Proposal: end to end encryption

Here is a proposed scheme for end-to-end encryption. In each of these examples we will imagine a chat between various users: User A, User B, User C etc...

One-to-one chat

1. Users A and B generate new public private key pairs and store the public key on their vcard / user profile
2. User A starts a new conversation with User B
3. User A downloads User B's public key from the vcard / profile
4. User A generates a new symmetric encryption key and encrypts the payload using it
5. User A then encrypts the symmetric key using User B's public key
6. User B receives the message and decrypts the symmetric key using their it using the private key
7. User B then decrypts the message using the symmetric key

Multi user chat

1. Users A, B and C generate new public private key pairs and store the public key on their vcard / user profile
2. User A starts a new conversation with Users B and C
3. User A downloads the public keys of Users B and C
4. User A generates a new symmetric key and encrypts the payload using it
5. User A then encrypts the symmetric key twice - once using User B's public key and again using User C's public key
6. The message is sent to Users B and C
7. Users B and C each find their version of the encrypted symmetric key and decrypt it using their private key
8. Each can then decrypt the payload

Multi device chat

Multi device chat is similar to multi-user chat. However, if User B has two devices - B1 and B2. Each device would generate it's own public / private key pair. Then any message addressed to B, would have the symmetric key for the payload encrypted twice too. Once for each device.