diff --git a/src/circuit/gadget/sinsemilla/chip.rs b/src/circuit/gadget/sinsemilla/chip.rs
index 183e84803..b8dddbebf 100644
--- a/src/circuit/gadget/sinsemilla/chip.rs
+++ b/src/circuit/gadget/sinsemilla/chip.rs
@@ -210,7 +210,35 @@ impl<C: CurveAffine> SinsemillaInstructions<C> for SinsemillaChip<C> {
         message: Vec<Option<bool>>,
         num_words: usize,
     ) -> Result<Vec<Self::MessagePiece>, Error> {
-        todo!()
+        // Message must have at most SinsemillaC words.
+        assert!(num_words <= SinsemillaC);
+
+        let message = if message.len() < num_words * K {
+            // If message is shorter than the number of words specified, pad it to the
+            // correct length.
+            let pad_len = num_words * K - message.len();
+            let mut message = message.clone();
+            message.extend_from_slice(&vec![None; pad_len]);
+            message
+        } else {
+            // If message is longer than the number of words specified, truncate it
+            // to the correct length.
+            message[..(num_words * K)].to_vec()
+        };
+
+        // Number of words that can be contained in a piece
+        let piece_num_words = C::Base::NUM_BITS as usize / K;
+        message
+            .chunks(piece_num_words * K)
+            .map(|piece| {
+                let num_words = (piece.len() + K - 1) / K;
+                self.witness_message_piece_bitstring(
+                    layouter.namespace(|| "message piece"),
+                    piece.to_vec(),
+                    num_words,
+                )
+            })
+            .collect()
     }
 
     #[allow(non_snake_case)]
@@ -220,7 +248,66 @@ impl<C: CurveAffine> SinsemillaInstructions<C> for SinsemillaChip<C> {
         message: Vec<Option<bool>>,
         num_words: usize,
     ) -> Result<Self::MessagePiece, Error> {
-        todo!()
+        println!("num_words: {}", num_words);
+        assert_eq!(message.len(), num_words * 10);
+        // Message piece must be at most `ceil(C::Base::NUM_BITS / 10)` bits
+        let max_len = C::Base::NUM_BITS / 10;
+        assert!(num_words <= max_len as usize);
+
+        // A `K`-bit bitstring.
+        struct Word([Option<bool>; K]);
+
+        // Chunk message into `K`-bit words.
+        let message: Vec<Word> = message
+            .chunks_exact(K)
+            .map(|word| Word(word.try_into().unwrap()))
+            .collect();
+
+        // Closure to parse a vector of K-bit words into a base field element.
+        let to_base_field = |words: &[Word]| -> Option<C::Base> {
+            let bits = words
+                .into_iter()
+                .map(|word| word.0.to_vec())
+                .flatten()
+                .collect::<Vec<Option<bool>>>();
+            let bytearray: Vec<Option<u8>> = bits
+                .chunks(8)
+                .map(|byte| {
+                    byte.iter().rev().fold(Some(0u8), |acc, bit| {
+                        acc.zip(*bit).map(|(acc, bit)| acc * 2 + bit as u8)
+                    })
+                })
+                .collect();
+
+            // Pad to 32 bytes
+            let pad_len = 32 - bytearray.len();
+            let bytearray: Option<Vec<u8>> = bytearray.into_iter().collect();
+            let bytearray: Option<Vec<u8>> = bytearray.map(|mut bytearray| {
+                bytearray.extend_from_slice(&vec![0; pad_len]);
+                bytearray
+            });
+
+            bytearray.map(|bytearray| C::Base::from_bytes(&bytearray.try_into().unwrap()).unwrap())
+        };
+
+        let config = self.config().clone();
+
+        layouter.assign_region(
+            || "message",
+            |mut region: Region<'_, C::Base>| {
+                let piece_value = to_base_field(&message);
+                let cell = region.assign_advice(
+                    || "message piece",
+                    config.bits,
+                    0,
+                    || piece_value.ok_or(Error::SynthesisError),
+                )?;
+                Ok(MessagePiece::new(
+                    CellValue::new(cell, piece_value),
+                    message.len(),
+                ))
+            },
+        )
     }
 
     fn witness_message_piece_field(
@@ -229,7 +316,23 @@ impl<C: CurveAffine> SinsemillaInstructions<C> for SinsemillaChip<C> {
         value: Option<C::Base>,
         num_words: usize,
     ) -> Result<Self::MessagePiece, Error> {
-        todo!()
+        let config = self.config().clone();
+
+        let cell = layouter.assign_region(
+            || "witness message piece",
+            |mut region| {
+                region.assign_advice(
+                    || "witness message piece",
+                    config.bits,
+                    0,
+                    || value.ok_or(Error::SynthesisError),
+                )
+            },
+        )?;
+        Ok(Self::prepare_message_piece(
+            &CellValue::new(cell, value),
+            num_words,
+        ))
     }
 
     fn prepare_message_piece(cell: &Self::CellValue, length: usize) -> Self::MessagePiece {