Croc: Securely transfer files and folders between two computers

Features

croc is a tool that allows any two computers to simply and securely transfer files and folders. AFAIK, croc is the only CLI file-transfer tool that does all of the following:

• Allows any two computers to transfer data (using a relay)
• Provides end-to-end encryption (using PAKE)
• Enables easy cross-platform transfers (Windows, Linux, Mac)
• Allows multiple file transfers
• Allows resuming transfers that are interrupted
• No need for local server or port-forwarding
• IPv6-first with IPv4 fallback
• Can use a proxy, like Tor

For more information about croc, see my blog post or read a recent interview I did.

Installation

You can download the latest release for your system, or install a release from the command-line:

curl https://getcroc.schollz.com | bash

Using Homebrew:

brew install croc

Using MacPorts:

sudo port selfupdate
sudo port install croc

You can install the latest release with Scoop, Chocolatey, or Winget:

scoop install croc
choco install croc
winget install schollz.croc

You can install the latest release with Nix:

nix-env -i croc

You can add this to your configuration.nix:

environment.systemPackages = [ pkgs.croc ];

First, install dependencies:

apk add bash coreutils
wget -qO- https://getcroc.schollz.com | bash

Install with pacman:

pacman -S croc

Install with dnf:

dnf install croc

Install with portage:

emerge net-misc/croc

Install with pkg:

pkg install croc

You can install from conda-forge globally with pixi:

pixi global install croc

Or install into a particular environment with conda:

conda install --channel conda-forge croc

Add the following one-liner function to your ~/.profile (works with any POSIX-compliant shell):

croc() { [ $# -eq 0 ] && set -- ""; mkdir -p "$HOME/.config/croc"; docker run --rm -it --user "$(id -u):$(id -g)" -v "$(pwd):/c" -v "$HOME/.config/croc:/.config/croc" -w /c -e CROC_SECRET docker.io/schollz/croc "$@"; }

You can also just paste it in the terminal for current session. On first run Docker will pull the image. croc via Docker will only work within the current directory and its subdirectories.

If you prefer, you can install Go and build from source (requires Go 1.22+):

go install github.com/schollz/croc/v10@latest

There is a 3rd-party F-Droid app available to download.

Usage

To send a file, simply do:

$ croc send [file(s)-or-folder]
Sending 'file-or-folder' (X MB)
Code is: code-phrase

Then, to receive the file (or folder) on another computer, run:

croc code-phrase

The code phrase is used to establish password-authenticated key agreement (PAKE) which generates a secret key for the sender and recipient to use for end-to-end encryption.

On Linux and macOS, the sending and receiving process is slightly different to avoid leaking the secret via the process name. You will need to run croc with the secret as an environment variable. For example, to receive with the secret ***:

CROC_SECRET=*** croc

For single-user systems, the default behavior can be permanently enabled by running:

croc --classic

You can send with your own code phrase (must be at least 6 characters):

croc send --code [code-phrase] [file(s)-or-folder]

To automatically overwrite files without prompting, use the --overwrite flag:

croc --yes --overwrite

To exclude folders from being sent, use the --exclude flag with comma-delimited exclusions:

croc send --exclude "node_modules,.venv" [folder]

You can pipe to croc:

cat [filename] | croc send

To receive the file to stdout, you can use:

croc --yes [code-phrase] > out

To send URLs or short text, use:

croc send --text "hello world"

You can send multiple files directly by listing the files and/or folders:

croc send [file1] [file2] [file3] [folder1] [folder2]

To show QR code (for mobile devices), use:

croc send --qr [file(s)-or-folder]

You can send files via a proxy by adding --socks5:

croc --socks5 "127.0.0.1:9050" send SOMEFILE

To choose a different elliptic curve for encryption, use the --curve flag:

croc --curve p521

For faster hashing, use the imohash algorithm:

croc send --hash imohash SOMEFILE

By default, the code phrase is copied to your clipboard. To disable this:

croc --disable-clipboard send [filename]

To copy the full command with the secret as an environment variable (useful on Linux/macOS):

croc --extended-clipboard send [filename]

This copies the full command like CROC_SECRET="code-phrase" croc (including any relay/pass flags).

To suppress all output (useful for scripts and automation):

croc --quiet send [filename]

Running Your Own Relay

You can run your own relay:

croc relay

By default, it uses TCP ports 9009-9013. You can customize the ports (e.g., croc relay --ports 1111,1112), but at least 2 ports are required.

To send files using your relay:

croc --relay "myrelay.example.com:9009" send [filename]

You can also run a relay with Docker:

docker run -d -p 9009-9013:9009-9013 -e CROC_PASS='YOURPASSWORD' docker.io/schollz/croc

To send files using your custom relay:

croc --pass YOURPASSWORD --relay "myreal.example.com:9009" send [filename]

To use custom ports, set CROC_PORTS (comma-separated) or CROC_PORT (base port):

docker run -d -p 9010-9011:9010-9011 -e CROC_PORTS='9010,9011' -e CROC_PASS='YOURPASSWORD' docker.io/schollz/croc

Acknowledgments

croc has evolved through many iterations, and I am thankful for the contributions! Special thanks to:

• @warner for the idea
• @tscholl2 for the encryption gists
• @skorokithakis for proxying two connections

And many more!