Secure Box is an add-on application that offers additional commands for terminal applications.
Package includes secure shell commands (client key management file transfer agent daemon) and
commands for management of keys X.509 certificates digests and etc.
Note "Pro" version is full functional with integrated terminal and user interface than allows you easily to manage secure shell sessions and parameters.

The Secure Shell (SSH) is a protocol for secure remote login and other secure network services over an insecure network.
It is intended to provide secure encrypted communications between two untrusted hosts over an insecure network.

Secure shell commands are port of PKIX-SSH (feature richest ssh implementation in the world) to Android platform.
PKIX-SSH offers widest range of supported key algorithms chippers macs for secure shell protocol.
For instance supported public key algorithms include X.509 certificate based keys:
Ed25519 : x509v3-ssh-ed25519
EC : x509v3-ecdsa-sha2-nistp256 x509v3-ecdsa-sha2-nistp384 x509v3-ecdsa-sha2-nistp521
RSA : x509v3-rsa2048-sha256 x509v3-ssh-rsa x509v3-sign-rsa
DSA : x509v3-ssh-dss x509v3-sign-dss
as well public key algorithms based on plan public keys:
EC : ecdsa-sha2-nistp256 ecdsa-sha2-nistp384 ecdsa-sha2-nistp521
RSA : ssh-rsa rsa-sha2-256 rsa-sha2-512
Ed25519 : ssh-ed25519
DSA : ssh-dss
Client and server support extension negotiation mechanism used in adaptive public key algorithm selection.

Auxiliary commands for management of keys X.509 certificates digests and etc are provided by OpenSSL command line tool.
This list of commands includes but not limited to
key management commands like genpkey and pkey ec and ecparam rsa dsa and dsaparam
commands for operation with keys - pkeyutl
commands for key data management - pkcs12 pkcs8 and pkcs7
commands for management of X.509 certificates revocation list and authorities - x509 crl and ca
time stamping authority tool - ts.

The complete list of commands including manual pages is available on application web-site.