CS578: Internet of Things

Security in IoT
Security in IoT Survey: https://ieeexplore.ieee.org/document/7005393

Dr. Manas Khatua

Assistant Professor, Dept. of CSE, IIT Guwahati
E-mail: manaskhatua@iitg.ac.in

“Peace comes from within. Do not seek it without.” – Gautama Buddha

Introduction
• IoT
• uses low-power low-rate wireless communication protocol stack
• millions of sensing and actuating devices are attached

• IoT security is the act of securing IoT devices and the networks
they're connected to.

• Security solutions employed in TCP/IP are ill suited for IoT

• Because of the constrained IoT node and network

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 Cont…
Traditional Network architecture of cloud-based IoT Solutions.

Source: Zhou et. al., “Security and Privacy for Cloud-Based IoT: Challenges, Countermeasures, and Future Directions” IEEE Comm. Magazine, Jan. 2017, pp. 26-33.

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 Security Requirements
Fundamental Requirements:
• Authentication
• Confidentiality – merely ensures that the
individual is who he or she
– refers to protecting claims to be
information from being
accessed by unauthorized
parties • Non-repudiation
– is the assurance that someone
• Integrity cannot deny the validity of
something
– Data must not be changed in
transit.
• Resilience
• Availability – is the ability to prepare for,
respond to and recover from
– is a guarantee of reliable an attack.
access to the information by
authorized people.
Few more Requirements - Privacy ;
Anonymity; Accountability; Trust

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Common Security Attacks
• Snooping : unauthorized access or interception of data.

• Traffic Analysis : obtain some other types of information by monitoring online traffic.

• Modification : modifies the information to make it beneficial to the attacker

• Masquerading or spoofing : the attacker impersonates somebody else.

• Replaying : the attacker replays the obtained/snooped copy of a message later on.

• Repudiation : The sender of the message might later deny that it has sent the message
OR the receiver of the message might later deny that it has received the message.

• Denial of Service (DoS): attacker may slow down or totally make unavailable the
service of a legitimate system.

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 Cryptography for Confidentiality
• It has a long history dating back at least as far as Julius Caesar
(dated: 100 BC).
• Cryptographic techniques allow a sender to disguise data so that
an intruder can gain no information from the intercepted data.

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 Cont…
• To create the ciphertext from the plaintext, Alice uses an
encryption algorithm and a key

• To create the plaintext from ciphertext, Bob uses a decryption

algorithm and a key

• Based on type of key

– Symmetric key systems : Alice’s and Bob’s keys are identical and are secret

– Asymmetric / public key systems : a pair of keys is used. One of the keys is
known to both Bob and Alice (indeed, it is known to the whole world).
The other key is known only by either Bob or Alice (but not both).

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 Message Digest for Integrity
• We must ensure integrity: the message should remain unchanged.

• One way to preserve the integrity of a document is through the use of a

fingerprint.

• The electronic equivalent of the document and fingerprint pair is the message
and digest pair.

• In general, message Digest is generated by a hash function

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Hash Function
• Cryptographic Hash Function is required to have the following properties:

– takes an input, m, and computes a fixed size string H(m) known as a hash

– It is computationally infeasible to find any two different messages x and y such

that H(x) = H(y)

• Popularly used
Hash Functions:
– MD5
– SHA-1

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 Message Authentication

• A digest can be used to check the integrity of a message.

• But, how to ensure the authentication of the message - the message indeed
originated from Alice

• Solution: we need to include a secret shared between Alice and Bob.

– This shared secret, which is nothing more than a string of bits, is called the
authentication key.
– Message digest of message and authentication key is called Message
Authentication Code (MAC).

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Cont…

• One nice feature of a MAC is that it does not require an encryption algorithm
• Note: MAC => Message Authentication Code / Message Integrity Code (MIC).
MAC Layer => Medium Access Control Layer

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 IoT PHY Layer (1/2)
• IEEE 802.15.4 PHY manages
– Physical RF transceiver of the sensing device, Channel selection,
– Energy management, and Signal management

• Standard supports multiple channels (e.g. 16 channels in the 2.4 GHz ISM radio band)

• Reliability is ensured by modulation techniques (at PHY layer):

– Direct Sequence Spread Spectrum (DSSS), Direct Sequence Ultra-Wideband (UWB), and Chirp Spread
Spectrum (CSS).
– They achieve reliability by occupying
• more bandwidth at a lower power spectral density (in W/Hz) in order to achieve less interference
along the frequency bands,
• together with an improved Signal to Noise (SNR) ratio at the receiver.

