fc8dc48020
git-subtree-dir: third_party/abseil_cpp git-subtree-mainline:ffb2ae54begit-subtree-split:768eb2ca28
104 lines
3.6 KiB
C++
104 lines
3.6 KiB
C++
// Copyright 2017 The Abseil Authors.
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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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// https://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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#ifndef ABSL_RANDOM_INTERNAL_SEED_MATERIAL_H_
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#define ABSL_RANDOM_INTERNAL_SEED_MATERIAL_H_
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#include <cassert>
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#include <cstdint>
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#include <cstdlib>
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#include <string>
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#include <vector>
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#include "absl/base/attributes.h"
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#include "absl/random/internal/fast_uniform_bits.h"
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#include "absl/types/optional.h"
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#include "absl/types/span.h"
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namespace absl {
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ABSL_NAMESPACE_BEGIN
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namespace random_internal {
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// Returns the number of 32-bit blocks needed to contain the given number of
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// bits.
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constexpr size_t SeedBitsToBlocks(size_t seed_size) {
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return (seed_size + 31) / 32;
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}
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// Amount of entropy (measured in bits) used to instantiate a Seed Sequence,
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// with which to create a URBG.
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constexpr size_t kEntropyBitsNeeded = 256;
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// Amount of entropy (measured in 32-bit blocks) used to instantiate a Seed
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// Sequence, with which to create a URBG.
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constexpr size_t kEntropyBlocksNeeded =
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random_internal::SeedBitsToBlocks(kEntropyBitsNeeded);
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static_assert(kEntropyBlocksNeeded > 0,
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"Entropy used to seed URBGs must be nonzero.");
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// Attempts to fill a span of uint32_t-values using an OS-provided source of
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// true entropy (eg. /dev/urandom) into an array of uint32_t blocks of data. The
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// resulting array may be used to initialize an instance of a class conforming
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// to the C++ Standard "Seed Sequence" concept [rand.req.seedseq].
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//
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// If values.data() == nullptr, the behavior is undefined.
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ABSL_MUST_USE_RESULT
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bool ReadSeedMaterialFromOSEntropy(absl::Span<uint32_t> values);
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// Attempts to fill a span of uint32_t-values using variates generated by an
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// existing instance of a class conforming to the C++ Standard "Uniform Random
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// Bit Generator" concept [rand.req.urng]. The resulting data may be used to
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// initialize an instance of a class conforming to the C++ Standard
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// "Seed Sequence" concept [rand.req.seedseq].
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//
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// If urbg == nullptr or values.data() == nullptr, the behavior is undefined.
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template <typename URBG>
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ABSL_MUST_USE_RESULT bool ReadSeedMaterialFromURBG(
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URBG* urbg, absl::Span<uint32_t> values) {
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random_internal::FastUniformBits<uint32_t> distr;
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assert(urbg != nullptr && values.data() != nullptr);
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if (urbg == nullptr || values.data() == nullptr) {
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return false;
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}
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for (uint32_t& seed_value : values) {
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seed_value = distr(*urbg);
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}
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return true;
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}
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// Mixes given sequence of values with into given sequence of seed material.
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// Time complexity of this function is O(sequence.size() *
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// seed_material.size()).
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//
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// Algorithm is based on code available at
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// https://gist.github.com/imneme/540829265469e673d045
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// by Melissa O'Neill.
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void MixIntoSeedMaterial(absl::Span<const uint32_t> sequence,
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absl::Span<uint32_t> seed_material);
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// Returns salt value.
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//
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// Salt is obtained only once and stored in static variable.
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//
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// May return empty value if optaining the salt was not possible.
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absl::optional<uint32_t> GetSaltMaterial();
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} // namespace random_internal
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ABSL_NAMESPACE_END
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} // namespace absl
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#endif // ABSL_RANDOM_INTERNAL_SEED_MATERIAL_H_
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