39 lines
1.1 KiB
Markdown
39 lines
1.1 KiB
Markdown
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# libfakerand
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## Introduction
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`libfakerand` intercepts various system calls that programs use to
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retrieve entropy. It replaces the entropy which would otherwise be
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used with the one supplied by the user. This means you can force
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programs to use a fixed value instead of a random one.
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`libfakerand` overrides the following functions:
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* `rand()`
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* `read()` function for `/dev/urandom` and `/dev/random`
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* `getrandom()`
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* `RAND_bytes()`
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## Usage
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You may use env variables `LD_PRELOAD` and `FAKERAND` along with a command:
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```
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LD_PRELOAD=./target/release/libfakerand.so FAKERAND=0 openssl rand -hex 16
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```
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Alternatively, set environment variables so that all programs running in that shell are effected:
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```
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export LD_PRELOAD=/usr/lib/fakerand/fakerand.so
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export FAKERAND=42
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```
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If you will be using it this way, it may make sense to place the .so file in `/usr/lib/fakerand`
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## Notes
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Statically linked libraries can't be overriden by `LD_PRELOAD`. For
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this reason, `libfakerand` can't override cases such as:
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```
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FAKERAND=42 LD_PRELOAD=./target/release/libfakerand.so awk 'BEGIN{srand(); print rand()}' 2>/dev/null
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```
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This is because `awk` is statically linked.
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