OpenSSL

see dates for cert.pem

openssl x509 -dates -noout -in /path/to/the/cert.pem
notBefore=Feb  1 00:37:22 2021 GMT
notAfter=May  2 00:37:22 2021 GMT

check cert for website

openssl s_client -connect <ServerName>:<port> -servername <ServerName> 2> /dev/null | openssl x509 -noout -dates

see info about a certificate

openssl s_client -connect <hostname>:<port> -showcerts

Create .rsa and .crt from pfx

Generate a .rsa from a .pfx

openssl pkcs12 -in monCertificat.pfx -nocerts -nodes -out  monCertificat.rsa

Generate a .crt from a .pfx

openssl pkcs12 -in monCertificat.pfx -clcerts -nokeys -out monCertificat.crt

Openssl encrypt

We can encrypt a file using OpenSSL using the following command:

openssl aes-256-cbc -e -in message.txt -out encrypted_message

We can decrypt the resulting file using the following command:

openssl aes-256-cbc -d -in encrypted_message -out original_message.txt

To make the encryption more secure and resilient against brute-force attacks, we can add -pbkdf2 to use the Password-Based Key Derivation Function 2 (PBKDF2); moreover, we can specify the number of iterations on the password to derive the encryption key using -iter NUMBER. To iterate 10,000 times, the previous command would become:

openssl aes-256-cbc -pbkdf2 -iter 10000 -e -in message.txt -out encrypted_message

Consequently, the decryption command becomes:

openssl aes-256-cbc -pbkdf2 -iter 10000 -d -in encrypted_message -out original_message.txt

In the following questions, we will use gpg and openssl on the AttackBox to carry out symmetric encryption.

GPG

We can encrypt a file using GnuPG (GPG) using the following command:

gpg --symmetric --cipher-algo CIPHER message.txt, where CIPHER is the name of the encryption algorithm. You can check supported ciphers using the command gpg --version. The encrypted file will be saved as message.txt.gpg.

The default output is in the binary OpenPGP format; however, if you prefer to create an ASCII armoured output, which can be opened in any text editor, you should add the option --armor. For example, gpg --armor --symmetric --cipher-algo CIPHER message.txt.

You can decrypt using the following command:

gpg --output original_message.txt --decrypt message.gpg

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