In the crypto puzzle, what is the difference between symmetric and asymmetric approaches for achieving confidentiality vs. data authenticity?

Question

Accepted Answer

For confidentiality, symmetric uses shared-key encryption while asymmetric uses the recipient's public key. For authenticity, symmetric uses MACs while asymmetric uses digital signatures with the sender's private key.

Goal
Symmetric Approach
Asymmetric Approach

Confidentiality
Encrypt with shared secret key (3DES, AES)
Encrypt with recipient's public key, decrypt with recipient's private key

Data Authenticity / Integrity
MAC (Message Authentication Code), e.g., HMAC with SHA-3
Digital signature: sign with sender's private key, verify with sender's public key

Key differences for authenticity:

Property
Symmetric (MAC)
Asymmetric (Signature)

Non-repudiation
No — both parties share the key, so either could have created the MAC
Yes — only the signer has the private key

Key management
Need pre-shared secret
Advantage: only need authentic public keys

Speed
Fast
Slower

Important: MAC provides integrity but not non-repudiation (either party could have generated it). Digital signatures provide both integrity and non-repudiation.
The asymmetric approach also includes: RSA, ECC, EdDSA, and newer schemes like those that won't be broken by quantum computers.

Goal	Symmetric Approach	Asymmetric Approach
Confidentiality	Encrypt with shared secret key (3DES, AES)	Encrypt with recipient's public key, decrypt with recipient's private key
Data Authenticity / Integrity	MAC (Message Authentication Code), e.g., HMAC with SHA-3	Digital signature: sign with sender's private key, verify with sender's public key

Property	Symmetric (MAC)	Asymmetric (Signature)
Non-repudiation	No — both parties share the key, so either could have created the MAC	Yes — only the signer has the private key
Key management	Need pre-shared secret	Advantage: only need authentic public keys
Speed	Fast	Slower