From e9a1608a8f8f520cbfd1e3d2cdecd1a193a8d453 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Pascal=20Eng=C3=A9libert?= <tuxmain@zettascript.org>
Date: Sun, 14 Jun 2026 21:40:19 +0200
Subject: [PATCH] Blog: Update flash filesystem encryption

---
 config.toml                                   |   6 +-
 .../blog/flash-filesystem-encryption/cbc.svg  |   6 +-
 .../blog/flash-filesystem-encryption/ctr.svg  |   6 +-
 .../flash-filesystem-encryption/diagram.py    | 149 +++++++++++++++++-
 .../blog/flash-filesystem-encryption/ecb.svg  |   6 +-
 .../blog/flash-filesystem-encryption/index.md |   6 +-
 .../blog/flash-filesystem-encryption/xts.svg  |   6 +-
 7 files changed, 165 insertions(+), 20 deletions(-)

diff --git a/config.toml b/config.toml
index e334038..34b4fdf 100644
--- a/config.toml
+++ b/config.toml
@@ -32,7 +32,7 @@ header_reads = "Reads"
 blog_published_on_date = "Posted by a human on"
 footer_mail = "Electronic missive:<br/>tuxmain ât zettascript ðøt org"
 footer_hosted = "Hosted in Bordeaux, France."
-footer_generated = "Site generated with"
+footer_generated = "Site written by a human and generated with"
 
 [extra.tr.eo]
 sitename = "txmn.tk"
@@ -43,7 +43,7 @@ header_reads = "Legaĵoj"
 blog_published_on_date = "Publikiĝita home je la"
 footer_mail = "Retadreso:<br/>tuxmain ĉe zettascript punkto org"
 footer_hosted = "Gastigata en Bordozo, en Francujo."
-footer_generated = "Retejo konstruita per"
+footer_generated = "Retejo home skribita kaj konstruita per"
 
 [extra.tr.fr]
 sitename = "txmn.tk"
@@ -54,7 +54,7 @@ header_reads = "Lectures"
 blog_published_on_date = "Publié par un humain le"
 footer_mail = "Courrier électronique&nbsp;:<br/>tuxmain çhĕz zettascript pøiñt org"
 footer_hosted = "Hébergé à Bordeaux en France."
-footer_generated = "Site généré avec"
+footer_generated = "Site écrit par un humain et généré avec"
 
 [languages.en]
 generate_feeds = true
diff --git a/content/blog/flash-filesystem-encryption/cbc.svg b/content/blog/flash-filesystem-encryption/cbc.svg
index c7c3544..6b25f9b 100644
--- a/content/blog/flash-filesystem-encryption/cbc.svg
+++ b/content/blog/flash-filesystem-encryption/cbc.svg
@@ -1,5 +1,5 @@
 <svg version="1.1" xmlns="http://www.w3.org/2000/svg" width="372" height="172" viewBox="0 0 372 172">
-	<!-- Generated by https://txmn.tk/blog/flash-filesystem-encryption/graph.py -->
+	<!-- Generated by https://txmn.tk/blog/flash-filesystem-encryption/diagram.py -->
 	<!-- Image released under license CC0 (public domain) -->
 	<title>CBC</title>
 	<style>
@@ -16,7 +16,7 @@
 			stroke-width: 2px;
 			fill: none;
 		}
-		path.f {
+		path.f, circle.f {
 			stroke: none;
 			fill: #000;
 		}
@@ -28,7 +28,7 @@
 			circle, line, rect, path.s {
 				stroke: #ddd;
 			}
-			path.f {
+			path.f, circle.f {
 				fill: #ddd;
 			}
 		}
diff --git a/content/blog/flash-filesystem-encryption/ctr.svg b/content/blog/flash-filesystem-encryption/ctr.svg
index da28597..3662c2d 100644
--- a/content/blog/flash-filesystem-encryption/ctr.svg
+++ b/content/blog/flash-filesystem-encryption/ctr.svg
@@ -1,5 +1,5 @@
 <svg version="1.1" xmlns="http://www.w3.org/2000/svg" width="288" height="172" viewBox="0 0 288 172">
-	<!-- Generated by https://txmn.tk/blog/flash-filesystem-encryption/graph.py -->
+	<!-- Generated by https://txmn.tk/blog/flash-filesystem-encryption/diagram.py -->
 	<!-- Image released under license CC0 (public domain) -->
 	<title>CTR</title>
 	<style>
@@ -16,7 +16,7 @@
 			stroke-width: 2px;
 			fill: none;
 		}
-		path.f {
+		path.f, circle.f {
 			stroke: none;
 			fill: #000;
 		}
@@ -28,7 +28,7 @@
 			circle, line, rect, path.s {
 				stroke: #ddd;
 			}
-			path.f {
+			path.f, circle.f {
 				fill: #ddd;
 			}
 		}
diff --git a/content/blog/flash-filesystem-encryption/diagram.py b/content/blog/flash-filesystem-encryption/diagram.py
index ff5cb58..9cfc6fa 100644
--- a/content/blog/flash-filesystem-encryption/diagram.py
+++ b/content/blog/flash-filesystem-encryption/diagram.py
@@ -31,7 +31,7 @@ SVG = """\
 			stroke-width: 2px;
 			fill: none;
 		}}
-		path.f {{
+		path.f, circle.f {{
 			stroke: none;
 			fill: {BLACK};
 		}}
@@ -43,7 +43,7 @@ SVG = """\
 			circle, line, rect, path.s {{
 				stroke: {WHITE};
 			}}
-			path.f {{
+			path.f, circle.f {{
 				fill: {WHITE};
 			}}
 		}}
@@ -89,6 +89,43 @@ class Svg:
 		"""
 		return Block(self, x, y, XOR_R)
 
