| // Copyright 2017 The Fuchsia Authors |
| // |
| // Use of this source code is governed by a MIT-style |
| // license that can be found in the LICENSE file or at |
| // https://opensource.org/licenses/MIT |
| |
| #pragma once |
| |
| #include <fbl/name.h> |
| #include <stddef.h> |
| #include <stdint.h> |
| |
| namespace crypto { |
| |
| namespace entropy { |
| |
| class Collector { |
| public: |
| virtual ~Collector(); |
| |
| // Returns a null-terminated name, in the buffer of size |len| at |buf|. |
| void get_name(char* name, size_t len) const { name_.get(len, name); } |
| |
| // Fills |len| bytes of memory at |buf| with random data from this entropy |
| // collector's entropy source. The bytes that are returned may not be |
| // perfectly random, i.e. they may be statistically dependent or biased. Use |
| // the BytesNeeded() method to determine how may random bytes are needed to |
| // collect a certain amount of entropy. |
| virtual size_t DrawEntropy(uint8_t* buf, size_t len) = 0; |
| |
| // Returns the number of bytes of random data that should be drawn via |
| // DrawEntropy() to get approximately |bits| bits of entropy. Note: |bits| |
| // must be no larger than 2^20 (= 1048576). |
| size_t BytesNeeded(size_t bits) const; |
| |
| protected: |
| // Initialize this entropy collector. |name| is used for debugging and |
| // testing, and it may be truncated if it is too long. |
| // |entropy_per_1000_bytes| is the (approximate) amount of min-entropy in |
| // each 1000 bytes of data returned by the entropy source. The amount of |
| // entropy in a byte from the entropy source is generally not an integer. |
| // Quoting the entropy per 1000 bytes supports non-integer values, without |
| // requiring floating-point or fixed-point arithmetic. It is an error if |
| // |entropy_per_1000_bytes| is 0 or is greater than 8000. |
| // |
| // TODO(andrewkrieger): document entropy source quality tests, and reference |
| // that document here, to explain how to find a good value for |
| // entropy_per_1000_bytes. |
| Collector(const char* name, size_t entropy_per_1000_bytes); |
| |
| private: |
| DISALLOW_COPY_ASSIGN_AND_MOVE(Collector); |
| |
| fbl::Name<ZX_MAX_NAME_LEN> name_; |
| |
| size_t entropy_per_1000_bytes_; |
| }; |
| |
| } // namespace entropy |
| |
| } // namespace crypto |