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/*
* Copyright 2015 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
#include <keymaster/key_blob_utils/ocb_utils.h>
#include <assert.h>
#include <openssl/aes.h>
#include <openssl/sha.h>
#include <hardware/keymaster_defs.h>
#include <keymaster/authorization_set.h>
#include <keymaster/android_keymaster_utils.h>
#include <keymaster/km_openssl/openssl_err.h>
#include <keymaster/new>
namespace keymaster {
class AeCtx {
public:
AeCtx() : ctx_(ae_allocate(nullptr)) {}
~AeCtx() {
ae_clear(ctx_);
ae_free(ctx_);
}
ae_ctx* get() { return ctx_; }
private:
ae_ctx* ctx_;
};
static keymaster_error_t BuildDerivationData(const AuthorizationSet& hw_enforced,
const AuthorizationSet& sw_enforced,
const AuthorizationSet& hidden,
UniquePtr<uint8_t[]>* derivation_data,
size_t* derivation_data_length) {
*derivation_data_length =
hidden.SerializedSize() + hw_enforced.SerializedSize() + sw_enforced.SerializedSize();
derivation_data->reset(new (std::nothrow) uint8_t[*derivation_data_length]);
if (!derivation_data->get())
return KM_ERROR_MEMORY_ALLOCATION_FAILED;
uint8_t* buf = derivation_data->get();
uint8_t* end = derivation_data->get() + *derivation_data_length;
buf = hidden.Serialize(buf, end);
buf = hw_enforced.Serialize(buf, end);
buf = sw_enforced.Serialize(buf, end);
return KM_ERROR_OK;
}
static keymaster_error_t InitializeKeyWrappingContext(const AuthorizationSet& hw_enforced,
const AuthorizationSet& sw_enforced,
const AuthorizationSet& hidden,
const KeymasterKeyBlob& master_key,
AeCtx* ctx) {
size_t derivation_data_length;
UniquePtr<uint8_t[]> derivation_data;
keymaster_error_t error = BuildDerivationData(hw_enforced, sw_enforced, hidden,
&derivation_data, &derivation_data_length);
if (error != KM_ERROR_OK)
return error;
SHA256_CTX sha256_ctx;
UniquePtr<uint8_t[]> hash_buf(new (std::nothrow) uint8_t[SHA256_DIGEST_LENGTH]);
if (!hash_buf.get())
return KM_ERROR_MEMORY_ALLOCATION_FAILED;
Eraser hash_eraser(hash_buf.get(), SHA256_DIGEST_LENGTH);
UniquePtr<uint8_t[]> derived_key(new (std::nothrow) uint8_t[AES_BLOCK_SIZE]);
if (!derived_key.get())
return KM_ERROR_MEMORY_ALLOCATION_FAILED;
Eraser derived_key_eraser(derived_key.get(), AES_BLOCK_SIZE);
if (!ctx->get() || !hash_buf.get() || !derived_key.get())
return KM_ERROR_MEMORY_ALLOCATION_FAILED;
// Hash derivation data.
Eraser sha256_ctx_eraser(sha256_ctx);
SHA256_Init(&sha256_ctx);
SHA256_Update(&sha256_ctx, derivation_data.get(), derivation_data_length);
SHA256_Final(hash_buf.get(), &sha256_ctx);
// Encrypt hash with master key to build derived key.
AES_KEY aes_key;
Eraser aes_key_eraser(AES_KEY);
if (0 !=
AES_set_encrypt_key(master_key.key_material, master_key.key_material_size * 8, &aes_key))
return TranslateLastOpenSslError();
AES_encrypt(hash_buf.get(), derived_key.get(), &aes_key);
// Set up AES OCB context using derived key.
if (ae_init(ctx->get(), derived_key.get(), AES_BLOCK_SIZE /* key length */, OCB_NONCE_LENGTH,
OCB_TAG_LENGTH) != AE_SUCCESS) {
memset_s(ctx->get(), 0, ae_ctx_sizeof());
return KM_ERROR_UNKNOWN_ERROR;
}
return KM_ERROR_OK;
}
keymaster_error_t OcbEncryptKey(const AuthorizationSet& hw_enforced,
const AuthorizationSet& sw_enforced, const AuthorizationSet& hidden,
const KeymasterKeyBlob& master_key,
const KeymasterKeyBlob& plaintext, const Buffer& nonce,
KeymasterKeyBlob* ciphertext, Buffer* tag) {
assert(ciphertext && tag);
if (nonce.available_read() != OCB_NONCE_LENGTH)
return KM_ERROR_INVALID_ARGUMENT;
AeCtx ctx;
if (!ctx.get())
return KM_ERROR_MEMORY_ALLOCATION_FAILED;
keymaster_error_t error =
InitializeKeyWrappingContext(hw_enforced, sw_enforced, hidden, master_key, &ctx);
if (error != KM_ERROR_OK)
return error;
if (!ciphertext->Reset(plaintext.key_material_size))
return KM_ERROR_MEMORY_ALLOCATION_FAILED;
int ae_err = ae_encrypt(ctx.get(), nonce.peek_read(), plaintext.key_material,
plaintext.key_material_size, nullptr /* additional data */,
0 /* additional data length */, ciphertext->writable_data(),
tag->peek_write(), 1 /* final */);
if (ae_err < 0) {
LOG_E("Error %d while encrypting key", ae_err);
return KM_ERROR_UNKNOWN_ERROR;
}
if (!tag->advance_write(OCB_TAG_LENGTH))
return KM_ERROR_UNKNOWN_ERROR;
assert(ae_err == static_cast<int>(plaintext.key_material_size));
return KM_ERROR_OK;
}
keymaster_error_t OcbDecryptKey(const AuthorizationSet& hw_enforced,
const AuthorizationSet& sw_enforced, const AuthorizationSet& hidden,
const KeymasterKeyBlob& master_key,
const KeymasterKeyBlob& ciphertext, const Buffer& nonce,
const Buffer& tag, KeymasterKeyBlob* plaintext) {
assert(plaintext);
if (nonce.available_read() != OCB_NONCE_LENGTH || tag.available_read() != OCB_TAG_LENGTH)
return KM_ERROR_INVALID_ARGUMENT;
AeCtx ctx;
if (!ctx.get())
return KM_ERROR_MEMORY_ALLOCATION_FAILED;
keymaster_error_t error =
InitializeKeyWrappingContext(hw_enforced, sw_enforced, hidden, master_key, &ctx);
if (error != KM_ERROR_OK)
return error;
if (!plaintext->Reset(ciphertext.key_material_size))
return KM_ERROR_MEMORY_ALLOCATION_FAILED;
int ae_err = ae_decrypt(ctx.get(), nonce.peek_read(), ciphertext.key_material,
ciphertext.key_material_size, nullptr /* additional data */,
0 /* additional data length */, plaintext->writable_data(),
tag.peek_read(), 1 /* final */);
if (ae_err == AE_INVALID) {
// Authentication failed! Decryption probably succeeded(ish), but we don't want to return
// any data when the authentication fails, so clear it.
plaintext->Clear();
LOG_E("Failed to validate authentication tag during key decryption", 0);
return KM_ERROR_INVALID_KEY_BLOB;
} else if (ae_err < 0) {
LOG_E("Failed to decrypt key, error: %d", ae_err);
return KM_ERROR_UNKNOWN_ERROR;
}
assert(ae_err == static_cast<int>(ciphertext.key_material_size));
return KM_ERROR_OK;
}
} // namespace keymaster
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