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+# Enhanced Sub-GHz Chat
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+
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+This is a plugin for the Flipper Zero that reimplements the Sub-GHz chat
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+feature that is available on the CLI. In addition it allows for basic
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+encryption of messages.
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+
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+The plugin has been tested on the official firmware (version 0.87.0) and on
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+Unleashed (version unlshd-057). Due to limitations of the official firmware,
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+the behavior is slightly different there.
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+
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+## Warning
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+
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+This plugin is in the early stages of development. It will inevitably have
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+bugs. You have been warned.
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+
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+## Usage
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+
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+Once opened the plugin will ask for a frequency to operate on which must be
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+entered in HZ.
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+
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+On the next screen the plugin will ask for a password to derive the
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+cryptographic key from. If nothing (on Unleashed) or a single space (on OFW) is
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+entered, the encryption is disabled.
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+
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+Finally the a message can be input. After the message is confirmed, the plugin
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+will switch to the chat view, where sent and received messages are displayed.
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+To view the chat view without entering a message, enter nothing (on Unleashed)
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+or a single space (on OFW). To go back to entering a message press the back
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+button.
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+
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+In the chat view the keyboard can be locked by pressing and holding the OK
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+button for a few seconds. To unlock the keyboard again quickly press the back
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+button three times.
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+
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+Pressing the back button when entering the frequency, the password or a message
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+will terminate the plugin.
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+
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+## Interoperability
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+
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+When encryption is disabled, the plugin can interoperate with the Sub-GHz chat
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+available on the Flipper's CLI. However, the CLI sends a sequence of escape
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+characters that are not interpreted by this plugin and will be displayed in the
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+chat view.
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+
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+## Encryption
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+
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+Messages are encrypted using 256 bit AES in GCM mode. Each message gets its own
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+random IV. On reception the tag generated by GCM is verified and the message
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+discarded if it doesn't match.
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+
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+The key for the encryption is derived from the password by applying SHA-256 to
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+the password once.
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+
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+Note that deriving the key with SHA-256 means that the security of your
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+messages depends entirely on the strength of the password. The plugin does not
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+use an elaborate key derivation function (KDF) to strengthen the password. A
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+weak passwords means weak encryption.
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+
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+Furthermore, the key is the same among all participants. That means that each
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+user with the key can impersonate every other user.
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+
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+The same key is used for all messages. This means that no forward-secrecy is
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+provided. If the key is compromised, all previous messages are compromised as
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+well.
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+
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+If you do not understand the implications of the caveats mentioned here, do not
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+expect to gain any security by using encryption.
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+
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+## Acknowledgements
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+
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+The implementations of AES and GCM are taken directly from
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+https://github.com/mko-x/SharedAES-GCM. They were released to the public domain
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+by Markus Kosmal.
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twisted_pear