librustzcash/zcash_client_backend/src/keys.rs

//! Helper functions for managing light client key material.
use zcash_address::unified::{self, Container, Encoding};
use zcash_primitives::{
    consensus,
    sapling::keys as sapling_keys,
    zip32::{AccountId, DiversifierIndex},
};

use crate::address::UnifiedAddress;

#[cfg(feature = "transparent-inputs")]
use zcash_primitives::legacy::keys::{self as legacy, IncomingViewingKey};

pub mod sapling {
    use zcash_primitives::zip32::{AccountId, ChildIndex};
    pub use zcash_primitives::zip32::{ExtendedFullViewingKey, ExtendedSpendingKey};

    /// Derives the ZIP 32 [`ExtendedSpendingKey`] for a given coin type and account from the
    /// given seed.
    ///
    /// # Panics
    ///
    /// Panics if `seed` is shorter than 32 bytes.
    ///
    /// # Examples
    ///
    /// ```
    /// use zcash_primitives::{
    ///     constants::testnet::COIN_TYPE,
    ///     zip32::AccountId,
    /// };
    /// use zcash_client_backend::{
    ///     keys::sapling,
    /// };
    ///
    /// let extsk = sapling::spending_key(&[0; 32][..], COIN_TYPE, AccountId::from(0));
    /// ```
    /// [`ExtendedSpendingKey`]: zcash_primitives::zip32::ExtendedSpendingKey
    pub fn spending_key(seed: &[u8], coin_type: u32, account: AccountId) -> ExtendedSpendingKey {
        if seed.len() < 32 {
            panic!("ZIP 32 seeds MUST be at least 32 bytes");
        }

        ExtendedSpendingKey::from_path(
            &ExtendedSpendingKey::master(seed),
            &[
                ChildIndex::Hardened(32),
                ChildIndex::Hardened(coin_type),
                ChildIndex::Hardened(account.into()),
            ],
        )
    }
}

#[cfg(feature = "transparent-inputs")]
fn to_transparent_child_index(j: DiversifierIndex) -> Option<u32> {
    let (low_4_bytes, rest) = j.0.split_at(4);
    let transparent_j = u32::from_le_bytes(low_4_bytes.try_into().unwrap());
    if transparent_j > (0x7FFFFFFF) || rest.iter().any(|b| b != &0) {
        None
    } else {
        Some(transparent_j)
    }
}

#[derive(Debug)]
#[doc(hidden)]
pub enum DerivationError {
    Orchard(orchard::zip32::Error),
    #[cfg(feature = "transparent-inputs")]
    Transparent(hdwallet::error::Error),
}

/// A set of viewing keys that are all associated with a single
/// ZIP-0032 account identifier.
#[derive(Clone, Debug)]
#[doc(hidden)]
pub struct UnifiedSpendingKey {
    account: AccountId,
    #[cfg(feature = "transparent-inputs")]
    transparent: legacy::AccountPrivKey,
    sapling: sapling::ExtendedSpendingKey,
    orchard: orchard::keys::SpendingKey,
}

#[doc(hidden)]
impl UnifiedSpendingKey {
    pub fn from_seed<P: consensus::Parameters>(
        params: &P,
        seed: &[u8],
        account: AccountId,
    ) -> Result<UnifiedSpendingKey, DerivationError> {
        if seed.len() < 32 {
            panic!("ZIP 32 seeds MUST be at least 32 bytes");
        }

        let orchard =
            orchard::keys::SpendingKey::from_zip32_seed(seed, params.coin_type(), account.into())
                .map_err(DerivationError::Orchard)?;

        #[cfg(feature = "transparent-inputs")]
        let transparent = legacy::AccountPrivKey::from_seed(params, seed, account)
            .map_err(DerivationError::Transparent)?;

        Ok(UnifiedSpendingKey {
            account,
            #[cfg(feature = "transparent-inputs")]
            transparent,
            sapling: sapling::spending_key(seed, params.coin_type(), account),
            orchard,
        })
    }

    pub fn to_unified_full_viewing_key(&self) -> UnifiedFullViewingKey {
        UnifiedFullViewingKey {
            #[cfg(feature = "transparent-inputs")]
            transparent: Some(self.transparent.to_account_pubkey()),
            sapling: Some(sapling::ExtendedFullViewingKey::from(&self.sapling).into()),
            orchard: Some((&self.orchard).into()),
            unknown: vec![],
        }
    }

    pub fn account(&self) -> AccountId {
        self.account
    }

    /// Returns the transparent component of the unified key at the
    /// BIP44 path `m/44'/<coin_type>'/<account>'`.
    #[cfg(feature = "transparent-inputs")]
    pub fn transparent(&self) -> &legacy::AccountPrivKey {
        &self.transparent
    }

