add pseudocode

main.typ

@@ -1,4 +1,6 @@
 #import "@preview/ichigo:0.1.0": config, prob
+#import "@preview/algorithmic:0.1.0"
+#import algorithmic: algorithm
 
 #show: config.with(
   course-name: "SMART CARDS & NFC",
@@ -20,9 +22,16 @@
 ][
 - The PiN_TRY_COUNTER is prone to turn off attacks.
   Each time the chip resets the ram value of the counter is cleared and one gets basically infinite retries.
-  todo solution
+
+  Solution:
+  - Store counter in non-volatile memory eg. EEPROM, flash, eMMC.
+  - Store counter in a secure server backend.
+
 - Depending on the implementation of the comparison operation, it might leak side-channel information.
   For example, if the comparison is done byte-wise, the attacker can determine the correct byte by comparing the time it takes to compare the bytes.
+
+  Solution:
+  - Implement a constant time comparison operation.
 ]
 
 #prob[
@@ -33,5 +42,33 @@
     ],
   )
 ][
-  todo solution
+  - The comparison of the entered pin and the reference pin is array entry wise.
+    If a entry doesn't match the comparison is short-handed and the function returns no match.
+    This is prone to a timing side-channel attack. If a pin digit matches the comparison takes longer than if it doesn't.
+
+    Solution:
+    - Implement a constant time comparison operation. (no comparison shorthand)
+
+    For example:
+    #algorithm({
+      import algorithmic: *
+      Function("Constant-Time-Compare", args: ("PIN", "Ref_PIN"), {
+        Cmt[Check if lengths are equal]
+        If(cond: $"length" ("PIN") != "length"("Ref_PIN")$, {
+          Return[false]
+        })
+        State[]
+        Cmt[Initialize result variable to 0]
+        Assign[$"result"$][$0$]
+        State[]
+        Cmt[Loop through each character in PIN and Ref_PIN]
+        For(cond: [$i=0$; $i < "length"("PIN") - 1$], {
+          Cmt[XOR corresponding characters and accumulate result]
+          Assign[$"result"$][$"result" or ("PIN"[i] xor "Ref_PIN"[i])$]
+        })
+        State[]
+        Cmt[Return true if result is 0, else false]
+        Return[$"result" == 0$]
+      })
+    })
 ]