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TLS Terminology

Basic TLS Handshake

The basic TLS Handshake is a negotiation between the client and server to verify the server's authentication and negotiate the details on how to communicate. During this handshake process, the client and the server decide on the TLS version (the highest mutually supported) and cipher suite. Only the server is authenticated in the basic TLS handshake.

TLS Handshake

The full TLS Handshake requires mutual authentication between the client and the server. During this process, the client must also prove the authenticity of its identity to the server before a connection can be established.

Cipher Suite

A cipher suite is the set of algorithms used for encrypting and authenticating data during secure communications between the client and server. The client and server must agree on the cipher suite before proceeding to communicate past the handshake.

PKI (Public Key Infrastructure)

PKI (Public Key Infrastructure) defines a set of roles and procedures for the management of digital certificates. This system is responsible for ensuring the authenticity of each certificate issued by the server and client. Within PKI, the CA (Certificate Authority) is responsible for issuing digital certificates. These certificates are used to verify the authenticity of the owner (server/client).

Public and Private Key

Public key cryptography is a system in which a mathematically-related pair of keys are used for encrypting and signing data. Each pair of keys in public key cryptography includes a widely disseminated public key and a private key known only to one party. By signing or encrypting data with a private key, any recipient can authenticate and/or decrypt the data using the matching public key. Data encrypted using a public key can only be decrypted by the holder of the private key. TLS uses public key cryptography during the TLS handshake.

Root CA Certificate

The root CA certificate establishes the authenticity of the Certificate Authority. This root certificate is the top-most certificate and is used to the sign the certificates issued by the certificate authority. As an example, in the MQTT with TLS demo, the root CA certificate could be configured to use a public MQTT broker (e.g., or when using AWS IoT Core, the root CA certificate would be one of the recommended IoT Core CA certificates.

mbed TLS

mbed TLS is an implementation of TLS that is specifically designed for memory constrained embedded IoT devices. It utilizes a minimal subset of the TLS stack.

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