From 3278146b1a2dda19ee2e9b8d3a4edaddf55fc99d Mon Sep 17 00:00:00 2001
From: ethicnology <ethicnology@pm.me>
Date: Thu, 14 Nov 2024 10:31:35 -0500
Subject: [PATCH] feat: pwd base85

---
 Cargo.toml               |  1 +
 README.md                |  4 +---
 src/lib.rs               |  2 ++
 src/pwd_base85.rs        | 30 ++++++++++++++++++++++++++++++
 tests/pwd_base85_test.rs | 15 +++++++++++++++
 5 files changed, 49 insertions(+), 3 deletions(-)
 create mode 100644 src/pwd_base85.rs
 create mode 100644 tests/pwd_base85_test.rs

diff --git a/Cargo.toml b/Cargo.toml
index 160e543..3630957 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -41,6 +41,7 @@ bitcoin = "0.32.4"
 bip39 = { version = "2.1.0", optional = true }
 sha3 = "0.10.8"
 base64 = "0.22.1"
+base85 = "2.0.0"
 
 [[example]]
 name = "mnemonic"
diff --git a/README.md b/README.md
index 4616b2f..bb5b8b3 100644
--- a/README.md
+++ b/README.md
@@ -18,9 +18,7 @@ This work is sponsored by [Bull Bitcoin](https://bullbitcoin.com) [<img
 - [x] [HEX](https://github.com/bitcoin/bips/blob/master/bip-0085.mediawiki#hex)
 - [x] [DRNG](https://github.com/bitcoin/bips/blob/master/bip-0085.mediawiki#bip85-drng)
 - [x] [PWD base64](https://github.com/bitcoin/bips/blob/master/bip-0085.mediawiki#user-content-PWD_BASE64)
-- [ ] [PWD base85](https://github.com/bitcoin/bips/blob/master/bip-0085.mediawiki#user-content-PWD_BASE85)
-- [ ] [RSA](https://github.com/bitcoin/bips/blob/master/bip-0085.mediawiki#user-content-RSA)
-- [ ] [RSA GPG](https://github.com/bitcoin/bips/blob/master/bip-0085.mediawiki#user-content-RSA_GPG)
+- [x] [PWD base85](https://github.com/bitcoin/bips/blob/master/bip-0085.mediawiki#user-content-PWD_BASE85)
 - [ ] [DICE](https://github.com/bitcoin/bips/blob/master/bip-0085.mediawiki#user-content-DICE)
 
 
diff --git a/src/lib.rs b/src/lib.rs
index b6ea475..19e049f 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -29,6 +29,7 @@ pub mod error;
 pub mod hex;
 pub mod mnemonic;
 pub mod pwd_base64;
+pub mod pwd_base85;
 pub mod wif;
 pub mod xprv;
 
@@ -37,6 +38,7 @@ pub use error::Error;
 pub use hex::*;
 pub use mnemonic::*;
 pub use pwd_base64::*;
+pub use pwd_base85::*;
 pub use wif::*;
 pub use xprv::*;
 
diff --git a/src/pwd_base85.rs b/src/pwd_base85.rs
new file mode 100644
index 0000000..4afc04b
--- /dev/null
+++ b/src/pwd_base85.rs
@@ -0,0 +1,30 @@
+use super::Error;
+use bitcoin::bip32::{ChildNumber, DerivationPath};
+use bitcoin::{bip32::Xpriv, key::Secp256k1, secp256k1};
+
+/// The `length` can be from 10 to 80 and defines number of bytes derived.
+///
+/// See [specs](https://github.com/bitcoin/bips/blob/master/bip-0085.mediawiki#pwd-base85) for more info.
+pub fn to_pwd_base85<C: secp256k1::Signing>(
+    secp: &Secp256k1<C>,
+    root: &Xpriv,
+    length: u32,
+    index: u32,
+) -> Result<String, Error> {
+    const BIP85_PWD_B64_APPLICATION_NUMBER: ChildNumber = ChildNumber::Hardened { index: 707785 };
+    if length < 10 || length > 80 {
+        return Err(Error::InvalidLength(length));
+    }
+    if index >= 0x80000000 {
+        return Err(Error::InvalidIndex(index));
+    }
+    let path = DerivationPath::from(vec![
+        BIP85_PWD_B64_APPLICATION_NUMBER,
+        ChildNumber::from_hardened_idx(length).unwrap(),
+        ChildNumber::from_hardened_idx(index).unwrap(),
+    ]);
+    let data = crate::derive(secp, root, &path)?;
+    let mut pwd = base85::encode(&data);
+    pwd.truncate(length.try_into().unwrap());
+    Ok(pwd)
+}
diff --git a/tests/pwd_base85_test.rs b/tests/pwd_base85_test.rs
new file mode 100644
index 0000000..4c32be2
--- /dev/null
+++ b/tests/pwd_base85_test.rs
@@ -0,0 +1,15 @@
+use std::str::FromStr;
+
+use bitcoin::{bip32::Xpriv, key::Secp256k1};
+
+#[test]
+fn test_pwd_base64() {
+    let root = Xpriv::from_str(
+        "xprv9s21ZrQH143K2LBWUUQRFXhucrQqBpKdRRxNVq2zBqsx8HVqFk2uYo8kmbaLLHRdqtQpUm98uKfu3vca1LqdGhUtyoFnCNkfmXRyPXLjbKb",
+    )
+    .unwrap();
+
+    let pwd_base64 = bip85_fork::to_pwd_base85(&Secp256k1::new(), &root, 12, 0).unwrap();
+    let expected = "_s`{TW89)i4`";
+    assert_eq!(expected, pwd_base64);
+}