Which part of the cipher "ECDHE-RSA-AES128-GCM-SHA256" is used for signatures?

The correct answer is that RSA is the part of the cipher "ECDHE-RSA-AES128-GCM-SHA256" used for signatures. RSA is a widely adopted public key cryptographic algorithm that allows for secure data transmission. In the context of secure communications, RSA is utilized for authenticating the parties involved in the exchange, ensuring that the messages or sessions have not been tampered with.

When a signature is created, it typically involves hashing a message and then encrypting that hash with a private key. This ensures the integrity and authenticity of the message, as only someone with the valid private key can generate a signature that can be verified by a public key. In this specific cipher string, RSA is responsible for signing the key exchange, thus confirming the identity of the communicating parties.

The other components play different roles: the ECDH portion sets up a secure channel for exchanging keys, which is vital for establishing the encrypted session; AES128-GCM then encrypts the data transmitted over this secure channel, and SHA256 serves as the hashing function used during various processes, including signature creation, but is not the mechanism for signing itself. This distinguishes RSA's unique function as the signature algorithm in this cipher suite.