Symmetric vs Asymmetric Encryption

The Memo SDK uses a hybrid encryption approach that combines both symmetric and asymmetric encryption. Understanding the difference between these two types of encryption helps explain why this approach is both secure and efficient.

Symmetric Encryption

Symmetric encryption uses the same key for both encryption and decryption.

Characteristics

• ✅ Same key used for both encryption and decryption
• ✅ Fast, suitable for encrypting large amounts of data
• ⚠️ Key needs secure transmission (this is why we use RSA to encrypt the AES key)

Example: AES

AES (Advanced Encryption Standard) is the most common symmetric encryption algorithm:

// AES symmetric encryption
aesKey := generateKey()           // Same key
cipherData := aes.Encrypt(data, aesKey)  // Encrypt with key
plainData := aes.Decrypt(cipherData, aesKey)  // Decrypt with same key

Common Symmetric Algorithms

• AES (Advanced Encryption Standard) - Used by Memo SDK
• DES, 3DES
• ChaCha20

Asymmetric Encryption

Asymmetric encryption uses a pair of keys: a public key and a private key.

Characteristics

• ✅ Public and private keys are a pair, different purposes
• ✅ Public key encrypts, private key decrypts
• ✅ Private key signs, public key verifies
• ⚠️ Slow, not suitable for encrypting large amounts of data

Example: RSA

RSA is the most common asymmetric encryption algorithm:

// RSA asymmetric encryption
publicKey, privateKey := generateKeyPair()  // A key pair
cipherData := rsa.Encrypt(data, publicKey)   // Encrypt with public key
plainData := rsa.Decrypt(cipherData, privateKey)  // Decrypt with private key

Common Asymmetric Algorithms

• RSA - Used by Memo SDK
• ECC (Elliptic Curve Cryptography)
• ElGamal

Comparison

Feature	Symmetric (AES)	Asymmetric (RSA)
Speed	✅ Very fast	⚠️ Slow (100-1000x slower than AES)
Key Management	⚠️ Need secure key transmission	✅ Public key can be public
Data Size Limit	✅ Unlimited	⚠️ Limited (2048-bit key can only encrypt 245 bytes)
Use Case	Encrypt large data	Encrypt small data, key exchange, signing
Key Distribution	⚠️ Challenging	✅ Easy (public key can be shared)

Why Use Hybrid Encryption?

The Memo SDK uses hybrid encryption to combine the best of both worlds:

Tip

Hybrid encryption uses symmetric encryption for data (fast) and asymmetric encryption for the key (secure key exchange).

Hybrid Encryption Advantages

1. Use AES (symmetric) to encrypt large data → Fast
2. Use RSA (asymmetric) to encrypt AES key → Solves key transmission problem
3. Combines both advantages: secure and efficient

How It Works in Memo SDK

// 1. Generate AES key (symmetric encryption)
aesKey := make([]byte, 32)  // Same key for encryption and decryption

// 2. Encrypt data with AES (symmetric encryption)
cipherData := aes.Encrypt(data, aesKey)

// 3. Encrypt AES key with RSA public key (asymmetric encryption)
encryptedKey := rsa.Encrypt(aesKey, publicKey)

// Decryption:
// 1. Decrypt AES key with RSA private key (asymmetric decryption)
aesKey := rsa.Decrypt(encryptedKey, privateKey)

// 2. Decrypt data with AES key (symmetric decryption)
data := aes.Decrypt(cipherData, aesKey)

Summary

• Symmetric encryption (AES): Fast, efficient for large data, but requires secure key distribution
• Asymmetric encryption (RSA): Solves key distribution problem, but slow for large data
• Hybrid encryption: Best of both worlds - fast data encryption with secure key exchange

Related Topics

• Learn about the complete encryption flow in the Memo SDK
• Understand GCM mode used for symmetric encryption
• Explore RSA OAEP padding used for asymmetric encryption