//! An implementation of Tor's current relay cell cryptography.

//!

//! These are not very good algorithms; they were the best we could come up with

//! in ~2002.  They are somewhat inefficient, and vulnerable to tagging attacks.

//! They should get replaced within the next several years.  For information on

//! some older proposed alternatives so far, see proposals 261, 295, and 298.

//!

//! I am calling this design `tor1`; it does not have a generally recognized

//! name.

use crate::{Error, Result, client::circuit::CircuitBinding, crypto::binding::CIRC_BINDING_LEN};

use cipher::{KeyIvInit, StreamCipher};

use digest::Digest;

use tor_cell::{chancell::ChanCmd, relaycell::msg::SendmeTag};

use tor_error::internal;

use typenum::Unsigned;

use super::{

    ClientLayer, CryptInit, InboundClientLayer, InboundRelayLayer, OutboundClientLayer,

    OutboundRelayLayer, RelayCellBody, RelayLayer,

};

/// Length of SENDME tag generated by this encryption method.

const SENDME_TAG_LEN: usize = 20;

/// A CryptState represents one layer of shared cryptographic state between

/// a relay and a client for a single hop, in a single direction.

///

/// For example, if a client makes a 3-hop circuit, then it will have 6

/// `CryptState`s, one for each relay, for each direction of communication.

///

/// Note that although `CryptState` is used to implement [`OutboundClientLayer`],

/// [`InboundClientLayer`], [`OutboundRelayLayer`], and [`InboundRelayLayer`],

/// each instance will only be used for one of these roles.

///

/// It is parameterized on a stream cipher and a digest type: most circuits

/// will use AES-128-CTR and SHA1, but v3 onion services use AES-256-CTR and

/// SHA-3.

struct CryptState<SC: StreamCipher, D: Digest + Clone> {

    /// Stream cipher for en/decrypting cell bodies.

    ///

    /// This cipher is the one keyed with Kf or Kb in the spec.

    cipher: SC,

    /// Digest for authenticating cells to/from this hop.

    ///

    /// This digest is the one keyed with Df or Db in the spec.

    digest: D,

    /// Most recent digest value generated by this crypto.

    last_sendme_tag: SendmeTag,

}

/// A pair of CryptStates shared between a client and a relay, one for the

/// outbound (away from the client) direction, and one for the inbound

/// (towards the client) direction.

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

pub(crate) struct CryptStatePair<SC: StreamCipher, D: Digest + Clone> {

    /// State for en/decrypting cells sent away from the client.

    fwd: CryptState<SC, D>,

    /// State for en/decrypting cells sent towards the client.

    back: CryptState<SC, D>,

    /// A circuit binding key.

    binding: CircuitBinding,

}

impl<SC: StreamCipher + KeyIvInit, D: Digest + Clone> CryptInit for CryptStatePair<SC, D> {

        // This corresponds to the use of the KDF algorithm as described in

        // tor-spec 5.2.2

        // Advances `seed` by `n` bytes, returning the advanced bytes

}

impl<SC, D> ClientLayer<ClientOutbound<SC, D>, ClientInbound<SC, D>> for CryptStatePair<SC, D>

where

    SC: StreamCipher,

    D: Digest + Clone,

{

}

/// An inbound relay layer, encrypting relay cells for a client.

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

#[derive(derive_more::From)]

pub(crate) struct RelayInbound<SC: StreamCipher, D: Digest + Clone>(CryptState<SC, D>);

impl<SC: StreamCipher, D: Digest + Clone> InboundRelayLayer for RelayInbound<SC, D> {

        // This is describe in tor-spec 5.5.3.1, "Relaying Backward at Onion Routers"

}

/// An outbound relay layer, decrypting relay cells from a client.

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

#[derive(derive_more::From)]

pub(crate) struct RelayOutbound<SC: StreamCipher, D: Digest + Clone>(CryptState<SC, D>);

impl<SC: StreamCipher, D: Digest + Clone> OutboundRelayLayer for RelayOutbound<SC, D> {

        // This is describe in tor-spec 5.5.2.2, "Relaying Forward at Onion Routers"

        } else {

        }

}

impl<SC: StreamCipher, D: Digest + Clone> RelayLayer<RelayOutbound<SC, D>, RelayInbound<SC, D>>

    for CryptStatePair<SC, D>

{

}

/// An outbound client layer, encrypting relay cells for a relay.

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

#[derive(derive_more::From)]

pub(crate) struct ClientOutbound<SC: StreamCipher, D: Digest + Clone>(CryptState<SC, D>);

impl<SC: StreamCipher, D: Digest + Clone> OutboundClientLayer for ClientOutbound<SC, D> {

        // This is a single iteration of the loop described in tor-spec

        // 5.5.2.1, "routing away from the origin."

}

/// An outbound client layer, decryption relay cells from a relay.

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

#[derive(derive_more::From)]

pub(crate) struct ClientInbound<SC: StreamCipher, D: Digest + Clone>(CryptState<SC, D>);

impl<SC: StreamCipher, D: Digest + Clone> InboundClientLayer for ClientInbound<SC, D> {

        // This is a single iteration of the loop described in tor-spec

        // 5.5.3, "routing to the origin."

