//! Relay cell cryptography

//!

//! The Tor protocol centers around "RELAY cells", which are transmitted through

//! the network along circuits.  The client that creates a circuit shares two

//! different sets of keys and state with each of the relays on the circuit: one

//! for "outbound" traffic, and one for "inbound" traffic.

//!

//! So for example, if a client creates a 3-hop circuit with relays R1, R2, and

//! R3, the client has:

//!   * An "inbound" cryptographic state shared with R1.

//!   * An "inbound" cryptographic state shared with R2.

//!   * An "inbound" cryptographic state shared with R3.

//!   * An "outbound" cryptographic state shared with R1.

//!   * An "outbound" cryptographic state shared with R2.

//!   * An "outbound" cryptographic state shared with R3.

//!

//! In this module at least, we'll call each of these state objects a "layer" of

//! the circuit's encryption.

//!

//! The Tor specification does not describe these layer objects very explicitly.

//! In the current relay cryptography protocol, each layer contains:

//!    * A keyed AES-CTR state. (AES-128 or AES-256)  This cipher uses a key

//!      called `Kf` or `Kb` in the spec, where `Kf` is a "forward" key used in

//!      the outbound direction, and `Kb` is a "backward" key used in the

//!      inbound direction.

//!    * A running digest. (SHA1 or SHA3)  This digest is initialized with a

//!      value called `Df` or `Db` in the spec.

//!

//! This `crypto::cell` module itself provides traits and implementations that

//! should work for all current future versions of the relay cell crypto design.

//! The current Tor protocols are instantiated in a `tor1` submodule.

#[cfg(feature = "bench")]

pub(crate) mod bench_utils;

#[cfg(feature = "counter-galois-onion")]

pub(crate) mod cgo;

pub(crate) mod tor1;

use crate::{Error, Result};

use derive_deftly::Deftly;

use tor_cell::{

    chancell::{BoxedCellBody, ChanCmd},

    relaycell::msg::SendmeTag,

};

use tor_memquota::derive_deftly_template_HasMemoryCost;

use super::binding::CircuitBinding;

/// Type for the body of a relay cell.

#[cfg_attr(feature = "bench", visibility::make(pub))]

#[derive(Clone, derive_more::From, derive_more::Into)]

pub(crate) struct RelayCellBody(BoxedCellBody);

impl AsRef<[u8]> for RelayCellBody {

}

impl AsMut<[u8]> for RelayCellBody {

}

/// Represents the ability for one hop of a circuit's cryptographic state to be

/// initialized from a given seed.

#[cfg_attr(feature = "bench", visibility::make(pub))]

pub(crate) trait CryptInit: Sized {

    /// Return the number of bytes that this state will require.

    fn seed_len() -> usize;

    /// Construct this state from a seed of the appropriate length.

    fn initialize(seed: &[u8]) -> Result<Self>;

    /// Initialize this object from a key generator.

}

/// A paired object containing the inbound and outbound cryptographic layers

/// used by a client to communicate with a single hop on one of its circuits.

///

/// TODO: Maybe we should fold this into CryptInit.

#[cfg_attr(feature = "bench", visibility::make(pub))]

pub(crate) trait ClientLayer<F, B>

where

    F: OutboundClientLayer,

    B: InboundClientLayer,

{

    /// Consume this ClientLayer and return a paired forward and reverse

    /// crypto layer, and a [`CircuitBinding`] object

    fn split_client_layer(self) -> (F, B, CircuitBinding);

}

/// A paired object containing the inbound and outbound cryptographic layers

/// used by a relay to implement a client's circuits.

///

#[allow(dead_code)] // To be used by relays.

#[cfg_attr(feature = "bench", visibility::make(pub))]

pub(crate) trait RelayLayer<F, B>

where

    F: OutboundRelayLayer,

    B: InboundRelayLayer,

{

    /// Consume this ClientLayer and return a paired forward and reverse

    /// crypto layers, and a [`CircuitBinding`] object

    fn split_relay_layer(self) -> (F, B, CircuitBinding);

}

/// Represents a relay's view of the inbound crypto state on a given circuit.

#[allow(dead_code)] // Relays are not yet implemented.

