diff --git a/book/source/03-cryptography.md b/book/source/03-cryptography.md
index 788eae5..4c9fd57 100644
--- a/book/source/03-cryptography.md
+++ b/book/source/03-cryptography.md
@@ -19,7 +19,7 @@ Here are two important properties of cryptographic hash functions:
 
 ## Symmetric-key cryptography
 
-[Symmetric-key cryptography](https://en.wikipedia.org/wiki/Symmetric-key_algorithm) uses the same cryptographic key for both encryption and decryption. Symmetric-key cryptographic systems support *encryption/decryption* operations.
+[Symmetric-key cryptography](https://en.wikipedia.org/wiki/Symmetric-key_algorithm) uses the same cryptographic key for both encryption and decryption, unlike asymmetric cryptography where a pair of keys is used: a public key for encryption and a corresponding private key for decryption. Symmetric-key cryptographic systems support *encryption/decryption* operations.
 
 Participants in symmetric-key operations need to exchange the shared secret over a secure channel.