replicat 1.4.1

Configurable and lightweight backup utility with deduplication and encryption.

[ ˈrɛplɪkət ]

Replicat

Configurable and lightweight backup utility with deduplication and encryption.

Compatibility

Python 3.8 (or newer) running on Linux, MacOS, or Windows.

Supported backup destinations

• local path
• Backblaze B2
• Amazon S3
• any S3-compatible service

You can implement and use your own adapter for pretty much any backup destination without changing the source code of Replicat (more on that later).

Installation

It's available on PyPI, so

pip install replicat

Reasoning

For various reasons, I wasn't entirely happy with any of the similar projects that I've tried.

Highlights/goals of Replicat:

• efficient, concise, easily auditable implementation
• high customisability
• few external dependencies
• well-documented behaviour
• unified repository layout
• API that exists

This project borrows a few ideas from those other projects, but not enough to be considered a copycat.

Basics

You can use Replicat to backup files from your machine to a repository, located on a backend such as a local directory or cloud storage (like Backblaze B2). Your files are transfered and stored in an optionally encrypted and chunked form, and references to chunks (i.e. their hash digests) are stored in snapshots along with file name and metadata. You can create, list, and delete snapshots, and, of course, restore original files from snapshots.

Replicat supports two types of repositories: encrypted (the default) and unencrypted. You may want to disable encryption if you trust your backend provider and network, for example.

Chunks, snapshots, and all other pieces of data inside unencrypted repositories are stored unencrypted.

In case of encrypted repositories, Replicat will use symmetric encryption to encrypt chunks and snapshots. In order to use encryption, you will need to choose a password and generate the key associated with that password (Replicat can do it for you). You'll need both the password and the matching key to unlock the repository, but how or where you're going to store them is up to you.

Actually, you can create multiple keys with different passwords and maybe share those with other people. If you ask Replicat to create a "shared" key, it will copy some of the secrets from your key to the new key, so that you and the owner of the new key could use deduplication features together, meaning data uploaded by you could be reused (referenced and decrypted) by the other person. That other person will also be able to create "shared" keys by copying secrets that were originally copied to their key from your key, and so on. This creates a web of trust of sorts. If any of this is not desirable, you can create "independent" keys.

Names of files, file timestamps, and other file metadata within snapshots are encrypted using a secret that never gets copied to other keys. That is, if you create a snapshot, owners of shared keys will be able to see it, but there will be no available information about it beyond its storage name and the table of chunk references (still, they might still be able to check whether you have ever uploaded a specific piece of data - that's what enables shared deduplication). No data will be accessible if a snapshot was created using an independent key.

High-level technical details

The key is a JSON object that contains parameters for the KDF, which will be used to derive user key from the password, and a private encrypted section, which can only be decrypted by the owner of the key and the matching password (i.e., it's encrypted and decrypted using the previously derived user key). The encrypted section contains secrets for the cryptographic primitives that control how the data is split into chunks, visibility of chunks of data, and more.

The storage names for chunks and snapshots in unencrypted repositories are simply the hash digests of their contents. For encrypted repositories, the storage name for the chunk is derived from the hash digest of its contents and one of the aforementioned secrets, in order to reduce the chance of successful "confirmation of file" attacks. The chunk itself is encrypted with the combination of the hash digest of its contents and another one of those secrets, since the usual convergent encryption is vulnerable to that same "confirmation of file" attack. Note that that these secrets get copied to shared keys in order to support shared deduplication. Table of chunk references in a snapshot also gets encrypted in a way that lets owners of shared keys to decrypt it. This helps Replicat to identify which chunks are still referenced by snapshots and which can be garbage collected.

Extremely cool, colorful, in-depth diagrams that I worked really hard on

Glossary:

• Encrypt(data, key)/Decrypt(data, key) - encrypts/decrypts data with the encryption key key using an authenticated encryption algorithm. It's normally used to encrypt/decrypt private sections in keys, as well as chunks and snapshots.

