90 lines
2.9 KiB
C++
90 lines
2.9 KiB
C++
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// 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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#include "absl/random/internal/randen.h"
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#include "absl/base/internal/raw_logging.h"
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#include "absl/random/internal/randen_detect.h"
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// RANDen = RANDom generator or beetroots in Swiss German.
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// 'Strong' (well-distributed, unpredictable, backtracking-resistant) random
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// generator, faster in some benchmarks than std::mt19937_64 and pcg64_c32.
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//
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// High-level summary:
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// 1) Reverie (see "A Robust and Sponge-Like PRNG with Improved Efficiency") is
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// a sponge-like random generator that requires a cryptographic permutation.
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// It improves upon "Provably Robust Sponge-Based PRNGs and KDFs" by
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// achieving backtracking resistance with only one Permute() per buffer.
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//
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// 2) "Simpira v2: A Family of Efficient Permutations Using the AES Round
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// Function" constructs up to 1024-bit permutations using an improved
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// Generalized Feistel network with 2-round AES-128 functions. This Feistel
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// block shuffle achieves diffusion faster and is less vulnerable to
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// sliced-biclique attacks than the Type-2 cyclic shuffle.
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//
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// 3) "Improving the Generalized Feistel" and "New criterion for diffusion
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// property" extends the same kind of improved Feistel block shuffle to 16
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// branches, which enables a 2048-bit permutation.
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//
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// We combine these three ideas and also change Simpira's subround keys from
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// structured/low-entropy counters to digits of Pi.
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namespace absl {
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namespace random_internal {
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namespace {
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struct RandenState {
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const void* keys;
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bool has_crypto;
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};
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RandenState GetRandenState() {
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static const RandenState state = []() {
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RandenState tmp;
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#if ABSL_RANDOM_INTERNAL_AES_DISPATCH
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// HW AES Dispatch.
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if (HasRandenHwAesImplementation() && CPUSupportsRandenHwAes()) {
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tmp.has_crypto = true;
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tmp.keys = RandenHwAes::GetKeys();
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} else {
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tmp.has_crypto = false;
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tmp.keys = RandenSlow::GetKeys();
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}
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#elif ABSL_HAVE_ACCELERATED_AES
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// HW AES is enabled.
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tmp.has_crypto = true;
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tmp.keys = RandenHwAes::GetKeys();
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#else
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// HW AES is disabled.
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tmp.has_crypto = false;
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tmp.keys = RandenSlow::GetKeys();
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#endif
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return tmp;
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}();
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return state;
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}
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} // namespace
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Randen::Randen() {
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auto tmp = GetRandenState();
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keys_ = tmp.keys;
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#if ABSL_RANDOM_INTERNAL_AES_DISPATCH
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has_crypto_ = tmp.has_crypto;
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#endif
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}
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} // namespace random_internal
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} // namespace absl
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