Cryptography

Presented By : Shibani Sarangi
IT Branch, Regd no. 1001289324
Guided By : Prof. X
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Cryptography
Vocabulary
Encryption &
Decryption
Transmission
Technique
Symmetric
Cryptography
Asymmetric
Cryptography

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Cryptography is the science of using
mathematics to encrypt and decrypt data.
Cryptography enables you to store
sensitive information or transmit it across
insecure networks so that it cannot be
read by anyone except the intended
recipient.

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Plaintext: Data that can be read and
understood without any special measures.
Encryption: The method of disguising
plaintext in such a way as to hide its
substance is called encryption.
Cipher text: Encrypting plaintext results in
unreadable gibberish called cipher text.
Decryption: The process of reverting
cipher text to its original plaintext is called
decryption.
Key: some secret piece of information

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Cryptanalysis: The art of breaking
ciphers, i.e. retrieving the plaintext without
knowing the proper key.
Cryptographers: People who do
cryptography
Cryptanalysts: Practitioners of
cryptanalysis.
Cryptology: The branch of mathematics
that studies the mathematical foundations
of cryptographic methods.

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For “secret writing”
To establish a shared secret when other
people (eavesdroppers) are listening.
TYPES
Mainly classified into two types :
1. Symmetric key cryptography
2. Asymmetric key cryptography

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encoder
decoder
(plaintext in -
ciphertext out)
ciphertextciphertext
msgmsg
(ciphertext in
- plaintext out)
(should understand
nothingnothing about the msg)
eavesdropper
bla-blabla-bla
cmbcmb--cmbcmb bla-blabla-bla
Cipher
msg
Plain text – in
Cipher text - out
Should understand NOTHING
about the message
Cipher text – in
Plain text - out

Cryptography
Symmetric key Asymmetric key
cryptography cryptography
(Public key cryptography)
Classical Modern
cryptography cryptography
Transposition Substitution Stream Block
cipher cipher cipher cipher
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In classical cryptography, a transposition
cipher changes one character from the
plaintext to another i.e. the order of the
characters is changed.

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Substitution cipher is a method of
encryption by which units of plaintext are
substituted with ciphertext according to a
regular system.

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A Stream Cipher is a symmetric or secret-
key encryption algorithm that encrypts a
single bit at a time. With a Stream Cipher, the
same plaintext bit or byte will encrypt to a
different bit or byte every time it is encrypted.
e.g. :
Plain text: Pay 100
Binary of plain text: 010111101
(hypothetical)
Key: 100101011 -----
Perform XOR
____________________
Cipher text 110010110 -----

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Block cipher technique involves encryption
of one block of text at a time .Decryption also
takes one block of encrypted text at a time.
Length of the block is usually 64 or 128 bits.
e.g. :
Plain text: four and five
Four and five
Key Key Key
wvfa ast wvfa ---

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Public key cryptography is an asymmetric
scheme that uses a Pair of keys for
encryption: a Public key, which encrypts
data, and a corresponding Private key (secret
key) for decryption.

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Cryptanalysis refers to the study of
ciphers, cipher text, or cryptosystems (that
is, to secret code systems) with a view to
finding weaknesses in them that will permit
retrieval of the plain text from the cipher
text, without necessarily knowing
the key or the algorithm. This is known
as breaking the cipher, cipher text, or
cryptosystem.
Unlike cryptography which is a clearly

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Known - plain text analysis
Chosen – plain text analysis (Differential
cryptanalysis)
Cipher text - only analysis
Man – in – the - middle attack

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It is a side channel attack which exploits
sounds emitted by computers or machines.
Modern acoustic cryptanalysis mostly focuses
on sounds emitted by computer keyboards and
internal computer components
Historically it has also been applied to impact
printers and electromechanical cipher machines.

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Use rubber keyboard or virtual keyboards
to prevent keystroke sounds.
Use acoustic printers.
Use Acoustic case for CPU.

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Cryptography, being an art of encrypting
and decrypting confidential information and
private messages, should be implemented in
the network security to prevent any leakage
and threat.
It can be done by using any of these
techniques discussed above for fortifying the
personal data transmission as well as for
secure transaction.
Acoustic cryptanalysis, being an art of

Yang, Sarah (14 September
2005), "Researchers recover typed text using
audio recording of keystrokes", UC Berkeley
News.
Adi Shamir & Eran Tromer. "Acoustic
cryptanalysis". Blavatnik School of Computer
Science, Tel Aviv University. Retrieved 1
November 2011.
http://en.wikipedia.org/wiki/Cryptography
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Cryptography

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