Cryptography with OpenSSL

We can use OpenSSL to do a several operations related with cryptography. The command below are the most commons options.

Symmetric-key Encryption

# List all Ciphers commands and algorithms
openssl list -cipher-commands
openssl list -cipher-algorithms


# AES encryption
openssl aes-256-cbc -in inseguro.txt -out seguro_aes.txt -pass pass:minhasenha

# AES decryption
openssl aes-256-cbc -d -in seguro_aes.txt -out novo.txt

Asymmetric-key Encryption

# Generate private key
openssl genrsa -out priv.pem 1024 
# openssl rsa -in priv.pem -text -noout

# Generate public key
openssl rsa -in priv.pem -pubout -out pub.pem
# openssl rsa -in pub.pem -pubin -text -noout

# Encrypt
openssl rsautl -encrypt -inkey pub.pem -pubin -in inseguro.txt -out seguro_rsa.enc

# Decrypt
openssl rsautl -decrypt -inkey priv.pem -in seguro_rsa.enc > novo_rsa.txt

Digital signature

# Signing
cat text.txt | openssl dgst -sha256 | cut -f 2 -d " " > soma.txt
openssl pkeyutl -sign -inkey priv.pem -in soma.txt | openssl enc -base64 > sign.base64

# Verify signature
cat text.txt | openssl dgst -sha256 | cut -f 2 -d " " > soma.txt
cat sign.base64 | openssl enc -base64 -d > text.sig
openssl pkeyutl -verify -pubin -inkey pub.pem -sigfile text.sig -in soma.txt

PKCS#10 X.509 Certificate Signing Request (CSR) Management

openssl req -x509 -newkey rsa:2048 -keyout private_key.pem -out public_cert.pem -days 365

SSH RSA Keys (Asymmetric)

# Generate public and private keys
ssh-keygen -t rsa -b 2048

# Copy public key to remote host
ssh-copy-id myuser@host.remote

# Backup the publics keys then concatenate with your public key on remote host
cp authorized_keys authorized_keys.bkp
cat id_rsa.pub >> authorized_keys

# Use other private key on ssh
ssh -i /path/to/private/key myuser@host