#[cfg_attr(feature = "bench", visibility::make(pub))]

pub(crate) trait InboundRelayLayer {

    /// Prepare a RelayCellBody to be sent towards the client,

    /// and encrypt it.

    ///

    /// Return the authentication tag.

    fn originate(&mut self, cmd: ChanCmd, cell: &mut RelayCellBody) -> SendmeTag;

    /// Encrypt a RelayCellBody that is moving towards the client.

    fn encrypt_inbound(&mut self, cmd: ChanCmd, cell: &mut RelayCellBody);

}

/// Represent a relay's view of the outbound crypto state on a given circuit.

#[allow(dead_code)]

#[cfg_attr(feature = "bench", visibility::make(pub))]

pub(crate) trait OutboundRelayLayer {

    /// Decrypt a RelayCellBody that is moving towards the client.

    ///

    /// Return an authentication tag if it is addressed to us.

    fn decrypt_outbound(&mut self, cmd: ChanCmd, cell: &mut RelayCellBody) -> Option<SendmeTag>;

}

/// A client's view of the cryptographic state shared with a single relay on a

/// circuit, as used for outbound cells.

#[cfg_attr(feature = "bench", visibility::make(pub))]

pub(crate) trait OutboundClientLayer {

    /// Prepare a RelayCellBody to be sent to the relay at this layer, and

    /// encrypt it.

    ///

    /// Return the authentication tag.

    fn originate_for(&mut self, cmd: ChanCmd, cell: &mut RelayCellBody) -> SendmeTag;

    /// Encrypt a RelayCellBody to be decrypted by this layer.

    fn encrypt_outbound(&mut self, cmd: ChanCmd, cell: &mut RelayCellBody);

}

/// A client's view of the crypto state shared with a single relay on a circuit,

/// as used for inbound cells.

#[cfg_attr(feature = "bench", visibility::make(pub))]

pub(crate) trait InboundClientLayer {

    /// Decrypt a CellBody that passed through this layer.

    ///

    /// Return an authentication tag if this layer is the originator.

    fn decrypt_inbound(&mut self, cmd: ChanCmd, cell: &mut RelayCellBody) -> Option<SendmeTag>;

}

/// Type to store hop indices on a circuit.

///

/// Hop indices are zero-based: "0" denotes the first hop on the circuit.

#[derive(Copy, Clone, Eq, PartialEq, Debug, Deftly)]

#[derive_deftly(HasMemoryCost)]

pub struct HopNum(u8);

impl HopNum {

    /// Return an object that implements [`Display`](std::fmt::Display) for printing `HopNum`s.

    ///

    /// This will display the `HopNum` as a 1-indexed value (the string representation of the first

    /// hop is `"#1"`).

    ///

    /// To display the zero-based underlying representation of the `HopNum`, use

    /// [`Debug`](std::fmt::Debug).

}

/// A helper for displaying [`HopNum`]s.

///

/// The [`Display`](std::fmt::Display) of this type displays the `HopNum` as a 1-based index

/// prefixed with the number sign (`#`). For example, the string representation of the first hop is

/// `"#1"`.

#[derive(Copy, Clone, Eq, PartialEq, Debug)]

pub struct HopNumDisplay(HopNum);

impl std::fmt::Display for HopNumDisplay {

}

impl From<HopNum> for u8 {

}

impl From<u8> for HopNum {

}

impl From<HopNum> for usize {

}

/// A client's view of the cryptographic state for an entire

/// constructed circuit, as used for sending cells.

#[cfg_attr(feature = "bench", visibility::make(pub), derive(Default))]

pub(crate) struct OutboundClientCrypt {

    /// Vector of layers, one for each hop on the circuit, ordered from the

    /// closest hop to the farthest.

    layers: Vec<Box<dyn OutboundClientLayer + Send>>,

}

/// A client's view of the cryptographic state for an entire

/// constructed circuit, as used for receiving cells.

#[cfg_attr(feature = "bench", visibility::make(pub), derive(Default))]

pub(crate) struct InboundClientCrypt {

    /// Vector of layers, one for each hop on the circuit, ordered from the

    /// closest hop to the farthest.

    layers: Vec<Box<dyn InboundClientLayer + Send>>,

}

impl OutboundClientCrypt {

    /// Return a new (empty) OutboundClientCrypt.

