- [Narrator] When researchers discovered
the tax on DES that rendered the
decades-old algorithm insecure,
security professionals faced a dilemma.
They had tons of old equipment designed to work with DES
but were no longer able to rely upon its security.
While the government worked to adopt
the new advanced encryption standard,
AES, which I'll cover in the next video,
practical security professionals around
the world discovered a workaround.
By using the DES algorithm on the same text multiple times,
they could achieve greater security.
Specifically three rounds of DES encryption
produces much stronger security
than existed with standard DES.
They called this approach Triple DES,
sometimes written as 3DES.
Here's how Triple DES works.
The person encrypting a message feeds it
into the DES algorithm using the first key, K1.
This produces ciphertext encrypted
with a standard DES algorithm.
The sender of the message then takes this output
and feeds it into the DES algorithm again,
this time using key two, producing a second ciphertext
that is now double encrypted.
The sender then takes this final output
and feeds it into DES a third time using a third key, K3,
producing the final Triple DES encrypted message.
The recipient then reverses this process,
feeding the message through the decryption function
in the reverse order, with key three
followed by key two and key one.
There are three different keying options for Triple DES.
In the first option, key one, key two, and key three
are all different from each other.
This is the strongest approach
and results in encryption with
an effective key strength of 112 bits.
In the second option, keys one and three are the same.
This requires fewer keys but reduces
the strength of the algorithm from 112 bits down to 80 bits.
And in the final option, all three keys are the same.
This emulates the standard DES algorithm
and is just as insecure as that standard approach.
It is included for backwards compatibility with DES
but is definitely not a good option.
At this point, you might be asking yourself
the question, why Triple DES?
Why not just use DES twice?
The answer is that using the algorithm twice
is subject to an attack known as
the meet-in-the-middle attack that makes it
no more secure than the standard DES algorithm.
Triple DES is still widely used today
and is considered a secure algorithm
when used in keying mode one.
The National Institute for Standards in Technology
considers keying mode one secure
for use through at least the year 2030.
Here are some of the key facts
that you should know about Triple DES.
Triple DES is a symmetric encryption algorithm.
It's also a block cipher that works on 64-bit blocks
and when used with three different keys,
it has an effective key length of 112 bits.
That method of operation, using three different keys,
is still considered secure today.