Implement PaymentAddress encoding and decoding

zcash_client_backend/src/constants/mainnet.rs

@@ -2,3 +2,11 @@
 ///
 /// [SLIP 44]: https://github.com/satoshilabs/slips/blob/master/slip-0044.md
 pub const COIN_TYPE: u32 = 133;
+
+/// The HRP for a Bech32-encoded mainnet [`PaymentAddress`].
+///
+/// Defined in section 5.6.4 of the [Zcash Protocol Specification].
+///
+/// [`PaymentAddress`]: sapling_crypto::primitives::PaymentAddress
+/// [Zcash Protocol Specification]: https://github.com/zcash/zips/blob/master/protocol/protocol.pdf
+pub const HRP_SAPLING_PAYMENT_ADDRESS: &str = "zs";

zcash_client_backend/src/constants/testnet.rs

@@ -2,3 +2,11 @@
 ///
 /// [SLIP 44]: https://github.com/satoshilabs/slips/blob/master/slip-0044.md
 pub const COIN_TYPE: u32 = 1;
+
+/// The HRP for a Bech32-encoded testnet [`PaymentAddress`].
+///
+/// Defined in section 5.6.4 of the [Zcash Protocol Specification].
+///
+/// [`PaymentAddress`]: sapling_crypto::primitives::PaymentAddress
+/// [Zcash Protocol Specification]: https://github.com/zcash/zips/blob/master/protocol/protocol.pdf
+pub const HRP_SAPLING_PAYMENT_ADDRESS: &str = "ztestsapling";

