 Digital Signatures Digital signatures are one of the main aspects of ensuring the security and integrity of the data that is recorded onto a blockchain. Similar to the handwritten signatures of the physical world, digital signatures are used to bind a person or entity to digital data. To understand how a digital signature is created, let's suppose that Bob wants to send a digitally signed document to Alice. To illustrate this example, we will use a document to be certified, a hash algorithm, a digest based on the content of the document, a public key, a private key, and its algorithms. Bob has two keys appearing in the form of random numbers and letters, a private key and a public key. A private key should always remain private, but in order to digitally sign a document for Alice, Bob needs to share his public key with her. She will need it later on to verify the authenticity of the document and the signature. When the document is sent, its content is run through a hashing algorithm. The algorithm creates a unique array of numbers and letters called a digest. The digest is then encrypted with Bob's private key, which finally outputs the digital signature of the document. A digital signature is a combination of the content of the document it certifies and the author's private key. But how can Alice verify the authenticity of the document? Any variation in the content of the document or in Bob's private key would create a different signature. So Alice can use the document and its digital signature to reverse the process and verify its legitimacy. Alice can run the document through the same hashing algorithm that Bob used previously, which will output a digest. If the document is untampered, the digest should be exactly the same. Additionally, as Bob ran the digest through his private key algorithm to create the digital signature, Alice can decrypt the digital signature with Bob's public key algorithm to also get a digest. If the signature is untampered, the digest should also be exactly the same. Finally, Alice will have two digests, one based on the digital signature and the other one based on the content of the document. If both digests match, then Alice can be sure that the message hasn't changed in transit and verify that Bob is actually the author. It is in this way that the digital signatures are one of the key parts of securing data on the blockchain and guaranteeing immutability.