crytto 0.2.0

An OpenSSL-based file encryption and decryption utility

filecrypt - OpenSSL file encryption

Author	M. Massenzio
Version	0.2.0
Updated	2016-09-11

overview

Uses OpenSSL library to encrypt a file using a private/public key pair and a one-time secret.

A full description of the process can be found here.

See also this blog entry for more details.

configuration

This uses a YAML file to describe the configuration; by default it assumes it is in /etc/filecrypt/conf.yml but its location can be specified using the -f flag.

The structure of the conf.yml file is as follows:

keys:
     private: sample.pem
     public: sample.pub
     secrets: .

store: keys.csv

# Where to store the encrypted file; the folder MUST already exist and the user
# have write permissions.
#out: /data/store/file

# Whether to securely delete the original plaintext file.
shred: true

logging:
   format: "%(asctime)s [%(levelname)-5s] %(message)s"
   level: DEBUG

The private/public keys are a key-pair generated using the openssl genrsa command; the encryption key used to actually encrypt the file will be created in the secrets folder, and afterward encrypted using the public key and stored in the location provided.

The name will be pass-key-nnnn.enc, where nnnn will be a random value between 1000 and 9999, that has not been already used for a file in that folder.

The name of the secret passphrase can also be defined by the user, using the --secret option (it will be left unmodified):

• if it does not exist a random secure one will be created, used for encryption, then encrypted and saved with the given path, while the plain-text temporary version securely destroyed; OR

• if it is the name of an already existing file, it will be decrypted, used to encrypt the file, then left unchanged on disk.

NOTE we recommend NOT to re-use encryption passphrases, but always generate a new secret.

NOTE it is currently not possible to specify a plain-text passphrase: we always assume that the given file has been encrypted using the private key.

The store file is a CSV list of:

"Original archive","Encryption key","Encrypted archive"
201511_data.tar.gz,/opt/store/pass-key-001.enc,201511_data.tar.gz.enc

a new line will be appended at the end; any comments will be left unchanged.

usage

keypair generation

We do not provide the means to generate them (this will be done at a later stage), but for now they can be generated using:

openssl genrsa -out ./key.pem 2048
openssl rsa -in key.pem -out key.pub -outform PEM -pubout

their path can then be specified in the conf.yaml file.

encryption

Always use the --help option to see the most up-to-date options available; anyway, the basic usage is (see the example configuration in examples/example_conf.yaml):

python3 main.py -f example_conf.yaml -s secret-key.enc plaintext.txt

will create an encrypted copy of the file to be stored as /data/store/201511_data.tar.gz.enc, the original file will not be securely destroyed (using shred) and the new encryption key to be stored, encrypted in /opt/store/pass-key-778.enc.

A new line will be appended to keys.csv:

/.../filecrypt/examples/plaintext.txt,secret-key.enc,/.../filecrypt/examples/plaintext.txt.enc

the full path to both files will always be used, regardless of whether a relative or absolute path was specified on the command line.

IMPORTANT >We recommend testing your configuration and command-line options on test files: shred erases files in a terminal way that is not recoverable: if you mess up, you will lose data. > >You have been warned.

decryption

To decrypt a file that has been encrypted using this utility, just run virtually the same command, but add the -d flag: we will automatically append the .enc extension to the file name given, and decrypt it using the passed in secret key (-s flag):

python3 main.py -f example_conf.yaml -s secret-key.enc -d plaintext.txt

NOTE > Use the name of the plaintext file, even if it does not currently exists: the encrypted file (which should obviously exist) will be assumed to be the same with a .enc trailing extension (in the case of the example above, it will look for plaintext.txt.enc in the current directory).

If the encryption key (--secret or -s) is not specified, then the application will try and locate the plaintext file in the keystore specified in the conf.yaml using the store key:

store: keys.csv
...

and derive the location of the encryption key from the entry, if one is found.

Please note that the full absolute path must match even if only a relative path was given at the command line, as files are always stored with their full path when saved to the key store.

references

• a detailed HOW-TO with the steps to encrypt a file manually;

• the original Ask Ubuntu post;

• OpenSSL;

• Ubuntu guide to OpenSSL.