Class 14: Digital Signatures
Computing in Molecular Biology and Genetics 1
Andrés Aravena, PhD
16 November 2020
Do I have your homework?
In the homework I asked you to send me a file
How can we verify that we have the same file?
How can we be sure that nobody changed it?
How to be sure without showing the content of the file?
Digital signature
An answer to these question is given by digital signatures
They are not digital pictures of a handwritten signature
Instead they are a unique number that identifies the exact document
This number is called digest. It is produced by a crypotgraphic hash function
Cryptographic hash function
MD5 hash function
The input is a file (all the characters)
The output is the digest
The same input produces always the same digest
Different inputs produce different digests
If the input changes, the digest changes
If the input changes a little, the digest changes a lot
How do you validate the file?
Go to http://onlinemd5.com/ or any other service you find on Google
The evaluation is done in your computer. The file is not sent by the internet
How do you validate the file?
You can take the file you attached, get the digest and compare with the one I created
If they are the same we are sure that I have your file
And we do not need to show the content
Application: Intellectual Property
Imagine you are working in a project
- You have an idea, a draft or some data that is confidential
- You do not want to make it public (yet)
- But you want to show that you have this document today
You can get the MD5 digest and publish it
- on a newspaper
- on Facebook
- or anywhere you can look back and show the date and the digest