**what is the idea of stream ciphers**

A **stream
cipher** is a symmetric key **cipher** where plaintext
digits are combined with a pseudorandom **cipher** digit **stream.**

In-stream cipher Encryption and Decryption are done on one symbol (such as a character or
a bit) at a time.

**How does a
stream cipher work?**

A stream cipher is an encryption algorithm that uses a
symmetric key to encrypt and decrypt a given amount of data. An
asymmetric cipher key, as opposed to an asymmetric cipher key, is an encryption
tool that is used in both encryption and decryption.

**For Encryption,**

Plain
Text and Keystream produce Cipher Text (The same keystream will be used for
decryption.).

The
Plaintext will undergo XOR operation with keystream bit-by-bit and produces the
Cipher Text.

Plain
Text: 10011001

Keystream: 11000011

`````````````````````

Cipher
Text: 01011010

**For Decryption,**

Cipher
Text and Keystream give the original Plain Text (The same keystream will be
used for encryption.).

The ciphertext will undergo XOR operation with keystream bit-by-bit and produces
the actual Plain Text.

Cipher
Text: 01011010

Keystream: 11000011

``````````````````````

Plain
Text: 10011001

## ----------------------- Types of Stream Cipher --------------------

**Synchronous
stream ciphers**

This state is updated in
essentially two ways: if the state changes independently of the plaintext
or ciphertext messages.

In an asynchronous** stream cipher,** a stream of pseudorandom digits is generated
independently of the plaintext and ciphertext messages and then combined with
the plaintext (to encrypt) or the ciphertext (to decrypt).

A *binary additive a stream cipher* is the term used for a stream cipher which XOR's the
bits with the bits of the plaintext. Encryption and decryption require that the
synchronous state cipher is in the same state, otherwise, the message cannot be
decrypted.

**Self-synchronizing
stream ciphers**

Such schemes are known
as **self-synchronizing stream ciphers**, **asynchronous stream
ciphers,** or **ciphertext autokey** (**CTAK**). The idea of self-synchronization was patented in 1946 and has the advantage that
the receiver will automatically synchronize with the keystream generator after
receiving *N* ciphertext digits.

**Stream cipher
vs. block cipher**

Block ciphers and stream
ciphers, while similar, are two distinct forms of symmetric key encryption. The main difference between these two modes of operations is the amount of data
they encrypt at one time.

While stream ciphers
perform data encryption one bit at a time, block ciphers encrypt fixed blocks
of information all at once. These predetermined blocks of data will typically
be either 64 or 128 bits long.

**Stream Cipher
Vulnerabilities**

Key Reuse

Bit-flipping Attack

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