Initial commit

src/key.rs

@@ -0,0 +1,81 @@
+use chacha20poly1305::{aead::heapless::Vec, AeadInPlace, KeyInit};
+use zeroize::{Zeroize, ZeroizeOnDrop};
+
+const KEY_SIZE: usize = 32;
+const PBKDF_SALT_SIZE: usize = 32;
+const CHACHA_SALT_SIZE: usize = 12;
+
+pub struct KeyDescription {
+	encrypted_key: [u8; KEY_SIZE],
+	pbkdf_salt: [u8; PBKDF_SALT_SIZE],
+	nonce: [u8; CHACHA_SALT_SIZE],
+	pbkdf_rounds: u32,
+}
+
+#[derive(Zeroize, ZeroizeOnDrop)]
+pub struct Key {
+	key: [u8; KEY_SIZE],
+}
+
+impl KeyDescription {
+	/// Measure the number of rounds to match the target time (in milliseconds)
+	/// `now` should return a timestamp in milliseconds
+	pub fn measure_rounds<F: Fn() -> u64>(target_time: u64, now: F) -> u32 {
+		let mut key = [0; KEY_SIZE];
+		let mut memory = [0; KEY_SIZE];
+		let salt = core::hint::black_box([0; PBKDF_SALT_SIZE]);
+		let passphrase = core::hint::black_box([0]);
+
+		let start_1 = (now)();
+		bcrypt_pbkdf::bcrypt_pbkdf_with_memory(passphrase, &salt, 1, &mut key, &mut memory)
+			.unwrap();
+		let end_1 = (now)();
+		let duration_1 = end_1 - start_1;
+
+		key = [0; KEY_SIZE];
+		memory = [0; KEY_SIZE];
+
+		let start_2 = (now)();
+		bcrypt_pbkdf::bcrypt_pbkdf_with_memory(passphrase, &salt, 17, &mut key, &mut memory)
+			.unwrap();
+		let end_2 = (now)();
+		let duration_2 = end_2 - start_2;
+
+		assert!(duration_2 > duration_1);
+
+		(target_time * 16 / (duration_2 - duration_1)) as u32
+	}
+
+	pub fn get_key(&self, passphrase: &mut [u8]) -> Result<Key, Error> {
+		let mut derived_key = [0; KEY_SIZE];
+
+		let mut memory = [0; KEY_SIZE];
+		bcrypt_pbkdf::bcrypt_pbkdf_with_memory(
+			&*passphrase,
+			&self.pbkdf_salt,
+			self.pbkdf_rounds,
+			&mut derived_key,
+			&mut memory,
+		)
+		.map_err(Error::Pbkdf)?;
+
+		passphrase.zeroize();
+
+		let mut key = Vec::<u8, KEY_SIZE>::from_slice(&self.encrypted_key)
+			.map_err(|_| Error::WrongKeySize)?;
+		let cipher = chacha20poly1305::ChaCha20Poly1305::new(&derived_key.into());
+		cipher
+			.decrypt_in_place(&self.nonce.into(), &[], &mut key)
+			.map_err(Error::Chacha)?;
+
+		Ok(Key {
+			key: key.into_array().map_err(|_| Error::WrongKeySize)?,
+		})
+	}
+}
+
+pub enum Error {
+	Chacha(chacha20poly1305::Error),
+	Pbkdf(bcrypt_pbkdf::Error),
+	WrongKeySize,
+}

src/lib.rs

@@ -0,0 +1,8 @@
+#![cfg_attr(not(test), no_std)]
+
+mod key;
+
+pub use key::*;
+
+#[cfg(test)]
+mod tests;

src/tests.rs

@@ -0,0 +1,13 @@
+use crate::*;
+
+#[test]
+fn test_measure_rounds() {
+	let rounds = KeyDescription::measure_rounds(500, || {
+		std::time::SystemTime::now()
+			.duration_since(std::time::UNIX_EPOCH)
+			.unwrap()
+			.as_millis() as u64
+	});
+
+	println!("{rounds}");
+}