    /// Returns the Sapling extended spending key component of this unified spending key.
    pub fn sapling(&self) -> &sapling::ExtendedSpendingKey {
        &self.sapling
    }

    /// Returns the Orchard spending key component of this unified spending key.
    pub fn orchard(&self) -> &orchard::keys::SpendingKey {
        &self.orchard
    }
}

/// A set of viewing keys that are all associated with a single
/// ZIP-0032 account identifier.
#[derive(Clone, Debug)]
#[doc(hidden)]
pub struct UnifiedFullViewingKey {
    #[cfg(feature = "transparent-inputs")]
    transparent: Option<legacy::AccountPubKey>,
    sapling: Option<sapling_keys::DiversifiableFullViewingKey>,
    orchard: Option<orchard::keys::FullViewingKey>,
    unknown: Vec<(u32, Vec<u8>)>,
}

#[doc(hidden)]
impl UnifiedFullViewingKey {
    /// Construct a new unified full viewing key, if the required components are present.
    pub fn new(
        #[cfg(feature = "transparent-inputs")] transparent: Option<legacy::AccountPubKey>,
        sapling: Option<sapling_keys::DiversifiableFullViewingKey>,
        orchard: Option<orchard::keys::FullViewingKey>,
    ) -> Option<UnifiedFullViewingKey> {
        if sapling.is_none() {
            None
        } else {
            Some(UnifiedFullViewingKey {
                #[cfg(feature = "transparent-inputs")]
                transparent,
                sapling,
                orchard,
                // We don't allow constructing new UFVKs with unknown items, but we store
                // this to allow parsing such UFVKs.
                unknown: vec![],
            })
        }
    }

    /// Parses a `UnifiedFullViewingKey` from its [ZIP 316] string encoding.
    ///
    /// [ZIP 316]: https://zips.z.cash/zip-0316
    pub fn decode<P: consensus::Parameters>(params: &P, encoding: &str) -> Result<Self, String> {
        let (net, ufvk) = unified::Ufvk::decode(encoding).map_err(|e| e.to_string())?;
        let expected_net = params.address_network().expect("Unrecognized network");
        if net != expected_net {
            return Err(format!(
                "UFVK is for network {:?} but we expected {:?}",
                net, expected_net,
            ));
        }

        let mut orchard = None;
        let mut sapling = None;
        #[cfg(feature = "transparent-inputs")]
        let mut transparent = None;

        // We can use as-parsed order here for efficiency, because we're breaking out the
        // receivers we support from the unknown receivers.
        let unknown = ufvk
            .items_as_parsed()
            .iter()
            .filter_map(|receiver| match receiver {
                unified::Fvk::Orchard(data) => orchard::keys::FullViewingKey::from_bytes(data)
                    .ok_or("Invalid Orchard FVK in Unified FVK")
                    .map(|addr| {
                        orchard = Some(addr);
                        None
                    })
                    .transpose(),
                unified::Fvk::Sapling(data) => {
                    sapling_keys::DiversifiableFullViewingKey::from_bytes(data)
                        .ok_or("Invalid Sapling FVK in Unified FVK")
                        .map(|pa| {
                            sapling = Some(pa);
                            None
                        })
                        .transpose()
                }
                #[cfg(feature = "transparent-inputs")]
                unified::Fvk::P2pkh(data) => legacy::AccountPubKey::deserialize(data)
                    .map_err(|_| "Invalid transparent FVK in Unified FVK")
                    .map(|tfvk| {
                        transparent = Some(tfvk);
                        None
                    })
                    .transpose(),
                #[cfg(not(feature = "transparent-inputs"))]
                unified::Fvk::P2pkh(data) => {
                    Some(Ok((unified::Typecode::P2pkh.into(), data.to_vec())))
                }
                unified::Fvk::Unknown { typecode, data } => Some(Ok((*typecode, data.clone()))),
            })
            .collect::<Result<_, _>>()?;

        Ok(Self {
            #[cfg(feature = "transparent-inputs")]
            transparent,
            sapling,
            orchard,
            unknown,
        })
    }

    /// Returns the string encoding of this `UnifiedFullViewingKey` for the given network.
    pub fn encode<P: consensus::Parameters>(&self, params: &P) -> String {
        let items = std::iter::empty()
            .chain(
                self.orchard
                    .as_ref()
                    .map(|fvk| fvk.to_bytes())
                    .map(unified::Fvk::Orchard),
            )
            .chain(
                self.sapling
                    .as_ref()
                    .map(|dfvk| dfvk.to_bytes())
                    .map(unified::Fvk::Sapling),
            )
            .chain(
                self.unknown
                    .iter()
                    .map(|(typecode, data)| unified::Fvk::Unknown {
                        typecode: *typecode,
                        data: data.clone(),
                    }),
            );
        #[cfg(feature = "transparent-inputs")]
        let items = items.chain(
            self.transparent
                .as_ref()
                .map(|tfvk| tfvk.serialize().try_into().unwrap())
                .map(unified::Fvk::P2pkh),
        );

        let ufvk = unified::Ufvk::try_from_items(items.collect())
            .expect("UnifiedFullViewingKey should only be constructed safely");
        ufvk.encode(&params.address_network().expect("Unrecognized network"))
    }

