Iot sdk thesis

Figure 2.5.5.1 TLS: Layered Architecture [23] 
TLS records are structures that carry the payload of four different types: 
1.
Handshake Messages
: Used for negotiating the algorithm and key establishment. 
2.
ChangeCipherSpec Messages
: Messages suggesting change in previously 
negotiated cryptographic algorithm.
3.
Alerts: 
Signalling errors. 
4.
Application Data:
Application-specific payload. 
Record layer is located above a reliable protocol like TCP. The record format is shown 
in the code-snippet below: 
struct
{ 
ContentType type; 
ProtocolVersion version; 
uint16 length; 
opaque payload[length]; 
} TLSRecord; 
Thus, the record defines the type of payload, version of the protocol, length of the 
payload and the payload itself. Each record is separately encrypted. Replay protection is 
provided by sequence numbers, which can be obtained by counting the records seen, as the 
records are sent over a reliable transport. In TLS, the encryption state is chained between the 
records, hence it is not possible to independently decrypt a record if previous record is lost for 
some reason.

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26 
TLS Handshake 
TLS handshake is the first interaction between the entities (TLS client and TLS server) 
trying to establish a secure connection. TLS Handshakes are used to negotiate the protocol suite 
that will be used for the session and establishing the keys required to encrypt and decrypt the 
records. The key can be established either by key exchange or by key generation [25]. For the 
simplicity of understanding, the handshake with key exchange method has been described. The 
handshake has been depicted below: 
Figure 2.5.1.2 TLS Handshake [23] 
Each of the messages and their purpose has been tabulated for easy understanding in 
Table 2.5.1.2