+	def plus(self, x, y):
+		xl = x-XOR_R
+		xr = x+XOR_R
+		yt = y-XOR_R
+		yb = y+XOR_R
+		size = XOR_R * 2
+		self.t += f"""\
+			<rect x="{xl}" y="{yt}" width="{size}" height="{size}"/>
+			<line x1="{xl}" y1="{y}" x2="{xr}" y2="{y}"/>
+			<line x1="{x}" y1="{yt}" x2="{x}" y2="{yb}"/>
+		"""
+		return Block(self, x, y, XOR_R)
+
+	def minus(self, x, y):
+		xl = x-XOR_R
+		xr = x+XOR_R
+		yt = y-XOR_R
+		size = XOR_R * 2
+		self.t += f"""\
+			<rect x="{xl}" y="{yt}" width="{size}" height="{size}"/>
+			<line x1="{xl}" y1="{y}" x2="{xr}" y2="{y}"/>
+		"""
+		return Block(self, x, y, XOR_R)
+
+	def rotl(self, x, y, t):
+		xl = x-XOR_R
+		yt = y-XOR_R
+		ymt = y-XOR_R/2
+		ymb = y+XOR_R/2
+		size = XOR_R * 2
+		self.t += f"""\
+			<rect x="{xl}" y="{yt}" width="{size}" height="{size}"/>
+			<text class="t" x="{x}" y="{ymt}">&lt;&lt;&lt;</text>
+			<text class="t" x="{x}" y="{ymb}">{t}</text>
+		"""
+		return Block(self, x, y, XOR_R)
+
 	def encrypt(self, x, y):
 		xl = x-ENCRYPT_SIZE//2
 		yt = y-ENCRYPT_SIZE//2
@@ -113,6 +150,28 @@ class Svg:
 		"""
 		return Block(self, x, y, ENCRYPT_SIZE//2)
 
+	def block(self, x, y, wcells, hcells, texts, borders):
+		cell_w = ENCRYPT_SIZE
+		cell_h = ENCRYPT_SIZE//2
+		w = cell_w * wcells
+		h = cell_h * hcells
+		xl = x-w//2
+		yt = y-h//2
+		self.t += f"""\
+			<rect x="{xl}" y="{yt}" width="{w}" height="{h}"/>
+		"""
+		for (tx, ty, t) in texts:
+			tx_ = (tx+0.5)*cell_w+xl
+			ty_ = (ty+0.5)*cell_h+yt
+			self.t += f"""<text class="t" x="{tx_}" y="{ty_}">{t}</text>\n"""
+		return Block(self, x, y, ENCRYPT_SIZE//2)
+
+	def knot(self, x, y):
+		self.t += f"""\
+			<circle class="f" r="4px" cx="{x}" cy="{y}"/>
+		"""
+		return Block(self, x, y, 0)
+
 ARROW_TIP_START = 8
 ARROW_TIP_BACK = 12
 ARROW_TIP_R = 6
@@ -244,6 +303,91 @@ def xts():
 	
 	return SVG.format(body=s.t, title="XTS", w=372, h=192, **ARGS)
 
