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EFF.org is the website of the Electronic Frontier Foundation, a nonprofit that defends civil liberties in the digital world. It provides accessible guides, explainers, and news on privacy, security, and encryption, including practical resources like the Surveillance Self-Defense guide.
More resources on Encryption Basics
Cryptography I
Cryptography is an indispensable tool for protecting information in computer systems. In this course you will learn the inner workings of cryptographic systems and how to correctly use them in real-world applications. The course begins with a detailed discussion of how two parties who have a shared secret key can communicate securely when a powerful adversary eavesdrops and tampers with traffic. We will examine many deployed protocols and analyze mistakes in existing systems. The second half of the course discusses public-key techniques that let two parties generate a shared secret key. Throughout the course participants will be exposed to many exciting open problems in the field and work on fun (optional) programming projects. In a second course (Crypto II) we will cover more advanced cryptographic tasks such as zero-knowledge, privacy mechanisms, and other forms of encryption.
Practical Cryptography for Developers
Hands-on guide, top rec in privacytoolsIO archives.
Cryptography Book
Free online book for developers, praised in r/cryptography.
Crypto101
Free PDF course on cryptography basics, frequently recommended on Reddit.
Public Key Cryptography - Computerphile
Basics of asymmetric encryption, recommended in privacy threads.
Symmetric Key Cryptography: The Basics
Computerphile explains symmetric encryption basics, highly upvoted in r/cryptography.