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/*
* Copyright (C) 2020 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.
*/
#pragma once
#include <stdlib.h>
namespace android {
namespace vold {
// Struct representing an encryption algorithm supported by vold.
// "config_name" represents the name we give the algorithm in
// read-only properties and fstab files
// "kernel_name" is the name we present to the Linux kernel
// "keysize" is the size of the key in bytes.
struct CryptoType {
// We should only be constructing CryptoTypes as part of
// supported_crypto_types[]. We do it via this pseudo-builder pattern,
// which isn't pure or fully protected as a concession to being able to
// do it all at compile time. Add new CryptoTypes in
// supported_crypto_types[] below.
constexpr CryptoType() : CryptoType(nullptr, nullptr, 0xFFFFFFFF) {}
constexpr CryptoType set_keysize(size_t size) const {
return CryptoType(this->config_name, this->kernel_name, size);
}
constexpr CryptoType set_config_name(const char* property) const {
return CryptoType(property, this->kernel_name, this->keysize);
}
constexpr CryptoType set_kernel_name(const char* crypto) const {
return CryptoType(this->config_name, crypto, this->keysize);
}
constexpr const char* get_config_name() const { return config_name; }
constexpr const char* get_kernel_name() const { return kernel_name; }
constexpr size_t get_keysize() const { return keysize; }
private:
const char* config_name;
const char* kernel_name;
size_t keysize;
constexpr CryptoType(const char* property, const char* crypto, size_t ksize)
: config_name(property), kernel_name(crypto), keysize(ksize) {}
};
// Use the named android property to look up a type from the table
// If the property is not set or matches no table entry, return the default.
const CryptoType& lookup_crypto_algorithm(const CryptoType table[], int table_len,
const CryptoType& default_alg, const char* property);
// Some useful types
constexpr CryptoType invalid_crypto_type = CryptoType();
constexpr CryptoType aes_256_xts = CryptoType()
.set_config_name("aes-256-xts")
.set_kernel_name("aes-xts-plain64")
.set_keysize(64);
constexpr CryptoType adiantum = CryptoType()
.set_config_name("adiantum")
.set_kernel_name("xchacha12,aes-adiantum-plain64")
.set_keysize(32);
// Support compile-time validation of a crypto type table
template <typename T, size_t N>
constexpr size_t array_length(T (&)[N]) {
return N;
}
constexpr bool isValidCryptoType(size_t max_keylen, const CryptoType& crypto_type) {
return ((crypto_type.get_config_name() != nullptr) &&
(crypto_type.get_kernel_name() != nullptr) &&
(crypto_type.get_keysize() <= max_keylen));
}
// Confirms that all supported_crypto_types have a small enough keysize and
// had both set_config_name() and set_kernel_name() called.
// Note in C++11 that constexpr functions can only have a single line.
// So our code is a bit convoluted (using recursion instead of a loop),
// but it's asserting at compile time that all of our key lengths are valid.
constexpr bool validateSupportedCryptoTypes(size_t max_keylen, const CryptoType types[],
size_t len) {
return len == 0 || (isValidCryptoType(max_keylen, types[len - 1]) &&
validateSupportedCryptoTypes(max_keylen, types, len - 1));
}
} // namespace vold
} // namespace android
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