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224e6eb089
These are available in sandboxes without access to files or devices. Also [they are safer and more straightforward](https://en.wikipedia.org/wiki/Entropy-supplying_system_calls) to use than `/dev/urandom` as reading from a file has quite a few edge cases: - Linux: `getrandom(buf, buflen, 0)`. [getrandom(2)](http://man7.org/linux/man-pages/man2/getrandom.2.html) was introduced in version 3.17 of the Linux kernel. - OpenBSD: `getentropy(buf, buflen)`. The [getentropy(2)](http://man.openbsd.org/cgi-bin/man.cgi/OpenBSD-current/man2/getentropy.2) function appeared in OpenBSD 5.6. - FreeBSD and NetBSD: `sysctl(KERN_ARND)`. Not sure when this was added but it has existed for quite a while. Alternatives: - Linux has sysctl `CTL_KERN` / `KERN_RANDOM` / `RANDOM_UUID` which gives 16 bytes of randomness. This may be available on older kernels, however [sysctl is deprecated on Linux](https://lwn.net/Articles/605392/) and even removed in some distros so we shouldn't use it. Add tests for `GetOSRand()`: - Test that no error happens (otherwise `RandFailure()` which aborts) - Test that all 32 bytes are overwritten (initialize with zeros, try multiple times) Discussion: - When to use these? Currently they are always used when available. Another option would be to use them only when `/dev/urandom` is not available. But this would mean these code paths receive less testing, and I'm not sure there is any reason to prefer `/dev/urandom`. Closes: #9676
58 lines
1.5 KiB
C++
58 lines
1.5 KiB
C++
// Copyright (c) 2009-2010 Satoshi Nakamoto
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// Copyright (c) 2009-2016 The Bitcoin Core developers
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// Distributed under the MIT software license, see the accompanying
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// file COPYING or http://www.opensource.org/licenses/mit-license.php.
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#ifndef BITCOIN_RANDOM_H
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#define BITCOIN_RANDOM_H
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#include "uint256.h"
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#include <stdint.h>
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/* Seed OpenSSL PRNG with additional entropy data */
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void RandAddSeed();
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/**
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* Functions to gather random data via the OpenSSL PRNG
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*/
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void GetRandBytes(unsigned char* buf, int num);
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uint64_t GetRand(uint64_t nMax);
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int GetRandInt(int nMax);
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uint256 GetRandHash();
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/**
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* Function to gather random data from multiple sources, failing whenever any
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* of those source fail to provide a result.
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*/
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void GetStrongRandBytes(unsigned char* buf, int num);
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/**
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* Fast randomness source. This is seeded once with secure random data, but
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* is completely deterministic and insecure after that.
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* This class is not thread-safe.
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*/
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class FastRandomContext {
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public:
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explicit FastRandomContext(bool fDeterministic=false);
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uint32_t rand32() {
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Rz = 36969 * (Rz & 65535) + (Rz >> 16);
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Rw = 18000 * (Rw & 65535) + (Rw >> 16);
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return (Rw << 16) + Rz;
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}
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uint32_t Rz;
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uint32_t Rw;
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};
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/* Number of random bytes returned by GetOSRand */
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static const ssize_t NUM_OS_RANDOM_BYTES = 32;
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/** Get 32 bytes of system entropy. Do not use this in application code: use
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* GetStrongRandBytes instead.
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*/
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void GetOSRand(unsigned char *ent32);
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#endif // BITCOIN_RANDOM_H
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