zcash_client_backend/src/encoding.rs

@@ -0,0 +1,173 @@
+//! Encoding and decoding functions for Zcash key and address structs.
+//!
+//! Human-Readable Prefixes (HRPs) for Bech32 encodings are located in the [`constants`]
+//! module.
+
+use bech32::{convert_bits, Bech32, Error};
+use pairing::bls12_381::Bls12;
+use sapling_crypto::{
+    jubjub::edwards,
+    primitives::{Diversifier, PaymentAddress},
+};
+use std::io::{self, Write};
+use zcash_primitives::JUBJUB;
+
+fn bech32_encode<F>(hrp: &str, write: F) -> String
+where
+    F: Fn(&mut dyn Write) -> io::Result<()>,
+{
+    let mut data: Vec<u8> = vec![];
+    write(&mut data).expect("Should be able to write to a Vec");
+
+    let converted =
+        convert_bits(&data, 8, 5, true).expect("Should be able to convert Vec<u8> to Vec<u5>");
+    let encoded = Bech32::new_check_data(hrp.into(), converted).expect("hrp is not empty");
+
+    encoded.to_string()
+}
+
+fn bech32_decode<T, F>(hrp: &str, s: &str, read: F) -> Result<Option<T>, Error>
+where
+    F: Fn(Vec<u8>) -> Option<T>,
+{
+    let decoded = s.parse::<Bech32>()?;
+    if decoded.hrp() == hrp {
+        convert_bits(decoded.data(), 5, 8, false).map(|data| read(data))
+    } else {
+        Ok(None)
+    }
+}
+
+/// Writes a [`PaymentAddress`] as a Bech32-encoded string.
+///
+/// # Examples
+///
+/// ```
+/// use pairing::bls12_381::Bls12;
+/// use rand::{SeedableRng, XorShiftRng};
+/// use sapling_crypto::{
+///     jubjub::edwards,
+///     primitives::{Diversifier, PaymentAddress},
+/// };
+/// use zcash_client_backend::{
+///     constants::testnet::HRP_SAPLING_PAYMENT_ADDRESS,
+///     encoding::encode_payment_address,
+/// };
+/// use zcash_primitives::JUBJUB;
+///
+/// let rng = &mut XorShiftRng::from_seed([0x3dbe6259, 0x8d313d76, 0x3237db17, 0xe5bc0654]);
+///
+/// let pa = PaymentAddress {
+///     diversifier: Diversifier([0u8; 11]),
+///     pk_d: edwards::Point::<Bls12, _>::rand(rng, &JUBJUB).mul_by_cofactor(&JUBJUB),
+/// };
+///
+/// assert_eq!(
+///     encode_payment_address(HRP_SAPLING_PAYMENT_ADDRESS, &pa),
+///     "ztestsapling1qqqqqqqqqqqqqqqqqqxrrfaccydp867g6zg7ne5ht37z38jtfyw0ygmp0ja6hhf07twjq6awtaj",
+/// );
+/// ```
+pub fn encode_payment_address(hrp: &str, addr: &PaymentAddress<Bls12>) -> String {
+    bech32_encode(hrp, |w| {
+        w.write_all(&addr.diversifier.0)?;
+        addr.pk_d.write(w)
+    })
+}
+
+/// Decodes a [`PaymentAddress`] from a Bech32-encoded string.
+///
+/// # Examples
+///
+/// ```
+/// use pairing::bls12_381::Bls12;
+/// use rand::{SeedableRng, XorShiftRng};
+/// use sapling_crypto::{
+///     jubjub::edwards,
+///     primitives::{Diversifier, PaymentAddress},
+/// };
+/// use zcash_client_backend::{
+///     constants::testnet::HRP_SAPLING_PAYMENT_ADDRESS,
+///     encoding::decode_payment_address,
+/// };
+/// use zcash_primitives::JUBJUB;
+///
+/// let rng = &mut XorShiftRng::from_seed([0x3dbe6259, 0x8d313d76, 0x3237db17, 0xe5bc0654]);
+///
+/// let pa = PaymentAddress {
+///     diversifier: Diversifier([0u8; 11]),
+///     pk_d: edwards::Point::<Bls12, _>::rand(rng, &JUBJUB).mul_by_cofactor(&JUBJUB),
+/// };
+///
+/// assert_eq!(
+///     decode_payment_address(
+///         HRP_SAPLING_PAYMENT_ADDRESS,
+///         "ztestsapling1qqqqqqqqqqqqqqqqqqxrrfaccydp867g6zg7ne5ht37z38jtfyw0ygmp0ja6hhf07twjq6awtaj",
+///     ),
+///     Ok(Some(pa)),
+/// );
+/// ```
+pub fn decode_payment_address(hrp: &str, s: &str) -> Result<Option<PaymentAddress<Bls12>>, Error> {
+    bech32_decode(hrp, s, |data| {
+        let mut diversifier = Diversifier([0; 11]);
+        diversifier.0.copy_from_slice(&data[0..11]);
+        edwards::Point::<Bls12, _>::read(&data[11..], &JUBJUB)
+            .ok()?
+            .as_prime_order(&JUBJUB)
+            .map(|pk_d| PaymentAddress { pk_d, diversifier })
+    })
+}
+
+#[cfg(test)]
+mod tests {
+    use pairing::bls12_381::Bls12;
+    use rand::{SeedableRng, XorShiftRng};
+    use sapling_crypto::{
+        jubjub::edwards,
+        primitives::{Diversifier, PaymentAddress},
+    };
+    use zcash_primitives::JUBJUB;
+
+    use super::{decode_payment_address, encode_payment_address};
+    use crate::constants;
+
+    #[test]
+    fn payment_address() {
+        let rng = &mut XorShiftRng::from_seed([0x3dbe6259, 0x8d313d76, 0x3237db17, 0xe5bc0654]);
+
+        let addr = PaymentAddress {
+            diversifier: Diversifier([0u8; 11]),
+            pk_d: edwards::Point::<Bls12, _>::rand(rng, &JUBJUB).mul_by_cofactor(&JUBJUB),
+        };
+
+        let encoded_main =
+            "zs1qqqqqqqqqqqqqqqqqqxrrfaccydp867g6zg7ne5ht37z38jtfyw0ygmp0ja6hhf07twjqj2ug6x";
+        let encoded_test =
+            "ztestsapling1qqqqqqqqqqqqqqqqqqxrrfaccydp867g6zg7ne5ht37z38jtfyw0ygmp0ja6hhf07twjq6awtaj";
+
+        assert_eq!(
+            encode_payment_address(constants::mainnet::HRP_SAPLING_PAYMENT_ADDRESS, &addr),
+            encoded_main
+        );
+        assert_eq!(
+            decode_payment_address(
+                constants::mainnet::HRP_SAPLING_PAYMENT_ADDRESS,
+                encoded_main
+            )
+            .unwrap(),
+            Some(addr.clone())
+        );
+
+        assert_eq!(
+            encode_payment_address(constants::testnet::HRP_SAPLING_PAYMENT_ADDRESS, &addr),
+            encoded_test
+        );
+        assert_eq!(
+            decode_payment_address(
+                constants::testnet::HRP_SAPLING_PAYMENT_ADDRESS,
+                encoded_test
+            )
+            .unwrap(),
+            Some(addr)
+        );
+    }
+}

zcash_client_backend/src/lib.rs

@@ -4,4 +4,5 @@
 //! light clients.
 
 pub mod constants;
+pub mod encoding;
 pub mod keys;