Data at rest means it is stored somewhere such as a storage area network (SAN) or network-attached storage (NAS) drive, or in cloud storage. All sensitive data needs to be protected by applying symmetric or asymmetric encryption, explained in the previous section, with proper key management.
Data in transit means data in motion and transferred over the network. You may encrypt data at rest in the source and destination, but your data transfer pipeline needs to be secure when transferring data. When transferring data over an unencrypted protocol such as HTTP, it can get leaked by an attack such as an eavesdropping or man-in-the-middle (MITM) attack.
In an eavesdropping attack, the attacker captures a small packet from a network and uses it to search for any other type of information. A MITM attack is a tampering-based attack, where the attacker secretly alters the communication to start communication on behalf of the receiver. These kinds of attacks...