diff --git a/ch04_keys.adoc b/ch04_keys.adoc
index 35f1c9ec..041e7ad7 100644
--- a/ch04_keys.adoc
+++ b/ch04_keys.adoc
@@ -88,7 +88,7 @@ signatures.
 ==== Private Keys
 
 A
-private key is simply a number, picked at random.  Control
+private ((("public key cryptography", "private keys", "generating", id="pub-key-private-generate")))((("private keys", "generating", id="private-key-generate")))key is simply a number, picked at random.  Control
 over the private key is the root of user control over all funds
 associated with the corresponding Bitcoin public key. The private key is
 used to create signatures that are used to spend bitcoins by proving
@@ -152,7 +152,7 @@ bits):
 ====
 The size of Bitcoin's private key space, (2^256^) is an unfathomably
 large number. It is approximately 10^77^ in decimal. For comparison, the
-visible universe is estimated to contain 10^80^ atoms.
+visible universe is estimated to((("public key cryptography", "private keys", "generating", startref="pub-key-private-generate")))((("private keys", "generating", startref="private-key-generate"))) contain 10^80^ atoms.
 ====
 
 [[elliptic_curve]]