2. Cryptographic Tools Cryptographic algorithms important
element in security services review various types of elements
symmetric encryption public-key (asymmetric) encryption digital
signatures and key management secure hash functions 3. Symmetric
Encryption universal technique for providingconfidentiality also
referred to as single-key encryption two requirements for secure
use: need a strong encryption algorithm sender and receiver must
have obtained copies ofthe secret key in a secure fashion and must
keep the key secure 4. Symmetric Encryption 5. Attacking Symmetric
Encryption Cryptanalytic AttacksBrute-Force Attack rely on: try all
possible keys on some nature of the algorithm ciphertext until an
intelligible plus some knowledge of the general translation into
plaintext is characteristics of the plaintextobtained even some
sample plaintext- ciphertext pairson average half of all possible
keysmust be tried to achieve success exploits the characteristics
of thealgorithm to attempt to deduce aspecific plaintext or the key
beingused if successful all future and pastmessages encrypted with
that keyare compromised 6. Average Time for Exhaustive Search
Number of Time Required at 1Time Required atKey Size (bits)
Alternative Keys Decryption/s 106 Decryptions/s32232 = 4.3 109 231
s = 35.8 minutes 2.15 milliseconds56256 = 7.2 1016255 s = 1142
years10.01 hours 1282128 = 3.4 1038 2127 s= 5.4 1024 years 5.4 1018
years 1682168 = 3.7 1050 2167 s= 5.9 1036 years 5.9 1030 years26
characters26! = 4 10262 1026 s = 6.4 1012 years6.4 106
years(permutation) 7. Symmetric Encryption Algorithms 8. Data
Encryption Standard (DES) most widely used encryption scheme
referred to as the Data Encryption Algorithm uses 64 bit plaintext
block and 56 bit key toproduce a 64 bit ciphertext block strength
concerns: concerns about algorithm DES is the most studied
encryption algorithm in existence use of 56-bit key Electronic
Frontier Foundation (EFF) announced in July 1998that it had broken
a DES encryption 9. Data Encryption Standard (DES) Linux machines
have deleted DES from VPNnegotiations because it takes minutes or
less tobreak. This breaks the standard for VPN negotiations.
Windows 2000 server shows 3DES butnegotiates DES. 10. Time to Break
a Codeassuming 106 decryptions/ms 11. Triple DES (3DES) repeats
basic DES algorithm three times usingeither two or three unique
keys attractions: 168-bit key length overcomes the vulnerability
tobrute-force attack of DES underlying encryption algorithm is the
same as inDES drawbacks: algorithm is sluggish in software uses a
64-bit block size 12. Advanced Encryption Standard (AES) needed
aNIST called forselectedreplacement forproposals for a Rijndael in
3DES new AES in 1997November 2001should have a security strength
equal to or better than 3DESsignificantly improved 3DES was
notefficiencyreasonable for long published as FIPS 197 term use
symmetric block cipher128 bit data and128/192/256 bit keys 13.
Practical Security Issues typically data unit is larger than a
single 64-bit or128-bit block electronic codebook (ECB) mode the
simplest approach to multiple-block encryption each block is
encrypted using the same key exploit regularities in the plaintext
modes of operation alternative techniques to increase the security
forlarge sequences overcomes the weaknesses of ECB 14. Block Cipher
EncryptionStreamEncryption 15. Block & Stream Ciphers Block
Cipher processes the input one block of elements at a time produces
an output block for each input block can reuse keys more
commonStream Cipher processes the input elements continuously
produces output one element at a time primary advantage is that
they are almost always fasterand use far less code encrypts
plaintext one byte at a time pseudorandom stream is one that is
unpredictablewithout knowledge of the input key 16. Random and
XORPseudorandom is nort random. Linux has areal random number
generator./dev/randomAnd the pseudorandom is /dev/urandom.The
pseudorandom is fast.You can program it to collect real
randomdata.Random XOR with real random is notbreakable until you
get access to the key. 17. Quantum computingA formula to factor
large numbers can breakmany formulas.Quantum computers can break
almost anynormal encryption.Random XOR is theoretically not
breakableby the availability of both.Many people who want to
control informationshall not like the use of RXOR and shallresist
it. 18. GPGGPG is available for windows also. Need asimple way to
run it.Assignment.Gnu Privacy Guard.