    /// Prepare a cell body to sent away from the client.

    ///

    /// The cell is prepared for the `hop`th hop, and then encrypted with

    /// the appropriate keys.

    ///

    /// On success, returns a reference to tag that should be expected

    /// for an authenticated SENDME sent in response to this cell.

    /// Add a new layer to this OutboundClientCrypt

    /// Return the number of layers configured on this OutboundClientCrypt.

}

impl InboundClientCrypt {

    /// Return a new (empty) InboundClientCrypt.

    /// Decrypt an incoming cell that is coming to the client.

    ///

    /// On success, return which hop was the originator of the cell.

    // TODO(nickm): Use a real type for the tag, not just `&[u8]`.

        }

    /// Add a new layer to this InboundClientCrypt

    /// Return the number of layers configured on this InboundClientCrypt.

    ///

    /// TODO: use HopNum

    #[allow(dead_code)]

}

/// Standard Tor relay crypto, as instantiated for RELAY cells.

pub(crate) type Tor1RelayCrypto =

    tor1::CryptStatePair<tor_llcrypto::cipher::aes::Aes128Ctr, tor_llcrypto::d::Sha1>;

/// Standard Tor relay crypto, as instantiated for the HSv3 protocol.

///

/// (The use of SHA3 is ridiculously overkill.)

#[cfg(feature = "hs-common")]

pub(crate) type Tor1Hsv3RelayCrypto =

    tor1::CryptStatePair<tor_llcrypto::cipher::aes::Aes256Ctr, tor_llcrypto::d::Sha3_256>;

#[cfg(test)]

mod test {

    // @@ begin test lint list maintained by maint/add_warning @@

    #![allow(clippy::bool_assert_comparison)]

    #![allow(clippy::clone_on_copy)]

    #![allow(clippy::dbg_macro)]

    #![allow(clippy::mixed_attributes_style)]

    #![allow(clippy::print_stderr)]

    #![allow(clippy::print_stdout)]

    #![allow(clippy::single_char_pattern)]

    #![allow(clippy::unwrap_used)]

    #![allow(clippy::unchecked_duration_subtraction)]

    #![allow(clippy::useless_vec)]

    #![allow(clippy::needless_pass_by_value)]

    //! <!-- @@ end test lint list maintained by maint/add_warning @@ -->

    use super::*;

    use rand::{seq::IndexedRandom as _, RngCore};

    use tor_basic_utils::{test_rng::testing_rng, RngExt as _};

    use tor_bytes::SecretBuf;

    use tor_cell::relaycell::RelayCellFormat;

    pub(crate) fn add_layers(

        cc_out: &mut OutboundClientCrypt,

        cc_in: &mut InboundClientCrypt,

        pair: Tor1RelayCrypto,

    ) {

        let (outbound, inbound, _) = pair.split_client_layer();

        cc_out.add_layer(Box::new(outbound));

        cc_in.add_layer(Box::new(inbound));

    }

    #[test]

    fn roundtrip() {

        // Take canned keys and make sure we can do crypto correctly.

        use crate::crypto::handshake::ShakeKeyGenerator as KGen;

        fn s(seed: &[u8]) -> SecretBuf {

            seed.to_vec().into()

        }

        let seed1 = s(b"hidden we are free");

        let seed2 = s(b"free to speak, to free ourselves");

        let seed3 = s(b"free to hide no more");

        let mut cc_out = OutboundClientCrypt::new();

        let mut cc_in = InboundClientCrypt::new();

        let pair = Tor1RelayCrypto::construct(KGen::new(seed1.clone())).unwrap();

        add_layers(&mut cc_out, &mut cc_in, pair);

        let pair = Tor1RelayCrypto::construct(KGen::new(seed2.clone())).unwrap();

        add_layers(&mut cc_out, &mut cc_in, pair);

        let pair = Tor1RelayCrypto::construct(KGen::new(seed3.clone())).unwrap();

        add_layers(&mut cc_out, &mut cc_in, pair);

        assert_eq!(cc_in.n_layers(), 3);

        assert_eq!(cc_out.n_layers(), 3);

        let (mut r1f, mut r1b, _) = Tor1RelayCrypto::construct(KGen::new(seed1))

