![]() The key file and the directory access should be limited to the site user for security reasons. The key should be created on the monitoring server and put in a save directory below site user home directory. How to create a private key with OPENSSL and extract the public key is meanwhile public knowledge and I dont want to explain it here again. On the monitoring server the secret is then decrypted with the private key and used to decrypt the content. The secret will be then encrypted with the public key and both, the symmetric encrypted content and the asymmetric encrypted secret is then sent to the monitoring server. As we cannot create infinite long key´s we need to go a little detour which at the end use again symmetric encryption for the content but in a very secure way.Īs a first step we create on the agent side a random secret which we use to do the symmetric encryption of the content. With OPENSSL it is not possible to encrypt a content which length is longer than the length of the key used for encryption. There are tons of articles about this subject in the internet available and everybody could make his own choice. It is not the final conclusion about securing the agent and I also don’t want to discuss what are the best ciphers to be used for encryption or what is the best key length. This article just show a concept how OPENSSL could be used to asymmetric encryption of the agent content. Nevertheless II provide here a secure solution using OPENSSL to encrypt agent output. Unjustly GPG has a bad reputation and is called complex and complicated, which is not really the case in my opinion. Please share if you liked it.I already wrote a How-To Article about asymmetric agent encryption with GNU GPG here: Asymmetric agent encryption with GNU PGP. Thanks to the OpenSSL development team for producing such a handy tool. Refer to the list of ciphers to see exactly what is available, but bear in mind that CBC mode is considered to be better. Regarding AES, if you wish to use ECB mode with it instead, use -aes-256-ecb rather than -aes-256-cbc in the example. There are modes other than CBC mode available for your encryption purposes, such as ECB mode. The mode (the algorithms mode of operation) we chose to use above was CBC (cipher block chaining) mode. Unfortunately twofish is not yet available in the list of openssl ciphers. Blowfish is still a good algorithm but its author (Bruce Schneier) recommends that you should use the "twofish" algorithm instead if available. Cipher StrengthĪES and Triple DES are considered to be strong. #OPENSSL ENCRYPTO PASSWORD#You'll be prompted to enter the password you used when encrypting the file. To then decrypt myfile.enc, run: openssl enc -d -bf-cbc -in myfile.enc -out myfile.txt To encrypt a file called myfile.txt using Blowfish in CBC mode, run: openssl enc -bf-cbc -salt -in myfile.txt -out myfile.enc Simple Encryption/Decryption using Blowfish To then decrypt myfile.enc, run: openssl enc -d -des-ede3-cbc -in myfile.enc -out myfile.txt This will prompt you for a password, then create the encrypted file myfile.enc (Again: use a strong password and don't forget it, as you'll need it for the decryption stage!). To encrypt a file called myfile.txt using Triple DES in CBC mode, run: openssl enc -des-ede3-cbc -salt -in myfile.txt -out myfile.enc Simple Encryption/Decryption using Triple DES Note that if you omit the "-out myfile.txt" part, the decrypted contents of your file get sent to standard output (so if your doing this on the command line, you'll see it displayed in front of you). To then decrypt myfile.enc, run: openssl enc -d -aes-256-cbc -in myfile.enc -out myfile.txt This will prompt you for a password, then create the encrypted file myfile.enc (NB: use a strong password and don't forget it, as you'll need it for the decryption stage!). To encrypt a file called myfile.txt using AES in CBC mode, run: openssl enc -aes-256-cbc -salt -in myfile.txt -out myfile.enc We'll show examples using AES, Triple DES, and Blowfish. The OpenSSL command line tool is installed as part of Ubuntu (and most other distributions) by default, you can see which ciphers are available for use via the command line use by running: openssl list-cipher-commands Simply put, a cipher is a particular algorithm used to encrypt and decrypt data. ![]()
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