Introduction to cryptography: AES, SHA-256, RSA
Hashes, encryption, keys and signatures.
Level 101 · 15 lessons · 12 practice labs
Lessons
Core ideas
- Why cryptography: You will understand the needs for confidentiality, integrity and authentication, and how cryptography meets them, using everyday examples.
- A short history: from Caesar to Enigma, and why they fell
- Hashing: SHA-256: You will learn that a hash works like a fingerprint of data, is one-way, and how SHA-256 shows whether a file has changed.
- HMAC: You will learn how HMAC proves both that a message is unchanged and that it came from someone who knows the secret key.
- Short task: hash a file, change one byte and see the difference
Encryption
- Symmetric encryption: AES: You will understand symmetric encryption (AES), where one key locks and unlocks, and why sharing that key is the real difficulty, by trying it on your own lab files.
- Password hashing: You will understand why passwords are stored as salted, slow hashes instead of plain text, and how that limits the damage if a database is stolen.
- RSA key pairs: You will learn to generate an RSA key pair made of a public and a private key, and which one is shared and which must be kept secret.
- Encryption and signatures with RSA: You will learn to encrypt a message and to sign and verify one with RSA, and why the roles of the keys are reversed in these two jobs.
- Diffie-Hellman key exchange: You will understand step by step how two parties can agree on a shared secret key with Diffie-Hellman even if their traffic is overheard.
- Hybrid encryption: You will understand why hybrid encryption is used everywhere: a fast symmetric key protects the data and a public key protects that key.
- Short task: encrypt a file with AES and share the key with RSA
Trust
- Certificates: self-signed and CSR: You will learn to read what is inside a certificate, create a self-signed one and a signing request (CSR), and why self-signed is not enough outside a lab.
- Chain of trust and revocation lists: You will understand how trust in a certificate is built through a chain starting at a root authority, and how stolen certificates are invalidated through revocation lists.
- Capstone: secure file exchange: Between two fictional companies you will encrypt and sign a file before sending it, then verify its integrity and the sender on the receiving side.
Practice labs
- Hash a file, change one byte and show the difference: Take the SHA-256 hash of a lab file, change one byte, hash it again and write a short note comparing the two hashes.
- Find the tampered file using a hash list: Compare files in Tarçınlı Fırın's recipe folder with the hash list, find the altered one and record it in the report.
- Verify message integrity with HMAC: Verify the HMAC of ten incoming messages with the lab's shared key, separate the forged ones and explain why a plain hash isn't enough.
- Encrypt a file with AES and decrypt it: Encrypt a lab file with AES, show the ciphertext is unreadable, then decrypt it with the right key and verify the hash is unchanged.
- Find the archive encrypted with weak settings: Inspect the algorithm and key-derivation settings of three encrypted archives in the lab and re-encrypt the weak one.
- Audit where the encryption key lives and fix it: Detect that Ayçiçeği Gıda's backup script keeps the key beside the encrypted file, separate the key and verify the backup still opens.
- Generate an RSA key pair and sign a document: Generate an RSA key pair for the lab, sign a document and show the signature verifies with the public key.
- Find the document whose signature fails: Verify the signatures of five received documents with the sender's public key, separate the one that fails and note the likely cause.
- Encrypt with AES and share the key with RSA: Encrypt a file with a random AES key, wrap the key with the recipient's RSA public key and verify the recipient can open it.
- Show the difference between a self-signed certificate and a CSR: Produce both a self-signed certificate and a CSR for the lab and write a short table comparing their fields.
- Find the revoked certificate in a chain: Validate the lab certificate chain against the revocation list, find the revoked certificate and explain what that means.
- Set up a secure file exchange end to end: Set up an encrypted, signed and hash-verified file exchange between Kumsal Turizm and a partner, and collect evidence for every step.
About this course
Hashes, encryption, keys and signatures.
What you will learn
- Core ideas
- Encryption
- Trust
Prerequisites
No prior knowledge is needed; the course starts from zero.
Lab environment
Lessons run in your own Kali Linux terminal that opens in the browser. Nothing to install; the lab starts clean in every lesson.
Frequently asked questions
- Is this course right for my level?
- The course is at beginner level; every term is explained where it first appears.
- Is there anything to install?
- No. Every lesson runs in your own lab environment that opens in the browser.
- How do lessons work?
- Each lesson has 8 to 10 steps and a short quiz. Early steps show the command to type, later steps give less help; if two attempts fail, the solution opens.
- Can I try it for free?
- Yes. The first three lessons of every course are free.