diff --git a/book/source/03-cryptography.md b/book/source/03-cryptography.md
index c63cb97..f26e32e 100644
--- a/book/source/03-cryptography.md
+++ b/book/source/03-cryptography.md
@@ -21,13 +21,13 @@ Here are two important properties of cryptographic hash functions:
 - ["Pre-image resistance"](https://en.wikipedia.org/wiki/Preimage_attack): Given a hash value, it should be very difficult to determine the original data it represents.
 - ["Collision resistance"](https://en.wikipedia.org/wiki/Collision_resistance): It should be very difficult to find two distinct pieces of data that map to the same hash value.
 
-## Message Authentication Codes
+## Message authentication codes
 
-[Message Authentication Codes](https://en.wikipedia.org/wiki/Message_authentication_code) (MAC, also called authentication tags) are small pieces of information, which can be used to verify the integrity and authenticity of a message.
-They are calculated over the original message using a (symmetric) secret key.
-The recipient of a message containing a MAC, who is also in posession of the secret key can verify that the message has not been tampered with.
+A [message authentication code](https://en.wikipedia.org/wiki/Message_authentication_code) (MAC), also known as an authentication tag, is a small piece of information used to verify the integrity and authenticity of a message.
 
-[HMAC](https://en.wikipedia.org/wiki/HMAC) is a hash-based message authentication code, which is used in the OpenPGP protocol.
+It is derived from the original message using a (symmetric) secret key. The recipient of a message containing a MAC, who is also in possession of the secret key, can verify that the message has not been altered.
+
+[HMAC](https://en.wikipedia.org/wiki/HMAC) is a type of MAC that relies on a hash function. It is used in the OpenPGP protocol.
 
 ### Key Derivation Functions