Symmetric Encryption

Symmetric encryption uses a single shared key for both encryption and decryption. It is the workhorse of modern cryptography — fast, efficient, and used to protect the vast majority of data at rest and in transit.

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How Symmetric Encryption Works

Sender:    Plaintext  ──▶  [ AES Encrypt + Key ]  ──▶  Ciphertext
Receiver:  Ciphertext ──▶  [ AES Decrypt + Key ]  ──▶  Plaintext

Both parties must possess the same secret key. The fundamental challenge is: how do you securely share the key?

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Block Ciphers vs Stream Ciphers

Feature	Block Cipher	Stream Cipher
Processing	Encrypts fixed-size blocks (e.g., 128 bits)	Encrypts one bit or byte at a time
Speed	Slightly slower per byte	Very fast, especially in hardware
Use case	File encryption, disk encryption, TLS	Real-time communications, wireless
Examples	AES, DES, 3DES, Blowfish	ChaCha20, RC4 (deprecated)

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DES (Data Encryption Standard)

DES was adopted as a US federal standard in 1977: