- [Instructor] RC4 is a symmetric stream cipher
that was widely used to encrypt network communications.
Invented in 1987 by the famous
cryptographer Ron Rivest of RSA security
RCA was maintained as a proprietary trade secret algorithm
unless someone leaked it on the Internet in 1994.
Since the algorithm was not protected by a patent
it then became available in the public domain.
As a strong and efficient stream cipher
RC4 was widely used for many years
in a variety of network based encryption schemes.
On the wireless networking side
both the wired equivalent privacy or WEP
and wi-fi protected access or WPA protocols
allowed the use of RC4.
At the application layer both the secure sockets layer, SSL,
and its replacement transport layer security, TLS,
allowed the use of RC4 as their
underlying cryptographic algorithm.
The RC4 stream cipher works by creating a stream
of bits to use as the encryption key.
This stream has many of the qualities of a random string
but it is not quite random because it is initialized
using a selected encryption key.
This makes it possible for both the sender
and recipient of a message to use the same key
to generate the same key stream.
There were many attempts to break RC4
cryptography over the years
but most were not serious enough to jeopardize
the overall security of the algorithm.
However the algorithm reached an
unfortunate tipping point in 2015
when security researchers demonstrated
a series of fatal flaws in RC4.
It is now widely believed that
government intelligence agencies
may have the ability to break RC4 encryption
and most security professionals
recommend against using the algorithm.
Let's look at some key facts about RC4.
RC4 is a symmetric encryption algorithm.
It is a stream cipher
and allows a variable length key between 40 and 2,048 bits.
RC4 is no longer considered secure
for use on modern networks.