Next: Cryptogrpahy.
Corresponds with Chapter 2 of
textbook.
When not stated explicitly, the slide is based on material or has been
provided by the textbook (Security in Computing by Pfleeger and
Pfleeger. ISBN-10: 0132390779 ISBN-13: 978-0132390774
ITEC345 © Material from slides derived from Pfleeger or Neil Daswani.
Summary
• So far we looked at various threats,
exploits and vulnerabilities to:
– Application programs (buffer overflows, race
conditions)
– Applications on web (SQL injection, XSS and
Hidden Parameter manipulation)
– Physical security
– Personnel security
• NEXT: Securing computing
infrastructures.
ITEC345 © Material from slides derived from Pfleeger or Neil Daswani.
Remember: Security is holistic.
• “Holistic” because it requires:
– Technological security – security
achieved using technological means.
– Physical security, and,
– Administrative security.
• The next 7-8 weeks we will study
various aspects of technological
security.
ITEC345 © Material from slides derived from Pfleeger or Neil Daswani.
Security is holistic. (2)
• The next 7-8 weeks we will study
various aspects of technological
security.
• Given that there are several
technological security mechanisms our
goals is to cover a wide-variety of
those without going too much into
depth.
– Later courses: 445 and 455 will go into
depth in some of those topics.
ITEC345 © Material from slides derived from Pfleeger or Neil Daswani.
Overview of our coverage of technological
security.
•
•
•
•
Cryptography
Application program security.
OS security
Network security.
• Next: cryptography.
ITEC345 © Material from slides derived from Pfleeger or Neil Daswani.
Encoding vs Encrypting
- Encoding: represent information as data
(in some specific format).
- zip code, area code, ISBN, …
- ASCII code, unicode, …
- error codes …
- class java.util.Date; program design
Not about secrecy/security.
- Encryption: secure data from attackers.
ITEC345 © Material from slides derived from Pfleeger or Neil Daswani.
Why study cryptography?
• Forms the foundation of many
security mechanism.
• Clearly the basis for network security
and OS security.
ITEC345 © Material from slides derived from Pfleeger or Neil Daswani.
Cryptography
“ Many savages at the present day regard their
names as vital parts of themselves, and therefore
take great pains to conceal their real names, lest
these should give to evil-disposed persons a handle
by which to injure their owners.” —The Golden
Bough, Sir James George Frazer
(Quote obtained from: Cryptography and Network Security Slides by
Dr. Lawrie Brown. Slides
at:http://www.box.net/shared/h164at4gsc).
ITEC345 © Material from slides derived from Pfleeger or Neil Daswani.
Cryptography
• Cryptography is not just encryption/decryption!.
• Aspects of cryptography (we will study):
– Two types of cryptography:
• Symmetric key (also called private key or secret key)
• Asymmetric key (also called public key cryptography)
– In addition cryptography also includes another
interesting mechanism:
• Secure hash functions (also called message digests) – used for
creating digital signatures and for assuring integrity of data.
• These three types are used for achieving various
things:
• Encryption and decryption of messages.
• Exchanging passwords or other secret information.
• Creating digital signatures.
ITEC345 © Material from slides derived from Pfleeger or Neil Daswani.
Cryptography and mathematics.
• Cryptography is a course (or multiple courses) by itself!
– Involves a lot of mathematics.
– Cannot be covered as a one single topic easily.
• Our focus and plan:
– First: Encryption/Decryption using symmetric key
cryptography
– Next: Flavor of asymmetric key cryptography and its
difference from symmetric key and
– Then: secure hash functions and
– Finally: using all of them for various tasks: confidentiality,
integrity, authentication and non-repudiation.
• Mathematics will be covered in ITEC 455 (network
security).
• Alternatively, read Chapter 12.
ITEC345 © Material from slides derived from Pfleeger or Neil Daswani.
Encryption/Decryption.
• What is encryption?
• Decryption?
In 5th grade, teacher placed me and my best friend
on opposite side of room. We pass notes… but
teacher could intercept!
Solution: Captain Justice's Decoder Pencil.
ITEC345 © Material from slides derived from Pfleeger or Neil Daswani.
Three parts to cryptography
• Most cryptographic algorithms are used
for:
– Encryption: encoding a message so that its
meaning is not obvious.
– Decryption: reverse process
• Crypt analysis: this is the key vulnerability
and deals with breaking the encryption.
