OpenSSL

openssl aes-256-cbc -in 123.txt -out encrypted_123

openssl aes-256-cbc -d -in encrypted_123 -out abc.txt

openssl genrsa -out private.key 2048

openssl req -new -key private.key -out certificate.csr

openssl req -x509 -nodes -days 365 -newkey rsa:2048 -keyout private.key -out certificate.crt

openssl x509 -in certificate.crt -text -noout

openssl x509 -noout -modulus -in certificate.crt | openssl md5
openssl rsa -noout -modulus -in private.key | openssl md5

openssl md5 filename

openssl sha256 filename

openssl s_client -connect example.com:443

openssl s_client -connect example.com:443 -showcerts