• Hash(data) - computes the hash digest of data using a hashing algorithm. It's used to check integrity of data and to derive encryption keys for chunks and snapshots.

• Mac(data, key) - computes the message authentication code for data using suitable key and a MAC algorithm. It's mainly used to verify ownership of chunks.

• SlowKdf(ikm, salt[, context])/FastKdf(ikm, salt[, context]) - calls a "slow"/"fast" key derivation function to obtain an encryption key from ikm using salt and an optional context. As a general rule, replicat uses "slow" KDF for low-entropy inputs and "fast" KDF for high-entropy inputs. The output length will match the encryption key length of the chosen encryption algorithm.

• UserKey - encryption key derived as SlowKdf(Password, UserKdfParams), where Password is the user's password and UserKdfParams is the salt. UserKey is used to encrypt sensitive personal data: private sections in keys and file metadata in snapshots.

• SharedKey, SharedKdfParams, SharedMacKey, SharedChunkerKey - secrets stored in the private sections of keys. SharedKey and SharedKdfParams are used to derive encryption keys using "fast" KDF (they will encrypt shared data, like chunks and chunk references). SharedMacKey is the MAC key. SharedChunkerKey personalises content-defined chunking (CDC) to prevent watermarking attacks.

• GetChunkLocation(name, authentication_tag)/GetSnapshotLocation(name, authentication_tag) - obtains the location for a chunk/snapshot using its name and the corresponding authentication tag.

• Upload(data, location) - uploads data to the backend to the given location.

• Download(location) - downloads data from the backend at the given location.

Command line interface

The installer will create the replicat command (same as python -m replicat). There are several available subcommands:

• init - initialises the repository using the provided settings
• snapshot - creates a new snapshot in the repository
• list-snapshots/ls - lists snapshots
• list-files/lf - lists files across snapshots
• restore - restores files from snapshots
• add-key - creates a new key for the encrypted repository
• delete - deletes snapshots by their names
• clean - performs garbage collection
• upload-objects - uploads objects to the backend (a low-level command)
• download-objects - downloads objects from the backend (a low-level command)
• list-objects - lists objects at the backend (a low-level command)
• delete-objects - deletes objects from the backend (a low-level command)

⚠️ WARNING: commands that read from or upload to the repository can safely be run concurrently; however, there are presently no guards in place that would make it safe for you to run destructive actions (delete, clean) concurrently with those actions unless you use independent keys (see the explanation above). I do plan to implement them soon-ish, but in the meantime DO NOT use shared keys (or, naturally, the same key) to snapshot and clean at the same time, for example.

As far as the upcoming implementation of such guards, it'll be based on locks. I'm familiar with the lock-free deduplication strategy (like in Duplicacy), but I don't like it much.

There are several command line arguments that are common to all subcommands:

• -r/--repository - used to specify the type and location of the repository backend (backup destination). The format is <backend>:<connection string>, where <backend> is the short name of a Replicat-compatible backend and <connection string> is open to interpretation by the adapter for the selected backend. Examples: b2:bucket-name for the B2 backend or local:some/local/path for the local backend (or just some/local/path, since the <backend>: part can be omitted for local destinations). If the backend requires additional arguments, they will appear in the --help output. Refer to the section on backends for more detailed information.

• -q/--hide-progress - suppresses progress indication for commands that support it

• -c/--concurrent - the number of concurrent connections to the backend

• --cache-directory - specifies the directory to use for cache. --no-cache disables cache completely.

• -v/--verbose - increases the logging verbosity. The default verbosity is warning, -v means info, -vv means debug.

Encrypted repositories require a key and a matching password for every operation:

• -K/--key-file - the path to the key file
• -p/--password - the password in plaintext. However, it's more secure to provide the password in a file via the -P/--password-file argument, or as an environment variable REPLICAT_PASSWORD.

If the backend requires additional parameters (account name, client secret, some boolean flag, or literally anything else), you'll also be able to set them via command line arguments or in the configuration file. Refer to Backends section to learn more.

