big_int library provides a set of functions for calculations with arbitrary length integers and bitsets

Functions from this package are useful for number theory
applications. For example, in two-keys cryptography.

See /tests/RSA.php in the package for example of simple
implementation of RSA-like cryptoalgorithm.
See http://pear.php.net/packages/Crypt_RSA/ project for
more complex implementation of RSA-like crypto, which
supports key generating, encrypting/decrypting, generating
and validating of digital sign.

The package has many bitset functions, which allow to work
with arbitrary length bitsets.

This package is much faster than bundled into PHP BCMath
and consists almost all functions, which are implemented
in PHP GMP extension, but it needn't any external libraries.