What is encryption and how is it used?

Question

Accepted Answer

**Encryption** transforms data into an unreadable form (ciphertext) that can only be decrypted with the right key — protecting confidentiality. Understanding **symmetric vs asymmetric** encryption, and **data in transit vs at rest**, is important for protecting sensitive data.

## Symmetric vs asymmetric encryption

```text
SYMMETRIC → ONE shared key encrypts AND decrypts (e.g. AES):
  ✓ fast, efficient → for bulk data (encrypting files, databases)
  ✗ both parties need the same key (key distribution is the challenge)
ASYMMETRIC → a KEY PAIR: PUBLIC key (encrypt / verify) + PRIVATE key (decrypt / sign):
  → encrypt with the public key, only the private key decrypts (e.g. RSA, ECC)
  ✓ solves key distribution (share the public key freely); enables signatures
  ✗ slower → used for key exchange, signatures, not bulk data
→ Often COMBINED: asymmetric to exchange a symmetric key, then symmetric for the data
  (e.g. how TLS works).
```

## Data in transit vs at rest

```text
IN TRANSIT → data moving over a network → encrypt with TLS/HTTPS (protect from eavesdropping)
AT REST → data stored (databases, disks, backups, files) → encrypt so a breach/stolen disk
  doesn't expose it (database encryption, disk encryption, encrypted fields)
→ protect data BOTH while moving AND while stored.
```

## Important practices

```text
✓ Use STANDARD, vetted algorithms/libraries (AES, RSA, TLS) — NEVER roll your own crypto
✓ KEY MANAGEMENT is critical → protect keys (the security depends on key secrecy);
  use key management systems; rotate keys; don't hardcode keys
✓ Hashing ≠ encryption → hashing is one-way (passwords); encryption is reversible (with the key)
✓ Encrypt sensitive data (PII, credentials, financial); use HTTPS everywhere
```

## Why it matters

Understanding encryption is important because it's **fundamental to protecting sensitive data**, both in transit and at rest, so it's valuable security knowledge for handling data securely.

Encryption (transforming data into unreadable ciphertext decryptable only with the right key) protects **confidentiality**, and understanding its forms and uses is necessary for protecting sensitive data.

Understanding **symmetric vs asymmetric encryption** — symmetric (one shared key, fast, for bulk data, but with key-distribution challenges) versus asymmetric (a public/private key pair solving key distribution and enabling signatures, but slower, used for key exchange and signatures) — and that they're **often combined** (asymmetric to exchange a symmetric key, then symmetric for the data, as in TLS) is important conceptual knowledge for understanding how encryption works in practice.

Understanding **data in transit vs at rest** is practically essential: encrypting data **in transit** (with TLS/HTTPS, protecting from network eavesdropping) and **at rest** (stored data, so a breach or stolen disk doesn't expose it) — protecting data both while moving and while stored, a key practice for comprehensive data protection.

Understanding **important practices** — using **standard vetted algorithms and never rolling your own crypto** (a critical rule, since custom crypto is almost always flawed), the criticality of **key management** (security depends on key secrecy — protecting, rotating, and not hardcoding keys), the distinction that **hashing is one-way (for passwords) while encryption is reversible**, and encrypting sensitive data — reflects correct encryption usage.

Since protecting sensitive data is critical and encryption (in transit and at rest, with the right algorithms and key management) is the fundamental mechanism for confidentiality, and since understanding the types, uses, and practices (especially never rolling your own crypto and managing keys) is important for handling data securely, understanding encryption is valuable, practically-relevant security knowledge — fundamental for protecting sensitive data's confidentiality, important for handling data securely both in transit and at rest, and a core topic for any developer working with sensitive information.