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Zack Scholl 2018-06-26 21:46:23 -07:00
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@ -93,15 +93,15 @@ Or, you can [install Go](https://golang.org/dl/) and build from source with `go
# How does it work?
*croc* is similar to [magic-wormhole](https://github.com/warner/magic-wormhole#design) in spirit. Like *magic-wormhole*, *croc* generates a code phrase for you to share with your friend which allows secure end-to-end transfering of files and folders through a intermediary relay that connects the TCP ports between the two computers. The standard relay is on a public IP address (default `cowyo.com`), but before transmitting the file the two instances of *croc* send out UDP broadcasts to determine if they are both on the local network, and use a local relay instead of the cloud relay in the case that they are both local.
*croc* is similar to [magic-wormhole](https://github.com/warner/magic-wormhole#design) in spirit. Like *magic-wormhole*, *croc* generates a code phrase for you to share with your friend which allows secure end-to-end transferring of files and folders through a intermediary relay that connects the TCP ports between the two computers. The standard relay is on a public IP address (default `cowyo.com`), but before transmitting the file the two instances of *croc* send out UDP broadcasts to determine if they are both on the local network, and use a local relay instead of the cloud relay in the case that they are both local.
The code phrase allows the relay to match the receiver and the sender. Once matched, the relay shares the public keys so that the sender and recipient can further authenticate whether or not they have the right person. Once both sides verify and consent to the transfer, then the sender will encrypt the data using the recipient's public key, so that only they can decrypt the data. After a succesful transfer, the public key is stored and next time it is not prompted and automatically trusted (TOFU).
The code phrase allows the relay to match the receiver and the sender. Once matched, the relay shares the public keys so that the sender and recipient can further authenticate whether or not they have the right person. Once both sides verify and consent to the transfer, then the sender will encrypt the data using the recipient's public key, so that only they can decrypt the data. After a successful transfer, the public key is stored and next time it is not prompted and automatically trusted (TOFU).
The transfer uses [Go channels](https://golang.org/doc/effective_go.html?h=chan#channels) and parallel connections to pipe all the data. After the transmission the channels are destroyed and all the connection and meta data information is wiped from the relay server. The encrypted file data never is stored on the relay.
**Security**
The first time you use croc you will generate a unique NaCl box keypair (which uses Curve25519, XSalsa20 and Poly1305) that is unique to your computer. This keypair is used to transfer the encryption key to the recipient, and gaurantees that only the recipient can decrypt the encryption key to decrypt the file data. The encryption key is a cryptographically generated random 20 characters. The file data is encrypted using the encryption key with AES-256. This method gaurantees that all the file data going over the wire is secure, and that the only person who can decrypt it is the recipient (i.e. a MITM attacker cannot decrypt it without the keypair on the recipient's computer).
The first time you use croc you will generate a unique NaCl box keypair (which uses Curve25519, XSalsa20 and Poly1305) that is unique to your computer. This keypair is used to transfer the encryption key to the recipient, and guarantees that only the recipient can decrypt the encryption key to decrypt the file data. The encryption key is a cryptographically generated random 20 characters. The file data is encrypted using the encryption key with AES-256. This method guarantees that all the file data going over the wire is secure, and that the only person who can decrypt it is the recipient (i.e. a MITM attacker cannot decrypt it without the keypair on the recipient's computer).
The keypair also serves as a second method of authentication. After both the sender and recipient enter their code phrases, they will be able to see each other's public keys. If the public key of the other person does not match what they say it should be (i.e. an attacker is trying to use the same code phrase to get your file - possible though unlikely), then you can cancel the transfer.