Parity Signer is a mobile application that allows any smartphone to act as an air-gapped crypto wallet. This is also known as "cold storage".
You can create Kusama and Ethereum accounts, sign messages/transactions, and transfer funds to and from these accounts without any sort of connectivity enabled on the device.
You must turn off or even physically remove the smartphone's Wifi, Mobile Network, and Bluetooth to ensure that the mobile phone containing these accounts will not be exposed to any online threat.
Disabling the mobile phone's networking abilities is a requirement for the app to be used as intended.
Have a look at the tutorial on our wiki to learn how to use Parity Signer together with Polkadot-js app for Kusama, or MyCrypto app and Parity Fether for Ethereum.
Any data transfer from or to the app happens using QR code. By doing so, the most sensitive piece of information, the private keys, will never leave the phone. The Parity Signer mobile app can be used to store any Kusama or Ethereum account, this includes KSM, ETH, ETC as well as Ether from various testnets (Kovan, Ropsten...).
Parity-Signer is GPL 3.0 licensed.