Which cryptographic technique provides secure key exchange?

Which cryptographic technique provides secure key exchange?

• A. Diffie-Hellman (D-H)
• B. RSA
• C. AES
• D. Elliptic-curve encryption

Answer: (A)

Sharing a secret securely over an insecure channel is the goal, and Diffie-Hellman does exactly that. It lets two parties each generate a private value and exchange public values, then combine their private value with the other side’s public value to compute a common shared secret. An eavesdropper only sees the public values and cannot derive the secret without solving a hard math problem, so the session key remains protected. When used with ephemeral parameters (ephemeral Diffie-Hellman), this approach also provides forward secrecy, meaning past communications stay secure even if one party’s private key is later compromised. RSA, AES, and generic “elliptic-curve encryption” aren’t focused on establishing a shared secret in this way. RSA is mainly for encrypting data or creating digital signatures, AES is a symmetric cipher that requires the key to be known beforehand, and elliptic-curve options that aren’t clearly defined as a Diffie-Hellman variant don’t by themselves establish a secure key exchange.

Sharing a secret securely over an insecure channel is the goal, and Diffie-Hellman does exactly that. It lets two parties each generate a private value and exchange public values, then combine their private value with the other side’s public value to compute a common shared secret. An eavesdropper only sees the public values and cannot derive the secret without solving a hard math problem, so the session key remains protected. When used with ephemeral parameters (ephemeral Diffie-Hellman), this approach also provides forward secrecy, meaning past communications stay secure even if one party’s private key is later compromised.

RSA, AES, and generic “elliptic-curve encryption” aren’t focused on establishing a shared secret in this way. RSA is mainly for encrypting data or creating digital signatures, AES is a symmetric cipher that requires the key to be known beforehand, and elliptic-curve options that aren’t clearly defined as a Diffie-Hellman variant don’t by themselves establish a secure key exchange.