/*
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* Copyright 2017 The Android Open Source Project
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*
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* 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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*
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* http://www.apache.org/licenses/LICENSE-2.0
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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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*/
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#include <keymaster/km_openssl/ckdf.h>
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#include <assert.h>
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#include <openssl/aes.h>
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#include <openssl/cmac.h>
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#include <keymaster/km_openssl/openssl_err.h>
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#include <keymaster/km_openssl/openssl_utils.h>
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#include <keymaster/serializable.h>
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namespace keymaster {
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inline uint32_t div_round_up(uint32_t dividend, uint32_t divisor) {
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return (dividend + divisor - 1) / divisor;
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}
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size_t min(size_t a, size_t b) {
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return a < b ? a : b;
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}
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DEFINE_OPENSSL_OBJECT_POINTER(CMAC_CTX)
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keymaster_error_t ckdf(const KeymasterKeyBlob& key, const KeymasterBlob& label,
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const keymaster_blob_t* context_chunks, size_t num_chunks,
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KeymasterKeyBlob* output) {
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// Note: the variables i and L correspond to i and L in the standard. See page 12 of
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// http://nvlpubs.nist.gov/nistpubs/Legacy/SP/nistspecialpublication800-108.pdf.
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const uint32_t blocks = div_round_up(output->key_material_size, AES_BLOCK_SIZE);
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const uint32_t L = output->key_material_size * 8; // bits
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const uint32_t net_order_L = hton(L);
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CMAC_CTX_Ptr ctx(CMAC_CTX_new());
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if (!ctx.get()) return KM_ERROR_MEMORY_ALLOCATION_FAILED;
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auto algo = EVP_aes_128_cbc();
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switch (key.key_material_size) {
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case AES_BLOCK_SIZE:
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/* Already set */
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break;
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case AES_BLOCK_SIZE * 2:
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algo = EVP_aes_256_cbc();
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break;
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default:
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return KM_ERROR_UNSUPPORTED_KEY_SIZE;
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}
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if (!CMAC_Init(ctx.get(), key.key_material, key.key_material_size, algo,
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nullptr /* engine */)) {
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return TranslateLastOpenSslError();
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}
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auto output_pos = const_cast<uint8_t*>(output->begin());
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memset(output_pos, 0, output->key_material_size);
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for (uint32_t i = 1; i <= blocks; ++i) {
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// Data to mac is i || label || 0x00 || context || L, with i and L represented in 32 bits,
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// in network order.
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// i
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uint32_t net_order_i = hton(i);
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if (!CMAC_Update(ctx.get(), reinterpret_cast<uint8_t*>(&net_order_i),
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sizeof(net_order_i))) {
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return TranslateLastOpenSslError();
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}
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// label
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if (!CMAC_Update(ctx.get(), label.data, label.data_length)) {
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return TranslateLastOpenSslError();
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}
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// 0x00
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uint8_t zero = 0;
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if (!CMAC_Update(ctx.get(), &zero, sizeof(zero))) return TranslateLastOpenSslError();
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// context
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for (size_t chunk = 0; chunk < num_chunks; ++chunk) {
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if (!CMAC_Update(ctx.get(), context_chunks[chunk].data,
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context_chunks[chunk].data_length)) {
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return TranslateLastOpenSslError();
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}
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}
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// L
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uint8_t buf[4];
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memcpy(buf, &net_order_L, 4);
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if (!CMAC_Update(ctx.get(), buf, sizeof(buf))) TranslateLastOpenSslError();
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size_t out_len;
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if (output_pos <= output->end() - AES_BLOCK_SIZE) {
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if (!CMAC_Final(ctx.get(), output_pos, &out_len)) return TranslateLastOpenSslError();
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output_pos += out_len;
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} else {
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uint8_t cmac[AES_BLOCK_SIZE];
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if (!CMAC_Final(ctx.get(), cmac, &out_len)) return TranslateLastOpenSslError();
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size_t to_copy = output->end() - output_pos;
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memcpy(output_pos, cmac, to_copy);
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output_pos += to_copy;
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}
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CMAC_Reset(ctx.get());
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}
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assert(output_pos == output->end());
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return KM_ERROR_OK;
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}
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} // namespace keymaster
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