crytto 0.7.2

An OpenSSL-based file encryption and decryption utility

filecrypt - OpenSSL file encryption

Author M. Massenzio

---

Version 0.7.2 Updated 2020-04-30 Code bitbucket.org

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.

installation

Install directly from PyPi:

pip install crytto

Please note the package name (filecrypt was conflicting with the existing FileCrypt package name, and crypto was already taken).

This requires OpenSSL to be installed on your machine:

sudo apt-get install openssl

Alternatively, clone the project from github and follow the instructions below:

git clone [e-mail]:marco/filecrypt.git

Once cloned, you can try out functionality by packaging it as a self-contained executable: use the package.sh script to generate a filecrypt.pyz self-extracting executable (make sure to set the x permission on *nix systems) and then you can encrypt/decrpyt files (see the configuration section first).

```shell script # To encrypt ./filecrypt.pyz -o test.enc /path/to/my_plaintext.txt

To decrypt:

./filecrypt.pyz -d -o /path/to/whatever.txt test.enc ```

Once all dependencies are installed:

pip install -r requirements.txt

tests can be run via:

./run_tests.sh

See both the run_tests and package scripts for examples of how to use encryption/decryption.

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

##
# Any option below is optional and can be omitted.
#
# Where to store the encrypted file; the folder MUST already exist and the user
# have write permissions.  Defaults to the current directory; can be overridden
# using --out on the command line.
#
#out: /data/store/file

# Whether to securely delete the original plaintext file; by default it is kept.
# It can be overridden by using `--keep` when running `filecrypt`.  True by default.
shred: true

# Optional logging configuration - mostly useful to
# diagnose issues.  Default is WARN level.
logging:
   format: "%(asctime)s [%(levelname)-5s] %(message)s"
   level: WARN

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:

filecrypt my_secret.txt

which will create a my_secret.txt.enc file in the current directory, unless a different one has been specified using the out option in /etc/filecrypt/conf.yml.

A completely random and cryptographically secure key will have been created; used; and then encrypted to the secrets location, its full path stored in the CSV keystore named in the store option of the YAML configuration file.

Finally, the plaintext version of this key will have been safely destroyed.

A more elaborate one (see the example configuration in examples/example_conf.yaml):

filecrypt --conf example_conf.yaml -s secret-key.enc plaintext.txt

will create an encrypted copy of the file to be stored as /data/store/plaintext.txt.enc; the original file will not be securely destroyed (using shred); and the encryption key name and location (the current directory, and secret-key.enc) to be stored in the keys.csv file:

# Fragment of example_conf.yaml
...
store: keys.csv
out: /data/store
shred: false

Specifying the encryption destination

By default, the encrypted filename has the same name as the plaintext file, with the .enc extension appended; and it is saved to either the current directory or the out location specified in the configuration YAML.

By using the --out (-o) option, it is possible to specify the location of the output encrypted file, either absolute, or relative to the current directory:

filecrypt -o mysecret.ser my_secret.doc

or:

filecrypt -o secret/files/mysecret.ser my_secret.doc

Regardless of the means of specifying the input/outpup files, the full path to both files will always be used in the CSV keystore, 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, use the -d flag:

decrypt -o example_conf.yaml -d plaintext.txt

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 only the filename is used to lookup the key and so two encrypted filenames in different directories but with the same name will be assumed to have been encrypted with the same passphrase.

The passphrase file, is stored with its full path: if you move the keys, or rename any of the folder in their path, you will have to update the keystore (or use the -s flag when decrypting).

As with encryption, the --out flag can be used to specify the output file; otherwise, the current directory will be used.

The encrypted file will be left untouched: the --keep flag may be used, but will have no effect and the value of the shred: option will be ignored.

As the encrypted file is already cryptographically secure a simple rm my_secret.doc.enc will be sufficient to guarantee privacy.

sharing files

As of 0.5.x, crytto supports encrypting a file using solely a Public Key, and then the resulting ecnrypted file can be securely decrypted by the owner of the Secret Key.

The main use case is to enable Alice to send Bob an encrypted file, once Bob has given her a copy of his Public key; call the latter bob.pub and the file to share my_secret.txt, then Alice can execute:

filecrypt --send --key bob.pub --out my-secret.ser my_secret.txt

after encryption, in the current directory there will be the following two new files:

my-secret.ser
pass-key-000854.enc

the former is the encrypted contents of my_secret.txt and the latter the encrypted passphrase (leaving out the --out argument would have made the encrypted file's name my_secret.txt.enc).

Those files can be both sent to Bob or, even better, provided to him separately for added security; either way, upon receiving them, Bob can run the following (we assume the bob.pub was the private half of the configured key pair that he keeps in his configuration file):

filecrypt -s pass-key-000854.enc --out alice_secret.txt -d my-secret.ser

(again, leaving out the --out is useful when using the defaults, as the my_secret.txt.enc would have turned back into my_secret.txt -- in this case, the plaintext decrypted file would have been called my-secret.ser.out).

references

• a detailed HOW-TO with the steps to encrypt a file manually;
• the original Ask Ubuntu post;
• OpenSSL;
• Ubuntu guide to OpenSSL.