Figure 2-1
Notes based on © William Stallings, Cryptography and Network Security. Slides by © Dr.
ITEC345
©Australian
MaterialDefence
from slides
from Pfleeger or Neil Daswani.
Lawrie Brown,
Institute derived
(http://www.box.net/shared/h164at4gsc)
Next:
• Symmetric key cryptography:
– This is what most layperson’s call as
cryptographic algorithms.
– Primarily used for
encryption/decryption.
– Also called: secret-key cryptography or
private-key cryptography.
Notes based on © William Stallings, Cryptography and Network Security. Slides by © Dr.
Lawrie
Brown,©
Australian
Defence
ITEC345
Material
fromInstitute(http://www.box.net/shared/h164at4gsc)
slides derived from Pfleeger or Neil Daswani.
Notations we will use in discussing
symmetric cryptography
• Notations used to discuss symmetric
cryptography:
•
•
•
•
•
M = message (plaintext)
C = cipher text (the encrypted text)
E = encryption function
D = decryption function
K = key (secret key, usually a number)
E.g.,
C = E(M, K) (read this in English as: cipher text is
generated by applying the encryption function on the
message “M” and key “K”.
Notes based on © William Stallings, Cryptography and Network Security. Slides by © Dr.
Lawrie Brown, Australian Defence Institute(http://www.box.net/shared/h164at4gsc)
ITEC345 © Material from slides derived from Pfleeger or Neil Daswani.
What is symmetric cryptography?
• In symmetric key cryptography:
– The same secret key is used for
both encryption and decryption.
– The word “symmetric” comes from the above fact – same
key for both functions.
• E.g.,: If secret key is “K”, then:
– C = E (M, K) and
– M = D (C, K) (message is decryption of cipher text with the
same key “K”.
• E.g., (simple example) Caeser substitution cipher (next slide).
Notes based on © William Stallings, Cryptography and Network Security. Slides by © Dr.
Lawrie Brown, Australian Defence Institute
ITEC345 © Material from slides derived from Pfleeger or Neil Daswani.
Example of a symmetric encryption:
Caeser Substitution Cipher
•
•
•
•
Consider the following:
M = MEET ME AT CENTRAL PARK
C = PHHW PH DW FHQWUDO SDUN
Secret key:
(plaintext)
(ciphertext)
– Plain: ABCDEFGHIJKLMNOPQRSTUVWXYZ
– Cipher:DEFGHIJKLMNOPQRSTUVWXYZABC
• i.e., we replace each alphabet with another alphabet. E.g.,
character ‘A’ replaced by ‘D’, ‘B’ by ‘E’ etc..
• So what is the key?
– The key is simply something like: “shift 3”, i.e., shift the alphabets to the
right by 3 positions.
Notes based on © William Stallings, Cryptography and Network Security. Slides by © Dr.
Lawrie Brown, Australian Defence Institute(http://www.box.net/shared/h164at4gsc)
ITEC345 © Material from slides derived from Pfleeger or Neil Daswani.
Caeser cipher.
• Is the Caeser cipher secure?
• If not, why not?
– How easy is it to break Caeser cipher?
– What process did you use?
• E.g., what does this message mean?
LWHF LV FRRO
In particular, the security of a
cryptographic algorithm is tested using:
cryptanalysis.
Notes based on © William Stallings, Cryptography and Network Security. Slides by © Dr.
Lawrie Brown,
Institute.derived
(http://www.box.net/shared/h164at4gsc)
ITEC345
©Australian
MaterialDefence
from slides
from Pfleeger or Neil Daswani.
Cryptanalysis
• Used to test cryptographic techniques (e.g, how do
we know how secure an encryption is?).
– Two techniques are used: cryptanalysis and
brute-force.
• Cryptanalysis: Based on understanding the
“nature” of the cryptographic algorithm.
– Exploits characteristics of the algorithm to:
• Attempt to deduce plaintext (OR)
• Deduce the key being used.
– Deducing key is more dangerous!
• Brute-force: Try out all possible keys.
Notes based on © William Stallings, Cryptography and Network Security. Slides by © Dr.
ITEC345
Material
fromInstitute.
slides(http://www.box.net/shared/h164at4gsc)
derived from Pfleeger or Neil Daswani.