If you often use many of these arguments, and their values mostly stay the same between invocations, you may find it easier to put them in a configuration file instead. There are three arguments related to that:

• --profile - load settings from this profile in the configuration file
• --config - path to the configuration file (check --help for the default config location)
• --ignore-config - ignore the configuration file

Note that values from CLI always take precedence over options from the configuration file. Specifically, to build the final configuration, Replicat considers command line arguments, environment variables, the configuration file (either the default one or the one supplied via --config), and global defaults, in that order.

Names of configuration file options mostly match the long names of command line arguments (e.g., hide-progress = true matches --hide-progress, repository = "s3:bucket" matches -r s3:bucket), but you can always refer to the Configuration file section for full reference.

init examples

# Unencrypted repository 'some:repository'. The --encryption none flag disables encryption
$ replicat init -r some:repository --encryption none
# Encrypted repository with initial password taken from string.
# The new key will be printed to stdout
$ replicat init -r some:repository -p 'password string'
# Encrypted repository with initial password taken from a file.
# The new key will be written to 'path/to/key/file'
$ replicat init -r some:repository -P path/to/password/file -o path/to/key/file
# Specifies the cipher
$ replicat init -r some:repository -p '...' --encryption.cipher.name chacha20_poly1305
# Specifies settings for the cipher and the hash algorithm
$ replicat init -r some:repository \
    -p '...' \
    --encryption.cipher.name aes_gcm \
    --encryption.cipher.key_bits 128 \
    --hashing.name sha2 \
    --hashing.bits 256
# Specifies the KDF name and parameters (for the key)
$ replicat init -r some:repository \
    -p '...' \
    --encryption.kdf.name scrypt \
    --encryption.kdf.n 2097152
# Specifies the chunking parameters
$ replicat init -r some:repository \
    -p '...' \
    --chunking.min-length 128_000 \
    --chunking.max-length 2_048_000
# Equivalent (dashes in argument names are converted to underscores)
$ replicat init -r some:repository \
    -p '...' \
    --chunking.min_length 128_000 \
    --chunking.max_length 2_048_000

The main takeaway here is that you can disable encryption simply by setting --encryption none. Check the Custom settings section for more.

snapshot examples

# Unlocks the repository, uploads provided files in encrypted chunks,
# using no more than 10 concurrent connections, creating a snapshot
$ replicat snapshot -r some:repository \
    -P path/to/password/file \
    -K path/to/key/file \
    -c 10 \
    -n 'A note (optional)'
    image.jpg some-directory another-directory and/more.text
# Uploads one file in chunks using 5 concurrent connections, while restricting
# the bandswith to 512 KB per second. Creates a new snapshot without any note
$ replicat snapshot -r some:repository --limit-rate 512K file.log

list-snapshots/ls examples

# Unlocks the repository and lists all of the snapshots
$ replicat list-snapshots -r some:repository -P path/to/password/file -K path/to/key/file
# Same, but without the table header
$ replicat ls -r some:repository -P path/to/password/file -K path/to/key/file --no-header
# Lists snapshots with names that match any of the regexes passed via -S/--snapshot-regex
# In this example, Replicat will only list snapshots whose names start with '123456'
# OR include substring 'abcdef'
$ replicat ls -r some:repository \
    -P path/to/password/file \
    -K path/to/key/file \
    -S '^123456' \
    -S abcdef
# Lists the snapshots, but instead of the default set of columns, displays just the
# snapshot name, the number of files in the snapshot, and the total size of the snapshot
# (in that order). Oh, there's also --no-header
$ replicat ls -r some:repository \
    -P path/to/password/file \
    -K path/to/key/file \
    --no-header \
    --columns name,file_count,size

