Today we use cryptography in almost everywhere. From surfing the web over https, to working remotely over ssh. Although most developers don't need to implement cryptography primitives, the knowledge and understanding of these building block allows them to better deploy them in their application. In modern crypto we have all the building block to develop secure application. However, we see instances of insecure code everywhere. Most of these vulnerabilities are not because of theoretic shortcomings, but due to bad implementation or a flawed protocol design. Cryptography is a delicate art where nuances matter, and failure to comprehend the subtleties of these building blocks leads to critical vulnerabilities. To add insult to injury most of the resources available are either outdated or wrong, and inarguably, using bad crypto more dangerous than not using it.In this tutorial we look at the basic building blocks of modern cryptography. We will cover the encryption techniques, hashing mechanisms, and key devastation algorithms. Furthermore we review two of the most widely used protocol suites, SSL and PGP. We conclude by implementing a simplified version of Pretty Good Privacy (PGP), that is used for encryption of texts, e-mails, files, directories, and whole disk partitions.

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