What does "confidentiality" actually mean in cryptography — does it prevent eavesdropping?

Question

Accepted Answer

Confidentiality does NOT mean preventing eavesdropping. It means ensuring intercepted messages cannot be understood — the attacker can capture the ciphertext but cannot recover the plaintext.
This is a critical distinction:
Common misconception: "Encryption prevents eavesdropping"
Reality: Encryption prevents understanding of eavesdropped data
You cannot physically prevent someone from tapping a network cable or capturing WiFi packets. What you can prevent is them making sense of what they captured.
Similarly for other attacks:

You can't prevent someone from inserting a message — but you can prevent the receiver from accepting it as genuine (using a MAC)
You can't prevent replaying — but you can detect it (using sequence numbers)

Key insight: Cryptographic protection mechanisms don't prevent attacks from happening — they make attacks ineffective. The attacker can still perform the attack, but it won't achieve its goal.