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1. By Rajesh Azmera Shakun Yawatkar atDigital Systems Group
ISAC, Bangalore
2. Objectives Study of basics of cryptography and different
cryptographic methods. Study of CCSDS security needs and
recommendations Comparison of several cryptographic algorithms
Finding the best cryptographic algorithm for satellite security(
downlink in RS satellites)
3. Overview Aspects of Satellite Security and their
Countermeasures Introduction to Cryptography Classification of
Cryptography Attacks and their classification Various Cryptographic
Algorithms and their comparison CCSDS Recommendations Comparison of
Block and Stream Ciphers Conclusion
4. Aspects of Satellite Security Access Control: Process of
granting access to the resources of a system only to authorized
users, programs, processes. Enable only approved operators to
access mission control systems Authentication: Ability to verify
the identity of a user or device. Only authenticated telecommands
are obeyed by the onboard systems. Availability: Assurance that a
system will be usable when it has to be. Spread Spectrum and
Frequency Hopping techniques can be used to prevent jamming.
5. Aspects of Satellite Security Continued Confidentiality:
Ensures that data is disclosed only to the authorized systems.
Prevents disclosure of sensitive information contained within space
mission data system. Confidentiality of uplink and downlink data
Prevents analysis of communication traffic by unauthorized system.
CRYPTOGRAPHY COMES INTO PICTURE. Data Integrity: Ensuring that data
transmitted from a source is not modified, altered or destroyed
Mission data has not been manipulated in any way during
Transmission. Appending Integrity Check Value (ICV) to the data
structure A form of sequence numbering for stream of data.
Accountability: Ensures that the system actions are logged with the
identity of the entity initiating the action and the data and time
the action occurred( Auditing)
6. Classes of Missions with respect to security High Security
Missions: Government or Military section Protection of mission data
from unauthorized access, Prevention from detection, interception,
and exploitation Moderate Security Missions: Commercial
Communications, Meteorological and Remote Sensing Missions
Protection from unauthorized access, protect payload data Minimal
Security Missions: Other space missions Confidentiality requirement
for specific telemetry information
7. Introduction to Cryptography Need of Cryptography:
Confidentiality, Authentication, Integrity and Non- repudiation are
needed in various applications like Radio Communication, Telephonic
Communication Network Communication Mobile Communication
Internet
8. Cryptography Cryptography is the science of protecting data,
which provides means and methods of converting data into unreadable
form, so that The data cannot be accessed for unauthorized use. The
content of the data frames is hidden. The authenticity of the data
can be established. The undetected modification of the data is
avoided. The originator of the message cannot disown the data.
9. Model for Network Security
10. Some Important Terms Plaintext: An original intelligible
message or data that is fed into the algorithm as input.
Ciphertext: The coded message is known as Ciphertext. It depends
upon the plaintext and the secret key Encryption: The process of
conversion of plaintext into ciphertext is known as Encryption
Decryption: Restoring the plaintext from ciphertext is known as
Decryption. Cryptanalysis: Techniques used for deciphering a
message without any knowledge of enciphering details fall into the
area of Cryptanalysis. Cryptology: The areas of cryptography and
cryptanalysis together are called Cryptology.
11. Classification of Cryptographic Techniques Symmetric Key
Cryptography also known as Secret Key Cryptography Problem: Process
of transferring keys to the recipient is prone to risk. Includes a
authorized third party.
12. Asymmetric (Public Key) Cryptography: This technique is
very slow as compared to symmetric one.
13. Combined Technique
14. Cryptographic Algorithms in Symmetric KeyCryptography Data
Encryption Standard (DES) Extensively studied since its publication
and is the best known algorithm Developed by IBM in 1970 s. 64-bit
block size and 56-bit key In multiuser environment, secure key
distribution may be difficult Most recently DES cracking machine
was used to recover 56-bit key in 22 hrs. Result: DES is not
secure, Banned by U.S. Government.
15. Triple DES Minor Variation of DES, three times slower than
DES More secure than DES EDE(Encrypt- Decrypt-Encrypt) Encrypts
plaintext data with a 56-bit key. The ciphertext obtained is
decrypted with different key giving garbage data. And this garbage
data is again encrypted using the first key. Some other algorithms
are IDEA, RC4, RC5, CAST 128
16. Advanced Encryption Standard (AES) National Institute of
Standards and Technology (NIST) realized the need of new secure
algorithm to replace DES. And arranged a competition. One of the
criteria for the arranged competition was the ability to support
128-bit blocks of plaintext. The finalists of the competition were
MARS: by IBM RC6: by Ron Rivest of RSA Labs Twofish: from
Counterpane Internet Security (highly suitable for microprocessors
and smart cards Serpent: by Ross Anderson, Eli Bihan and Lars
Knudsen Rijndael: by Daemen and Rijmen Of all these, Rijndael was
judged best and announced to be new AES.