• PHY data frames occupy at most 128 bytes

– packets are small in order to minimize the probability of errors take place in low-energy wireless
communication environments
• <SYNC Header 5 byte> <PHY Header 1 byte><PHY Payload 127 byte>

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IoT MAC Layer (2/2)
• IEEE 802.15.4 MAC manages • IEEE 802.15.4 can support network topologies
– accesses to the physical channel – peer-to-peer,
– network beaconing – star,
– cluster networks
– validation of frames
– guaranteed time slots (GTS)
– node association/joining • Devices are identified using
– link level security – 16-bit short identifier
• usually employed in restricted environments
– data services – 64-bit EUI-64

• Types of devices based on the • Collisions during data communications are

capabilities and roles in the network managed by CSMA/CA
– FFD
– RFD

• Types of frames • IEEE 802.15.4e devices are

– Data
– synchronize to a slot frame structure
– ACK – Slotframe is a group of slots repeating over time
– Beacon
– Command
• Association request, Association response, • Time synchronization is done using
Disassociation notification, Data request, Beacon
request, GTS request, etc. – acknowledgment-based, or
– frame-based method

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 Security in IoT PHY & MAC
• Security Suite in MAC:
– IEEE 802.15.4 standard support various security suite at the MAC layer,

– Security suites are distinguished by

• security guarantees provided, and size of message integrity data employed CTR Mode

Security suite includes security mechanisms

defined for MAC layer frames

CBC Mode

AES: Advanced Encryption Standard MAC: Message Authentication Code

CBC: Cypher Block Chaining CTR: Counter Mode CCM: CTR + CBC

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Achieved Security Requirements

Security Suites Achieved Security Remarks

Requirements
AES-CTR Confidentiality
AES-CBC-MAC-32, Data Authenticity, MAC/MIC is created from 802.15.4 MAC
AES-CBC-MAC-64, Integrity, layer header plus the payload data
AES-CBC-MAC-128
AES-CCM-32, Confidentiality,
AES-CCM-64, Data Authenticity,
AES-CCM-128 Integrity

AES: Advanced Encryption Standard MAC: Message Authentication Code

CBC: Cypher Block Chaining CTR: Counter Mode CCM: CTR + CBC

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Data Frame with Security Header

• Security Enabled Bit field of the Frame Control field being set
• Auxiliary Security Header is employed only when security is used
 Security Control field identifies the Security Level mode
 Frame Counter used to ensure sequential freshness of frames sent by this device.

 Standard employs 128-bit keys that is known implicitly by the two communication parties,
OR determined from information transported in the Key Identifier field.
◦ Key Source subfield specifies the group key originator
◦ Key Index subfield identifies a key from a specific source

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 Security-related information
• The various security suites require transportation of security-related
information for different configurations
Security Suites Achieved Security
Requirements
AES-CTR Confidentiality

AES-CBC-MAC-X Data Authenticity

Integrity
AES-CCM-X Confidentiality
Data Authenticity
Integrity

• Protection against message replay attack:

 Frame Counter and Key Control fields are commonly used to achieve the protection in all security modes

 Frame Counter sets the unique message ID by the sender

 The key counter (Key Control field) is incremented if the maximum value for the Frame Counter is reached.

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Cont…
• To support semantic security and also replay protection,
 each block is encrypted using a different nonce or Initialization Vector (IV).

• Initialization Vector (IV) can be

 a pseudorandom number,
OR
 [ Frame Counter (4B), Key Counter (1B), Flags (1B), sender’s address (8B), Block
Counter (2B) ]

 Block counter: The sender breaks the original packet into 16-byte blocks, with each
block identified by its own block counter.

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Access Control
Access Control Mechanisms:
IEEE 802.15.4 MAC also provides access control functionalities

The 802.15.4 radio chips of the device stores an access control lists (ACL)
• maximum of 255 entries (generally for 255 destination address)

Each ACL entry stores

◦ an IEEE 802.15.4 address,
◦ a Security Suite identifier field
◦ the security material required to process security
• cryptographic Key for suites supporting encryption,
• the Nonce or IV,
• the most recently received packet’s identifier in the Replay Counter field

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 Added Security with TSCH
• IEEE 802.15.4 - 2011 provides security services at the MAC layer
• IEEE 802.14.4e - 2012 introduces few modifications in security services corresponding to
different modes

• Addendum defines the possibility of using null and 4 or 5-byte Frame Counter values
– Frame counter is used to ensure sequential freshness of frames sent by this device.
– It can be set to the global Absolute Slot Number (ASN) of the network
• usage of the ASN as a global frame counter value enables
– time-dependent security,
– replay protection and
– semantic security.

