keyfork-mnemonic-util: add MnemonicBase::from_nonstandard_bytes

crates/keyfork-shard/src/lib.rs

@@ -249,7 +249,10 @@ pub trait Format {
         let our_key = EphemeralSecret::random();
         let our_pubkey_mnemonic = Mnemonic::from_bytes(PublicKey::from(&our_key).as_bytes())?;
         let shared_secret = our_key.diffie_hellman(&PublicKey::from(their_pubkey));
-        assert!(shared_secret.was_contributory(), bug!("shared secret might be insecure"));
+        assert!(
+            shared_secret.was_contributory(),
+            bug!("shared secret might be insecure")
+        );
         let hkdf = Hkdf::<Sha256>::new(None, shared_secret.as_bytes());
 
         let mut shared_key_data = [0u8; 256 / 8];
@@ -289,12 +292,15 @@ pub trait Format {
 
         // encrypt data
         let encrypted_bytes = shared_key.encrypt(nonce, plaintext_bytes.as_slice())?;
+        assert_eq!(
+            encrypted_bytes.len(),
+            ENCRYPTED_LENGTH as usize,
+            bug!("encrypted bytes size != expected len"),
+        );
+        let mut mnemonic_bytes = [0u8; ENCRYPTED_LENGTH as usize];
+        mnemonic_bytes.copy_from_slice(&encrypted_bytes);
 
-        assert_eq!(encrypted_bytes.len(), ENCRYPTED_LENGTH as usize);
+        let payload_mnemonic = Mnemonic::from_nonstandard_bytes(mnemonic_bytes);
-
-        // safety: size of out_bytes is constant and always % 4 == 0
-        let payload_mnemonic = unsafe { Mnemonic::from_raw_bytes(&encrypted_bytes) };
-        dbg!(payload_mnemonic.words().len());
 
         #[cfg(feature = "qrcode")]
         {
@@ -515,7 +521,10 @@ pub fn remote_decrypt(w: &mut impl Write) -> Result<(), Box<dyn std::error::Erro
         );
 
         let shared_secret = our_key.diffie_hellman(&PublicKey::from(pubkey));
-        assert!(shared_secret.was_contributory(), bug!("shared secret might be insecure"));
+        assert!(
+            shared_secret.was_contributory(),
+            bug!("shared secret might be insecure")
+        );
         let hkdf = Hkdf::<Sha256>::new(None, shared_secret.as_bytes());
 
         let mut shared_key_data = [0u8; 256 / 8];

crates/util/keyfork-mnemonic-util/src/bin/keyfork-mnemonic-from-seed.rs

@@ -8,7 +8,7 @@ fn main() -> Result<(), Box<dyn std::error::Error>> {
     input.read_line(&mut line)?;
     let decoded = smex::decode(line.trim())?;
 
-    let mnemonic = unsafe { Mnemonic::from_raw_bytes(&decoded) };
+    let mnemonic = Mnemonic::from_raw_bytes(&decoded) ;
 
     println!("{mnemonic}");
 

crates/util/keyfork-mnemonic-util/src/lib.rs

@@ -125,6 +125,13 @@ impl Wordlist for English {
     }
 }
 
+struct AssertValidMnemonicSize<const N: usize>;
+
+impl<const N: usize> AssertValidMnemonicSize<N> {
+    const OK_CHUNKS: () = assert!(N % 4 == 0, "bytes must be a length divisible by 4");
+    const OK_SIZE: () = assert!(N <= 1024, "bytes must be less-or-equal 1024");
+}
+
 /// A BIP-0039 mnemonic with reference to a [`Wordlist`].
 #[derive(Debug, Clone, PartialEq, Eq)]
 pub struct MnemonicBase<W: Wordlist> {
@@ -276,7 +283,36 @@ where
             return Err(MnemonicGenerationError::InvalidByteLength(bit_count));
         }
 
