Advanced settings
Advanced holds the croc options most people never need: proxies, the encryption curve, an upload speed limit, ports and a few more. Every default is croc's own, so you can ignore this page unless you know you need something here.
On iOS, open Settings from the home toolbar and tap Advanced. On macOS, open Settings (⌘,) and choose the Advanced tab. Reset to Defaults at the bottom puts every setting back after a confirmation, and removes the saved proxies.
Each field checks what you type and shows a message under it. If a saved value is not usable, a transfer fails to start with "An Advanced setting can't be used" instead of falling back to something else.
Who has to match
| Setting | Default | Affects | Other device must match? |
|---|---|---|---|
| Curve | P-256 | Receiving | No, the sender uses the receiver's choice |
| File hash | xxHash | Sending | No, the receiver uses the sender's choice |
| SOCKS5 proxy | None | This device | No |
| HTTP proxy | None | This device | No |
| Built-in DNS resolver | Off | This device | No |
| Multicast address (macOS only) | 239.255.255.250 | Both devices | Yes, the same address, to find each other on the local network |
| Sender IP | None | Receiving | No, but it must be the sender's address and base port |
| Upload speed limit | No limit | Sending | No |
| Base port | 9009 | Sending | A receiver that connects by sender IP must use it |
| Parallel connections | 4 | Sending | No |
| Multiplexing | On | Sending | No, the receiver follows |
"Sending" means the setting applies when this device sends; the receiving device follows what the sender does.
Security
Curve picks the key-exchange curve: P-256 (the default), P-384, P-521, SIEC or Ed25519. The receiver's choice wins: the sender switches to it, so the two devices never have to match, and the setting only matters when this device receives.
File hash picks how the sender fingerprints files so the receiver can check them: xxHash (the default), imohash, MD5 or HighwayHash. Only the sender's choice matters.
Network
SOCKS5 proxy and HTTP proxy send this device's connections through a proxy. Enter host:port, or an address such as socks5://user:password@host:1080 (SOCKS5: socks5:// or socks5h://; HTTP: http:// or https://). If both are set, the SOCKS5 proxy is used. Connections to devices on your local network skip the proxy. The proxies also apply to Send as link uploads, downloads and revokes.
A proxy address can contain a password, so CrocApp keeps both proxies in the Keychain, never in the settings file, and never shows them in an error message.
Built-in DNS resolver looks up relay names with croc's own resolver instead of the system's. It is off by default and only affects this device.
Multicast address is the group croc uses to find other devices on the local network. Both devices must use the same address, or they will not find each other locally (unless Local network only is on, they can still connect through a relay). It must be an IPv4 multicast address, from 224.0.0.0 to 239.255.255.255. This setting is available on macOS only for now: iOS needs an Apple entitlement for multicast that CrocApp does not have, so iOS always uses the default address.
Sender IP is for receiving. Enter the sender's address and port, such as 192.168.1.20:9009 or [fe80::1]:9009, and CrocApp connects straight to the sender and skips relays and discovery. The port is the sender's Base port, 9009 unless they changed it. The sender must be reachable at that address, for example on the same network. If nothing answers there, the receive fails at once; it does not fall back to a relay. While it is set, the trust badge on a receive reads "Straight to the sender, no relay in between".
Performance
Upload speed limit caps how fast this device sends, in bytes per second: digits with an optional k, m or g, such as 500k, 2m or 1g. Leave it blank for no limit.
Base port and Parallel connections set the ports the sender's local relay listens on: the base port, then one more per connection. With the defaults that is 9009 to 9013. The last port must stay at or below 65535. They matter when a receiver connects by sender IP, or when something else on your device already uses those ports.
Multiplexing is on by default. Turning it off sends over one data connection. The receiving device follows.
See also
- Power options for relay, connection, compression and confirmation settings.
- Receiving files for connecting by sender IP.
- Settings and trust for where settings are stored.