17. Rijndael Algorithm Fixed Block Sixe of 128-bits and key
size of 128, 192 or 256 bits. Operates on 4*4 matrix of bytes,
termed the state. 8 or 10 or 12 rounds as per the respective key
size. Each round consists of several processing steps.
18. High-level description of the algorithm: Key Expansion-
round keys are derived from the cipher key using Rijndaels key
schedule Initial Round Add Round Key- each byte of the state is
combined with the round key using bitwise xor Rounds SubBytes- a
non-linear substitution step where each byte is replaced with
another according to a lookup table. ShiftRows- a transposition
step where each row of the state is shifted cyclically a certain
number of steps. MixColumns- a mixing operation which operates on
the columns of the state, combining the four bytes in each column.
AddRoundKey Final Round (no MixColumns) SubBytes ShiftRows
AddRoundKey
20. Algorithms in Asymmetric Cryptography The most common
algorithm is RSA. Ronald Rivest, Adi Shamir, and Leonard Adleman
developed the RSA system in 1977; RSA stands for the first letter
in each of its inventors last names. Take two large primes, p and
q, and compute their product n = pq: n is called the modulus.
Choose a number e less than n and relatively prime to (p-1)(q-1),
Which means e and (p - 1)(q - 1) have no common factors except 1.
Find another number d such that (ed - 1) is divisible by (p - 1)(q
- 1). The values e and d are called the public and private
exponents/keys. The public key is the pair (n; e); the private key
is (n; d). The factors p and q may be destroyed or kept with the
private key.
21. It is currently difficult to obtain the private key d from
the public key (n; e). However if one could factor n into p and q,
then one could obtain the private key d. Thus the security of the
RSA system is based on the assumption that factoring is
difficult.
22. Symmetric encryption are further classified as Block
ciphers It encrypts plain text and decipher the text blocks of a
fixed length. Stream ciphers In this plain text bits are combined
with a pseudorandom cipher bit stream by exclusive or operation. In
this plain text bits are encrypted one at a time.
23. Different types of Block ciphers are:1. Electronic Code
Book Mode(ECB).2. Cipher-Block Chaining Mode(CBC).3. Cipher
Feed-Back Mode(CFB).4. Output Feed Back Mode(OFB).5. Counter
Mode(CTR).
24. Electronic Code Book mode - Each plain text block is
encrypted by the underlying algorithm Block Encryption, transmitted
and decrypted . The last fragment of the message is suitably padded
with zero to make it block size. Disadvantage Identical plain text
block has identical cipher text block, where it does not provide
serious message confidentiality.
25. Cipher Block Chaining Mode- Co is initialization vector
which is used as the seed for the process.Initialization vector- A
block of bits is used by several modes torandomize the
encryption.
26. Cipher Feed back Mode-The cipher key stream is extracted
from the outputs of the block cipherencryption whose inputs are
taken as the feedback from the cipher textstream. Before the
feedback is available , an initialization vector is used asa
seed.
27. Out put Feed back Mode- This is almost similar to the CFB
mode ,except that the block cipher encryption takes the feedback
directly from its own outputs.
28. Counter Mode(CTR)-
29. Comparison of Block mode:
30. Stream classified into two types1. Synchronous stream
Cipher- In this type of cipher the sender and receiver must be
exactly in step/synchronized for decryption to be successful. If
digits are added or removed from the message during transmission,
synchronization is lost, however a single bit is lost and error
doesnt propagate.2. Self-synchronous Stream cipher- In this type,
if digits are added/removed during the transmission synchronization
can be attained by the algorithm.In this stream ciphers padding is
not required as in case of block ciphers.
31. Various types of attacks that are possible oncryptographic
systemsThere are two types of basic attacks: Passive attack. Active
attack.Passive attack: This type of attack is generally
accomplished byeavesdropping and modification of data is not
possible.A space system can be subjected to two principle types of
passive attacks : Compromise of Data confidentiality- Disclosure of
information flowing between ground and space systems Compromise of
traffic flow confidentiality-Disclosure of information like volume,
source and destination of the information. eg: traffic
analysis.These are difficult to detect because they dont involve
alteration of data.
32. Active attacks-Some of the possible types of attacks to be
considered for space systemsare: Modification of messages- This
kind of attack occurs when some amount of data is altered resulting
in undesirable effects. Replay Attack- when a message or part of it
is stored and repeated at later time to produce undesirable effect.
