7.7K
KEOpenSSL is an open-source cryptography toolkit that handles SSL/TLS protocols, certificate management, encryption, and hashing. It comes pre-installed on virtually every Linux and macOS system, and it's the backbone of most secure communication on the internet.
These 7 commands cover the scenarios you'll actually run into:
openssl s_client -connect host:443 :
Opens a raw TLS connection and prints the full handshake: certificate chain, cipher suite, TLS version and verify result. Use it to debug SSL misconfigs or inspect what a server actually presents.
openssl x509 -in cert.pem -text -noout :
Decodes and prints every field of a certificate in human-readable form: subject, issuer, validity dates, SANs and key usage.
openssl x509 -enddate -noout -in cert.pem :
Pulls the expiry date from any PEM certificate. Combine with shell date arithmetic to get remaining days before a cert catches you off guard.
openssl genrsa -out key.pem 2048 :
Generates an RSA private key. Always the first step before creating a CSR or self-signed certificate.
openssl req -new -x509 -key key.pem -out cert.pem -days 365 :
Creates a self-signed certificate in one command. No CA needed. Perfect for local development and internal tools.
openssl enc -aes-256-cbc -pbkdf2 -in file -out file.enc :
Encrypts any file with AES-256. Always include -pbkdf2 for secure key derivation. Reverse with -d to decrypt.
openssl pkcs12 -export -in cert.pem -inkey key.pem -out bundle.p12 :
Bundles a certificate and private key into a single password-protected .p12 file. Required for servers and load balancers that expect PKCS12 format.
Whether you're a developer setting up HTTPS, a security engineer auditing a server, or a sysadmin managing certificates, OpenSSL is the one tool that's always there when you need it.
Bookmark this one, you'll come back to it
#openssl #cybersecurity #infosec #linux #networksecurity
@kerem.tech