+# ChaCha Quarter Round
+def chacha_qr():
+	ax = 16 + 64*0
+	bx = 16 + 64*1
+	cx = 16 + 64*2
+	dx = 16 + 64*3
+	y = [64 + 32*i for i in range(12)]
+
+	s = Svg()
+	a1 = s.text(ax, 16, "a")
+	b1 = s.text(bx, 16, "b")
+	c1 = s.text(cx, 16, "c")
+	d1 = s.text(dx, 16, "d")
+	P1 = s.plus(ax, y[0])
+	N1 = s.knot(bx, y[0])
+	N2 = s.knot(ax, y[1])
+	X1 = s.xor(dx, y[1])
+	R1 = s.rotl(dx, y[2], "16")
+	N3 = s.knot(dx, y[3])
+	P2 = s.plus(cx, y[3])
+	N4 = s.knot(cx, y[4])
+	X2 = s.xor(bx, y[4])
+	R2 = s.rotl(bx, y[5], "12")
+	N5 = s.knot(bx, y[6])
+	P3 = s.plus(ax, y[6])
+	N6 = s.knot(ax, y[7])
+	X3 = s.xor(dx, y[7])
+	R3 = s.rotl(dx, y[8], "8")
+	N7 = s.knot(dx, y[9])
+	P4 = s.plus(cx, y[9])
+	N8 = s.knot(cx, y[10])
+	X4 = s.xor(bx, y[10])
+	R4 = s.rotl(bx, y[11], "7")
+	a2 = s.text(ax, y[-1]+48, "a")
+	b2 = s.text(bx, y[-1]+48, "b")
+	c2 = s.text(cx, y[-1]+48, "c")
+	d2 = s.text(dx, y[-1]+48, "d")
+
+	a1.to(P1)
+	P1.to(P3)
+	P3.to(a2)
+
+	b1.to(X2)
+	X2.to(R2)
+	R2.to(X4)
+	X4.to(R4)
+	R4.to(b2)
+
+	c1.to(P2)
+	P2.to(P4)
+	P4.to(c2)
+
+	d1.to(X1)
+	X1.to(R1)
+	R1.to(X3)
+	X3.to(R3)
+	R3.to(d2)
+
+	N1.to(P1)
+	N2.to(X1)
+	N3.to(P2)
+	N4.to(X2)
+	N5.to(P3)
+	N6.to(X3)
+	N7.to(P4)
+	N8.to(X4)
+	
+	return SVG.format(body=s.t, title="ChaCha Quarter Round", w=372, h=y[-1]+64, **ARGS)
+
+def chacha_encryption():
+	s = Svg()
+	B = s.block(64, 32, 4, 4, [
+		(1.5, 0, "const"),
+		(1.5, 1.5, "K"),
+		(0.5, 3, "count"),
+		(2.5, 3, "nonce"),
+	],
+	[])
+	P = s.text(16, 144, "P")
+	E = s.encrypt(64, 96)
+	X = s.xor(64, 144)
+	C = s.text(64, 180, "C")
+	
+	return SVG.format(body=s.t, title="ChaCha Encryption", w=372, h=192, **ARGS)
+
 def save(name, data):
 	f = open(f"{name}.svg", "w")
 	f.write(data)
@@ -254,3 +398,4 @@ if __name__ == "__main__":
 	save("ctr", ctr())
 	save("cbc", cbc())
 	save("xts", xts())
+	save("../flash-filesystem-encryption-2/chacha-encryption", chacha_encryption())
diff --git a/content/blog/flash-filesystem-encryption/ecb.svg b/content/blog/flash-filesystem-encryption/ecb.svg
index 1b791b2..c54f5da 100644
--- a/content/blog/flash-filesystem-encryption/ecb.svg
+++ b/content/blog/flash-filesystem-encryption/ecb.svg
@@ -1,5 +1,5 @@
 <svg version="1.1" xmlns="http://www.w3.org/2000/svg" width="288" height="128" viewBox="0 0 288 128">
-	<!-- Generated by https://txmn.tk/blog/flash-filesystem-encryption/graph.py -->
+	<!-- Generated by https://txmn.tk/blog/flash-filesystem-encryption/diagram.py -->
 	<!-- Image released under license CC0 (public domain) -->
 	<title>ECB</title>
 	<style>
@@ -16,7 +16,7 @@
 			stroke-width: 2px;
 			fill: none;
 		}
-		path.f {
+		path.f, circle.f {
 			stroke: none;
 			fill: #000;
 		}
@@ -28,7 +28,7 @@
 			circle, line, rect, path.s {
 				stroke: #ddd;
 			}
-			path.f {
+			path.f, circle.f {
 				fill: #ddd;
 			}
 		}
diff --git a/content/blog/flash-filesystem-encryption/index.md b/content/blog/flash-filesystem-encryption/index.md
index 4d1f46f..54e14b8 100644
--- a/content/blog/flash-filesystem-encryption/index.md
+++ b/content/blog/flash-filesystem-encryption/index.md
@@ -90,7 +90,7 @@ The problem is that flash memories are slow and become damaged after a limited n
 
