044a89ef55
Headers and Unit tests have been updated to match the v17 spec. Documentation can be found here: https://developers.devsite.corp.google.com/widevine/drm/client/oemcrypto/v17
118 lines
4.3 KiB
C++
118 lines
4.3 KiB
C++
// Copyright 2019 Google LLC. All Rights Reserved. This file and proprietary
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// source code may only be used and distributed under the Widevine License
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// Agreement.
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#ifndef WVCDM_CORE_CDM_RANDOM_H_
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#define WVCDM_CORE_CDM_RANDOM_H_
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#include <mutex>
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#include <random>
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#include <string>
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namespace wvutil {
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// CdmRandomGenerator is a thread safe, pseudo-random number generator.
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// It's purpose is to simplified interface for C++11's <random> library.
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// Some of the methods use a "device specific" random seed, if the
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// compiler/device does not support device specific randomizers, then the
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// actual value supplied may not be random. The generator is designed to
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// meet the C++ named requirement UniformRandomBitGenerator to allow it to
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// be used with standard library functions / class which are designed to
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// work with the standard library generators.
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class CdmRandomGenerator {
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public:
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// Result type of operator().
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using result_type = unsigned int;
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// Inclusive boundaries of operator().
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static constexpr unsigned int min() { return 0; }
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static constexpr unsigned int max() { return RAND_MAX; }
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// The maximum number of bytes that can be generated at once for
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// `RandomData()`.
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static constexpr size_t kMaxRandomDataLength = 8192; // 8 kB
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// Initializes the pseudo-random generator with a value from a device
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// specific random number generator.
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CdmRandomGenerator();
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// Initializes the pseudo-random generator with the specified seed value.
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explicit CdmRandomGenerator(unsigned int seed) : generator_(seed) {}
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// All of these methods are thread-safe.
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// Seeds the pseudo-random generator with a value from a device specific
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// random number generator.
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void Seed();
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// Seeds the pseudo-random generator with the specified seed value.
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// This is somewhat similar to `srand()` from the C standard library;
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// except that the sequence generated from successive calls to `Rand()`
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// will not necessarily be the same as they would be from the
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// standard library `rand()`. This is due to the underlying pseudo-random
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// generator that is used.
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void Seed(unsigned int seed);
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// Returns a pseudo-random integer.
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// This is similar to `rand()` from the C standard library. The integer
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// returned is in the range of [min(), max()].
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unsigned int Rand();
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// Allows for RNG to be callable.
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unsigned int operator()() { return Rand(); }
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// Returns a pseudo-random integer within the provided inclusive range.
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uint64_t RandomInRange(uint64_t lower, uint64_t upper);
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uint64_t RandomInRange(uint64_t upper) { return RandomInRange(0, upper); }
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// Returns a byte string containing randomized bytes of the specified
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// length.
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// If |length| is greater than |CdmRandomGenerator::kMaxRandomDataLength|,
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// then an error is logged and an empty string is returned.
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std::string RandomData(size_t length);
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// Random true/false using Bernoulli distribution of equal probability.
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bool RandomBool();
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private:
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// Mutex is used to lock the object, and allowing it to be used
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// concurrently in different threads.
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std::mutex generator_lock_;
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// The `default_random_engine` depends on the compiler used and
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// potentially its version. This is important to know if you need to
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// create reproducible tests between platforms.
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std::default_random_engine generator_;
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};
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// Provides a static interface to a process-wide instance of
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// CdmRandomGenerator.
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class CdmRandom {
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public:
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static unsigned int Rand() { return GetInstance()->Rand(); }
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static uint64_t RandomInRange(uint64_t lower, uint64_t upper) {
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return GetInstance()->RandomInRange(lower, upper);
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}
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static uint64_t RandomInRange(uint64_t upper) {
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return GetInstance()->RandomInRange(upper);
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}
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static std::string RandomData(size_t length) {
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return GetInstance()->RandomData(length);
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}
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static bool RandomBool() { return GetInstance()->RandomBool(); }
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private:
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// These are intended to be used by tests if needed.
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static void Seed(unsigned int seed) { GetInstance()->Seed(seed); }
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static void Seed() { GetInstance()->Seed(); }
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// Returns the process-wide instance of CdmRandomGenerator.
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// It the global instance has not yet been created, then a new instance
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// is created using a device-specific random seed.
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static CdmRandomGenerator* GetInstance();
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};
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} // namespace wvutil
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#endif // WVCDM_CORE_CDM_RANDOM_H_
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