Encryption involves making the contents of a document secret by encoding its data.
Key encryption uses a sequence of bits (called a key) in an algorithm performed
on the data in a document. After the document has been encrypted it can be read only
by using the proper key to decrypt or reverse the algorithm. Security is
provided because only the intended receiver of the document has the proper key
required to decrypt the document.
act as a last means of defense against an intruder. Even if an intruder has bypassed all
other levels of security, the data may still be safe if it is encrypted.
If an encrypted document is valid, it provides the following assurances:
The document was actually send by the stated party
The document has not been altered in transit
The document can be viewed only by its intended recipient.
A hacker may attempt to read an encrypted document by repeatedly trying all possible
sequences of bits to decrypt the file. This is referred to as a brute force attack.
The more bits that are used in the key, the more difficult it is for a hacker to discover
the key. For example, a 16 bit key can have one of 2^16 possible different values. A 128
bit key can have one of 2^128 possible different values. Obviously, it's going to take a
hacker much longer to crack a document encrypted with a 128 bit key than to crack a document
encrypted with a 16 bit key.
DES (Data Encryption Standard) is an encryption algorithm developed by IBM in the 1970s.
DES uses a 56 bit key. Today's powerful computers make it possible for a hacker to crack
a DES key within a couple of days. 3DES (Triple DES) provides higher security by using
three different 56 bit keys to encrypt a document.
Today more advanced encryption algorithms are used. The AES (Advanced Encryption Standard)
uses multiple 128, 160, 192, or 256 bit keys to encrypt a document. With the RSA encryption
standard (named after its inventors Ronald Rivest, Adi Shamir, and Leonard Adleman) a key is
created by choosing two large prime numbers and multiplying them together. RC4 is a standard
that uses multiple keys as long as 2048 bits to encrypt a document.
Private Key Encryption
There are two kinds of key encryption: private key and public key. In
private key encryption a single key is used that only the sender and the receiver know.
Private key encryption is also called symmetric encryption because the same key is
used to both encrypt and decrypt the document.