# Blockchain and IoT Convergence--A Systematic Survey on Technologies, Protocols and Security
## 4 Internet of Things
### IoT Weaknesses
#### 4.1.2 Sensors and Devices: Perception Layer  
Perception layer collects all information/data from physical environment like temperature, speed, time, humidity etc. It is nothing but collection of sensors, actuators which forms Wireless Sensor Network (WSN). In this layer many of the Cloud attack are present but adapted to the specific protocols used at this level (RFID, WSN, NFC, BLUETOOTH etc.). Other common vulnerabilities concern to identity and password theft. Attackers adopt several mechanisms to find passwords, using known dictionaries and vulnerabilities in password creation programs.  
Common password hack:  
* Brute force/Dictionary Attack: This attack is launched by guessing passwords containing all possible combinations of letters, numbers and alphanumeric character or by using precomputed dictionary of passwords [16].  
* Social hacking: This attack exploits human weaknesses. Instead of using a generic dictionary, private information of the target person is collected, and a tailored dictionary is created. RFID common vulnerabilities [17; 18] :
* DoS Attack: denial-of-Service attack is accomplished by flooding the targeted machine with superfluous requests from a fake RFID device.
* Eavesdropping: an antenna is used to record communications between legitimate RFID tags and readers. Eavesdropping attacks can be done in both directions: tag to reader and reader to tag
* Skimming: in this case, the attacker observes the information exchanged between a legitimate tag and legitimate reader. Through the extracted data, the attacker attempts to make a cloned tag which imitates the original RFID tag. Very dangerous in case of RFID chips in credit cards, passports and another personal RFID hardware.
* Replay Attack: similar to a MITM attack, in Replay attacks, the communicating signal between the tag and the reader is intercepted, recorded and replayed. NFC common vulnerabilities [19; 20]:
* Phishing attack: phishing is a type of scam carried out on the Internet by a malicious attacker trying to deceive the victim by convincing them to provide personal information, financial data or access codes, pretending to be a reliable entity in a digital communication.
* User Tracking: in case tags use the same unique ID for anti-collision technique, an attacker can easily track them by compromising the secrecy of the entire NFC system.
* Relay attack: this concerns the intrusion within a communication between device and NFC, the ability to read data coming from the source device and send it back to the destination device.
* Eavesdropping: the attack is perpetrated via an antenna used to record communications between NFC devices. Although NFC communication takes place between very close devices, this type of attack is feasible. The purpose of the attack can be two-fold, theft of information or corrupting the information exchanged, making it useless.
* Spoofing: some mobile devices are configured to run automatically the commands received by NFC tags. In a spoofing attack, a third party pretends to be another entity to induce a user to touch his device against the tag programmed specifically to execute malicious code.