            .unwrap()

            .split_relay_layer();

        let (mut r2f, mut r2b, _) = Tor1RelayCrypto::construct(KGen::new(seed2))

            .unwrap()

            .split_relay_layer();

        let (mut r3f, mut r3b, _) = Tor1RelayCrypto::construct(KGen::new(seed3))

            .unwrap()

            .split_relay_layer();

        let cmd = ChanCmd::RELAY;

        let mut rng = testing_rng();

        for _ in 1..300 {

            // outbound cell

            let mut cell = Box::new([0_u8; 509]);

            let mut cell_orig = [0_u8; 509];

            rng.fill_bytes(&mut cell_orig);

            cell.copy_from_slice(&cell_orig);

            let mut cell = cell.into();

            let _tag = cc_out.encrypt(cmd, &mut cell, 2.into()).unwrap();

            assert_ne!(&cell.as_ref()[9..], &cell_orig.as_ref()[9..]);

            assert!(r1f.decrypt_outbound(cmd, &mut cell).is_none());

            assert!(r2f.decrypt_outbound(cmd, &mut cell).is_none());

            assert!(r3f.decrypt_outbound(cmd, &mut cell).is_some());

            assert_eq!(&cell.as_ref()[9..], &cell_orig.as_ref()[9..]);

            // inbound cell

            let mut cell = Box::new([0_u8; 509]);

            let mut cell_orig = [0_u8; 509];

            rng.fill_bytes(&mut cell_orig);

            cell.copy_from_slice(&cell_orig);

            let mut cell = cell.into();

            r3b.originate(cmd, &mut cell);

            r2b.encrypt_inbound(cmd, &mut cell);

            r1b.encrypt_inbound(cmd, &mut cell);

            let (layer, _tag) = cc_in.decrypt(cmd, &mut cell).unwrap();

            assert_eq!(layer, 2.into());

            assert_eq!(&cell.as_ref()[9..], &cell_orig.as_ref()[9..]);

            // TODO: Test tag somehow.

        }

        // Try a failure: sending a cell to a nonexistent hop.

        {

            let mut cell = Box::new([0_u8; 509]).into();

            let err = cc_out.encrypt(cmd, &mut cell, 10.into());

            assert!(matches!(err, Err(Error::NoSuchHop)));

        }

        // Try a failure: A junk cell with no correct auth from any layer.

        {

            let mut cell = Box::new([0_u8; 509]).into();

            let err = cc_in.decrypt(cmd, &mut cell);

            assert!(matches!(err, Err(Error::BadCellAuth)));

        }

    }

    #[test]

    fn hop_num_display() {

        for i in 0..10 {

            let hop_num = HopNum::from(i);

            let expect = format!("#{}", i + 1);

            assert_eq!(expect, hop_num.display().to_string());

        }

    }

    /// Helper: Clear every field in the tor1 `cell` that is reserved for cryptography by relay cell

    /// format `version.

    ///

    /// We do this so that we can be sure that the _other_ fields have all been transmitted correctly.

    fn clean_cell_fields(cell: &mut RelayCellBody, format: RelayCellFormat) {

        use super::tor1;

        match format {

            RelayCellFormat::V0 => {

                cell.0[tor1::RECOGNIZED_RANGE].fill(0);

                cell.0[tor1::DIGEST_RANGE].fill(0);

            }

            RelayCellFormat::V1 => {

                cell.0[0..16].fill(0);

            }

            _ => {

                panic!("Unrecognized format!");

            }

        }

    }

    /// Helper: Test a single-hop message, forward from the client.