        } else {

        }

}

/// Location in the relay cell for our "recognized" field.

pub(super) const RECOGNIZED_RANGE: std::ops::Range<usize> = 1..3;

/// Location in the relay cell for our "Digest" field.

pub(super) const DIGEST_RANGE: std::ops::Range<usize> = 5..9;

/// An all-zero digest value.

pub(super) const EMPTY_DIGEST: &[u8] = &[0, 0, 0, 0];

/// Functions on RelayCellBody that implement the digest/recognized

/// algorithm.

///

/// The current relay crypto protocol uses two wholly inadequate fields to

/// see whether a cell is intended for its current recipient: a two-byte

/// "recognized" field that needs to be all-zero; and a four-byte "digest"

/// field containing a running digest of all cells (for this recipient) to

/// this one, seeded with an initial value (either Df or Db in the spec).

///

/// These operations are described in tor-spec section 6.1 "Relay cells"

//

// TODO: It may be that we should un-parameterize the functions

// that use RCF: given our timeline for deployment of CGO encryption,

// it is likely that we will never actually want to  support `tor1` encryption

// with any other format than RelayCellFormat::V0.

impl RelayCellBody {

    /// Returns the byte slice of the `recognized` field.

    /// Returns the mut byte slice of the `recognized` field.

    /// Returns the byte slice of the `digest` field.

    /// Returns the mut byte slice of the `digest` field.

    /// Prepare a cell body by setting its digest and recognized field.

        // TODO(nickm) can we avoid this clone?  Probably not.

        // TODO PERF: Make sure this compiles nicely.

    /// Check whether this just-decrypted cell is now an authenticated plaintext.

    ///

    /// This method returns true if the `recognized` field is all zeros, and if the

    /// `digest` field is a digest of the correct material.

    /// If it returns true, it also sets `rcvg` to the appropriate authenticated

    /// SENDME tag to use if acknowledging this message.

    ///

    /// If this method returns false, then either further decryption is required,

    /// or the cell is corrupt.

    ///

    // TODO #1336: Further optimize and/or benchmark this.

        use crate::util::ct;

        // Validate 'Recognized' field

        // Now also validate the 'Digest' field:

        // Add bytes up to the 'Digest' field

        // Add zeroes where the 'Digest' field is

        // Add the rest of the bytes

        // Clone the digest before finalize destroys it because we will use

        // it in the future

            // Copy useful things out of this cell (we keep running digest)

}

/// Benchmark utilities for the `tor1` module.

#[cfg(feature = "bench")]

pub mod bench_utils {

    pub use super::ClientInbound;

    pub use super::ClientOutbound;

    pub use super::CryptStatePair;

    pub use super::RelayInbound;

    pub use super::RelayOutbound;

    /// The throughput for a relay cell in bytes with the Tor1 scheme.

    pub const TOR1_THROUGHPUT: u64 = 498;

}

#[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_time_subtraction)]

    #![allow(clippy::useless_vec)]

    #![allow(clippy::needless_pass_by_value)]

    #![allow(clippy::string_slice)] // See arti#2571

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

    use crate::crypto::cell::{

        InboundClientCrypt, OutboundClientCrypt, Tor1RelayCrypto, test::add_layers,

    };

    use super::*;

    // From tor's test_relaycrypt.c

    #[test]

    fn testvec() {

        use digest::XofReader;

        use digest::{ExtendableOutput, Update};

        // (The ....s at the end here are the KH ca)

        const K1: &[u8; 92] =

            b"    'My public key is in this signed x509 object', said Tom assertively.      (N-PREG-VIRYL)";

        const K2: &[u8; 92] =

            b"'Let's chart the pedal phlanges in the tomb', said Tom cryptographically.  (PELCG-GBR-TENCU)";

        const K3: &[u8; 92] =

            b"     'Segmentation fault bugs don't _just happen_', said Tom seethingly.        (P-GUVAT-YL)";

        const SEED: &[u8;108] = b"'You mean to tell me that there's a version of Sha-3 with no limit on the output length?', said Tom shakily.";

        let cmd = ChanCmd::RELAY;

        // These test vectors were generated from Tor.

        let data: &[(usize, &str)] = &include!("../../../testdata/cell_crypt.rs");

        let mut cc_out = OutboundClientCrypt::new();

        let mut cc_in = InboundClientCrypt::new();

        let pair = Tor1RelayCrypto::initialize(&K1[..]).unwrap();

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

        let pair = Tor1RelayCrypto::initialize(&K2[..]).unwrap();

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

        let pair = Tor1RelayCrypto::initialize(&K3[..]).unwrap();

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

        let mut xof = tor_llcrypto::d::Shake256::default();

        xof.update(&SEED[..]);

        let mut stream = xof.finalize_xof();

        let mut j = 0;

        for cellno in 0..51 {

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

            body[0] = 2; // command: data.

            body[4] = 1; // streamid: 1.

            body[9] = 1; // length: 498

            body[10] = 242;

            stream.read(&mut body[11..]);

            let mut cell = body.into();

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

            if cellno == data[j].0 {

                let expected = hex::decode(data[j].1).unwrap();

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

                j += 1;

            }

        }

    }

}