89 lines
3.7 KiB
C
89 lines
3.7 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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#ifndef ABSL_RANDOM_INTERNAL_RANDEN_TRAITS_H_
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#define ABSL_RANDOM_INTERNAL_RANDEN_TRAITS_H_
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// HERMETIC NOTE: The randen_hwaes target must not introduce duplicate
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// symbols from arbitrary system and other headers, since it may be built
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// with different flags from other targets, using different levels of
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// optimization, potentially introducing ODR violations.
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#include <cstddef>
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#include "absl/base/config.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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// RANDen = RANDom generator or beetroots in Swiss High 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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// Combine these three ideas and also change Simpira's subround keys from
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// structured/low-entropy counters to digits of Pi (or other random source).
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// RandenTraits contains the basic algorithm traits, such as the size of the
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// state, seed, sponge, etc.
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struct RandenTraits {
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// Size of the entire sponge / state for the randen PRNG.
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static constexpr size_t kStateBytes = 256; // 2048-bit
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// Size of the 'inner' (inaccessible) part of the sponge. Larger values would
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// require more frequent calls to RandenGenerate.
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static constexpr size_t kCapacityBytes = 16; // 128-bit
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// Size of the default seed consumed by the sponge.
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static constexpr size_t kSeedBytes = kStateBytes - kCapacityBytes;
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// Assuming 128-bit blocks, the number of blocks in the state.
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// Largest size for which security proofs are known.
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static constexpr size_t kFeistelBlocks = 16;
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// Ensures SPRP security and two full subblock diffusions.
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// Must be > 4 * log2(kFeistelBlocks).
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static constexpr size_t kFeistelRounds = 16 + 1;
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// Size of the key. A 128-bit key block is used for every-other
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// feistel block (Type-2 generalized Feistel network) in each round.
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static constexpr size_t kKeyBytes = 16 * kFeistelRounds * kFeistelBlocks / 2;
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};
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// Randen key arrays. In randen_round_keys.cc
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extern const unsigned char kRandenRoundKeys[RandenTraits::kKeyBytes];
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extern const unsigned char kRandenRoundKeysBE[RandenTraits::kKeyBytes];
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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_RANDEN_TRAITS_H_
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