git clone 'https://github.com/avodonosov/secure-random.git'
secure-random provides a cryptographically secure pseudo-random number generator (CSPRNG) for Common Lisp.
Example: (SECURE-RANDOM:NUMBER 10) ⇒ 9
We define an abstract interface for CSPRNG and provide a default implementation of that interface.
The library API. ~~~~~~~~~~~~~~~~
Class SECURE-RANDOM:GENERATOR. The base class for all the possible implementations of a secure random number generator.
Special variable SECURE-RANDOM:GENERATOR. Current value of the random number generator. Used as the default value for the library functions parameter GENERATOR.
Generic function BYTES (COUNT GENERATOR) ⇒ random bytes. The only generic function which needs to be implemented by a subclass of SECURE-RANDOM:GENERATOR. Generates COUNT cryptographically strong pseudo-random bytes using the random number generator GENERATOR. Returns the bytes as a SIMPLE-ARRAY with ELEMENT-TYPE '(UNSIGNED-BYTE 8). Signals an ERROR in case of problems (for example when the random number generator failed to initialize itself with enough entrophy).
Function NUMBER (LIMIT &optional (GENERATOR GENERATOR)) ⇒ random number. Returns a cryptographically strong pseudo-random number that is a non-negative number less than LIMIT and of the same type as LIMIT (in the current implementation, only INTEGER type is supporeted). LIMIT is a positive number. GENERATOR is an instance of a subclass of the SECURE-RANDOM:GENERATOR. Signals an ERROR in case of problems (for example when the random number generator failed to initialize itself with enough entrophy).
Implementation notes. ~~~~~~~~~~~~~~~~~~~~~
The default implementation uses OpenSSL random number generator (via cl+ssl library). We started from the OpenSSL usage because it's the simplest way.
Implementation of a pure Common Lisp CSPRNG is desirable, but it would require to write much more code. The problem is not in the CSPRNG algorithms themself, which are relatively simple (just read for example the Wikipedia article, and use Ironclad for the required building blocks). But the problem is in initialization of CSPRNG. Any CSPRNG needs to be initialized by some unguessable value. OpenSSL can gather the initial value from a platform specific service (/dev/random on Unix'es where it present, Windows Crypto API, Entropy Gathering Daemon, etc.). The pure Lisp CSPRNG library would need to re-implement all this code for gathering a truly unguessable initial value.
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