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// Copyright 2017 The Abseil Authors.
//
// 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
//
// https://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 "absl/random/internal/randen.h"
#include "absl/base/internal/raw_logging.h"
#include "absl/random/internal/randen_detect.h"
// RANDen = RANDom generator or beetroots in Swiss German.
// 'Strong' (well-distributed, unpredictable, backtracking-resistant) random
// generator, faster in some benchmarks than std::mt19937_64 and pcg64_c32.
//
// High-level summary:
// 1) Reverie (see "A Robust and Sponge-Like PRNG with Improved Efficiency") is
// a sponge-like random generator that requires a cryptographic permutation.
// It improves upon "Provably Robust Sponge-Based PRNGs and KDFs" by
// achieving backtracking resistance with only one Permute() per buffer.
//
// 2) "Simpira v2: A Family of Efficient Permutations Using the AES Round
// Function" constructs up to 1024-bit permutations using an improved
// Generalized Feistel network with 2-round AES-128 functions. This Feistel
// block shuffle achieves diffusion faster and is less vulnerable to
// sliced-biclique attacks than the Type-2 cyclic shuffle.
//
// 3) "Improving the Generalized Feistel" and "New criterion for diffusion
// property" extends the same kind of improved Feistel block shuffle to 16
// branches, which enables a 2048-bit permutation.
//
// We combine these three ideas and also change Simpira's subround keys from
// structured/low-entropy counters to digits of Pi.
namespace absl {
ABSL_NAMESPACE_BEGIN
namespace random_internal {
namespace {
struct RandenState {
const void* keys;
bool has_crypto;
};
RandenState GetRandenState() {
static const RandenState state = []() {
RandenState tmp;
#if ABSL_RANDOM_INTERNAL_AES_DISPATCH
// HW AES Dispatch.
if (HasRandenHwAesImplementation() && CPUSupportsRandenHwAes()) {
tmp.has_crypto = true;
tmp.keys = RandenHwAes::GetKeys();
} else {
tmp.has_crypto = false;
tmp.keys = RandenSlow::GetKeys();
}
#elif ABSL_HAVE_ACCELERATED_AES
// HW AES is enabled.
tmp.has_crypto = true;
tmp.keys = RandenHwAes::GetKeys();
#else
// HW AES is disabled.
tmp.has_crypto = false;
tmp.keys = RandenSlow::GetKeys();
#endif
return tmp;
}();
return state;
}
} // namespace
Randen::Randen() {
auto tmp = GetRandenState();
keys_ = tmp.keys;
#if ABSL_RANDOM_INTERNAL_AES_DISPATCH
has_crypto_ = tmp.has_crypto;
#endif
}
} // namespace random_internal
ABSL_NAMESPACE_END
} // namespace absl
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