diff --git a/book/source/drawio/cert-validity-key-expiration.drawio b/book/source/drawio/cert-validity-key-expiration.drawio
new file mode 100644
index 0000000..0f63f6b
--- /dev/null
+++ b/book/source/drawio/cert-validity-key-expiration.drawio
@@ -0,0 +1 @@
+<mxfile host="app.diagrams.net" modified="2023-11-09T18:37:31.908Z" agent="5.0 (X11)" etag="CHE7VbVeDg4v-laCrwRr" version="21.0.1" type="device"><diagram name="Page-1" id="2YBvvXClWsGukQMizWep">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</diagram></mxfile>
\ No newline at end of file
diff --git a/book/source/drawio/cert-validity-key-expiration.png b/book/source/drawio/cert-validity-key-expiration.png
new file mode 100644
index 0000000..06a202d
Binary files /dev/null and b/book/source/drawio/cert-validity-key-expiration.png differ
diff --git a/book/source/drawio/cert-validity-simple.drawio b/book/source/drawio/cert-validity-simple.drawio
new file mode 100644
index 0000000..991fa94
--- /dev/null
+++ b/book/source/drawio/cert-validity-simple.drawio
@@ -0,0 +1 @@
+<mxfile host="app.diagrams.net" modified="2023-11-09T17:52:39.946Z" agent="5.0 (X11)" etag="sYTyf2mXicL_ydLRoJxl" version="21.0.1" type="device"><diagram name="Page-1" id="2YBvvXClWsGukQMizWep">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</diagram></mxfile>
\ No newline at end of file
diff --git a/book/source/drawio/cert-validity-simple.png b/book/source/drawio/cert-validity-simple.png
new file mode 100644
index 0000000..36ab24a
Binary files /dev/null and b/book/source/drawio/cert-validity-simple.png differ
diff --git a/book/source/drawio/cert-validity-subkey.drawio b/book/source/drawio/cert-validity-subkey.drawio
new file mode 100644
index 0000000..f241774
--- /dev/null
+++ b/book/source/drawio/cert-validity-subkey.drawio
@@ -0,0 +1 @@
+<mxfile host="app.diagrams.net" modified="2023-11-09T18:03:34.394Z" agent="5.0 (X11)" etag="TfwtBB18-_Ys4L9oGnGs" version="21.0.1" type="device"><diagram name="Page-1" id="2YBvvXClWsGukQMizWep">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</diagram></mxfile>
\ No newline at end of file
diff --git a/book/source/drawio/cert-validity-subkey.png b/book/source/drawio/cert-validity-subkey.png
new file mode 100644
index 0000000..6c0571a
Binary files /dev/null and b/book/source/drawio/cert-validity-subkey.png differ