Croc: Easily and securely send things from one computer to another

This project is supported by Github sponsors.

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
• local server or port-forwarding not needed
• ipv6-first with ipv4 fallback
• can use proxy, like tor

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

Install

Download the latest release for your system, or install a release from the command-line:

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

On macOS you can install the latest release with Homebrew:

On macOS you can also install the latest release with MacPorts:

sudo port selfupdate
sudo port install croc

On Windows you can install the latest release with Scoop, Chocolatey, or Winget:

winget install schollz.croc

On Unix you can install the latest release with Nix:

On Alpine Linux you have to install dependencies first:

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

On Arch Linux you can install the latest release with pacman:

On Fedora you can install with dnf:

On Gentoo you can install with portage:

On Termux you can install with pkg:

On FreeBSD you can install with pkg:

Or, you can install Go and build from source (requires Go 1.17+):

go install github.com/schollz/croc/v9@latest

On Android 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, you can just do

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.

There are a number of configurable options (see --help). A set of options (like custom relay, ports, and code phrase) can be set using --remember.

Custom code phrase

You can send with your own code phrase (must be more than 6 characters).

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

Allow overwriting without prompt

By default, croc will prompt whether to overwrite a file. You can automatically overwrite files by using the --overwrite flag (recipient only). For example, receive a file to automatically overwrite:

croc --yes --overwrite 

Use pipes – stdin and stdout

You can pipe to croc:

cat [filename] | croc send

In this case croc will automatically use the stdin data and send and assign a filename like “croc-stdin-123456789”. To receive to stdout at you can always just use the --yes will automatically approve the transfer and pipe it out to stdout.

croc --yes [code-phrase]> out

All of the other text printed to the console is going to stderr so it will not interfere with the message going to stdout.

Send text

Sometimes you want to send URLs or short text. In addition to piping, you can easily send text with croc:

croc send --text "hello world"

This will automatically tell the receiver to use stdout when they receive the text so it will be displayed.

Use a proxy

You can use a proxy as your connection to the relay by adding a proxy address with --socks5. For example, you can send via a tor relay:

croc --socks5 "127.0.0.1:9050" send SOMEFILE

Change encryption curve

You can choose from several different elliptic curves to use for encryption by using the --curve flag. Only the recipient can choose the curve. For example, receive a file using the P-521 curve:

croc --curve p521 

Available curves are P-256, P-348, P-521 and SIEC. P-256 is the default curve.

Change hash algorithm

You can choose from several different hash algorithms. The default is the xxhash algorithm which is fast and thorough. If you want to optimize for speed you can use the imohash algorithm which is even faster, but since it samples files (versus reading the whole file) it can mistakenly determine that a file is the same on the two computers transferring – though this is only a problem if you are syncing files versus sending a new file to a computer.

croc send --hash imohash SOMEFILE

Self-host relay

The relay is needed to staple the parallel incoming and outgoing connections. By default, croc uses a public relay but you can also run your own relay:

By default it uses TCP ports 9009-9013. Make sure to open those up. You can customized the ports (e.g. croc relay --ports 1111,1112), but you must have a minimum of 2 ports for the relay. The first port is for communication and the subsequent ports are used for the multiplexed data transfer.

You can send files using your relay by entering --relay to change the relay that you are using if you want to custom host your own.

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

Note, when sending, you only need to include the first port (the communication port). The subsequent ports for data transfer will be transmitted back to the user from the relay.

Self-host relay (docker)

If it’s easier you can also run a relay with Docker:

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

Be sure to include the password for the relay otherwise any requests will be rejected.

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

Note: when including --pass YOURPASSWORD you can instead pass a file with the password, e.g. --pass FILEWITHPASSWORD.

License

MIT

Acknowledgements

croc has gone through many iterations, and I am awed by all the great contributions! If you feel like contributing, in any way, by all means you can send an Issue, a PR, or ask a question.

Thanks @warner for the idea, @tscholl2 for the encryption gists, @skorokithakis for code on proxying two connections. Finally thanks for making pull requests @maximbaz, @meyermarcel, @Girbons, @techtide, @heymatthew, @Lunsford94, @lummie, @jesuiscamille, @threefjord, @marcossegovia, @csleong98, @afotescu, @callmefever, @El-JojA, @anatolyyyyyy, @goggle, @smileboywtu, @nicolashardy, @fbartels, @rkuprov, @hreese, @xenrox and Ipar!