85 lines
2.5 KiB
C
85 lines
2.5 KiB
C
// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Hardware crypto support Copyright 2017 Espressif Systems (Shanghai) PTE LTD
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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#include "crypto/includes.h"
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#include "crypto/common.h"
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#include "mbedtls/aes.h"
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/**
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* fast_aes_unwrap - Unwrap key with AES Key Wrap Algorithm (128-bit KEK) (RFC3394)
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* @kek: Key encryption key (KEK)
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* @n: Length of the plaintext key in 64-bit units; e.g., 2 = 128-bit = 16
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* bytes
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* @cipher: Wrapped key to be unwrapped, (n + 1) * 64 bits
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* @plain: Plaintext key, n * 64 bits
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* Returns: 0 on success, -1 on failure (e.g., integrity verification failed)
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*/
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int
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fast_aes_unwrap(const uint8_t *kek, int n, const uint8_t *cipher, uint8_t *plain)
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{
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uint8_t a[8], *r, b[16];
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int32_t i, j;
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int32_t ret = 0;
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mbedtls_aes_context ctx;
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/* 1) Initialize variables. */
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os_memcpy(a, cipher, 8);
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r = plain;
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os_memcpy(r, cipher + 8, 8 * n);
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mbedtls_aes_init(&ctx);
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ret = mbedtls_aes_setkey_dec(&ctx, kek, 128);
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if (ret < 0) {
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mbedtls_aes_free(&ctx);
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return ret;
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}
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/* 2) Compute intermediate values.
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* For j = 5 to 0
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* For i = n to 1
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* B = AES-1(K, (A ^ t) | R[i]) where t = n*j+i
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* A = MSB(64, B)
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* R[i] = LSB(64, B)
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*/
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for (j = 5; j >= 0; j--) {
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r = plain + (n - 1) * 8;
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for (i = n; i >= 1; i--) {
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os_memcpy(b, a, 8);
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b[7] ^= n * j + i;
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os_memcpy(b + 8, r, 8);
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ret = mbedtls_internal_aes_decrypt(&ctx, b, b);
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if (ret != 0) {
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break;
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}
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os_memcpy(a, b, 8);
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os_memcpy(r, b + 8, 8);
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r -= 8;
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}
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}
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mbedtls_aes_free(&ctx);
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/* 3) Output results.
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*
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* These are already in @plain due to the location of temporary
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* variables. Just verify that the IV matches with the expected value.
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*/
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for (i = 0; i < 8; i++) {
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if (a[i] != 0xa6) {
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return -1;
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}
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}
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return ret;
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}
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