Install php-phpseclib by entering the following commands in the terminal:
sudo apt update sudo apt install php-phpseclib
Description:
implementations of an arbitrary-precision integer arithmetic library
The PHP Secure Communications Library are fully PKCS#1 (v2.1) compliant RSA, DES, 3DES, RC4, Rijndael, AES, Blowfish, Twofish, SSH-1, SSH-2, SFTP, and X.509 implementations.
Homepage: http://phpseclib.sourceforge.net/
Version: 2.0.9-1
Section: universe/php