pogcli 0.1.4

File encryption and backup utility

Pretty Ok Gncryption

• File encryption and backups!
• Uses nacl.SecretBox and zstandard!
• Chunks up large files!
• Can be used to generate encrypted archives locally, or as a backup tool that pushes to cloud storage providers. (s3, b2, ...tbd)
• There is a GUI: pogui.

This tool is built around symmetric encryption -- specifically libsodium's crypto_secretbox, which is XSalsa20+Poly1305. Doing asymmetric PGP-like things is not in the cards -- but there is an experimental use case using asymmetric crypto that will likely be supported.

• Still in beta!
• Don't rely on this to keep your government leaks secret!

Installation

Use pip:

pip install pogcli

or from source,

python setup.py build
python setup.py install

Usage

Credentials

• Pog does not manage cloud storage credentials -- it asks that you configure your environment with API keys before use.
  • To validate s3 credentials:
    • awscli ls <bucket_name>
  • To validate b2 credentials:
    • b2 ls <bucket_name>

Using a password or keyfiles

1. symmetric keyfile
   • any file can be used as a keyfile.
   • the contents of the keyfile will be hashed, and that hash will become the cryptographic key
   • cryptographic randomness (ex: 1024 bytes from /dev/urandom) is recommended
2. asymmetric keyfiles
   • the pog-create-keypair script will generate an "encrypt" and "decrypt" keypair.
   • encrypt is used for creating archives
   • decrypt is used for extracting them
3. Password entry
   • if no keyfiles are specified, Pog supports password entry for creating or reading archives

Creating cloud archives and backups

• Consider an S3 backup:

pog /home/user/my_file.txt --keyfile=/home/user/secret.keyfile --save-to=s3://my-bucket --store-absolute-paths

This does a few things:

1. my_file.txt is encrypted with secret.keyfile. If the file is sufficiently large, it is split into multiple pieces during encryption.
2. The encrypted contents ("blob") of my_file.txt is saved to the s3 bucket my-bucket, under the top-level data/ subdirectory.
3. An encrypted "manifest" file is created, named according to the time the archive was created. This manifest file acts as an index from filenames (/home/user/my_file) to one or more encrypted blobs. a. The --store-absolute-paths flag tells the manifest to resolve ambiguous paths with the absolute path (/home/user/my_file) instead of the relative path (my_file). This can be useful to have when extracting archives or backups.
4. The manifest file is also saved to my-bucket in s3.

---

• Here is another example, with a series of directories:

pog /opt/games /opt/apps /opt/music --encryption-keyfile=secret.encrypt --save-to=s3://my-bucket,b2://my-b2-bucket

• This will recursively go through those 3 directories, gathering up all files and saving the encrypted blobs to both s3 and b2.

The command line help (pog -h) shows other useful examples.

Creating local archives

• It is also possible to use Pog to encrypt a single file.

pog /home/myfile.original > outputs.txt

• and to decrypt:

pog --decrypt $(cat outputs.txt) > myfile.copy

Reading archives and backups

For a given manifest file (2020-01-23T12:34:56.012345.mfn), we can download and extract the archive like so:

pog --decrypt s3:/my-bucket/2020-01-23T12:34:56.012345.mfn --keyfile=/home/user/secret.keyfile

• The --decrypt flag should be specified for read+decrypt -- the default behavior is to write+encrypt.
• If a --decryption-keyfile is provided, --decrypt is assumed.
• If a local manifest file is provided, it is assumed that the data blobs are already downloaded into the working directory.

Algorithm

• files are compressed with zstandard, and split ("chunked") into blobs. The default chunk size is 50MB.

• blob contents are encrypted with crypto_secretbox. The key is 256 bits, independent per-blob, and stored in the blob header.

• the blob header is encrypted in one of 3 ways:

  • crypto_secretbox with key=sha256(argon2.ID with time_cost=8, memory_cost=102400, parallelism=8, hash_len=32)
    • this is what is used when you get a password prompt
  • crypto_secretbox with key=sha256(keyfile contents)
    • this is what the --keyfile option does
  • crypto_sealedbox with an X25519 key pair
    • this is what --decryption-keyfile and --encryption-keyfile do
    • an X25519 key pair can be generated with pog-create-keypair.

• the file->blob relationship is stored in an encrypted manifest file (.mfn), which also stores file metadata -- e.g. last modified time.

  • the .mfn can be thought of as the dictionary for the archive.
  • blobs can be decrypted without the manifest, IF the blob order is correct. However, only the file contents are stored in the blobs. The original file name and file metadata will not survive the trip.

• blobs are named by urlsafe base64(sha256(sha256(secret) + sha256(content)). The "secret" is derived from the encryption key.

  • the goal is to pseudo-randomize the names of the blobs, while still keeping them consistent for backups run with the same key.
  • we want to "leak" the content hash only to the extent it's necessary to save work on successive backups (e.g. "I don't need to reupload blob X, it already exists")
  • because we use the content hash for this purpose, we can achieve some amount of file de-duplication.

Disclaimer

I'm a not a cryptographer, just an engineer with internet access.