1 // Copyright 2017 The Abseil Authors.
2 //
3 // Licensed under the Apache License, Version 2.0 (the "License");
4 // you may not use this file except in compliance with the License.
5 // You may obtain a copy of the License at
6 //
7 //      https://www.apache.org/licenses/LICENSE-2.0
8 //
9 // Unless required by applicable law or agreed to in writing, software
10 // distributed under the License is distributed on an "AS IS" BASIS,
11 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
12 // See the License for the specific language governing permissions and
13 // limitations under the License.
14 
15 #include "absl/random/internal/randen.h"
16 
17 #include "absl/base/internal/raw_logging.h"
18 #include "absl/random/internal/randen_detect.h"
19 
20 // RANDen = RANDom generator or beetroots in Swiss German.
21 // 'Strong' (well-distributed, unpredictable, backtracking-resistant) random
22 // generator, faster in some benchmarks than std::mt19937_64 and pcg64_c32.
23 //
24 // High-level summary:
25 // 1) Reverie (see "A Robust and Sponge-Like PRNG with Improved Efficiency") is
26 //    a sponge-like random generator that requires a cryptographic permutation.
27 //    It improves upon "Provably Robust Sponge-Based PRNGs and KDFs" by
28 //    achieving backtracking resistance with only one Permute() per buffer.
29 //
30 // 2) "Simpira v2: A Family of Efficient Permutations Using the AES Round
31 //    Function" constructs up to 1024-bit permutations using an improved
32 //    Generalized Feistel network with 2-round AES-128 functions. This Feistel
33 //    block shuffle achieves diffusion faster and is less vulnerable to
34 //    sliced-biclique attacks than the Type-2 cyclic shuffle.
35 //
36 // 3) "Improving the Generalized Feistel" and "New criterion for diffusion
37 //    property" extends the same kind of improved Feistel block shuffle to 16
38 //    branches, which enables a 2048-bit permutation.
39 //
40 // We combine these three ideas and also change Simpira's subround keys from
41 // structured/low-entropy counters to digits of Pi.
42 
43 namespace absl {
44 ABSL_NAMESPACE_BEGIN
45 namespace random_internal {
46 namespace {
47 
48 struct RandenState {
49   const void* keys;
50   bool has_crypto;
51 };
52 
GetRandenState()53 RandenState GetRandenState() {
54   static const RandenState state = []() {
55     RandenState tmp;
56 #if ABSL_RANDOM_INTERNAL_AES_DISPATCH
57     // HW AES Dispatch.
58     if (HasRandenHwAesImplementation() && CPUSupportsRandenHwAes()) {
59       tmp.has_crypto = true;
60       tmp.keys = RandenHwAes::GetKeys();
61     } else {
62       tmp.has_crypto = false;
63       tmp.keys = RandenSlow::GetKeys();
64     }
65 #elif ABSL_HAVE_ACCELERATED_AES
66     // HW AES is enabled.
67     tmp.has_crypto = true;
68     tmp.keys = RandenHwAes::GetKeys();
69 #else
70     // HW AES is disabled.
71     tmp.has_crypto = false;
72     tmp.keys = RandenSlow::GetKeys();
73 #endif
74     return tmp;
75   }();
76   return state;
77 }
78 
79 }  // namespace
80 
Randen()81 Randen::Randen() {
82   auto tmp = GetRandenState();
83   keys_ = tmp.keys;
84 #if ABSL_RANDOM_INTERNAL_AES_DISPATCH
85   has_crypto_ = tmp.has_crypto;
86 #endif
87 }
88 
89 }  // namespace random_internal
90 ABSL_NAMESPACE_END
91 }  // namespace absl
92