From 5684bfaa23e1549e9e1263371fbaf112b5f49a20 Mon Sep 17 00:00:00 2001
From: lukas-heilgenbrunner <lukas.heiligenbrunner@gmail.com>
Date: Tue, 22 Oct 2024 15:11:53 +0200
Subject: [PATCH] add flowchart

---
 main.typ | 51 ++++++++++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 50 insertions(+), 1 deletion(-)

diff --git a/main.typ b/main.typ
index fe640a9..fe113d3 100644
--- a/main.typ
+++ b/main.typ
@@ -1,6 +1,18 @@
 #import "@preview/ichigo:0.1.0": config, prob
 #import "@preview/algorithmic:0.1.0"
 #import algorithmic: algorithm
+#import "@preview/fletcher:0.5.1" as fletcher: diagram, node, edge
+#import fletcher.shapes: house, hexagon
+
+#let blob(pos, label, tint: white, ..args) = node(
+	pos, align(center, label),
+	width: 26mm,
+	fill: tint.lighten(60%),
+	stroke: 1pt + tint.darken(20%),
+	corner-radius: 5pt,
+	..args,
+)
+
 
 #show: config.with(
   course-name: "SMART CARDS & NFC",
@@ -20,7 +32,7 @@
   )
 
 ][
-- The PiN_TRY_COUNTER is prone to turn off attacks.
+- 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.
 
   Solution:
@@ -32,6 +44,43 @@
 
   Solution:
   - Implement a constant time comparison operation.
+
+- PIN_TRY_COUNTER is incremented after the comparison operation.
+  If the operation is interrupted due to a non atomic operation, the counter not incremented.
+
+  Solution:
+  - Do counter++ before comparison. This way the attacker can't determine if the counter is incremented or not.
+
+    #sym.arrow.r See flowchart
+  - Implement a atomic operation for the counter incrementation.
+
+  #align(center)[
+  #diagram(
+	spacing: 8pt,
+	cell-size: (8mm, 10mm),
+	edge-stroke: 1pt,
+	edge-corner-radius: 5pt,
+	mark-scale: 70%,
+	debug: false,
+
+	blob((2,0), [PIN Verification], tint: yellow, shape: fletcher.shapes.pill),
+	edge("-|>"),
+	blob((2,1), [PIN_Try_Counter < LIMIT], tint: green, shape: fletcher.shapes.hexagon, width: 35mm),
+	edge("ll,dddd", "-|>", label: "No"),
+	edge("-|>", "d"),
+	blob((0,5), [Result: Card/Pin blocked], tint: yellow, shape: fletcher.shapes.pill),
+
+	blob((2,2), [Pin_try_counter++], tint: blue, shape: fletcher.shapes.rect, width: auto),
+	edge("-|>"),
+	blob((2,3), [PIN == Ref_PIN?], tint: green, shape: fletcher.shapes.hexagon, width: auto),
+edge("l,d", "-|>", label: "Yes"),
+edge( "r,dd", "-|>", label: "No"),
+		blob((1,4), [Pin_try_counter = 0], tint: blue, shape: fletcher.shapes.rect, width: auto),
+    edge("-|>"),
+		blob((1,5), [PIN Verification], tint: yellow, shape: fletcher.shapes.pill),
+		blob((3,5), [PIN Verification], tint: yellow, shape: fletcher.shapes.pill),
+  )
+  ]
 ]
 
 #prob[