ECDSA, the Elliptic Curve Digital Signature Algorithm, is a public-key signature scheme used to prove identity and integrity. In SSH, it can authenticate a server host key or a user key, letting clients verify that the key they received was signed by the expected private key. Because it uses elliptic-curve cryptography, ECDSA can provide strong security with relatively small keys and efficient verification.
In cyber security, ECDSA matters because authentication only works when the software checks the signature correctly and binds it to the right algorithm and curve. Attackers look for validation bugs that accept a key with the wrong curve, skip checks, or trust a weak host-key workflow; that can open the door to man-in-the-middle impersonation. Defenders rely on strict key verification, careful curve matching, and up-to-date libraries to keep SSH identity checks trustworthy.