diff --git a/smart_contracts_vulnerabilities/random_numbers.md b/smart_contracts_vulnerabilities/random_numbers.md
index 3216a0e..9b1e307 100644
--- a/smart_contracts_vulnerabilities/random_numbers.md
+++ b/smart_contracts_vulnerabilities/random_numbers.md
@@ -6,4 +6,6 @@
 
 <br>
 
-* [randao](https://github.com/randao/randao)
+
+* [ethereum randomness ](https://eth2book.info/altair/part2/building_blocks/randomness)
+* [randao github](https://github.com/randao/randao)