Secure Box is an add-on application that offers additional commands for terminal applications (1)(2)(3).
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 parameteres.

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:
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 ec and ecparam rsa dsa and dsaparam genpkey and pkey
commands for management of X.509 certificates revocation list and authorities - x509 crl and ca
commands for key data management - pkcs12 pkcs8 and pkcs7
commands for operation will keys - pkeyutl
time stamping authority tool - ts.

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

Notes:
(1) Application is best integrated with terminal "TermOne Plus".
(2) Starting with Android 9.0 (Pie) SELinux permission are hardened and do not allow any more one application to share its file system tree. This prevent SecureBox to "export" packaged binaries for use by other applications. As work-around "TermOne Plus" (3.1) and SecureBox (2.1) start to "share user id". This is incompatible modification that requires reinstall of application. Another side effect is that terminal application have full access to SecureBox binaries and configuration files!
(3) Android 10.0 does not allow execution from "writable" directories. SecureBox 2.2 offers new packaging model suitable for Android 10.0. Also new packgind model requires respective support from terminal application - added in "TermOne Plus" 3.2.