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 that
customizes how the cipher text is produced.
Cryptanalysis: The art of breaking ciphers, i.e.
retrieving the plaintext without knowing the proper
Cryptographers: People who do cryptography
Cryptanalysts: Practitioners of cryptanalysis.
Cryptology: The branch of mathematics that studies
the mathematical foundations of cryptographic
Cipher: The Encoder, i.e., the encryption/decryption
For “secret writing”
To establish a shared secret when other people
(eavesdroppers) are listening.
Mainly classified into two types :
Symmetric key cryptography
Asymmetric key cryptography
(plaintext in -
- plaintext out)
nothingnothing about the msg)
Plain text – in
Cipher text - out
Should understand NOTHING
about the message
Cipher text – in
Plain text - out
In classical cryptography, a transposition
cipher changes one character from the
plaintext to another i.e. the order of the
characters is changed.
Substitution cipher is a method of
encryption by which units of plaintext are
substituted with ciphertext according to a
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.
Plain text: Pay 100
Binary of plain text: 010111101
Key: 100101011 -----
Cipher text 110010110 -----
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.
Plain text: four and five
Four and five
Key Key Key
wvfa ast wvfa ---
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)
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
Unlike cryptography which is a clearly
Known - plain text analysis
Chosen – plain text analysis (Differential
Cipher text - only analysis
Man – in – the - middle attack
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.
Use rubber keyboard or virtual keyboards
to prevent keystroke sounds.
Use acoustic printers.
Use Acoustic case for CPU.
Cryptography, being an art of encrypting
and decrypting confidential information and
private messages, should be implemented in
the network security to prevent any leakage
It can be done by using any of these
techniques discussed above for fortifying the
personal data transmission as well as for
Acoustic cryptanalysis, being an art of
Yang, Sarah (14 September
2005), "Researchers recover typed text using
audio recording of keystrokes", UC Berkeley