardware assist, already using (or wanting to use) mbed TLS:
00033  *     Use this source file, and define NS_USE_EXTERNAL_MBED_TLS so that
00034  *     it uses the external mbed TLS library. That library must be built with
00035  *     MBEDTLS_AES_C enabled, and it must be on the include path.
00036  *
00037  * 4) Platform with context-capable hardware assist, already using mbed TLS:
00038  *     Use this source file, and define NS_USE_EXTERNAL_MBED_TLS so that
00039  *     it uses the external mbed TLS library. That library must be built with
00040  *     MBEDTLS_AES_C enabled. Attach your hardware-accelerated AES to mbed TLS
00041  *     by defining MBEDTLS_AES_ALT; it will then be used both by users
00042  *     of arm_hal_aes.h, and other users of mbed TLS.
00043  */
00044 
00045 /* Get the API we are implementing from libService */
00046 #include "platform/arm_hal_aes.h"
00047 #include "platform/arm_hal_interrupt.h"
00048 
00049 /* Either pull in the external mbed TLS header for its AES functions, or
00050  * pull in our own local cut-down copy of the mbed TLS code.
00051  */
00052 #ifdef NS_USE_EXTERNAL_MBED_TLS
00053 #include "mbedtls/aes.h"
00054 #else
00055 #include "aes_mbedtls.c"
00056 #endif /* NS_USE_EXTERNAL_MBED_TLS */
00057 
00058 struct arm_aes_context {
00059     mbedtls_aes_context ctx;
00060     bool reserved;
00061 };
00062 
00063 static arm_aes_context_t context_list[ARM_AES_MBEDTLS_CONTEXT_MIN];
00064 
00065 static arm_aes_context_t *mbed_tls_context_get(void)
00066 {
00067     platform_enter_critical();
00068     for (int i = 0; i < ARM_AES_MBEDTLS_CONTEXT_MIN; i++) {
00069         if (!context_list[i].reserved) {
00070             //Reserve context
00071             context_list[i].reserved = true;
00072             platform_exit_critical();
00073             return &context_list[i];
00074         }
00075     }
00076 
00077     platform_exit_critical();
00078     return NULL;
00079 }
00080 
00081 arm_aes_context_t *arm_aes_start(const uint8_t key[static 16])
00082 {
00083     arm_aes_context_t *context = mbed_tls_context_get();
00084     if (context) {
00085         mbedtls_aes_init(&context->ctx);
00086         if (0 != mbedtls_aes_setkey_enc(&context->ctx, key, 128)) {
00087             return NULL;
00088         }
00089     }
00090     return context;
00091 }
00092 
00093 void arm_aes_encrypt(arm_aes_context_t *aes_context, const uint8_t src[static 16], uint8_t dst[static 16])
00094 {
00095     mbedtls_aes_crypt_ecb(&aes_context->ctx, MBEDTLS_AES_ENCRYPT, src, dst);
00096 }
00097 
00098 void arm_aes_finish(arm_aes_context_t *aes_context)
00099 {
00100     mbedtls_aes_free(&aes_context->ctx);
00101     platform_enter_critical();
00102     aes_context->reserved = false;
00103     platform_exit_critical();
00104 }