Lawrie
Brown, ©
Australian
Defence
Cryptanalysis of Caesar Cipher
• In Caeser ciphper:
• There are only 26 possible secret keys:
– E.g., Shift right by 1, shift right by 2 etc..,
– Attacker can easily try each key in turn
• a brute force search
• given ciphertext, just try all shifts of
letters.
• Hence, it is easy to break.
© Dr. Lawrie Brown, Australian Defence Institute
Notes based©
onMaterial
© William Stallings,
Cryptography
and
Network
Security.or
Slides
© Dr.
ITEC345
from slides
derived
from
Pfleeger
NeilbyDaswani.
Lawrie Brown, Australian Defence Institute. (http://www.box.net/shared/h164at4gsc)
Classical Substitution Ciphers
• Caeser cipher is a classic example of
“substitution ciphers”
• where letters of plaintext are replaced by
other letters or by numbers or symbols
• or if plaintext is viewed as a sequence of
bits, then substitution involves replacing
plaintext bit patterns with ciphertext bit
patterns
© Dr. Lawrie Brown, Australian Defence Institute
Notes based ©
on Material
© William Stallings,
Cryptography
andfrom
Network
Security. or
Slides
by Daswani.
© Dr.
ITEC345
from slides
derived
Pfleeger
Neil
Lawrie Brown, Australian Defence Institute. (http://www.box.net/shared/h164at4gsc)
Classical Substitution Ciphers
• Caeser cipher is an example of
“substitution ciphers”
• where letters of plaintext are replaced by other
letters or by numbers or symbols
• or if plaintext is viewed as a sequence of bits, then
substitution involves replacing plaintext bit patterns
with ciphertext bit patterns
• In general, such substitution ciphers are
not very secure. We will see why.
© Dr. Lawrie Brown, Australian Defence Institute
Notes based©onMaterial
© William Stallings,
Cryptography
Network
Security.or
Slides
© Dr.
ITEC345
from slides
derivedandfrom
Pfleeger
NeilbyDaswani.
Lawrie Brown, Australian Defence Institute. (http://www.box.net/shared/h164at4gsc)
Why substitution cipher is not secure (1)
• We know Caeser cipher is not very secure
because there are only 26 possible keys.
• Alternative: a substitution cipher with
several possible keys.
– E.g., instead of using a single key “3”, use
multiple keys “3”, “4”, “5”, where first character
substituted by the third character, 2nd by the
4th and so on…
© William Stallings, Cryptography and
Network Security. Slides by © Dr. Lawrie
Brown, Australian Defence Institute
Notes based on © William Stallings, Cryptography and Network Security. Slides by © Dr.
Lawrie Brown, Australian Defence Institute
ITEC345 © Material from slides derived from Pfleeger or Neil Daswani.
•
1William
Stallings, Cryptography and Network Security
Why substitution cipher is not secure (2).
How secure is this?
• instead of using a single key (e.g. 3),
• use multiple keys. (For example: “3”, “4”, “5”, where first
character is substituted by the third character, 2nd by the 4th
and so on…)
– E.g.,
• ‘A’ is substituted by ‘B’ (i.e., a character 1 place away),
• ‘B’ is substituted by ‘D’ (i.e., a character 2 places away)
• ‘C’ is substituted by ‘G’ (i.e., a character 5 places away).
• How secure are such
ciphers/mathematically? In other words,
how many keys must you try before you
break this cipher?
Notes based on © William Stallings, Cryptography and Network Security. Slides by © Dr.
Lawrie Brown, Australian Defence Institute
ITEC345 © Material from slides derived from Pfleeger or Neil Daswani.
Why substitution cipher is not secure (3).
• For the problem on previous slide, there are 26!
possible keys. Why?
– First character ‘A’ can be substituted with any of the 26
characters.
– Second character ‘B’ will now only have 25 other
characters to substitute it (the one used for A cannot
be used again – that was our intention).
– Third character ‘C’ will now have only 24 other
characters to substituted it.
• Hence, we have: 26 * 25 * 24 *…. * 1 = 26! Possible
secret keys.
Notes based on © William Stallings,
Cryptography and Network Security. Slides
by © Dr. Lawrie Brown, Australian Defence
Institute.
(http://www.box.net/shared/h164at4gsc)
ITEC345 © Material from slides derived from Pfleeger or Neil Daswani.
How big is big?
