`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)
For more information about `croc`, see [my blog post](https://schollz.com/software/croc6) or read a [recent interview I did](https://console.substack.com/p/console-91).
On Windows you can install the latest release with [Scoop](https://scoop.sh/), [Chocolatey](https://chocolatey.org), or [Winget](https://learn.microsoft.com/en-us/windows/package-manager/):
On Linux this behavior is disabled by default to avoid leaking the [secret via the process name](https://nvd.nist.gov/vuln/detail/CVE-2023-43621) ([see below](README.md#receiving-on-linux)).
The code phrase is used to establish password-authenticated key agreement ([PAKE](https://en.wikipedia.org/wiki/Password-authenticated_key_agreement)) 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`.
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:
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`.
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:
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.
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 customize 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.
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:
`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](https://github.com/warner) for the [idea](https://github.com/warner/magic-wormhole), [@tscholl2](https://github.com/tscholl2) for the [encryption gists](https://gist.github.com/tscholl2/dc7dc15dc132ea70a98e8542fefffa28), [@skorokithakis](https://github.com/skorokithakis) for [code on proxying two connections](https://www.stavros.io/posts/proxying-two-connections-go/). Finally thanks for making pull requests [@maximbaz](https://github.com/maximbaz), [@meyermarcel](https://github.com/meyermarcel), [@Girbons](https://github.com/Girbons), [@techtide](https://github.com/techtide), [@heymatthew](https://github.com/heymatthew), [@Lunsford94](https://github.com/Lunsford94), [@lummie](https://github.com/lummie), [@jesuiscamille](https://github.com/jesuiscamille), [@threefjord](https://github.com/threefjord), [@marcossegovia](https://github.com/marcossegovia), [@csleong98](https://github.com/csleong98), [@afotescu](https://github.com/afotescu), [@callmefever](https://github.com/callmefever), [@El-JojA](https://github.com/El-JojA), [@anatolyyyyyy](https://github.com/anatolyyyyyy), [@goggle](https://github.com/goggle), [@smileboywtu](https://github.com/smileboywtu), [@nicolashardy](https://github.com/nicolashardy), [@fbartels](https://github.com/fbartels), [@rkuprov](https://github.com/rkuprov), [@hreese](https://github.com/hreese), [@xenrox](https://github.com/xenrox) and [Ipar](https://github.com/lpar)!
