Step 12 provided a gentle introduction to asymmetric cryptography. It also pointed out that the blockchain uses public cryptographic keys as account numbers and utilizes the public-to-private approach of asymmetric cryptography for transferring ownership among accounts. However, that was only half of the story. The blockchain needs to ensure that only the lawful owner can transfer his or her property to other accounts. This is the point were the concept of authorization enters the scene. Hence, this step explains how asymmetric cryptography is used within the blockchain for authorizing transactions. In particular, this step is devoted to the concept of digital signatures, which utilize the private-to-public approach of asymmetric cryptography.