59 lines
2.1 KiB
Markdown
59 lines
2.1 KiB
Markdown
# The Protocol
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### Key Derivation Function
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doesnt seem to be any reason to use a key derivation function.
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## Registration:
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- User sends a `Register` requset giving them a public key and encrypting using the server's public key
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- Server sends the user a `VerificationRequired` (not in current code, as the 6 digit code does that for now) message & a 6-digit code (Secure channel)
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- User sends the server a `ConfirmRegister` with the 6-digit code, signed using the key provided at previous stage
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- Server verifies the signature and code, and if both are valid it sends a last `Confirm` and the registration process is done
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## Login
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Login is done by a challenge, the user sends a `Login` request, the server sends a random block of 16 bytes for the user to sign,
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then the server validates the signature with the known saved key.
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## Passing messages
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In order to send a message from A to B, A will ask the server for B's key,
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A will then encrypt the message using B's key, append a signature, and send a `SendMessage`
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request with the payload having the structure of `Enc_b(Message object) + Signature_A(Message object)`.
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The server will hold on to the message until B will send a `GetMessages` request
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to the server.
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## Requests
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- Register:
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data: Phone - 8 bytes, RSA key size (payload length) - 2 bytes
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- ConfirmRegister (signed & encrypted 6 digit code)
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data: 6 bytes for the 6 digit code, 4 bytes for signature length
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- Login:
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data: 8 bytes of user's phone
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- ConfirmLogin (signed hash):
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data: hash length
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- GetMessages:
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data: EMPTY
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- GetUserKey:
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extra data: 8 bytes (4 bits per digit) of whoever we want to get the key of
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- SendMessage:
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extra data: 8 bytes (4 bits per digit) of who to send the data, 4 bytes (32bit) for length in bytes
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I think it all can go into a:
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```
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{
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Version byte (0) - 1 byte,
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RequestType - 1 byte,
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looping counter - 1 byte,
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data - up to 13,
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} = 16 bytes = 128 bits
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```
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Encryption and Hashes used:
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public keys: RSA-1024 (can be of somewhat arbitrary length)
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Hashes: SHA3-256
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symmetric keys: AES-CFB-256 with PCKS7 padding (when needed as most stuff are made to fit in 1 block)
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