Cryptography Works
Cryptography is the practice and study of techniques for secure communication in the presence of third parties called adversaries. It’s fundamentally about converting readable data (plaintext) into an unreadable format (ciphertext) to prevent unauthorized access, and then converting the ciphertext back to plaintext for authorized parties. Here’s a detailed explanation of how it works, followed by examples:
How Cryptography Works:
Encryption:
Key Generation: Cryptography often involves the use of keys, which are pieces of information used in the encryption process. Keys can be symmetric (one key for both encryption and decryption) or asymmetric (public key for encryption, private key for decryption).
Encryption Algorithm: This is the method used to transform plaintext into ciphertext. The algorithm applies the key to the data in a manner that should be complex enough to resist decryption without the key.
Decryption:
Using the corresponding key, the ciphertext is transformed back into plaintext. If symmetric encryption is used, the same key is used for both processes; in asymmetric encryption, the private key decodes what the public key has encoded.
Security Measures:
Confidentiality: Ensures that only the intended recipient can read the message.
Integrity: Ensures the data has not been altered in transit.
Authentication: Confirms the identity of the sender.
Non-repudiation: Prevents the sender from denying sending the message.
Key Cryptographic Systems:
Symmetric Cryptography:
Example: AES (Advanced Encryption Standard):
Process: Both sender and receiver use the same secret key. The data is encrypted using AES, which involves multiple rounds of substitution and permutation operations.
Usage: Commonly used for securing data on devices, in VPNs, and for file encryption.
Asymmetric (Public-Key) Cryptography:
Example: RSA (Rivest–Shamir–Adleman):
Process: Uses two keys – a public key for encryption which anyone can access, and a private key for decryption, which only the owner has. Data encrypted with one key can only be decrypted with the other.
Usage: Digital signatures, SSL/TLS for secure web browsing, email encryption.
Hash Functions:
Example: SHA-256 (Secure Hash Algorithm 256-bit):
Process: Takes an input (or ‘message’) and returns a fixed-size string of bytes, typically used for verifying data integrity. It’s one-way; you can’t get the original message from the hash.
Usage: Password storage, file or message integrity checks.
Digital Signatures:
Example: Using RSA for signing:
Process: A hash of the message is encrypted with the sender’s private key. The recipient can decrypt this hash with the sender’s public key and compare it with a hash of the received message to confirm authenticity and integrity.
Usage: Software distribution, legal documents.
Practical Examples:
Email Encryption: Using PGP (Pretty Good Privacy), one can encrypt an email so only the person with the corresponding private key can read it.
Secure Web Browsing: HTTPS uses SSL/TLS where the server’s public key encrypts the session, ensuring that data exchanged between your browser and the server remains confidential.
Password Hashing: When you create an account online, your password is not stored in plaintext; instead, a hash of your password is stored. When you log in, your entered password is hashed again, and this hash is compared to the stored one for verification.
Cryptography is crucial for digital security, ensuring that personal data, financial transactions, and confidential communications remain private and secure. However, its effectiveness relies heavily on the strength of the algorithms, the secrecy of the keys, and adherence to best practices in key management and protocol implementation.