    /// Returns the transparent component of the unified key at the
    /// BIP44 path `m/44'/<coin_type>'/<account>'`.
    #[cfg(feature = "transparent-inputs")]
    pub fn transparent(&self) -> Option<&legacy::AccountPubKey> {
        self.transparent.as_ref()
    }

    /// Returns the Sapling diversifiable full viewing key component of this unified key.
    pub fn sapling(&self) -> Option<&sapling_keys::DiversifiableFullViewingKey> {
        self.sapling.as_ref()
    }

    /// Returns the Orchard full viewing key component of this unified key.
    pub fn orchard(&self) -> Option<&orchard::keys::FullViewingKey> {
        self.orchard.as_ref()
    }

    /// Attempts to derive the Unified Address for the given diversifier index.
    ///
    /// Returns `None` if the specified index does not produce a valid diversifier.
    // TODO: Allow filtering down by receiver types?
    pub fn address(&self, j: DiversifierIndex) -> Option<UnifiedAddress> {
        let sapling = if let Some(extfvk) = self.sapling.as_ref() {
            Some(extfvk.address(j)?)
        } else {
            None
        };

        #[cfg(feature = "transparent-inputs")]
        let transparent = if let Some(tfvk) = self.transparent.as_ref() {
            match to_transparent_child_index(j) {
                Some(transparent_j) => match tfvk
                    .derive_external_ivk()
                    .and_then(|tivk| tivk.derive_address(transparent_j))
                {
                    Ok(taddr) => Some(taddr),
                    Err(_) => return None,
                },
                // Diversifier doesn't generate a valid transparent child index.
                None => return None,
            }
        } else {
            None
        };
        #[cfg(not(feature = "transparent-inputs"))]
        let transparent = None;

        UnifiedAddress::from_receivers(None, sapling, transparent)
    }

    /// Searches the diversifier space starting at diversifier index `j` for one which will
    /// produce a valid diversifier, and return the Unified Address constructed using that
    /// diversifier along with the index at which the valid diversifier was found.
    ///
    /// Returns `None` if no valid diversifier exists
    pub fn find_address(
        &self,
        mut j: DiversifierIndex,
    ) -> Option<(UnifiedAddress, DiversifierIndex)> {
        // If we need to generate a transparent receiver, check that the user has not
        // specified an invalid transparent child index, from which we can never search to
        // find a valid index.
        #[cfg(feature = "transparent-inputs")]
        if self.transparent.is_some() && to_transparent_child_index(j).is_none() {
            return None;
        }

        // Find a working diversifier and construct the associated address.
        loop {
            let res = self.address(j);
            if let Some(ua) = res {
                break Some((ua, j));
            }
            if j.increment().is_err() {
                break None;
            }
        }
    }

    /// Returns the Unified Address corresponding to the smallest valid diversifier index,
    /// along with that index.
    pub fn default_address(&self) -> (UnifiedAddress, DiversifierIndex) {
        self.find_address(DiversifierIndex::new())
            .expect("UFVK should have at least one valid diversifier")
    }
}

#[cfg(test)]
mod tests {
    use super::{sapling, UnifiedFullViewingKey};
    use zcash_primitives::{
        consensus::MAIN_NETWORK,
        zip32::{AccountId, ExtendedFullViewingKey},
    };

    #[cfg(feature = "transparent-inputs")]
    use {
        crate::encoding::AddressCodec,
        zcash_primitives::legacy::{
            self,
            keys::{AccountPrivKey, IncomingViewingKey},
        },
    };

    #[cfg(feature = "transparent-inputs")]
    fn seed() -> Vec<u8> {
        let seed_hex = "6ef5f84def6f4b9d38f466586a8380a38593bd47c8cda77f091856176da47f26b5bd1c8d097486e5635df5a66e820d28e1d73346f499801c86228d43f390304f";
        hex::decode(&seed_hex).unwrap()
    }

    #[test]
    #[should_panic]
    fn spending_key_panics_on_short_seed() {
        let _ = sapling::spending_key(&[0; 31][..], 0, AccountId::from(0));
    }

