This video explains the purpose of digital signatures and how they work. It begins by reviewing encryption and decryption using an asymmetric pair of keys, and then explains the significance of this when it comes to digital signatures, namely that it doesn’t matter which of the key pair is made public and which is kept private. The video then illustrates the digital signing process. Specifically, the creation of a hash value for the document (also known as a digest) using a hash algorithm such as SHA256 (which was created by the National Security Agency). It shows how document digest is then encrypted using the sender’s private key before being attached to the document. When the document is received, the recipient decrypts the digest using the sender’s public key. The recipient also recalculates the hash. If the hash values match, the recipient can be confident that document has not been tampered with in transit. The role of a certification authority is also covered. A certification authority issues its customer with a special file called a digital certificate which binds their public key to identifying information. This video also mentions the importance of digital signatures which it comes to cryptocurrencies. A cryptocurrency such as Bitcoin requires a secure mechanism for updating its decentralised ledger.