As an application, the stream cipher is used to encrypt the DVD contents in off-line mode and to decrypt the encrypted D

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As an application, the stream cipher is used to encrypt the DVD
contents in off-line mode and to decrypt the encrypted DVD in real
time to playback the contents. The decryption is integrated with
the media player in such a way that no saving or copying is
possible during playback mode.
Stream ciphers work well for large or small chucks of data.
They`re suitable for smaller data sizes because no block size is
required. And if speed is a concern, stream ciphers are your
answer, because they use a simpler transformation that typically
involves an xor`d keystream.
ii)
The major drawbacks of Caesar cipher is that it can easily be
broken, even in cipher-text only scenario. Various methods have
been detected which crack the cipher text using frequency analysis
and pattern words. One of the approaches is using brute force to
match the frequency distribution of letters.
One way to make a Caesar cipher a bit harder to break is to use
different shifts at different positions in the message. For
example, we could shift the first character by 25, the second by
14, the third by 17, and the fourth by 10.
iii)
Secure Hash Algorithms, also known as SHA, are a family of
cryptographic functions designed to keep data secured. It works by
transforming the data using a hash function: an algorithm that
consists of bitwise operations, modular additions, and compression
functions.
Some of the standout features of the SHA algorithm are as
follows:
Message Length: The length of the cleartext should be less than
264 bits. The size needs to be in the comparison area to keep the
digest as random as possible.
Digest Length: The length of the hash digest should be 256 bits
in SHA 256 algorithm, 512 bits in SHA-512, and so on. Bigger
digests usually suggest significantly more calculations at the cost
of speed and space.
Irreversible: By design, all hash functions such as the SHA 256
are irreversible. You should neither get a plaintext when you have
the digest beforehand nor should the digest provide its original
value when you pass it through the hash function again.
vi)
Cryptography and Web Security. Today, cryptography is the
fundamental technology used to protect information as it travels
over the Internet. Every day, encryption is used to protect the
content of web transactions, email, newsgroups, chat, web
conferencing, and telephone calls as they are sent over the
Internet.
Encryption takes plain text, like a text message or email, and
scrambles it into an unreadable format — called “cipher text.” This
helps protect the confidentiality of digital data either stored on
computer systems or transmitted through a network like the
Internet.
TLS uses a combination of symmetric and asymmetric cryptography,
as this provides a good compromise between performance and security
when transmitting data securely.
With symmetric cryptography, data is encrypted and decrypted
with a secret key known to both sender and recipient; typically 128
but preferably 256 bits in length (anything less than 80 bits is
now considered insecure). Symmetric cryptography is efficient in
terms of computation, but having a common secret key means it needs
to be shared in a secure manner.
Asymmetric cryptography uses key pairs – a public key, and a
private key. The public key is mathematically related to the
private key, but given sufficient key length, it is computationally
impractical to derive the private key from the public key. This
allows the public key of the recipient to be used by the sender to
encrypt the data they wish to send to them, but that data can only
be decrypted with the private key of the recipient.
The advantage of asymmetric cryptography is that the process of
sharing encryption keys does not have to be secure, but the
mathematical relationship between public and private keys means
that much larger key sizes are required. The recommended minimum
key length is 1024 bits, with 2048 bits preferred, but this is up
to a thousand times more computationally intensive than symmetric
keys of equivalent strength (e.g. a 2048-bit asymmetric key is
approximately equivalent to a 112-bit symmetric key) and makes
asymmetric encryption too slow for many purposes.
For this reason, TLS uses asymmetric cryptography for securely
generating and exchanging a session key. The session key is then
used for encrypting the data transmitted by one party, and for
decrypting the data received at the other end. Once the session is
over, the session key is discarded.