OpenSSL:
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> File Encryption:
openssl enc -aes-256-cbc -salt -in file.input -out file.enc

> File Decryption:
openssl enc -d -aes-256-cbc -in file.enc -out file.output

> Hash Function (checksum):
SHA512: "sha512sum FILE"

> Generate a private key:
openssl genrsa -aes256 -out private.key 4096

> Get Public Key:
openssl rsa -in private.key -pubout -out public.key

> Encrypt a file using PUBLIC KEY:
openssl pkeyutl -encrypt -in test.txt -out test.txt.enc -pubin -inkey keys/public.key

> Decrypt a file using PRIVATE KEY:
openssl pkeyutl -decrypt -in test.txt.enc -out test.txt -inkey keys/private.key

> Digital Signature: (sign a file and produce separate signature):
openssl dgst -sha256 -sign keys/private.key -out signature.sha256 test.txt

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

> View Certificate Details:
openssl x509 -in cert.pem -text -noout