    fn test_fwd_one_hop<CS, RS, CF, CB, RF, RB>(format: RelayCellFormat)

    where

        CS: CryptInit + ClientLayer<CF, CB>,

        RS: CryptInit + RelayLayer<RF, RB>,

        CF: OutboundClientLayer,

        CB: InboundClientLayer,

        RF: OutboundRelayLayer,

        RB: InboundRelayLayer,

    {

        let mut rng = testing_rng();

        assert_eq!(CS::seed_len(), RS::seed_len());

        let mut seed = vec![0; CS::seed_len()];

        rng.fill_bytes(&mut seed[..]);

        let (mut client, _, _) = CS::initialize(&seed).unwrap().split_client_layer();

        let (mut relay, _, _) = RS::initialize(&seed).unwrap().split_relay_layer();

        for _ in 0..5 {

            let mut cell = RelayCellBody(Box::new([0_u8; 509]));

            rng.fill_bytes(&mut cell.0[..]);

            clean_cell_fields(&mut cell, format);

            let msg_orig = cell.clone();

            let ctag = client.originate_for(ChanCmd::RELAY, &mut cell);

            assert_ne!(cell.0[16..], msg_orig.0[16..]);

            let rtag = relay.decrypt_outbound(ChanCmd::RELAY, &mut cell);

            clean_cell_fields(&mut cell, format);

            assert_eq!(cell.0[..], msg_orig.0[..]);

            assert_eq!(rtag, Some(ctag));

        }

    }

    /// Helper: Test a single-hop message, backwards towards the client.

    fn test_rev_one_hop<CS, RS, CF, CB, RF, RB>(format: RelayCellFormat)

    where

        CS: CryptInit + ClientLayer<CF, CB>,

        RS: CryptInit + RelayLayer<RF, RB>,

        CF: OutboundClientLayer,

        CB: InboundClientLayer,

        RF: OutboundRelayLayer,

        RB: InboundRelayLayer,

    {

        let mut rng = testing_rng();

        assert_eq!(CS::seed_len(), RS::seed_len());

        let mut seed = vec![0; CS::seed_len()];

        rng.fill_bytes(&mut seed[..]);

        let (_, mut client, _) = CS::initialize(&seed).unwrap().split_client_layer();

        let (_, mut relay, _) = RS::initialize(&seed).unwrap().split_relay_layer();

        for _ in 0..5 {

            let mut cell = RelayCellBody(Box::new([0_u8; 509]));

            rng.fill_bytes(&mut cell.0[..]);

            clean_cell_fields(&mut cell, format);

            let msg_orig = cell.clone();

            let rtag = relay.originate(ChanCmd::RELAY, &mut cell);

            assert_ne!(cell.0[16..], msg_orig.0[16..]);

            let ctag = client.decrypt_inbound(ChanCmd::RELAY, &mut cell);

            clean_cell_fields(&mut cell, format);

            assert_eq!(cell.0[..], msg_orig.0[..]);

            assert_eq!(ctag, Some(rtag));

        }

    }

    fn test_fwd_three_hops_leaky<CS, RS, CF, CB, RF, RB>(format: RelayCellFormat)

    where

        CS: CryptInit + ClientLayer<CF, CB>,

        RS: CryptInit + RelayLayer<RF, RB>,

        CF: OutboundClientLayer + Send + 'static,

        CB: InboundClientLayer,

        RF: OutboundRelayLayer,

        RB: InboundRelayLayer,

    {

        let mut rng = testing_rng();

        assert_eq!(CS::seed_len(), RS::seed_len());

        let mut client = OutboundClientCrypt::new();

        let mut relays = Vec::new();

        for _ in 0..3 {

            let mut seed = vec![0; CS::seed_len()];

            rng.fill_bytes(&mut seed[..]);

            let (client_layer, _, _) = CS::initialize(&seed).unwrap().split_client_layer();

            let (relay_layer, _, _) = RS::initialize(&seed).unwrap().split_relay_layer();

            client.add_layer(Box::new(client_layer));

            relays.push(relay_layer);

        }

        'cell_loop: for _ in 0..32 {

            let mut cell = RelayCellBody(Box::new([0_u8; 509]));

            rng.fill_bytes(&mut cell.0[..]);

            clean_cell_fields(&mut cell, format);

            let msg_orig = cell.clone();

            let cmd = *[ChanCmd::RELAY, ChanCmd::RELAY_EARLY]

                .choose(&mut rng)

                .unwrap();

            let hop: u8 = rng.gen_range_checked(0_u8..=2).unwrap();

            let ctag = client.encrypt(cmd, &mut cell, hop.into()).unwrap();

            for r_idx in 0..=hop {

                let rtag = relays[r_idx as usize].decrypt_outbound(cmd, &mut cell);

                if let Some(rtag) = rtag {

                    clean_cell_fields(&mut cell, format);

                    assert_eq!(cell.0[..], msg_orig.0[..]);

                    assert_eq!(rtag, ctag);

                    continue 'cell_loop;

