src/tasks/mod.rs

@@ -9,8 +9,8 @@ use tasks01::{
     gfmul::gfmul_task,
     pad_oracle::padding_oracle,
     pfmath::{
-        gfdiv, gfpoly_add, gfpoly_divmod, gfpoly_make_monic, gfpoly_mul, gfpoly_pow, gfpoly_powmod,
-        gfpoly_sort, gfpoly_sqrt,
+        gfdiv, gfpoly_add, gfpoly_diff, gfpoly_divmod, gfpoly_make_monic, gfpoly_mul, gfpoly_pow,
+        gfpoly_powmod, gfpoly_sort, gfpoly_sqrt,
     },
     poly2block::poly2block,
     sea128::sea128,
@@ -145,6 +145,12 @@ pub fn task_deploy(testcase: &Testcase) -> Result<Value> {
 
             Ok(json)
         }
+        "gfpoly_diff" => {
+            let result = gfpoly_diff(args)?;
+            let json = json!({"F'" : result.to_c_array()});
+
+            Ok(json)
+        }
 
         _ => Err(anyhow!(
             "Fatal. No compatible action found. Json data was {:?}. Arguments were; {:?}",

src/tasks/tasks01/pfmath.rs

@@ -97,6 +97,14 @@ pub fn gfpoly_sqrt(args: &Value) -> Result<Polynomial> {
     Ok(result)
 }
 
+pub fn gfpoly_diff(args: &Value) -> Result<Polynomial> {
+    let poly_f = Polynomial::from_c_array(&args["F"].clone());
+
+    let result = poly_f.diff();
+
+    Ok(result)
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;

src/utils/field.rs

@@ -24,6 +24,10 @@ impl FieldElement {
         87, 00, 00, 00, 00, 00, 00, 00, 00, 00, 00, 00, 00, 00, 00, 00, 01,
     ];
 
+    pub fn zero(self) -> Self {
+        FieldElement::new(vec![0])
+    }
+
     pub const fn new(field_element: Vec<u8>) -> Self {
         Self { field_element }
     }

src/utils/poly.rs

@@ -292,6 +292,19 @@ impl Polynomial {
 
         Polynomial::new(result)
     }
+
+    pub fn diff(mut self) -> Self {
+        // Pop first element
+        self.polynomial.remove(0);
+
+        for (position, element) in self.polynomial.iter_mut().enumerate() {
+            if position % 2 == 1 {
+                *element = FieldElement::new(vec![0; 16]);
+            }
+        }
+
+        self
+    }
 }
 
 impl Clone for Polynomial {
@@ -645,26 +658,6 @@ mod tests {
     // Note this useful idiom: importing names from outer (for mod tests) scope.
     use super::*;
 
-    /*
-    * TODO: Consider removing
-    #[test]
-    fn coefficients_to_byte_arr_xex_test1() {
-        let coefficients: Vec<u8> = vec![0];
-        let byte_array = vec![
-            01, 00, 00, 00, 00, 00, 00, 00, 00, 00, 00, 00, 00, 00, 00, 00,
-        ];
-        assert_eq!(coefficients_to_byte_arr_xex(coefficients), byte_array)
-    }
-
-    #[test]
-    fn coefficients_to_byte_arr_xex_test2() {
-        let coefficients: Vec<u8> = vec![127, 12, 9, 0];
-        let byte_array = vec![
-            01, 12, 00, 00, 00, 00, 00, 00, 00, 00, 00, 00, 00, 00, 00, 80,
-        ];
-        assert_eq!(coefficients_to_byte_arr_xex(coefficients), byte_array)
-    }
-    */
     #[test]
     fn byte_indices_0x01() {
         let byte: u8 = 0x01;
@@ -1192,4 +1185,25 @@ mod tests {
 
         assert_eq!(json!(result.to_c_array()), expected);
     }
+
+    #[test]
+    fn test_poly_diff() {
+        let json1 = json!([
+            "IJustWannaTellYouAAAAA==",
+            "HowImFeelingAAAAAAAAAA==",
+            "GottaMakeYouAAAAAAAAAA==",
+            "UnderstaaaaaaaaaaaaanQ=="
+        ]);
+        let expected = json!([
+            "HowImFeelingAAAAAAAAAA==",
+            "AAAAAAAAAAAAAAAAAAAAAA==",
+            "UnderstaaaaaaaaaaaaanQ=="
+        ]);
+        let element1: Polynomial = Polynomial::from_c_array(&json1);
+        eprintln!("Starting poly sqrt");
+
+        let result = element1.diff();
+
+        assert_eq!(json!(result.to_c_array()), expected);
+    }
 }

test_json/sandbox.json

@@ -0,0 +1,15 @@
+{
+  "testcases": {
+    "sandbox": {
+      "action": "gfpoly_diff",
+      "arguments": {
+        "F": [
+          "IJustWannaTellYouAAAAA==",
+          "HowImFeelingAAAAAAAAAA==",
+          "GottaMakeYouAAAAAAAAAA==",
+          "UnderstaaaaaaaaaaaaanQ=="
+        ]
+      }
+    }
+  }
+}