Botan 3.8.1
Crypto and TLS for C&
rng.h
Go to the documentation of this file.
1/*
2* Random Number Generator base classes
3* (C) 1999-2009,2015,2016 Jack Lloyd
4* 2023 René Meusel - Rohde & Schwarz Cybersecurity
5*
6* Botan is released under the Simplified BSD License (see license.txt)
7*/
8
9#ifndef BOTAN_RANDOM_NUMBER_GENERATOR_H_
10#define BOTAN_RANDOM_NUMBER_GENERATOR_H_
11
12#include <botan/concepts.h>
13#include <botan/exceptn.h>
14#include <botan/secmem.h>
15
16#include <array>
17#include <chrono>
18#include <concepts>
19#include <span>
20#include <string>
21#include <type_traits>
22
23namespace Botan {
24
25class Entropy_Sources;
26
27/**
28* An interface to a cryptographic random number generator
29*/
31 public:
32 /**
33 * Userspace RNGs like HMAC_DRBG will reseed after a specified number
34 * of outputs are generated. Set to zero to disable automatic reseeding.
35 */
36 static constexpr size_t DefaultReseedInterval = 1024;
37
38 /**
39 * Number of entropy bits polled for reseeding userspace RNGs like HMAC_DRBG
40 */
41 static constexpr size_t DefaultPollBits = 256;
42
43 /**
44 * Default poll timeout
45 */
46 static constexpr auto DefaultPollTimeout = std::chrono::milliseconds(50);
47
48 virtual ~RandomNumberGenerator() = default;
49
51
52 /*
53 * Never copy a RNG, create a new one
54 */
57
58 /**
59 * Randomize a byte array.
60 *
61 * May block shortly if e.g. the RNG is not yet initialized
62 * or a retry because of insufficient entropy is needed.
63 *
64 * @param output the byte array to hold the random output.
65 * @throws PRNG_Unseeded if the RNG fails because it has not enough entropy
66 * @throws Exception if the RNG fails
67 */
68 void randomize(std::span<uint8_t> output) { this->fill_bytes_with_input(output, {}); }
69
70 void randomize(uint8_t output[], size_t length) { this->randomize(std::span(output, length)); }
71
72 /**
73 * Returns false if it is known that this RNG object is not able to accept
74 * externally provided inputs (via add_entropy, randomize_with_input, etc).
75 * In this case, any such provided inputs are ignored.
76 *
77 * If this function returns true, then inputs may or may not be accepted.
78 */
79 virtual bool accepts_input() const = 0;
80
81 /**
82 * Incorporate some additional data into the RNG state. For
83 * example adding nonces or timestamps from a peer's protocol
84 * message can help hedge against VM state rollback attacks.
85 * A few RNG types do not accept any externally provided input,
86 * in which case this function is a no-op.
87 *
88 * @param input a byte array containing the entropy to be added
89 * @throws Exception may throw if the RNG accepts input, but adding the entropy failed.
90 */
91 void add_entropy(std::span<const uint8_t> input) { this->fill_bytes_with_input({}, input); }
92
93 void add_entropy(const uint8_t input[], size_t length) { this->add_entropy(std::span(input, length)); }
94
95 /**
96 * Incorporate some additional data into the RNG state.
97 */
98 template <typename T>
99 requires std::is_standard_layout<T>::value && std::is_trivial<T>::value
100 void add_entropy_T(const T& t) {
101 this->add_entropy(reinterpret_cast<const uint8_t*>(&t), sizeof(T));
102 }
103
104 /**
105 * Incorporate entropy into the RNG state then produce output.
106 * Some RNG types implement this using a single operation, default
107 * calls add_entropy + randomize in sequence.
108 *
109 * Use this to further bind the outputs to your current
110 * process/protocol state. For instance if generating a new key
111 * for use in a session, include a session ID or other such
112 * value. See NIST SP 800-90 A, B, C series for more ideas.
113 *
114 * @param output buffer to hold the random output
115 * @param input entropy buffer to incorporate
116 * @throws PRNG_Unseeded if the RNG fails because it has not enough entropy
117 * @throws Exception if the RNG fails
118 * @throws Exception may throw if the RNG accepts input, but adding the entropy failed.
119 */
120 void randomize_with_input(std::span<uint8_t> output, std::span<const uint8_t> input) {
121 this->fill_bytes_with_input(output, input);
122 }
123
124 void randomize_with_input(uint8_t output[], size_t output_len, const uint8_t input[], size_t input_len) {
125 this->randomize_with_input(std::span(output, output_len), std::span(input, input_len));
126 }
127
128 /**
129 * This calls `randomize_with_input` using some timestamps as extra input.
