Which encryption algorithm is used by WPA2 in pre-shared key (PSK) mode?

WPA2 in pre-shared key (PSK) mode primarily uses AES-128 (Advanced Encryption Standard with a 128-bit key) for strong encryption. This is often referred to as CCMP (Counter Mode with Cipher Block Chaining Message Authentication Code Protocol), which incorporates AES. TKIP with RC4 was used by WPA and is considered less secure. While AES-256 offers stronger encryption, it is not the standard or default for WPA2-PSK; AES-128 provides sufficient security for most enterprise and home networks. RC4 alone is a stream cipher that was used in WEP and WPA (with TKIP) but is now considered insecure.