Which of the following offers the LEAST secure encryption capabilities?

Twofish is a strong, NIST-evaluated symmetric block cipher with key sizes up to 256 bits, offering robust encryption capabilities.

PAP sends the username and password as unencrypted cleartext during the authentication exchange, providing no protection against eavesdropping or replay attacks. All other options either use symmetric encryption algorithms or challenge-response mechanisms that at minimum avoid transmitting credentials in the clear.

NTLM uses a challenge-response mechanism with cryptographic hashing (MD4/MD5), which avoids sending the plaintext password over the network.

CHAP uses a three-way handshake with a shared secret and MD5 hash, ensuring the password is never transmitted directly across the wire.