                }

            }

            panic!("None of the relays thought that this cell was recognized!");

        }

    }

    fn test_rev_three_hops_leaky<CS, RS, CF, CB, RF, RB>(format: RelayCellFormat)

    where

        CS: CryptInit + ClientLayer<CF, CB>,

        RS: CryptInit + RelayLayer<RF, RB>,

        CF: OutboundClientLayer,

        CB: InboundClientLayer + Send + 'static,

        RF: OutboundRelayLayer,

        RB: InboundRelayLayer,

    {

        let mut rng = testing_rng();

        assert_eq!(CS::seed_len(), RS::seed_len());

        let mut client = InboundClientCrypt::new();

        let mut relays = Vec::new();

        for _ in 0..3 {

            let mut seed = vec![0; CS::seed_len()];

            rng.fill_bytes(&mut seed[..]);

            let (_, client_layer, _) = CS::initialize(&seed).unwrap().split_client_layer();

            let (_, relay_layer, _) = RS::initialize(&seed).unwrap().split_relay_layer();

            client.add_layer(Box::new(client_layer));

            relays.push(relay_layer);

        }

        for _ in 0..32 {

            let mut cell = RelayCellBody(Box::new([0_u8; 509]));

            rng.fill_bytes(&mut cell.0[..]);

            clean_cell_fields(&mut cell, format);

            let msg_orig = cell.clone();

            let cmd = *[ChanCmd::RELAY, ChanCmd::RELAY_EARLY]

                .choose(&mut rng)

                .unwrap();

            let hop: u8 = rng.gen_range_checked(0_u8..=2).unwrap();

            let rtag = relays[hop as usize].originate(cmd, &mut cell);

            for r_idx in (0..hop.into()).rev() {

                relays[r_idx as usize].encrypt_inbound(cmd, &mut cell);

            }

            let (observed_hop, ctag) = client.decrypt(cmd, &mut cell).unwrap();

            assert_eq!(observed_hop, hop.into());

            clean_cell_fields(&mut cell, format);

            assert_eq!(cell.0[..], msg_orig.0[..]);

            assert_eq!(ctag, rtag);

        }

    }

    macro_rules! integration_tests { { $modname:ident($fmt:expr, $ctype:ty, $rtype:ty) } => {

        mod $modname {

            use super::*;

            #[test]

            fn test_fwd_one_hop() {

                super::test_fwd_one_hop::<$ctype, $rtype, _, _, _, _>($fmt);

            }

            #[test]

            fn test_rev_one_hop() {

                super::test_rev_one_hop::<$ctype, $rtype, _, _, _, _>($fmt);

            }

            #[test]

            fn test_fwd_three_hops_leaky() {

                super::test_fwd_three_hops_leaky::<$ctype, $rtype, _, _, _, _>($fmt);

            }

            #[test]

            fn test_rev_three_hops_leaky() {

                super::test_rev_three_hops_leaky::<$ctype, $rtype, _, _, _, _>($fmt);

            }

        }

    }}

    integration_tests! { tor1(RelayCellFormat::V0, Tor1RelayCrypto, Tor1RelayCrypto) }

    #[cfg(feature = "hs-common")]

    integration_tests! { tor1_hs(RelayCellFormat::V0, Tor1Hsv3RelayCrypto, Tor1Hsv3RelayCrypto) }

    #[cfg(feature = "counter-galois-onion")]

    integration_tests! {

        cgo_aes128(RelayCellFormat::V1,

            cgo::CryptStatePair<aes::Aes128Dec, aes::Aes128Enc>,// client

            cgo::CryptStatePair<aes::Aes128Enc, aes::Aes128Enc> // relay

        )

    }

    #[cfg(feature = "counter-galois-onion")]

    integration_tests! {

        cgo_aes256(RelayCellFormat::V1,

            cgo::CryptStatePair<aes::Aes256Dec, aes::Aes256Enc>,// client

            cgo::CryptStatePair<aes::Aes256Enc, aes::Aes256Enc> // relay

        )

    }

}