Problem: no e2e encrypted messaging support

[yihuang]

add commands for users to generate a separate keypair for asymmetric encryption, the pubkey is published to on-chain state for encryption, private key is saved in local keyring for decryption.

Libraries/Tools

We need something that can be used programmatically in golang.

• age seems to be a well-maintained library and tool for asymmetric encryption.

New Commands

• cronosd gen-encryption-key [name] This command will generate a new key for age encryption, the private key is saved in the keyring, and the public key is outputted.
• cronosd set-encryption-key [pub-key] --from user-address The tx should be signed by the user, and the encryption key is stored associated with the user address.
• cronosd encrypt [recipients] [message] This command will load the associated encryption keys for one or many recipients, and encrypt the message to all of them.

User Flow

1. User generates a new keypair locally using age-keygen:

   $ age-keygen -o privatekey.txt
   Public key: [PUBLIC KEY]
   

2. User can publish a [PUBLIC KEY] to chain:

   $ cronosd set-encryption-key [PUBLIC KEY]
   

3. User save the private key in the keyring:

   $ cronosd keyring-add-raw "encryptionkey" "$(cat privatekey.txt)"
   

4. Third party then can encrypt private messages to multiple users:

   $ cronosd encrypt [recipients] [MESSAGE]
   

   The encrypted message can be published anywhere, depending on the application.

Tracking

• [x] #1407 basic e2ee module structure
• [x] #1413
• [x] #1411
• [x] #1409
• [ ] #1415