What does 128-bit AES-GCM (Galois Counter Mode) represent in a cipher suite?

The designation of 128-bit AES-GCM (Galois Counter Mode) in a cipher suite refers specifically to symmetric bulk encryption. AES, or Advanced Encryption Standard, is a symmetric key encryption algorithm that encrypts data in fixed-size blocks (128 bits in this case). The "128-bit" refers to the key size being used within the algorithm, which directly impacts the strength of the encryption.

GCM, or Galois Counter Mode, is a mode of operation for AES that not only provides confidentiality through encryption but also provides integrity through an authentication tag. This means that not only can data be securely encrypted and decrypted using the same key, but it can also ensure that any alterations to the data can be detected.

In symmetric encryption schemes like AES, the same secret key is used for both encryption and decryption, which is fundamental to this class of encryption methods. This characteristic of using a shared key for both operations showcases why AES-GCM is categorized under symmetric bulk encryption.

Other options present concepts that do not apply to the AES-GCM designation. For instance, hash functions are used for data integrity and not for encrypting data. Signature ciphers relate more to digital signatures, which authenticate the origin of data rather than encrypting it