list-files/lf examples

# Unlocks the repository and lists all versions of all the files
$ replicat list-files -r some:repository -P path/to/password/file -K path/to/key/file
# Same, but without the table header
$ replicat lf -r some:repository -P path/to/password/file -K path/to/key/file --no-header
# Only lists files with paths that match any of the regexes passed via -F/--file-regex
# (in this example, PNGs and text files) IF they are included in snapshots that match
# the -S regex(es) (i.e., snapshot names that start with '1234beef')
$ replicat lf -r some:repository \
    -P path/to/password/file \
    -K path/to/key/file \
    -F '\.t[e]?xt$' \
    -F '\.png$' \
    -S '^1234beef'
# Lists all versions of all the files, but instead of the default set of columns,
# displays the original path of the file first, then the snapshot name, the hash digest
# of the file, and the file access time (recorded at the time of the snapshot creation)
$ replicat lf -r some:repository \
    -P path/to/password/file \
    -K path/to/key/file \
    --columns snapshot_name,path,digest,atime

restore examples

# Unlocks the repository and restores the latest versions of all files to target directory,
# while limiting the download speed to at most 10 MB per second
$ replicat restore -r some:repository \
    -P path/to/password/file \
    -K path/to/key/file \
    --limit-rate 10M \
    target-directory
# Unlocks the repository and restores the latest versions of files that match any of the
# -F regex(es) from snapshots that match any of the -S regex(es)
$ replicat restore -r some:repository \
    -P path/to/password/file \
    -K path/to/key/file \
    -F '\.jpg$' \
    -F '^/root' \
    -S 'abcdef' \
    -S '12345' \
    target-directory

add-key examples

# Creates an independent key, which will be printed to stdout
$ replicat add-key -N path/to/file/with/new/password
# Unlocks the repository and creates a shared key (i.e. with shared secrets)
$ replicat add-key -r some:repository \
    -p 'your password' \
    -K your/key/file \
    -n 'new password as a string' \
    ---shared
# Creates an independent key, which will be written to path/to/new/key/file
$ replicat add-key -r some:repository -n 'new password as a string' -o path/to/new/key/file
# Creates an independent key with some custom encryption key derivation settings
$ replicat add-key -r some:repository \
    --encryption.kdf.name scrypt \
    --encryption.kdf.n 4194304
# Uses your password to create a new key with the copy of data in your key, but with
# different encryption key derivation settings (same as in the previous example).
# The new key will be printed to stdout
$ replicat add-key -r some:repository \
    -P your/password/file \
    -K your/key/file \
    --encryption.kdf.n 4_194_304 \
    --clone

This shows a way to customize the KDF parameters for the key, arguably making the data stored in your key better protected (to the point of probable overkill with values like this). Use the Custom settings section as reference.

delete examples

# Unlocks the repository and deletes snapshots by name (as returned by ls/list-snapshots).
# Chunks that aren't referenced by any other snapshot will be deleted automatically
$ replicat delete -r some:repository \
    -P path/to/password/file \
    -K path/to/key/file \
    NAME1 NAME2 NAME3 ...
# Same, but doesn't ask for confirmation
$ replicat delete -r some:repository \
    -P path/to/password/file \
    -K path/to/key/file \
    NAME1 NAME2 NAME3 ... \
    --yes

clean examples

# Unlocks the repository and deletes all chunks that are not referenced by any snapshot
$ replicat clean -r some:repository -P path/to/password/file -K path/to/key/file

upload-objects examples

# Uploads local files directly to the repository without any additional processing.
# File path -> resulting name:
#   '/working/directory/some/file' -> 'some/file'
#   '/working/directory/another/file' -> 'another/file'
#   '/working/directory/another/directory/another-file' -> 'another/directory/another-file'
#   '/absolute/directory/path/with-file' -> 'absolute/directory/path/with-file'
#   '/absolute/file' -> 'absolute/file'
/working/directory$ replicat upload-objects -r some:repository \
                        some/file \
                        /working/directory/another/directory \
                        /absolute/directory/path \
                        /absolute/file
# Uploads local files that do not yet exist in the repository (only checks the file names)
$ replicat upload-objects -r some:repository --skip-existing some/file some/directory
# Same, but additionally limits the upload speed to 2 MiB per second
$ replicat upload-objects \
    -r some:repository \
    --skip-existing \
    -L 2MiB \
    some/file some/directory