• Is 262 big? Is 26! big?
• Current computers run at _____,
which means _____ ops per sec.
• 10 9 ops requires ~ ____ sec.
• 1012 ops requires ~ ____ ____s.
• 1015 ops requires ~ ____ ____s.
• 1018 ops requires ~ ____ ____s.
Age of universe?
#particles in univ.?
ITEC345 © Material from slides derived from Pfleeger or Neil Daswani.
How easy is it to break a substitution cipher?
• So, brute-force means checking 26! ≈
4 x 1026 keys
• with so many keys, we might think it
is secure
• but would be WRONG!
• Why? problem is language
characteristics
© William Stallings, Cryptography and
Network Security. Slides by © Dr. Lawrie
Brown, Australian Defence
Institute(http://www.box.net/shared/h164at
4gsc)
Notes based on © William Stallings, Cryptography and Network Security. Slides by © Dr.
Lawrie Brown, Australian Defence Institute. (http://www.box.net/shared/h164at4gsc)
ITEC345 © Material from slides derived from Pfleeger or Neil Daswani.
Why substitution cipher is not secure (3).
Language Redundancy and Cryptanalysis
• human languages are redundant
• E.g., can you decipher this quote?
“Fr lds to ngr. ngr lds to ht.
Ht lds to sffrng.”
• In English,
–
–
–
–
-
letters are not equally commonly used
in English e is by far the most common letter
then T,A,O,I,N,S,R (mnemonic: "creations")
other letters are remarkably rare e.g. Z,J,K,Q,X
Some letters disproportionally common at word-start;
some words disproportionally common at document-start
- After 'q', ____
• This makes text easier to guess!
© William Stallings, Cryptography and
Network Security. Slides by © Dr. Lawrie
Notes based on © William Stallings, Cryptography and Network
Security.
Slides by © Dr.Defence Institute
Australian
ITEC345
© Material from slides derived fromBrown,
Pfleeger
or
Neil Daswani.
Lawrie Brown, Australian Defence Institute. (http://www.box.net/shared/h164at4gsc)
English Letter Frequencies – shows that ‘e’ is most commonly
used. Every use of ‘e’ in the text can easily be identified by
the cryptanalyst.
© William Stallings, Cryptography and
Network Security. Slides by © Dr. Lawrie
Brown, Australian Defence Institute
Notes based on © William Stallings, Cryptography and Network Security. Slides by © Dr.
Lawrie
Brown, Australian
Defence
Institute.
ITEC345
© Material
from
slides(http://www.box.net/shared/h164at4gsc)
derived from Pfleeger or Neil Daswani.
Using language characteristics to
break substitution cipher
• Example of using English characteristics:
Consider the cipher text:
wklv phvvdjh lv qrw wrr kdug wr euhdn
____ _______ __ ___ ___ ____ __ _____
Look for words such as “too” , “am” try to guess what
each word may map in cipher text.
This message has been enciphered with a 27-symbol
alphabet: A – Z + blank character.
© William Stallings, Cryptography and
Network Security. Slides by © Dr. Lawrie
Brown, Australian Defence Institute
Notes based on © William Stallings, Cryptography and Network Security. Slides by © Dr.
Lawrie Brown,
Institute.derived
(http://www.box.net/shared/h164at4gsc)
ITEC345
©Australian
MaterialDefence
from slides
from Pfleeger or Neil Daswani.
So how useful is substitution ciphers?
• We have seen that substitution
ciphers are not “by themselves” very
secure.
• So do they have any use at all?
Notes based on © William Stallings, Cryptography and Network Security. Slides by © Dr.
Lawrie Brown,
Institute.derived
(http://www.box.net/shared/h164at4gsc)
ITEC345
©Australian
MaterialDefence
from slides
from Pfleeger or Neil Daswani.
So how useful are substitution ciphers?
• Not in practice. But conceptually:
• Principle of timeliness in security: a
security measure must be strong enough to
keep out the attacker only for the life of
the data.
• E.g., if Corp.HQ e-mails quarterly earnings
to a branch office 5min before the public
shareholder announcment,
a cipher that takes longer than 5 minutes
to break is sufficient!
Notes based on © William Stallings, Cryptography and Network Security. Slides by © Dr.