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 Cont…
• IEEE 802.15.4e MAC frame employs two bits from the reserved space of security control
filed:
– bit 5 to enable suppression of the Frame Counter field i.e. null
– bit 6 to distinguish between a Frame Counter field occupying 4 or 5 bytes

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Adaptation Layer Protocol
• 6LoWPAN is currently a key technology to support
Internet communications in the IoT

• It defines:
– Header compression
• Compress the NET and TRN layer headers
– Neighbor discovery
– Address auto-configuration TCP/IP

6LoWPAN

• It supports four header types:

– Not 6LoWPAN
LLN
– Dispatch
– Mesh Addressing
– Fragmentation

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Security in 6LoWPAN
• No security mechanisms are currently defined in the context of the
6LoWPAN adaptation layer

• But many relevant documents include discussions on the security

vulnerabilities, requirements and approaches to consider for the usage
of network layer security

 RFC 6606: identifies the importance of addressing security and the

usefulness of AES-CCM available at the hardware of IEEE 802.15.4 sensing
platforms.

 RFC 3971: SEcure Neighbor Discovery (SEND)

 RFC 3972: Cryptographically Generated Addresses

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RPL
RPL protocol supports many control messages
• DIO (DODAG Information Object)
• DIS (DODAG Information Solicitation)
• DAO (Destination Advertisement Object)
• DAO-ACK (DAO acknowledgment)
• CC (Consistency Check)
• Etc.

• RPL builds a Destination Oriented Directed Acyclic Graph (DODAG) topology

 Each DODAG starting from root has unique ID
 Parameters used: link costs, node attributes (e.g. rank), node status information
 Function: objective function (OF).

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Security in RPL
• RPL specification defines
– secure versions of the various routing control message exchange

– three security modes

• Unsecured

• Preinstalled
– using a pre-configured symmetric key
– Achieve: Confidentiality, Integrity, Data authentication

• Authenticated
– A device may initially join the network using a pre-configured key, and then obtain a different
key from the key authority with which it may start functioning as a router.

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RPL Control Message

Image source: https://www.researchgate.net/publication/326960497_RPL_messages_and_their_structure

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Security in RPL
T: indicate the type of counter filed – timestamp or
incremental counter value

Algorithm: specifies the encryption, MAC, and signature

scheme the network uses

KIM: Key Identifier Mode

-- indicates whether the key used for packet protection is
determined implicitly or explicitly and
-- indicates the particular representation of the Key Identifier field

Fig: Security fields after the 4-byte ICMP LVL: Security Level
-- indicates the provided packet security and allows for varying levels
header for a secure RPL control message
of data authentication and, optionally, of data confidentiality

Flags: Reserved Flag Fileds

Counter: can represent counter or timestamp

-- Semantic security and protection against packet replay attacks is
provided with the help of the Counter field

Key Identifier:
-- indicates which key was used to protect the packet
Fig: Format of the Security field
RFC 6550 (RPL) defines all the fields in details.

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Security in RPL
• Support of Confidentiality & delay protection
– Using AES-CCM(Counter with CBC-MAC)
– MAC is applied on entire IPV6 packet

• Support of Integrity and Data Authenticity:

– Using AES-CCM-128
– OR, using RSA with SHA-256

• Support of Semantic Security and Protection Against Replay Attacks:

– It is provided with the help of the Counter field

• Support for Key Management:

– The KIM (Key Identifier Mode) field of the Security section illustrates different key
management approaches

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CoAP
CoAP: Constrained Application Protocol

• For constrained and low-power networks.

• Follows the request-response messaging

pattern

• The request is sent using Confirmable (CON)

or Non-Confirmable (NON) message.
• Uses stop-and-wait mechanism with
exponential backoff to achieve reliability

• Response is sent using several scenarios (e.g.

piggy-backed, separate response, etc)
Other Features:
 Very efficient RESTful protocol (i.e. uses REST: Representational State Transfer architecture)

 Low header overhead and parsing complexity

 Uses both asynchronous & synchronous messaging

 Mainly uses for UDP communications

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CoAP Security
• CoAP Protocol defines bindings to DTLS (Datagram Transport-Layer Security)
to transparently apply security to all CoAP messages

• Security Modes in CoAP:

– NoSec
• CoAP messages are transmitted without security applied.