-        Ok(unsafe { Self::from_raw_bytes(bytes) })
+        Ok( Self::from_raw_bytes(bytes) )
+    }
+
+    /// Generate a [`Mnemonic`] from the provided data and [`Wordlist`]. The data may be of a size
+    /// of a factor of 4, up to 1024 bytes.
+    ///
+    /// ```rust
+    /// use keyfork_mnemonic_util::Mnemonic;
+    /// let data = b"hello world!";
+    /// let mnemonic = Mnemonic::from_nonstandard_bytes(*data);
+    /// ```
+    ///
+    /// If an invalid size is requested, the code will fail to compile:
+    ///
+    /// ```rust,compile_fail
+    /// use keyfork_mnemonic_util::Mnemonic;
+    /// let mnemonic = Mnemonic::from_nonstandard_bytes([0u8; 53]);
+    /// ```
+    ///
+    /// ```rust,compile_fail
+    /// use keyfork_mnemonic_util::Mnemonic;
+    /// let mnemonic = Mnemonic::from_nonstandard_bytes([0u8; 1024 + 4]);
+    /// ```
+    pub fn from_nonstandard_bytes<const N: usize>(bytes: [u8; N]) -> MnemonicBase<W> {
+        #[allow(clippy::let_unit_value)]
+        {
+            let () = AssertValidMnemonicSize::<N>::OK_CHUNKS;
+            let () = AssertValidMnemonicSize::<N>::OK_SIZE;
+        }
+        Self::from_raw_bytes(&bytes) 
     }
 
     /// Generate a [`Mnemonic`] from the provided data and [`Wordlist`]. The data is expected to be
@@ -292,11 +328,12 @@ where
     /// Create a Mnemonic using an arbitrary length of given data. The length does not need to
     /// conform to BIP-0039 standards, but should be a multiple of 32 bits or 4 bytes.
     ///
-    /// # Safety
+    /// # Panics
-    ///
     /// This function can potentially produce mnemonics that are not BIP-0039 compliant or can't
     /// properly be encoded as a mnemonic. It is assumed the caller asserts the byte count is `% 4
-    /// == 0`. If the assumption is incorrect, code may panic.
+    /// == 0`. If the assumption is incorrect, code may panic. The
+    /// [`MnemonicBase::from_nonstandard_bytes`] function may be used to generate entropy if the
+    /// length of the data is known at compile-time.
     ///
     /// # Examples
     /// ```rust
@@ -315,11 +352,10 @@ where
     /// // NOTE: Data is of invalid length, 31
     /// let data = b"AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA";
     /// let mnemonic = unsafe { Mnemonic::from_raw_bytes(data.as_slice()) };
-    /// let mnemonic_text = mnemonic.to_string();
-    /// // NOTE: panic happens here
-    /// let new_mnemonic = Mnemonic::from_str(&mnemonic_text).unwrap();
     /// ```
-    pub unsafe fn from_raw_bytes(bytes: &[u8]) -> MnemonicBase<W> {
+    pub fn from_raw_bytes(bytes: &[u8]) -> MnemonicBase<W> {
+        assert!(bytes.len() % 4 == 0);
+        assert!(bytes.len() <= 1024);
         MnemonicBase {
             data: bytes.to_vec(),
             marker: PhantomData,
@@ -520,12 +556,30 @@ mod tests {
     }
 
     #[test]
-    fn can_do_up_to_1024_bits() {
+    fn can_do_up_to_8192_bits() {
-        let entropy = &mut [0u8; 128];
+        let mut entropy = [0u8; 1024];
         let mut random = std::fs::File::open("/dev/urandom").unwrap();
         random.read_exact(&mut entropy[..]).unwrap();
-        let mnemonic = unsafe { Mnemonic::from_raw_bytes(&entropy[..]) };
+        let mnemonic = Mnemonic::from_nonstandard_bytes(entropy);
         let words = mnemonic.words();
-        assert!(words.len() == 96);
+        assert_eq!(words.len(), 768);
+    }
+
+    #[test]
+    #[should_panic]
+    fn fails_over_8192_bits() {
+        let entropy = &mut [0u8; 1024 + 4];
+        let mut random = std::fs::File::open("/dev/urandom").unwrap();
+        random.read_exact(&mut entropy[..]).unwrap();
+        let _mnemonic = Mnemonic::from_raw_bytes(&entropy[..]);
+    }
+
+    #[test]
+    #[should_panic]
+    fn fails_over_invalid_size() {
+        let entropy = &mut [0u8; 255];
+        let mut random = std::fs::File::open("/dev/urandom").unwrap();
+        random.read_exact(&mut entropy[..]).unwrap();
+        let _mnemonic = Mnemonic::from_raw_bytes(&entropy[..]);
     }
 }