Portability

phpseclib doesn't require any extensions. For purposes of speed, OpenSSL, GMP or libsodium are used, if they're available, but they are not required.

Interoperability

phpseclib is designed to be fully interoperable with standardized cryptography libraries and protocols.

Long-term support

Don't have PHP 8.1+? Try phpseclib 3.0 (PHP 5.6+), phpseclib 2.0 (PHP 5.3+) or phpseclib 1.0 (PHP 4.4+).