Cryptography Lessons

Vinod

Ruby on Rails

Take online lessons from cyber security analysts on applied cryptography, key management and secure-by-design DevSecOps practices covering Authenticated Encryption, the modern RSA cryptosystem, Public Key infrastructure (PKI) solutions for example Venafi certificates to block cipher, key exchange in public key cryptography, solution design of modern public key encryption systems and configuration management tools (Ansible, Puppet or Chef), Message Integrity of MAC systems to ensure data integrity, to . Find Cryptography Lessons WFH freelancers on January 21, 2025 who work remotely. Read less

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Top Frequently Asked Questions

What to Know

How does cryptography work?

Cryptography is the science of securing information by encoding it in a way that makes it unreadable to anyone except those possessing special knowledge, usually referred to as a key.

Here's an overview of the core technical processes involved in cryptography, with explanations and examples:

1. Encryption

Explanation: Encryption transforms readable data, known as plaintext, into an unreadable format, called ciphertext, using an algorithm and a key.

Technical Process:
Symmetric Encryption: Uses the same key for encryption and decryption.

Example: AES (Advanced Encryption Standard)

How It Works: AES operates on a 4x4 column-major order matrix of bytes, termed the state, which is subjected to several rounds of substitution, permutation, and mixing operations. Each round involves:

Substitute Bytes: Each byte in the state is replaced with another according to a substitution table (S-box).

Shift Rows: Rows of the state are shifted cyclically by different offsets.

Mix Columns: A mixing operation which combines the four bytes in each column.

Add Round Key: Each byte of the state is combined with a round key using XOR.

Asymmetric Encryption: Uses a pair of keys - public for encryption and private for decryption.
Example: RSA (Rivest–Shamir–Adleman)

How It Works:
Key Generation: Two large prime numbers are chosen to compute n = p * q, where p and q are the primes. Then, e (public exponent) and d (private exponent) are calculated such that e * d ≡ 1 (mod (p-1)(q-1)).
Encryption: Message M is encrypted as C = M^e mod n.
Decryption: Ciphertext C is decrypted back to M with M = C^d mod n.

2. Hashing

Explanation: Hashing transforms data into a fixed-size value or hash, typically for ensuring data integrity or password storage.

Technical Process:
One-Way Function: The hash function is designed to be computationally infeasible to reverse.
Collision Resistance: It's difficult to find two different inputs with the same hash value.
Example: SHA-256 (Secure Hash Algorithm 256-bit)

How It Works:
Data is processed in 512-bit chunks, with padding if necessary. Each chunk is then subjected to a series of logical operations, including AND, OR, XOR, and modular addition, spread over 64 rounds. Each round mixes the current hash state with a portion of the data chunk and a constant to produce a new state. The final hash is the result of all these operations.

3. Digital Signatures

Explanation: Digital signatures provide authenticity and non-repudiation by signing a piece of data, ensuring it came from the signer and has not been altered.

Technical Process:
Signing: The data (or its hash) is encrypted with the sender's private key.

Verification: The signature is decrypted with the sender's public key, and the result is compared with the hash of the received data.
Example: Using RSA for Digital Signatures:

How It Works:
Signing: Hash the message M to get H(M). Then, sign it with the private key d: S = H(M)^d mod n.
Verification: Anyone can verify by hashing M again to get H(M) and checking if S^e mod n = H(M), where e is the public key.

4. Key Exchange

Explanation: Securely exchanging keys over potentially insecure channels is critical for symmetric encryption.

Technical Process:
Diffie-Hellman Key Exchange:

How It Works:
Two parties agree on two public numbers, a prime p and a base g.
Each party chooses a secret number (a for Alice, b for Bob).
They compute and share A = g^a mod p and B = g^b mod p.
Each can then compute the shared secret key as K = B^a mod p or K = A^b mod p, which will be the same for both due to the properties of modular exponentiation.

5. Random Number Generation

Explanation: Cryptography relies on randomness, especially for key generation, to ensure unpredictability.

Technical Process:
True Random Number Generators (TRNG): Use physical phenomena like thermal noise to generate randomness.
Pseudo-Random Number Generators (PRNG): Use algorithms to produce sequences that appear random but are generated from a seed. Cryptographically secure PRNGs are designed to be unpredictable even if part of the sequence is known.
Example: Fortuna PRNG
How It Works: Accumulates entropy from various system events and uses a cascade of hash functions to generate random bytes. It includes mechanisms for reseeding to maintain randomness quality over time.

6. Implementation Considerations

Key Management: Securely generating, storing, transmitting, and disposing of keys.
Algorithm Agility: The ability to switch between different cryptographic algorithms to respond to new vulnerabilities or standards.
Side-Channel Attacks Mitigation: Protecting against attacks that exploit implementation details like timing or power consumption.

Cryptography involves not just these processes but also continuous research and adaptation to new threats and computational capabilities. Each part of the cryptographic process is designed with security in mind, balancing usability, performance, and protection.

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