    #[cfg(feature = "transparent-inputs")]
    #[test]
    fn pk_to_taddr() {
        let taddr =
            legacy::keys::AccountPrivKey::from_seed(&MAIN_NETWORK, &seed(), AccountId::from(0))
                .unwrap()
                .to_account_pubkey()
                .derive_external_ivk()
                .unwrap()
                .derive_address(0)
                .unwrap()
                .encode(&MAIN_NETWORK);
        assert_eq!(taddr, "t1PKtYdJJHhc3Pxowmznkg7vdTwnhEsCvR4".to_string());
    }

    #[test]
    fn ufvk_round_trip() {
        let account = 0.into();

        let orchard = {
            let sk = orchard::keys::SpendingKey::from_zip32_seed(&[0; 32], 0, 0).unwrap();
            Some(orchard::keys::FullViewingKey::from(&sk))
        };

        let sapling = {
            let extsk = sapling::spending_key(&[0; 32], 0, account);
            Some(ExtendedFullViewingKey::from(&extsk).into())
        };

        #[cfg(feature = "transparent-inputs")]
        let transparent = {
            let privkey =
                AccountPrivKey::from_seed(&MAIN_NETWORK, &[0; 32], AccountId::from(0)).unwrap();
            Some(privkey.to_account_pubkey())
        };

        let ufvk = UnifiedFullViewingKey::new(
            #[cfg(feature = "transparent-inputs")]
            transparent,
            sapling,
            orchard,
        )
        .unwrap();

        let encoded = ufvk.encode(&MAIN_NETWORK);

        // test encoded form against known values
        let encoded_with_t = "uview1tg6rpjgju2s2j37gkgjq79qrh5lvzr6e0ed3n4sf4hu5qd35vmsh7avl80xa6mx7ryqce9hztwaqwrdthetpy4pc0kce25x453hwcmax02p80pg5savlg865sft9reat07c5vlactr6l2pxtlqtqunt2j9gmvr8spcuzf07af80h5qmut38h0gvcfa9k4rwujacwwca9vu8jev7wq6c725huv8qjmhss3hdj2vh8cfxhpqcm2qzc34msyrfxk5u6dqttt4vv2mr0aajreww5yufpk0gn4xkfm888467k7v6fmw7syqq6cceu078yw8xja502jxr0jgum43lhvpzmf7eu5dmnn6cr6f7p43yw8znzgxg598mllewnx076hljlvynhzwn5es94yrv65tdg3utuz2u3sras0wfcq4adxwdvlk387d22g3q98t5z74quw2fa4wed32escx8dwh4mw35t4jwf35xyfxnu83mk5s4kw2glkgsshmxk";
        let _encoded_no_t = "uview12z384wdq76ceewlsu0esk7d97qnd23v2qnvhujxtcf2lsq8g4hwzpx44fwxssnm5tg8skyh4tnc8gydwxefnnm0hd0a6c6etmj0pp9jqkdsllkr70u8gpf7ndsfqcjlqn6dec3faumzqlqcmtjf8vp92h7kj38ph2786zx30hq2wru8ae3excdwc8w0z3t9fuw7mt7xy5sn6s4e45kwm0cjp70wytnensgdnev286t3vew3yuwt2hcz865y037k30e428dvgne37xvyeal2vu8yjnznphf9t2rw3gdp0hk5zwq00ws8f3l3j5n3qkqgsyzrwx4qzmgq0xwwk4vz2r6vtsykgz089jncvycmem3535zjwvvtvjw8v98y0d5ydwte575gjm7a7k";
        #[cfg(feature = "transparent-inputs")]
        assert_eq!(encoded, encoded_with_t);
        #[cfg(not(feature = "transparent-inputs"))]
        assert_eq!(encoded, _encoded_no_t);

        let decoded = UnifiedFullViewingKey::decode(&MAIN_NETWORK, &encoded).unwrap();
        let reencoded = decoded.encode(&MAIN_NETWORK);
        assert_eq!(encoded, reencoded);

        #[cfg(feature = "transparent-inputs")]
        assert_eq!(
            decoded.transparent.map(|t| t.serialize()),
            ufvk.transparent.as_ref().map(|t| t.serialize()),
        );
        assert_eq!(
            decoded.sapling.map(|s| s.to_bytes()),
            ufvk.sapling.map(|s| s.to_bytes()),
        );
        assert_eq!(
            decoded.orchard.map(|o| o.to_bytes()),
            ufvk.orchard.map(|o| o.to_bytes()),
        );

        let decoded_with_t = UnifiedFullViewingKey::decode(&MAIN_NETWORK, encoded_with_t).unwrap();
        #[cfg(feature = "transparent-inputs")]
        assert_eq!(
            decoded_with_t.transparent.map(|t| t.serialize()),
            ufvk.transparent.as_ref().map(|t| t.serialize()),
        );
        #[cfg(not(feature = "transparent-inputs"))]
        assert_eq!(decoded_with_t.unknown.len(), 1);
    }
}