Cryptographically secure pseudo-random number generator for Common Lisp

secure-random

Overview.
~~~~~~~~~

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.

Contact.
~~~~~~~~

Send questions or comments to avodonosov@yandex.ru


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