diff --git a/plonky2_verifier/challenger.go b/plonky2_verifier/challenger.go
new file mode 100644
index 0000000..3d60c83
--- /dev/null
+++ b/plonky2_verifier/challenger.go
@@ -0,0 +1,139 @@
+package plonky2_verifier
+
+import (
+	"github.com/consensys/gnark/frontend"
+)
+
+type V = frontend.Variable
+
+type Challenger struct {
+	sponge_state: [SPONGE_WIDTH]V
+	input_buffer: []V
+	output_buffer: []V
+}
+
+// pub struct Challenger {
+//     sponge_state: [GoldilocksField; SPONGE_WIDTH],
+//     input_buffer: Vec<GoldilocksField>,
+//     output_buffer: Vec<GoldilocksField>
+// }
+
+func NewChallenger() Challenger {
+	var sponge_state [SPONGE_WIDTH]V
+	for i := 0; i < SPONGE_WIDTH; i++ {
+		sponge_state[i] = 0
+	}
+	return Challenger {
+		sponge_state: sponge_state,
+		input_buffer: []V{},
+		output_buffer: []V{},
+	}
+}
+//     pub fn new() -> Challenger {
+//         return Challenger {
+//             sponge_state: [GoldilocksField::ZERO; SPONGE_WIDTH],
+//             input_buffer: Vec::with_capacity(SPONGE_RATE),
+//             output_buffer: Vec::with_capacity(SPONGE_RATE)
+//         };
+//     }
+
+func (c *Challenger) observe_elements(elements []V) {
+	for _, element := range elements {
+		c.observe_element(element)
+	}
+}
+//     pub fn observe_elements(&mut self, elements: &[GoldilocksField]) {
+//         for &element in elements {
+//             self.observe_element(element);
+//         }
+//     }
+
+func (c *Challenger) observe_hash(hash []V) {
+	c.observe_elements(hash)
+}
+//     pub fn observe_hash(&mut self, hash: Vec<GoldilocksField>) {
+//         self.observe_elements(&hash.to_vec())
+//     }
+
+func (c *Challenger) observe_element(element V) {
+	c.output_buffer = V[]{}
+	c.input_buffer = append(c.input_buffer, element)
+	if len(c.input_buffer) == SPONGE_RATE {
+		c.duplexing()
+	}
+}
+//     pub fn observe_element(&mut self, element: GoldilocksField) {
+//         self.output_buffer.clear();
+//         self.input_buffer.push(element);
+//         if self.input_buffer.len() == SPONGE_RATE {
+//             self.duplexing();
+//         }
+//     }
+
+func (c *Challenger) observe_cap(cap [][]V) {
+	for _, hash := range cap {
+		c.observe_hash(hash)
+	}
+}
+//     pub fn observe_cap(&mut self, cap: &Vec<Vec<GoldilocksField>>) {
+//         for hash in cap.into_iter() {
+//             self.observe_hash(hash.clone());
+//         }
+//     }
+
+func (c *Challenger) duplexing() {
+	if len(c.input_buffer) > SPONGE_RATE { panic("buffer too large") }
+
+	for i, input := range c.input_buffer {
+		c.sponge_state[i] = input
+	}
+	c.input_buffer = V[]{}
+
+	c.sponge_state = poseidon(c.sponge_state)
+
+	c.output_buffer = c.sponge_state[:SPONGE_RATE]
+}
+//     fn duplexing(&mut self) {
+//         assert!(self.input_buffer.len() <= SPONGE_RATE);
+
+//         for (i, input) in self.input_buffer.drain(..).enumerate() {
+//             self.sponge_state[i] = input;
+//         }
+
+//         self.sponge_state = poseidon(self.sponge_state);
+
+//         self.output_buffer.clear();
+//         self.output_buffer
+//             .extend_from_slice(&self.sponge_state[0..SPONGE_RATE]);
+//     }
+
+func (c *Challenger) get_challenge() V {
+	if len(c.input_buffer) > 0 || len(c.output_buffer) == 0 {
+		c.duplexing()
+	}
+	result := c.output_buffer[len(c.output_buffer) - 1]
+	c.output_buffer = c.output_buffer[:len(c.output_buffer) - 1]
+	return result
+}
+//     pub fn get_challenge(&mut self) -> GoldilocksField {
+//         if !self.input_buffer.is_empty() || self.output_buffer.is_empty() {
+//             self.duplexing();
+//         }
+
+//         self.output_buffer
+//             .pop()
+//             .expect("Output buffer should be non-empty")
+//     }
+
+func (c *Challenger) get_n_challenges(n int) []V {
+	result := make([]V, n)
+	for i := 0; i < n; i++ {
+		result[i] = c.get_challenge()
+	}
+	return result
+}
+//     pub fn get_n_challenges(&mut self, n: usize) -> Vec<GoldilocksField> {
+//         (0..n).map(|_| self.get_challenge()).collect()
+//     }
+// }
+