diff --git a/ch04.asciidoc b/ch04.asciidoc
index b7907c5e..0e36a9d0 100644
--- a/ch04.asciidoc
+++ b/ch04.asciidoc
@@ -64,7 +64,7 @@ More accurately, the private key can be any number between +1+ and +n - 1+, wher
 	
 [TIP]
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-Do not write your own code to create a random number or use a "simple" random number generator offered by your programming language. Use a cryptographically secure pseudorandom number generator (CSPRNG) with a seed from a source of sufficient entropy. Study the documentation of the random number generator library you choose to make sure it is cryptographically secure. Correct implementation of the CSPRNG is critical to the security of the keys.
+((("warnings and cautions", "random number generation")))Do not write your own code to create a random number or use a "simple" random number generator offered by your programming language. Use a cryptographically secure pseudorandom number generator (CSPRNG) with a seed from a source of sufficient entropy. Study the documentation of the random number generator library you choose to make sure it is cryptographically secure. Correct implementation of the CSPRNG is critical to the security of the keys.
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 The following is a randomly generated private key (k) shown in hexadecimal format (256 binary digits shown as 64 hexadecimal digits, each 4 bits):