Symmetric Key Cryptography
All cryptographic algorithms involve substituting one thing for another,
e.g., taking a piece of plaintext and
computing the appropriate ciphertext that forms the encrypted
message. Before studying a modern key-based
cryptograph
Why does RSA work?
The RSA encryption/decryption above appears rather magical. Why
should it be that by applying the
encryption algorithm and then the decryption algorithm, one recovers
the original message? In order to
understand why RSA works, we'll nee
Public Key Encryption
For more than 2000 years (since the time of the Caesar cipher and up to
the 1970's), encrypted communication
required that the two communicating parties share a common secret the symmetric key used for encryption
and decryption. One
Data Encryption Standard (DES)
Let us now fast forward to modern time and examine the Data
Encryption Standard (DES) , a
symmetric key encryption standard published in 1977 and updated
most recently in 1993 by the US National
Bureau of Standards for comme
Authentication
Authentication is the process of proving one's identity to someone else.
As humans, we authenticate each other in
many ways: we recognize each others' faces when we meet; we recognize
each others' voices on the telephone; we
are authenticat
Integrity
Think of the number of the times you've signed your name to a piece of
paper during the last week. You
sign checks, credit card statements, legal documents, and letters. Your
signature attests to the fact that
you (as opposed to someone else) ha
Kerberos
Kerberos is an authentication service developed at MIT that
uses symmetric
key encryption techniques and a Key Distribution Center.
Although it is conceptually the same as the
generic KDC we described in section 7.5.1, its vocabulary is
slightly
The Key Distribution Center
Suppose once again that Bob and Alice want to communicate
using symmetric key cryptography. They
have never met (perhaps they just met in an on-line chat room)
and thus have not established a shared
secret key in advance. How c
Hash Function Algorithms
Let's convince ourselves that a simple checksum, such
as the Internet checksum, would make a poor
message digest algorithm. Rather than performing 1
complement's arithmetic (as in the Internet
checksum), let us compute a checksum
Message Digests
We have seen above that public key encryption technology can
be used to create a digital signature.
One concern with signing data by encryption, however, is that
encryption and decryption are
computationally expensive. When digitally signi