download-objects examples

# Downloads all objects from the repository directly to the current working directory
# without any additional processing
$ replicat download-objects -r some:repository
# Same, but it downloads objects to 'different/directory' instead
$ replicat download-objects -r some:repository different/directory
# Same, but it skips objects that already exist locally (only checks the file names)
$ replicat download-objects -r some:repository --skip-existing different/directory
# Downloads objects whose paths match any the -O regex(es) (i.e., all objects inside of
# 'data' OR 'snapshots' top-level directories in the repository) to the current working
# directory, skipping existing objects and limiting the download speed to mere
# 1 gigabit per second
$ replicat download-objects -r some:repository -O '^data/' -O '^snapshots/' -S -L 1Gb

list-objects examples

# Lists all objects currently in the repository
$ replicat list-objects -r some:repository
# Only lists objects whose paths match any of the regexes passed via -O/--object-regex
# (i.e., all objects within 'data' AND 'snapshots' top-level directories in the repository)
$ replicat list-objects -r some:repository -O '^data/' -O '^snapshots/'

delete-objects examples

# Deletes objects by their full paths as returned by list-objects
$ replicat delete-objects -r some:repository object/path/1 object/path/2 ...
# Same, but doesn't ask for confirmation
$ replicat delete-objects -r some:repository object/path/1 object/path/2 ... -y

Check version

replicat --version

Configuration file

As mentioned in the Command line interface section, options that you can put in the configuration file mostly match CLI arguments, with few exceptions.

Option name	Type	Supported values	Notes
repository	string	<backend>:<connection string>
concurrent	integer	Integers greater than 0
hide‑progress	boolean	true, false
cache‑directory	path	Relative or absolute path
no‑cache	boolean	true, false
password	string	Password as a string	Cannot be used together with password-file
password‑file	path	Relative or absolute path	Cannot be used together with password
key	string	JSON as a string	Cannot be used together with key-file
key‑file	path	Relative or absolute path	Cannot be used together with key
log‑level	string	debug, info, warning, error, critical, fatal	CLI option -v increases logging verbosity starting from warning, while this option lets you set lower logging verbosity, such as error

If the backend requires additional parameters (account id, access key, numeric port, or literally anything else), Replicat lets you provide them via the configuration file. For example, if you see a backend-specific argument --some-backend-option in the --help output, the equivalent configuration file option will be called some-backend-option.

Here's an example configuration file (it uses TOML syntax)

concurrent = 10
# Relative paths work
cache-directory = "~/.cache/directory/for/replicat"

[debugging]
log-level = "info"
hide-progress = true

[my-local-repo]
repository = "some/local/path"
password = "<secret>"
key = """
{
    "kdf": { ... },
    "kdf_params": { "!b": "..." },
    "private": { "!b": "..." }
}
"""
concurrent = 15
no-cache = true

[some-s3-repo]
repository = "s3:bucket-name"
key-id = "..."
access-key = "..."
region = "..."

Options that you specify at the top of the configuration file are defaults and they will be inherited by all of the profiles. In the example above there are three profiles (not including the default one): debugging, my-local-repo, some-s3-repo. You can tell Replicat which profile to use via the --profile CLI argument.

Notice that some-s3-repo includes options that were not listed in the table. key-id, access-key, region are the aforementioned backend-specific options for the S3 backend. See Backends.

Backends

Run replicat commands with -r <backend>:<connection string> and additional arguments that are specific to the selected backend. Those arguments may have defaults and may also be provided via environment variables or profiles. Use

replicat <command> -r <backend>:<connection string> --help

to see them.

Local

The format is -r local:some/local/path or simply -r some/local/path.