Lawrie Brown,
Institute.derived
(http://www.box.net/shared/h164at4gsc)
ITEC345
©Australian
MaterialDefence
from slides
from Pfleeger or Neil Daswani.
What can make a substitution cipher better?
• So, our next goal is to make
substitution ciphers more secure?
• How? Any ideas?
ITEC345 © Material from slides derived from Pfleeger or Neil Daswani.
Making substitution cipher more effective
• Some ideas:
- shift each letter…
but change the shift-amount at each step!
– One – time pad.
– Using transposition (permutations).
ITEC345 © Material from slides derived from Pfleeger or Neil Daswani.
One time pad
• What if each letter in the message were
encrypted with a different key?
• E.g. shift by 4, then by 5, then by 6, …:
E("aaa",4) = "efg"
• Instead of adding one to the shift, add 7?
• Or, multiply-by-5-then-add-7?
• Or, have the next shift depend on the
current shift and the letter just
enciphered! (Enigma)
Notes based on © William Stallings, Cryptography and Network Security. Slides by © Dr.
Lawrie Brown,
Institute.derived
(http://www.box.net/shared/h164at4gsc)
ITEC345
©Australian
MaterialDefence
from slides
from Pfleeger or Neil Daswani.
One time pad
• The "5k+7 (mod 26)" sequence is a simple
pseudo-random-number generator:
1, 12, 15, 4, …
• What if we had a truly random sequence, as
our key?
• Advantage: cannot possibly break it any
part of it, so long as key is truly random.
• This is the idea behind a One-Time Pad
• Unbreakable … if you never re-use the pad!
Notes based on © William Stallings, Cryptography and Network Security. Slides by © Dr.
Lawrie Brown,
Institute.derived
(http://www.box.net/shared/h164at4gsc)
ITEC345
©Australian
MaterialDefence
from slides
from Pfleeger or Neil Daswani.
Other substitution ciphers…
• Several others including:
– Book ciphers.
• Next: an alternative to substitution:
transposition ciphers.
ITEC345 © Material from slides derived from Pfleeger or Neil Daswani.
Transposition cipher …
• Based on what you learnt so far,
What is the biggest weakness of a
substitution cipher – in other words
what makes it easy to break?
ITEC345 © Material from slides derived from Pfleeger or Neil Daswani.
Transposition (or permutation) cipher …
• Based on what you learnt so far,
What is the biggest weakness of a
substitution cipher – in other words
what makes it easy to break?
Substitution ciphers might preserve
(language) patterns in the input.
Transposition ciphers aim to break the
patterns.
ITEC345 © Material from slides derived from Pfleeger or Neil Daswani.
Two terms: confusion and diffusion.
• Substitution ciphers create
confusion: characters in the cipher
text are not what they are.
• Transposition ciphers: create
diffusion – they spread the
characters around breaking patterns.
In other words they create “jumbles”.
Notes based on © William Stallings, Cryptography and Network Security. Slides by © Dr.
Lawrie
Brown, Australian
Defence
ITEC345
© Material
fromInstitute.
slides(http://www.box.net/shared/h164at4gsc)
derived from Pfleeger or Neil Daswani.
Transposition cipher example: columnar
cipher
• In columnar transposition, words are
basically being jumbled.
Figure 2-4 Columnar Transposition.
ITEC345 © Material from slides derived from Pfleeger or Neil Daswani.
Transposition cipher: columnar cipher
• Example:
To encrypt: This is ITEC, we can
use the following transposition:
T h i
s
I
s
I
T E C
Read down the columns to get cipher text:
TssTh
EiIIC
ITEC345 © Material from slides derived from Pfleeger or Neil Daswani.
Summary so far …
• We have seen substitution and
transposition ciphers.
• These are trivial – though they
illustrate the concepts.
• Next: we will see how a mixture of
these ciphers are used in commercial
encryption/decryption algorithms:
DES and AES.
ITEC345 © Material from slides derived from Pfleeger or Neil Daswani.
DES encryption.
• Data Encryption Standard.
• Selected by the National Bureau of
Standards in 1976.
• Symmetric encryption – used 56 bit
keys.
• Uses a mix of substitution and
transposition (permutation)
ITEC345 © Material from slides derived from Pfleeger or Neil Daswani.
Slides image © Neil Daswani et
al, , Foundations of Security:
What every programmer needs to
know. ISBN-13: 978-1590597842
High level view of DES
• This is one round in DES.
