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43 lines
2.4 KiB
Markdown
43 lines
2.4 KiB
Markdown
# About
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Entropy is a simple go pkg and cmdline interface for manipulating entropy in the linux kernel.
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It achieves this by using the the IOCTL interface to /dev/(u)random.
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# Some basic theory
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The linux kernel simulates randomness by keeping a pool of data, estimating its information entropy, and generating data out of it using SHA hashes.
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When information is added to the pool it gets "mixed" into the pool with a CRC-like algorithm; it doesn't actually add the raw data.
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Optionally, when information is added, the entropy count of the pool can be incrememnted. This isn't a literal add, but rather an asymptotic algorithm that approaches the pool size.
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Information can be added to the pool by writing to `/dev/random` or `/dev/urandom`, but this will not increment the entropy count. This package/command provide an interface to the IOCTLs that provide extended userspace functionality for manipulating randomness. Of particular note, the `AddToEntCnt()` function adds bits to the entropy count and the `AddEntropy()` function adds bytes to the pool while also incrementing entropy bits.
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# Command
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The `entropy` command has the following usage information:
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```
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Usage: entropy <command> [<opts>...]
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Commands:
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get(entropy) - get the current system entropy.
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addto(entcnt) <num> - (superuser) Add <num> bits to the current entropy count.
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Note: this does not literally increase entropy count by <num>. The kernel adds using an asymptotic algorithm.
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See <drivers/char/random.c> for details.
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add(entropy) <file> [<quality>] - (superuser) Add the contents of <file> to entropy, incrementing entropy by the byte-length of the file.
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The optional <quality> specifies the percentage of total data to count as Shannon entropy (default: 1, which is highly unlikely).
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zap(entcnt) - (superuser) Clear the kernel entropy count.
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clear(pool) - (superuser) Clear the entropy pool and counters (on modern linux, this just does zapentcnt).
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reseed(crng) - (superuser) Reseed the CRNG.
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```
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# Package
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The `entropy` package provides a basic wrapper for all IOCTL functions provided by the kernel.
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# Authors
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- J. Lowell Wofford <lowell@lanl.gov> |