From 4afa29aed3d94c52526151219649dd775bbb3330 Mon Sep 17 00:00:00 2001
From: Mirek Kratochvil <exa.exa@gmail.com>
Date: Thu, 29 Oct 2026 22:15:56 +0100
Subject: expansion example

---
 README.md | 63 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 63 insertions(+)

diff --git a/README.md b/README.md
index aad74ca..fdbe1bc 100644
--- a/README.md
+++ b/README.md
@@ -256,6 +256,69 @@ mixing provided by this procedure (it **is** insufficient). Instead, run a few
 encryption rounds of random padding characters (i.e., a *nonce*) before
 starting the encryption of the actual plaintext (see below).
 
+#### Key expansion example!
+
+We start with the "sorted" board:
+
+```
+ _ A B C D E F
+ G H I J K L M
+ N O P Q R S T
+ U V W X Y Z .
+ , : ? ! ' ( )
+ 0 1 2 3 4 5 6
+ 7 8 9 + - * /
+```
+
+Let's say the password is `BANANA12345`; we pick the tiles in order, and put them
+down below. Repeating occurrences of `A` and `N` are ignored.
+
+```
+ _     C D E F
+ G H I J K L M
+   O P Q R S T
+ U V W X Y Z .
+ , : ? ! ' ( )
+ 0           6
+ 7 8 9 + - * /
+
+
+             5
+ 4 3 2 1 N A B
+```
+
+We add the space (`_`) to the "end" of the password:
+
+```
+       C D E F
+ G H I J K L M
+   O P Q R S T
+ U V W X Y Z .
+ , : ? ! ' ( )
+ 0           6
+ 7 8 9 + - * /
+
+
+           _ 5
+ 4 3 2 1 N A B
+```
+
+The rest of the board becomes an imaginary snake and follows the lines to the
+right and downwards, towards the password. Finally, the marker is placed to the
+upper left:
+
+```
+[C]D E F G H I
+ J K L M O P Q
+ R S T U V W X
+ Y Z . , : ? !
+ ' ( ) 0 6 7 8
+ 9 + - * / _ 5
+ 4 3 2 1 N A B
+```
+
+From this point, we can start the iterative encryption.
+
 ### Indistinguishable ciphertexts
 
 To get a different ciphertext even if the same plaintext is encrypted
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