Insider attack- Most of the computer crimes are the result of
insider attack. Software threats- programs like viruses , worms
etc.. to allow bypassing the usual security controls.
33. Attacks which are possible on stream ciphersPossible
attacks on stream ciphers are: Known Cipher text attack. Known
plain text attack. Chosen plain text attack. Chosen cipher text
attack. Side channel attack. Bit flipping attack.Known Cipher text
attack In this type of attack where the attackerassumed to have
access to set of cipher texts. The attack is completelysuccessful
if the plain text is deducted.Various techniques developed by the
cryptographers are: Traffic analysis. Brute force attack.
34. Know plain text attack : the attacker has the samples of
both thecipher text and plain text and use them to reveal the
information.Chosen plain text attack- Here the attacker has the
capability tochoose the plain text and obtain the corresponding
cipher text. The goalof the attack to gain some further information
which reduces the securityof the encryption scheme.Chosen cipher
text attack- In this attacker gather the information atleast in
part by part and obtaining its decryption under a unknown key.The
aim is to deduce the key. Key recovery method- a method to recover
the key.
35. Side channel attack- Side channel attacks are based on side
channelinformation, side cannel information is retrieved from
physicalimplementation instead of theoretical weakness. Here the
attackerstudies the power consumption of a cryptographic device and
uses itselectro magnetic radiation to find out the key.Bit flipping
attack- in this type of attack, attacker can change the ciphertext
in such a way that a predictable change in plain text is made.This
type of attack can be avoided by using message authentication
codes(MAC) to increase the likelihood that tampering will be
detected.
36. Attacks that are possible on block ciphers: Brute force
attack. Linear crypt analysis. Differential crypt analysis.Brute
force attack- It involves symmetrically checking all the
possiblekeys until the correct key is found. In the worst case,
this would involvetraversing entire search space.Linear crypt
analysis- In this attack it takes the advantage of
linearrelationships between a the input and output of cipher keys.
The usualapproach is to analyze the non linear components and
approximate them.
37. Differential crypt analysis- In this type of attack it
analyzes thedifferences in pair of plaintext on the difference of
resultant cipher texts.These differences can be used to assign
probabilities to the possible keysand locate the most possible
key.
38. Comparison of various algorithms based datarate, throughput
and hardware.Throughput- defined as the no.of bits encrypted and
decrypted inunit of time.Through put per slice-which measures the
hardwarecost, associated with the implementation resulting
throughput.Latency- time necessary to encrypt and decrypt a single
block ofplain text or cipher text.
39. Performance comparison of stream ciphers: Cipher Area
(Slices) Frequency (MHz) Throughput (Mbps) Through/Area A5/1 32
188.3 188.3 5.88 W7 608 96 768 1.26 E0 895 189 189 0.21 Helix 418
32 1024 2.45 RC4 140 60.8 120.8 0.86Hardware used- Xilinx Virtex
XC2v6000 1152-6 FPGA which contains33792 slices and 144 RAM
blocks.Conclusion- A5/1 is considered as best.
40. Performance comparison of Block ciphersIt consists of two
basic type of architectures-Basic Looping Architecture-
41. Full Looping Unrolling Architecture-
42. Architecture Area(CLBs) Frequency(MHz) Throughput(Mbps)
Latency(us) TDES_BLA 431 86 115 0.56 TDES_FLUA 14240 108 6900 0.44
IDEA_BLA 1852 50 356 0.18 IDEA_FLUA 11700 47 3008 0.19 CAST-128_BLA
2600 55 220 0.29 CAST-128_FLUA 24200 53 3392 0.30 MISTY1_BLA 4820
30 213 0.26 MISTY1_FLUA 13080 26 3328 0.30 KHAZAD_BLA 2250 65 462
0.12 KHAZAD_FLUA 9277 70 4480 0.11Hardware -Using VHDL, with
structural description logic, captured each oneof the block
ciphers. The VHDL codes were synthesized for XILINX(VIRTEX) FPGA
devices, using the Leonardo Spectrum tool,
VIRTEX1600EBG560-6Conclusion- KHAZAD is considered as best.
43. Performance comparison between Block and Stream
ciphers.
44. Conclusion obtained from above table : A5/1 is most
efficient but is the weakest Helix appears to be efficient but
requires software pre-computations which may not be practical.
LILI-II is not competitive with modern block ciphers and its
expensive synchronization limits its efficiency. SNOW2.0 considered
to be best and comparable to ICEBERG Comparison between ICEBERG and
AES shows that AES should be preferred for space application where
through put is compromised.