(16 such rounds are used for encrypting.)
This is also called
Feistal network
Called S-boxes
Called Permute
Boxes.
ITEC345 © Material from slides derived from Pfleeger or Neil Daswani.
Parts of DES: S-box (Substitution Box)
• n bits input; m bits output (n x m S-box)
• output is functionally determined by input
• Ex: If input = 011001, and
n bits
(say) output = 1001
S-box
• 2n possible inputs
m bits
• 2m possible outputs
• Exercise: how many possible distinct
substitution boxes could you build?
Slide © Neil Daswani et al, ,
• In DES: S-boxes fixed.
Foundations of Security: What
© Neil Daswani
every programmer needs to
know. ISBN-13: 978-1590597842
ITEC345 © Material from slides derived from Pfleeger or Neil Daswani.
Parts of a DES: Permute Functions
• Permutation Functions:
changes order of bits
Slides image © Neil Daswani et
al, , Foundations of Security:
What every programmer needs to
know. ISBN-13: 978-1590597842
– Example: P(b0b1b2)=b1b2b0
– P(101)=011
0
1
• Expansion Permutation:
changes order, and re-uses
bits more than once
– Example:
P’(b0b1b2)=b1b2b1b0b2
– P’(101)=01011
0
© Neil Daswani
ITEC345 © Material from slides derived from Pfleeger or Neil Daswani.
1
2
2
DES
• The "sub"keys used in each of the 16
rounds are derived from the original
key.
• To de-crypt: Just apply the subkeys
in opposite order
• This is important practically: same
hardware can be used.
ITEC345 © Material from slides derived from Pfleeger or Neil Daswani.
Key Strength
• Just search every possibility to break the key?
• 256 is possible to brute-force, though 57bits is
twice as hard; 58bits is 4x harder; 264 is 256x
bigger than 256.
• What about with 128-bit keys? 2128 possible keys
– too many to brute-force!
• But I still have my hardware for 56-bit key DES.
Idea: encrypt twice, with k1 then k2:
this is equivalent to using a 2x56 = 128 bit key.
© Neil Daswani
Slide © Neil Daswani et al, ,
Foundations of Security: What
every programmer needs to
know. ISBN-13: 978-1590597842
ITEC345 © Material from slides derived from Pfleeger or Neil Daswani.
3DES: Triple DES
• Do DES 3 times with 3 different keys
• E = f( f-1( f( M ,k1) ,k2) ,k3)
where f = DES
• Keying options (best to worst):
choose
– k1 ≠ k2 ≠ k3:
– k1 = k3:
– k1 = k2 = k3:
© Neil Daswani
168-bit (192-bit)
112-bit (128-bit)
56-bit (64-bit)
Slide © Neil Daswani et al, ,
Foundations of Security: What
every programmer needs to
know. ISBN-13: 978-1590597842
ITEC345 © Material from slides derived from Pfleeger or Neil Daswani.
© Neil Daswani
Some things to note
• Security depends on keys… algorithms are
public!
• Every additional bit adds twice as many
possibilities to have to search.
– Why? All previous keys: prepend 0; prepend 1.
• For 128-bit key, need to “attack”
mathematical properties of encryption
Slide © Neil Daswani et al, ,
Foundations of Security: What
algorithm
every programmer needs to
know. ISBN-13: 978-1590597842
• Hint: when encrypting: don’t invent your
own encryption algorithm!
Use existing, vetted ones.
ITEC345 © Material from slides derived from Pfleeger or Neil Daswani.
© Neil Daswani et al,
Foundations of Security: What
every programmer needs to
know. ISBN-13: 978-1590597842
AES (Rijndael)
• AES: Advanced Encryption Standard:
Rijndael ("Rein doll")
• Invented by 2 cryptographers from Belgium
• Selected by NIST from 15 competitors
• Selection Criteria: Security, Cost (speed,
memory), Implementation Considerations (hw,sw)
• Key size / Block size: 128, 192, or 256 bits
• 10, 12, or 14 rounds depending upon key/block size
• Has S-Boxes and XORs, but no Feistel network
© William Stallings,
Cryptography and Network
Security
ITEC345 © Material from slides derived from Pfleeger or Neil Daswani.
Next:
• Asymmetric ciphers.
ITEC345 © Material from slides derived from Pfleeger or Neil Daswani.