diff --git a/book/source/diag/keypair_pub.png b/book/source/diag/keypair_pub.png
new file mode 100644
index 0000000..984ae82
Binary files /dev/null and b/book/source/diag/keypair_pub.png differ
diff --git a/book/source/diag/keypair_pub.svg b/book/source/diag/keypair_pub.svg
new file mode 100644
index 0000000..6239a29
--- /dev/null
+++ b/book/source/diag/keypair_pub.svg
@@ -0,0 +1,75 @@
+<?xml version="1.0" encoding="UTF-8" standalone="no"?>
+<!-- Created with Inkscape (http://www.inkscape.org/) -->
+
+<svg
+   width="38.803001mm"
+   height="35.769001mm"
+   viewBox="0 0 38.803001 35.769001"
+   version="1.1"
+   id="svg895"
+   inkscape:version="1.3 (0e150ed6c4, 2023-07-21)"
+   sodipodi:docname="keypair_pub.svg"
+   inkscape:export-filename="keypair_pub.png"
+   inkscape:export-xdpi="128"
+   inkscape:export-ydpi="128"
+   xmlns:inkscape="http://www.inkscape.org/namespaces/inkscape"
+   xmlns:sodipodi="http://sodipodi.sourceforge.net/DTD/sodipodi-0.dtd"
+   xmlns="http://www.w3.org/2000/svg"
+   xmlns:svg="http://www.w3.org/2000/svg">
+  <sodipodi:namedview
+     id="namedview897"
+     pagecolor="#ffffff"
+     bordercolor="#000000"
+     borderopacity="0.25"
+     inkscape:showpageshadow="2"
+     inkscape:pageopacity="1"
+     inkscape:pagecheckerboard="0"
+     inkscape:deskcolor="#d1d1d1"
+     inkscape:document-units="mm"
+     showgrid="false"
+     inkscape:zoom="3.1390218"
+     inkscape:cx="36.794902"
+     inkscape:cy="39.662037"
+     inkscape:window-width="1920"
+     inkscape:window-height="1055"
+     inkscape:window-x="0"
+     inkscape:window-y="0"
+     inkscape:window-maximized="1"
+     inkscape:current-layer="layer1" />
+  <defs
+     id="defs892" />
+  <g
+     inkscape:label="Layer 1"
+     inkscape:groupmode="layer"
+     id="layer1"
+     transform="translate(-64.804822,-64.571863)">
+    <path
+       style="fill:#008000;stroke-width:0.055678"
+       inkscape:connector-curvature="0"
+       d="m 89.968955,72.548328 c -0.07545,-0.06413 -0.173403,-0.100289 -0.274569,-0.09921 h -8.838057 c -0.235714,-0.58344 -0.5875,-1.118748 -1.045896,-1.577145 -0.895819,-0.89582 -2.0881,-1.389296 -3.354486,-1.39088 -1.26604,6.02e-4 -2.457373,0.493837 -3.353723,1.390187 -0.896767,0.896767 -1.388432,2.086771 -1.389649,3.354218 -7.14e-4,2.616882 2.126624,4.744756 4.743457,4.743852 1.268733,1.42e-4 2.459253,-0.491545 3.355561,-1.387852 0.458495,-0.458495 0.808449,-0.993471 1.044891,-1.578121 l 2.904569,0.0011 c 0.119925,-7.07e-4 0.231372,-0.04871 0.314493,-0.13749 l 0.763357,-0.818936 0.767168,0.81907 c 0.08155,0.08579 0.192871,0.137292 0.313036,0.13626 0.117875,0.0012 0.232426,-0.04858 0.312307,-0.135305 l 0.766978,-0.821141 0.763746,0.820739 c 0.08156,0.0858 0.19502,0.135623 0.31293,0.13686 0.119855,-7.78e-4 0.222322,-0.03918 0.31462,-0.137362 l 0.765076,-0.819099 0.765839,0.818872 c 0.08297,0.09287 0.204721,0.140092 0.32763,0.137179 0.110663,-0.0053 0.21137,-0.0492 0.287581,-0.125412 0.01061,-0.01061 0.02169,-0.02257 0.03125,-0.0355 l 1.079724,-1.349485 c 0.146244,-0.182024 0.119274,-0.448037 -0.05931,-0.598432 z m -14.322469,1.677547 c -4.03e-4,0.745736 -0.603551,1.348884 -1.348509,1.348509 -0.745637,3.5e-5 -1.348686,-0.603013 -1.348283,-1.348283 -1.48e-4,-0.744732 0.602462,-1.348049 1.348396,-1.348622 0.744725,7.1e-5 1.347923,0.603735 1.348396,1.348396 z m 13.386848,-0.53955 c 0,0.08867 -0.03724,0.170172 -0.09499,0.227923 -0.05777,0.05777 -0.139279,0.09501 -0.227922,0.09498 l -7.520894,-0.0011 c -0.0083,-0.217556 -0.03183,-0.431575 -0.07029,-0.642944 l 7.59212,-7.63e-4 c 0.17725,-7e-6 0.321939,0.144681 0.321968,0.321896 z"
+       id="path4600-8-0-6-5-1-3" />
+    <text
+       xml:space="preserve"
+       style="font-style:normal;font-variant:normal;font-weight:normal;font-stretch:normal;font-size:3.52778px;font-family:'Courier 10 Pitch';-inkscape-font-specification:'Courier 10 Pitch, Normal';font-variant-ligatures:normal;font-variant-caps:normal;font-variant-numeric:normal;font-variant-east-asian:normal;opacity:1;fill:#000000;fill-opacity:1;stroke:none;stroke-width:0.2;stroke-dasharray:none;stroke-opacity:1"
+       x="65.669128"
+       y="93.610512"
+       id="text4813"><tspan
+         sodipodi:role="line"
+         style="font-style:normal;font-variant:normal;font-weight:normal;font-stretch:normal;font-size:3.52778px;font-family:'Courier 10 Pitch';-inkscape-font-specification:'Courier 10 Pitch, Normal';font-variant-ligatures:normal;font-variant-caps:normal;font-variant-numeric:normal;font-variant-east-asian:normal;fill:#000000;fill-opacity:1;stroke:none;stroke-width:0.2;stroke-dasharray:none;stroke-opacity:1"
+         x="65.669128"
+         y="93.610512"
+         id="tspan1">only public material of</tspan><tspan
+         sodipodi:role="line"
+         style="font-style:normal;font-variant:normal;font-weight:normal;font-stretch:normal;font-size:3.52778px;font-family:'Courier 10 Pitch';-inkscape-font-specification:'Courier 10 Pitch, Normal';font-variant-ligatures:normal;font-variant-caps:normal;font-variant-numeric:normal;font-variant-east-asian:normal;fill:#000000;fill-opacity:1;stroke:none;stroke-width:0.2;stroke-dasharray:none;stroke-opacity:1"
+         x="65.669128"
+         y="98.020233"
+         id="tspan2">cryptographic keypair</tspan></text>
+    <rect
+       style="fill:none;stroke:#000000;stroke-width:0.176389;stroke-dasharray:none;stroke-opacity:0.3512"
+       id="rect6679"
+       width="30.897322"
+       height="22.261703"
+       x="68.845375"
+       y="66.776726" />
+  </g>
+</svg>