45. CCSDS : The Consultative Committee for Space Data Systems,
formed in 1982 by the major space agencies of the world. Since its
establishment, actively developing recommendations for data and
information systems. CCSDS standardization reduces the cost burden
of missions by cost sharing between agencies and cost effective
commercialization.CCSDS recommendations Proposed only block cipher
for encryption than stream cipher because Block cipher are faster
and different algorithms can be implemented without changing the
hardware. Stream cipher can be susceptible to serious security
problems if used incorrectly.
46. Algorithm selection by CCSDS AES,BLOWFISH,TEA,IDEA,SEED
were considered but AES was recommended. BLOWFISH : It is the
predecessor of the AES finalist TWOFISH which was not on CCSDSs
list. Tiny Encryption Algorithm(TEA): It requires many rounds (64).
So extreme high speed is not achieved with cryptographic
weaknesses. IDEA: Strong but speed is not high. Also, IDEA is
patented and licensed. SEED: Korean algorithm, performance was not
outstanding and usage was limited to Korea. AES: Selected through
lengthy, open , international competition. Available worldwide on a
royalty free basis and not covered by any legal
restrictions/patents. AES USING COUNTER MODE OPERATION IS
RECOMMENDED BY CCSDS.
47. Advantages of counter mode: Counter mode is very efficient
in operation. Padding is not required. Single bit error results in
loss of single bit. Counter mode effectively converts block cipher
to stream cipher so that advantages of both can be achieved.
Parallel computation is possible.
48. Comparison between stream and block cipher:Stream cipher
Block cipher1. It encrypts and decrypts one bit data at a time. It
encrypts a block at a time of size M.2. Different algorithms cannot
be implemented using the Using block cipher hardware architecture
different types ofsame hardware. algorithm can be implemented
without changing the hardware3. Applications where the speed is
required it cannot It provides high speed though the encryption
isprovide high speed providing more encryption which is not
comparatively lower than that of stream ciphers.required by the
application4. Transmission error can affect only single bit.
Transmission error in one cipher text block has no effect on other
blocks in counter mode.5. Padding is not required. Padding is
required.6. Insertion and deletion of bits is not possible.
Insertion and deletion of blocks is possible.7. Less susceptible
for crypt analysis attack but if used More susceptible for crypt
analysis attack as compared toincorrectly, can be susceptible to
serious security problems. stream ciphers8. Through put is less
than block ciphers. Through put is high.9. Hardware required is
less. Hardware requirement is high.10. Difficult to implement in
software basis. Easy to implement compared to stream ciphering.11.
Cipher resynchronization is required when there is
Resynchronization is not required.error in a bit.12. Synchronous
stream cipher is periodic and key may No repetition is done because
key is generated randomly.repeat after d characters.13. Parallel
process of encryption can be done. Parallel process of encryption
cannot be done.
49. Conclusion: Security of Remote sensing satellites fall
under high or moderate levels. As the high resolution imaging
payloads generate data, large in size. So higher data rate is
required along with security. Stream ciphers cannot provide high
speed, block cipher are preferred. Block cipher in counter mode is
preferred so as to minimize BER. Considering the comparison between
various algorithms and CCSDS recommendations AES with counter mode
is preferred for satellite downlink data.
50. References : [1] RSA Laboratories, RSA Laboratories
Frequently Asked Questions About Todays Cryptography, Version 4.1,
RSA SecurityInc., 2000[2] Encryption algorithm Trade Survey, Report
Concerning Space Data System Standards, CCSDS-350.2-G-1, GreenBook,
Washington D.C.: CCSDS, March 2008.[3] Symmetric Encryption, Draft
Recommendation for Space Data Practices, CCSDS 353.0-R-1, Red Book,
WashingtonD.C., October 2008[4] Audia_S_Abd Al_R_Asedy, Ameer A.J
Al_ Swidi, An advantages and disadvantages of Block and Stream
Cipher, [5]Cryptography Basics[6] Advanced Encryption Standard,
Federal Information Processing Standards Publications197, November
26, 2001[7] Mohammed Atiquzzaman and Md. Shohrab Hossain, Security
Issues in Space Networks, [8] The Secret Satellite, www.apscc.or.kr
| APSCC Yearbook 2007 [9]Michalis Galanis, Paris Kitsos, Giorgos
Kostopoulos, Nicolas Sklavos, and Costas Goutis, Comparisonof the
Hardware Implementation of the Stream Ciphers, The International
Arab Journal of InformationTechnology, Vol. 2, No. 4, October
2005