fcp_cryptoauth 0.4.0

Implementation of the Futuristic Connectivity Protocol's CryptoAuth layer (cryptographic authentication and encryption over unreliable channels).
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//! Contains the `Session` structure, which stores the state of a
//! CryptoAuth session.

use std::fmt;

use cryptography::crypto_box;
use cryptography::crypto_box::{PrecomputedKey, PublicKey, SecretKey};
use keys::ToBase32;

#[derive(Debug, Clone, Eq, PartialEq)]
pub enum SessionState {
    UninitializedUnknownPeer,
    UninitializedKnownPeer,
    SentHello {
        shared_secret_key: PrecomputedKey,
    },
    ReceivedHello {
        their_temp_pk: PublicKey,
        shared_secret_key: PrecomputedKey,
    },
    WaitingKey {
        their_temp_pk: PublicKey,
        shared_secret_key: PrecomputedKey,
    }, // When we received a Hello from a lower key, don't send an Hello because it would reset their session
    SentKey {
        their_temp_pk: PublicKey,
        shared_secret_key: PrecomputedKey,
    },
    Established {
        their_temp_pk: PublicKey,
        /// Used to open RepeatKey packets
        handshake_shared_secret_key: PrecomputedKey,
        shared_secret_key: PrecomputedKey,
        initiator_is_me: bool,
    },
}

/// Stores the state of a CryptoAuth session (nonce, permanent keys,
/// temporary keys).
pub struct Session {
    pub state: SessionState,

    pub my_perm_pk: PublicKey,
    pub my_perm_sk: SecretKey,
    pub their_perm_pk: PublicKey,

    pub my_temp_pk: crypto_box::PublicKey,
    pub my_temp_sk: crypto_box::SecretKey,

    pub my_last_nonce: u32,
    pub their_nonce_offset: u32, // their last nonce
    pub their_nonce_bitfield: u64,
}

impl fmt::Debug for Session {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        f.debug_struct("fcp_cryptoauth::Session")
            .field("state", &self.state)
            .field("my_perm_pk", &self.my_perm_pk.to_base32())
            .field("their_perm_pk", &self.their_perm_pk.to_base32())
            .finish()
    }
}

impl Session {
    /// Creates a new session using permanent keys.
    /// 'initiator' determines whether we are the one to send the Hello packet
    /// (and receive the Key packet)
    pub fn new(
        my_pk: PublicKey,
        my_sk: SecretKey,
        their_pk: PublicKey,
        initial_state: SessionState,
    ) -> Session {
        // Temporary keys used only for this session.
        let (my_temp_pk, my_temp_sk) = crypto_box::gen_keypair();

        Session {
            state: initial_state,

            my_perm_pk: my_pk,
            my_perm_sk: my_sk,
            their_perm_pk: their_pk,

            my_temp_pk: my_temp_pk,
            my_temp_sk: my_temp_sk,

            my_last_nonce: 3u32,
            their_nonce_offset: 4u32,
            their_nonce_bitfield: 0u64,
        }
    }

    /// Resets the temporary keys.
    pub fn reset(&mut self) {
        let (my_temp_pk, my_temp_sk) = crypto_box::gen_keypair();
        self.my_temp_pk = my_temp_pk;
        self.my_temp_sk = my_temp_sk;
    }
}