B2

The format is -r b2:bucket-id or -r b2:bucket-name. This backend uses B2 native API and requires

• key ID (--key-id argument, or B2_KEY_ID environment variable, or key-id option in a profile)
• application key (--application-key argument, or B2_APPLICATION_KEY environment variable, or application-key option in a profile)

Sign into your Backblaze B2 account to generate them. Note that you can use the master application key or a normal (non-master) application key (which can also be restricted to a single bucket). Refer to official B2 docs for more information.

S3

The format is -r s3:bucket-name. Requires

• AWS key ID (--key-id argument, or S3_KEY_ID environment variable, or the key-id option in a profile)
• AWS access key (--access-key argument, or S3_ACCESS_KEY environment variable, or access-key option in a profile)
• region (--region argument, or S3_REGION environment variable, or region option in a profile)

S3-compatible

The format is -r s3c:bucket-name. Requires

• key ID (--key-id argument, or S3C_KEY_ID environment variable, or the key-id option in a profile)
• access key (--access-key argument, or S3C_ACCESS_KEY environment variable, or access-key option in a profile)
• host (--host argument, or S3C_HOST environment variable, or host option in a profile)
• region (--region argument, or S3C_REGION environment variable, or region option in a profile)

Host must not include the scheme. The default scheme is https, but can be changed via the --scheme argument (or, equivalently, the S3C_SCHEME environment variable or scheme option in a profile).

You can use S3-compatible backend to connect to B2, S3, and many other cloud storage providers that offer S3-compatible API.

Custom backends

replicat.backends is a namespace package, making it possible to add custom backends without changing replicat source code.

Suppose your backend of choice is a hypothetical low low cost cloud storage Proud Cloud (pc for short). The most barebones implementation of the Replicat-compatible adapter for the pc backend will require a directory with the following structure:

$ tree proud-cloud/
proud-cloud/
└── replicat
    └── backends
        └── pc.py

The -r argument of replicat commands will take the form of -r pc:<connection string>. Replicat will use it to locate the pc module inside the replicat.backends package, load the replicat.backends.pc.Client class, and pass the <connection string> to its constructor to create the backend instance. In case there are some additional parameters that are required to connect to Proud Cloud (account id, secret token, etc.), you should add them to the replicat.backends.pc.Client constructor as keyword-only arguments. If present, Replicat will generate the corresponding command line arguments with defaults and you'll even be able to use environment variables or profiles to provide them.

replicat.backends.pc.Client must subclass replicat.backends.base.Backend and implement all of the methods marked as abstract. You could use implementations of existing replicat.backends.base.Backend subclasses as examples. To make your implementation visible to Replicat, you'll need to add it to the module search path before invoking replicat (you could use the PYTHONPATH environment variable for that).

Here's an example:

# ./proud-cloud/replicat/backends/pc.py
from .base import Backend

class ProudCloud(Backend):
    def __init__(self, connection_string, *, account_id, secret, port=9_876, legacy=False):
        print(f'PC args: {connection_string=}, {account_id=}, {secret=}, {port=}, {legacy=}')
        ...
    ...

Client = ProudCloud

$ PYTHONPATH=proud-cloud replicat init -r pc:... --help
usage: replicat init [-h] [-r REPO] [-q] [-c CONCURRENT] [-v] [-K KEYFILE]
                     [-p PASSWORD | -P PASSWORD_FILE_PATH] [--account-id ACCOUNT_ID]
                     [--secret SECRET] [--port PORT] [--legacy LEGACY] [-o KEY_OUTPUT_FILE]

optional arguments:
  ...

arguments specific to the ProudCloud backend:
  --account-id ACCOUNT_ID
                        or the PROUDCLOUD_ACCOUNT_ID environment variable
  --secret SECRET       or the PROUDCLOUD_SECRET environment variable
  --port PORT           or the PROUDCLOUD_PORT environment variable, or the constructor default 9876
  --legacy LEGACY       or the PROUDCLOUD_LEGACY environment variable, or the constructor default False

$ PYTHONPATH=proud-cloud PROUDCLOUD_LEGACY=true PROUDCLOUD_SECRET='pr0ud' \
    replicat init -r pc:... \
    --account-id 12345 \
    --port 9877
PC args: connection_string='...', account_id=12345, secret='pr0ud', port=9877, legacy=True
...

