Tiger Woods’ website prominently features his handwritten signature. He also “signs” each of his blog posts with the same signature image. This signature can easily be copied, reused, and misused. I can “sign” this post just like he does:

I can also take this image and print it out on a contract. Perhaps I may need to do some photoshop tricks to make it look more authentic, but bottom line is that a handwritten signature or its image isn’t very secure. A secure signature needs to satisfy two requirements:

1. I can prove that I signed document A and not someone else (Signer authentication)

2. I can prove that the content of document A has not been modified in any way since I signed it (Document authentication)

Luckily, public-key cryptography algorithms have been developed to generate digital signatures that satisfy the above two properties. These digital signatures are much more secure than paper signatures. A paper signature can be forged, while a digital signature, done correctly, cannot be forged with existing computing technology. Let’s run through an imaginary scenario to see how it works. Tiger Woods has renegotiated his contract with Nike and is ready to sign.

Step 1: Tiger creates public and private keys for himself
Step 2: Tiger generates a unique digest of the contract
Step 3: Tiger signs the digest with his private key

That’s it. Anyone can then use Tiger’s public key to verify that he signed the contract (Signer Authentication) and use the digest to verify that the contract has not been modified since it was signed (Document Authentication). This algorithm is both simple and secure, has been around for over two decades, and is available in commercial products.

At Seravia, we make this even easier. We automatically generate a public and private key for each person as soon as they create an account. Digests are created for every contract. And digitally signing is a one-click process.

People are still using handwritten signatures like Tiger Woods’ above to sign contracts. We all need to stop relying on technology from 5000 BC, when bird feathers were used as pens, and embrace the digital age and digital signatures.