130 *
131 * For a stateful RNG using non-random but potentially unique data the
132 * extra input can help protect against problems with fork, VM state
133 * rollback, or other cases where somehow an RNG state is duplicated. If
134 * both of the duplicated RNG states later incorporate a timestamp (and the
135 * timestamps don't themselves repeat), their outputs will diverge.
136 *
137 * @param output buffer to hold the random output
138 * @throws PRNG_Unseeded if the RNG fails because it has not enough entropy
139 * @throws Exception if the RNG fails
140 * @throws Exception may throw if the RNG accepts input, but adding the entropy failed.
141 */
142 void randomize_with_ts_input(std::span<uint8_t> output);
143
144 void randomize_with_ts_input(uint8_t output[], size_t output_len) {
145 this->randomize_with_ts_input(std::span(output, output_len));
146 }
147
148 /**
149 * @return the name of this RNG type
150 */
151 virtual std::string name() const = 0;
152
153 /**
154 * Clear all internally held values of this RNG
155 * @post is_seeded() == false if the RNG has an internal state that can be cleared.
156 */
157 virtual void clear() = 0;
158
159 /**
160 * Check whether this RNG is seeded.
161 * @return true if this RNG was already seeded, false otherwise.
162 */
163 virtual bool is_seeded() const = 0;
164
165 /**
166 * Poll provided sources for up to poll_bits bits of entropy
167 * or until the timeout expires. Returns estimate of the number
168 * of bits collected.
169 *
170 * Sets the seeded state to true if enough entropy was added.
171 */
172 virtual size_t reseed(Entropy_Sources& srcs,
174 std::chrono::milliseconds poll_timeout = RandomNumberGenerator::DefaultPollTimeout);
175
176 /**
177 * Reseed by reading specified bits from the RNG
178 *
179 * Sets the seeded state to true if enough entropy was added.
180 *
181 * @throws Exception if RNG accepts input but reseeding failed.
182 */
183 virtual void reseed_from_rng(RandomNumberGenerator& rng,
184 size_t poll_bits = RandomNumberGenerator::DefaultPollBits);
185
186 // Some utility functions built on the interface above:
187
188 /**
189 * Fill a given byte container with @p bytes random bytes
190 *
191 * @todo deprecate this overload (in favor of randomize())
192 *
193 * @param v the container to be filled with @p bytes random bytes
194 * @throws Exception if RNG fails
195 */
196 void random_vec(std::span<uint8_t> v) { this->randomize(v); }
197
198 /**
199 * Resize a given byte container to @p bytes and fill it with random bytes
200 *
201 * @tparam T the desired byte container type (e.g std::vector<uint8_t>)
202 * @param v the container to be filled with @p bytes random bytes
203 * @param bytes number of random bytes to initialize the container with
204 * @throws Exception if RNG or memory allocation fails
205 */
206 template <concepts::resizable_byte_buffer T>
207 void random_vec(T& v, size_t bytes) {
208 v.resize(bytes);
209 random_vec(v);
210 }
211
212 /**
213 * Create some byte container type and fill it with some random @p bytes.
214 *
215 * @tparam T the desired byte container type (e.g std::vector<uint8_t>)
216 * @param bytes number of random bytes to initialize the container with
217 * @return a container of type T with @p bytes random bytes
218 * @throws Exception if RNG or memory allocation fails
219 */
220 template <concepts::resizable_byte_buffer T = secure_vector<uint8_t>>
221 requires std::default_initializable<T>
222 T random_vec(size_t bytes) {
223 T result;
224 random_vec(result, bytes);
225 return result;
226 }
227
228 /**
229 * Create a std::array of @p bytes random bytes
230 */
231 template <size_t bytes>
232 std::array<uint8_t, bytes> random_array() {
233 std::array<uint8_t, bytes> result;
234 random_vec(result);
235 return result;
236 }
237
238 /**
239 * Return a random byte
240 * @return random byte
241 * @throws PRNG_Unseeded if the RNG fails because it has not enough entropy
242 * @throws Exception if the RNG fails
243 */
244 uint8_t next_byte() {
245 uint8_t b;
246 this->fill_bytes_with_input(std::span(&b, 1), {});
247 return b;
248 }
249
250 /**
251 * @return a random byte that is greater than zero
252 * @throws PRNG_Unseeded if the RNG fails because it has not enough entropy
253 * @throws Exception if the RNG fails
254 */
256 uint8_t b = this->next_byte();
257 while(b == 0) {
258 b = this->next_byte();
259 }
260 return b;
261 }
262
263 protected:
264 /**
265 * Generic interface to provide entropy to a concrete implementation and to
266 * fill a given buffer with random output. Both @p output and @p input may
267 * be empty and should be ignored in that case. If both buffers are
268 * non-empty implementations should typically first apply the @p input data
269 * and then generate random data into @p output.