If you've created a Replicat-compatible adapter for a backend that Replicat doesn't already support and your implementation doesn't depend on additional third-party libraries (or at least they are not too heavy and can be moved to extras), consider submitting a PR to include it in this repository.

Custom settings

Replicat's default parameters and selection of cryptographic primitives should work well for most users but they do allow for some customisation if you know what you are doing.

Supported primitives and their parameters:

Name	Use	Parameters (with defaults)	Description	Notes
aes_gcm	AEAD	key_bits (256 [bits]), nonce_bits (96 [bits])	AES in GCM mode	Supports 128, 192, and 256 bit keys
chacha20_poly1305	AEAD		ChaCha20‑Poly1305
scrypt	Key derivation	n (2 ^ 20), r (8), p (1)	Scrypt KDF	Preferred for low-entropy inputs
blake2b	Hash, HMAC, key derivation	length (64 [bytes])	BLAKE2b	BLAKE2b-based "KDF" should only be used for high-entropy inputs
sha2	Hash	bits (512 [bits])	SHA2	Supported digest sizes are 224, 256, 384, and 512 bits
sha3	Hash	bits (512 [bits])	SHA3	Supported digest sizes are 224, 256, 384, and 512 bits
gclmulchunker	CDC	min_length (128K [bytes]), max_length (5.12M [bytes])	Content-defined chunking algorithm based on carry-less multiplication (CLMUL)

Encryption algorithm, hash algorithm, chunker, as well as their parameters are set for the entire repository and so apply to all users of the repository. By default, Replicat uses AES256-GCM for encryption, Scrypt (n is 2 ^ 20, r is 8, p is 1) as the KDF for the user's encryption key, BLAKE2b (as hash, "KDF", and HMAC), and GCLMULChunker as the chunker, which produces chunks between 128K and 5.12M in size with default parameters. KDF for the user's encryption key and KDF params can vary from key to key, though.

Repository settings

Repository-wide settings are stored in the file called config that gets uploaded to the root of the repository when you initialise it. Here's the default config:

{
    "hashing": {
        "name": "blake2b",
        "length": 64
    },
    "chunking": {
        "name": "gclmulchunker",
        "min_length": 128000,
        "max_length": 5120000
    },
    "encryption": {
        "cipher": {
            "name": "aes_gcm",
            "key_bits": 256,
            "nonce_bits": 96
        }
    }
}

Coincidentally, this hierarchy is how you're expected to provide your custom repository settings via CLI -- only in a flat representation.

For example, to disable encryption for the repository, you'd pass --encryption none to the init command. If instead you wish to reduce AES-GCM key size from the default 256 bits to 128 bits, all you need to do is pass --encryption.cipher.key_bits 128 (or, equivalently, --encryption.cipher.key-bits 128) during initialisation. To change the cipher from the default AES256-GCM to ChaCha20‑Poly1305, you'd use --encryption.cipher.name chacha20_poly1305. Note that when you set the name attribute like that, Replicat will load the default parameters for the new algorithm and also check if your settings are valid. It would be an error to provide any parameters for chacha20_poly1305, say.

Changing config after the repository has already been initialised may render existing data inaccessible.

Key settings

You may specify the KDF and its params whenever you create a new key, so either via init or via add-key. Similar to repository-wide settings, you'd use a flat hierarchical format for that. For example, in order to increase the work factor for Scrypt (the default KDF), you could pass --encryption.kdf.n 2097152 (next power of two after 1048576) to the command, or you could tweak Scrypt's r parameter the same way.

It's also possible to change the parameters for the existing key by cloning it via the add-key command. Simply set the --clone flag and provide the new KDF settings as shown in the previous paragraph.

Security

If you believe you've found a security issue with Replicat, please report it to [e-mail] (or DM me on Twitter or Telegram).