– PreSharedKey
• sensing devices that are pre-programmed with the symmetric cryptographic keys required to
support secure communications

– RawPublicKey
• A given device must be pre-programmed with an asymmetric key pair
• supports authentication based on public-keys
• The device has an identity calculated from its public key, and a list of identities and public
keys of the nodes it can communicate with.
• This is mandatory for implementing CoAP

– Certificates
• The device has an asymmetric key pair with an X.509 certificate
• supports authentication based on public-keys

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CoAP Security

Fig: Payload space with DTLS on 6LoWPAN environments

• Elliptic Curve Cryptography (ECC) is adopted to support the RawPublicKey and Certificates
security modes

 ECC supports device authentication using the Elliptic Curve Digital Signature Algorithm
(ECDSA), and also key agreement using the Elliptic Curve Diffie-Hellman Algorithm with
Ephemeral keys (ECDHE).

• PreSharedKey security mode requires the TLS_PSK_WITH_AES_128_CCM_8 suite, which supports

authentication using pre-shared symmetric keys and 8-byte nonce values, and encrypts and
produces 8-byte integrity codes.

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View from Operational Level
• Security Requirements from three Operation Levels:

 Information Level
 Integrity: received data should not been altered during the transmission
 Anonymity: identity of the data source should remain hidden
 Confidentiality: Data cannot be read by third parties
 Privacy: The client’s private information should not be disclosed

 Access Level
 Access Control: only legitimate users can access to the devices and the network for
administrative tasks
 Authentication: checks whether a device has the right to access a network and vice-versa
 Authorization: ensures that only the authorized devices /users get access to the network
services or resources.

 Functional Level
 Resilience: refers to network capacity in case of attacks and failures
 Self Organization: denotes the capability of an IoT system to adjust itself in order to remain
operational even in case of partial failure or attack
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Security Mechanisms for IoT
• Standard security mechanisms that have been designed to satisfy the security
requirements for IoT Services.

 Encryption:
 Standard Mechanisms:
 Symmetric mechanism: AES-128, AES-192, AES-256 with CTR or CBC or CCM mode
 Asymmetric mechanism: RSA , Elgamal

 Above mechanisms mainly used for confidentiality

 Authentication and Integrity protection are provided by Message Authentication Code (Symmetric
Mechanism), Digital Signature (Asymmetric Mechanism) and Hash Functions.

 Tag is computed and concatenated with message

 Tag is obtained by AES-CBE-MAC (Symmetric scheme), Digital Signature Algorithm

(Asymmetric scheme) , Elliptic Curve DSA (ECDSA), RSA with Hash Function e.g. MD5, SHA-160,
SHA-256, SHA-512

 Lightweight Cryptography:
 Block cipher : PRESENT, CLEIFA, PRINCE
 Hash function: PHOTON, SPONGENT

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Security Mechanisms for IoT
• Standard security mechanisms that have been designed to satisfy the
security requirements for IoT Services.

 Secure Hardware
 illegitimate user can perform side channel attacks as devices can be deployed in remote
areas with less protection
 It is possible to exploit both hardware and software solutions to eliminate or to mitigate

 e.g. PUF – Physically Unclonable Functions

 The basic concept of PUF is to exploit little differences introduced by the fabrication process of
the chip to generate a unique signature of each device.
 Shortcomings: increase of power consumption of the device

 Intrusion Detection Systems

 Complex anti-virus software and traffic analyzers cannot be used in IoT devices
 Lightweight IDS: anomalies in system parameters, like CPU usage, memory consumption,
and network throughput, may be indicative of an ongoing attack

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 Implementation in Commercial Device
 In general, IoT devices include at least two
microcontrollers:
 one responsible for the management and
processing of the data
 other for connectivity

 Most of the IoT devices use ARM

microcontrollers of Cortex-M series
• Require minimal costs, power, and size: M0, M0+,
and M23
• Offers balance between performance and energy
efficiency: M3 and M4
• high performance embedded applications: M7

TI CC2650
Sensor Tag
TI CC26xx Functional Block Diagram

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 Implementation in Commercial Device
 In general, IoT devices include at least two • In general, Cortex-M family
microcontrollers: do not integrate
 one responsible for the management and  any hardware pseudorandom
processing of the data number generator,
 other for connectivity  any module supporting
cryptographic algorithms
such as AES
 Most of the IoT devices use ARM
microcontrollers of Cortex-M series • Support for cryptographic
• Require minimal costs, power, and size: M0, M0+, algorithms is implemented
and M23 via software or by dedicated
• Offers balance between performance and energy co-processors
efficiency: M3 and M4
• high performance embedded applications: M7

Example:
 TI CC2540 MCU provides an AES security co-processor for encryption and decryption
 TI SoC CC2538 implements AES in hardware

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Important reference:
• Granjal et al., “Security for the Internet of Things: A Survey of Existing Protocols and Open Research Issues”
IEEE Communications Surveys & Tutorials, vol. 17, no. 3, 2015.

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