270 *
271 * This method must be implemented by all RandomNumberGenerator sub-classes.
272 *
273 * @param output Byte buffer to write random bytes into. Implementations
274 * should not read from this buffer.
275 * @param input Byte buffer that may contain bytes to be incorporated in
276 * the RNG's internal state. Implementations may choose to
277 * ignore the bytes in this buffer.
278 */
279 virtual void fill_bytes_with_input(std::span<uint8_t> output, std::span<const uint8_t> input) = 0;
280};
281
282/**
283* Convenience typedef
284*/
286
287/**
288* Hardware_RNG exists to tag hardware RNG types (PKCS11_RNG, TPM_RNG, Processor_RNG)
289*/
291 public:
292 void clear() final { /* no way to clear state of hardware RNG */
293 }
294};
295
296/**
297* Null/stub RNG - fails if you try to use it for anything
298* This is not generally useful except for in certain tests
299*/
301 public:
302 bool is_seeded() const override { return false; }
303
304 bool accepts_input() const override { return false; }
305
306 void clear() override {}
307
308 std::string name() const override { return "Null_RNG"; }
309
310 private:
311 void fill_bytes_with_input(std::span<uint8_t> output, std::span<const uint8_t> /* ignored */) override;
312};
313
314} // namespace Botan
315
316#endif
#define BOTAN_PUBLIC_API(maj, min)
Definition api.h:19
void clear() final
Definition rng.h:292
bool accepts_input() const override
Definition rng.h:304
void clear() override
Definition rng.h:306
std::string name() const override
Definition rng.h:308
bool is_seeded() const override
Definition rng.h:302
void randomize(std::span< uint8_t > output)
Definition rng.h:68
std::array< uint8_t, bytes > random_array()
Definition rng.h:232
virtual bool accepts_input() const =0
T random_vec(size_t bytes)
Definition rng.h:222
virtual ~RandomNumberGenerator()=default
void add_entropy(std::span< const uint8_t > input)
Definition rng.h:91
void randomize(uint8_t output[], size_t length)
Definition rng.h:70
uint8_t next_nonzero_byte()
Definition rng.h:255
static constexpr size_t DefaultPollBits
Definition rng.h:41
void random_vec(T &v, size_t bytes)
Definition rng.h:207
RandomNumberGenerator & operator=(const RandomNumberGenerator &rng)=delete
static constexpr size_t DefaultReseedInterval
Definition rng.h:36
static constexpr auto DefaultPollTimeout
Definition rng.h:46
virtual bool is_seeded() const =0
void randomize_with_ts_input(uint8_t output[], size_t output_len)
Definition rng.h:144
virtual size_t reseed(Entropy_Sources &srcs, size_t poll_bits=RandomNumberGenerator::DefaultPollBits, std::chrono::milliseconds poll_timeout=RandomNumberGenerator::DefaultPollTimeout)
Definition rng.cpp:51
void add_entropy(const uint8_t input[], size_t length)
Definition rng.h:93
virtual std::string name() const =0
virtual void reseed_from_rng(RandomNumberGenerator &rng, size_t poll_bits=RandomNumberGenerator::DefaultPollBits)
Definition rng.cpp:63
void randomize_with_ts_input(std::span< uint8_t > output)
Definition rng.cpp:27
void add_entropy_T(const T &t)
Definition rng.h:100
void random_vec(std::span< uint8_t > v)
Definition rng.h:196
virtual void fill_bytes_with_input(std::span< uint8_t > output, std::span< const uint8_t > input)=0
void randomize_with_input(std::span< uint8_t > output, std::span< const uint8_t > input)
Definition rng.h:120
RandomNumberGenerator(const RandomNumberGenerator &rng)=delete
void randomize_with_input(uint8_t output[], size_t output_len, const uint8_t input[], size_t input_len)
Definition rng.h:124
RandomNumberGenerator RNG
Definition rng.h:285