 > La peste soit du FAT&#8239;!
 >
->_Dom Juan_, Molière
+> _Dom Juan_, Molière
 
 Now that we've highlighted an important property of flash memories, it appears FAT32 may not be the best choice as a filesystem. Indeed, a modified block would stay at the same physical address, causing different regions of the storage to wear more rapidly than others. It would be better to spread the write operations across the entire space, in order to maximize the time before a failure happens.
 
@@ -200,7 +200,7 @@ Sectors must not be too long, however, as random access to block j needs computi
 
 AES128 needs 128 bits of key, however the user will only remember ASCII words, not fully random bytes. We need something to derive a key from a variable-length password. We could just compute a hash of the password, as the ESP32 provides a hardware implementation of SHA2, but for storing passwords it is better to use a dedicated function that is fast enough to run once but hard to bruteforce efficiently on optimized systems.
 
-[PBKDF2](https://fr.wikipedia.org/wiki/PBKDF2) chains thousands of calls to a hash function, each one depending on the previous one, so it is impossible to parallelize. However an attacker can run thousands of instances in parallel on a GPU or cryptocurrency-mining chip.
+[PBKDF2](https://en.wikipedia.org/wiki/PBKDF2) chains thousands of calls to a hash function, each one depending on the previous one, so it is impossible to parallelize. However an attacker can run thousands of instances in parallel on a GPU or cryptocurrency-mining chip.
 
 A popular choice as of today is [Argon2](https://en.wikipedia.org/wiki/Argon2), which is memory-hard: one instance requires efficient access to a big amoung of memory, potentially megabytes or even gigabytes, so it is difficult to optimize even on dedicated hardware. Problems are that its implementation is quite complicated (it will take too much ROM) and its specs are not even complete.
 
@@ -210,7 +210,7 @@ The benefit of password hashing functions on the ESP32 is a bit disappointing, w
 
 ### Storing the key
 
-It can be useful to use two keys: the first one, derived from the password, is used to encrypt the second key, which is written to the storage. The second key is use to encrypt the filesystem. This way, the password can be changed, as the second key does not depend on it. If you have to destroy the data in a hurry and you have a reason to think someone with a gun may force you to hand over the password, you just have to erase the stored key.
+It can be useful to use two keys: the first one, derived from the password, is used to encrypt the second key, which is written to the storage. The second key is use to encrypt the filesystem. This way, the password can be changed, as the second key does not depend on it. If you have to destroy the data in a hurry and you have a reason to think someone with a gun may force you to hand over the password, you just have to erase the stored key (however, in the case the attacker with a gun is a policeperson, erasing the key may be considered as destruction of evidence hence illegal).
 
 ## Active attacks and authentication
 
diff --git a/content/blog/flash-filesystem-encryption/xts.svg b/content/blog/flash-filesystem-encryption/xts.svg
index c12802c..219c618 100644
--- a/content/blog/flash-filesystem-encryption/xts.svg
+++ b/content/blog/flash-filesystem-encryption/xts.svg
@@ -1,5 +1,5 @@
 <svg version="1.1" xmlns="http://www.w3.org/2000/svg" width="372" height="192" viewBox="0 0 372 192">
-	<!-- Generated by https://txmn.tk/blog/flash-filesystem-encryption/graph.py -->
+	<!-- Generated by https://txmn.tk/blog/flash-filesystem-encryption/diagram.py -->
 	<!-- Image released under license CC0 (public domain) -->
 	<title>XTS</title>
 	<style>
@@ -16,7 +16,7 @@
 			stroke-width: 2px;
 			fill: none;
 		}
-		path.f {
+		path.f, circle.f {
 			stroke: none;
 			fill: #000;
 		}
@@ -28,7 +28,7 @@
 			circle, line, rect, path.s {
 				stroke: #ddd;
 			}
-			path.f {
+			path.f, circle.f {
 				fill: #ddd;
 			}
 		}