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openssl

Introduction​

This cheat sheet provides a quick reference for some common openssl commands and concepts. openssl is a versatile open-source tool for working with SSL/TLS certificates, cryptography, and secure communication.

openssl Concepts​

Generating RSA Key Pairs​

You can use openssl to generate RSA key pairs for various cryptographic operations.

  • Generate an RSA private key:

    openssl genpkey -algorithm RSA -out private-key.pem

  • Extract the public key from the private key:

    openssl rsa -pubout -in private-key.pem -out public-key.pem

Creating Self-Signed Certificates​

openssl can create self-signed SSL/TLS certificates for testing and development.

  • Generate a self-signed certificate:
    openssl req -x509 -newkey rsa:4096 -keyout key.pem -out cert.pem -days 365

Certificate Signing Requests (CSR)​

You can create certificate signing requests for obtaining certificates from certificate authorities.

  • Generate a CSR and private key:
    openssl req -newkey rsa:2048 -nodes -keyout myserver.key -out myserver.csr

Certificate Verification​

openssl can be used to verify certificates.

  • Verify a certificate against a CA certificate:
    openssl verify -CAfile ca-cert.pem server-cert.pem

Encrypting and Decrypting​

openssl can encrypt and decrypt files and data.

  • Encrypt a file using AES:

    openssl enc -aes-256-cbc -salt -in plaintext.txt -out encrypted.txt

  • Decrypt an AES-encrypted file:

    openssl enc -d -aes-256-cbc -in encrypted.txt -out decrypted.txt

openssl Command-Line​

  • Generate an RSA private key:

    openssl genpkey -algorithm RSA -out private-key.pem

  • Extract the public key from the private key:

    openssl rsa -pubout -in private-key.pem -out public-key.pem

  • Generate a self-signed certificate:

    openssl req -x509 -newkey rsa:4096 -keyout key.pem -out cert.pem -days 365

  • Generate a CSR and private key:

    openssl req -newkey rsa:2048 -nodes -keyout myserver.key -out myserver.csr

  • Verify a certificate against a CA certificate:

    openssl verify -CAfile ca-cert.pem server-cert.pem

  • Encrypt a file using AES:

    openssl enc -aes-256-cbc -salt -in plaintext.txt -out encrypted.txt

  • Decrypt an AES-encrypted file:

    openssl enc -d -aes-256-cbc -in encrypted.txt -out decrypted.txt

Conclusion​

This cheat sheet covers some common openssl commands and concepts. openssl is a powerful tool for working with SSL/TLS certificates, cryptography, and secure communication, making it essential for system administrators, developers, and security professionals; refer to the official openssl documentation for more in-depth information and advanced usage.