32 The process of randomization or the process being undertaken to secure a
message called plaintext into a hidden message called a cipher text is encrypted encryption. According to ISO 7498-2, terminology opposite
process, to
convert ciphertext
into plaintext,
called de
descriptions decryption. According to ISO 7498-2, more precise terminology for this process is to decipher.
2.6 Encryption
Encryption used to compare the data or information so they cannot read by people who don’t have permission. With data encryption your data will be encrypted with
a key. For opened the chipper text decrypt used another key. The key can be the same like key that used for encryption or different. [4]
Mathematically, the process for encryption E can be written as: E M = C
Where M is the plaintext message and C is the ciphertext Encrypted message. The process of decryption D can be written as:
DC = M
2.7 Elements of Encryption
Modern cryptographic techniques that available today can be classified as shown in Figure [4]:
33
Figure 2.7.1: Grouping of encryption along with examples 2.8 Digital Signature
What is digital signature? Here is an overview of the digital signature. Bob has been given 2 keys, one called
the public key and one called the private key David Youd, 1996.
Figure 2.8.1 Two Bobs Lock On
34
Figure 2.8.2 Public Key Bob
Bobs public key available to everyone who needs it the private key saved for himself, where that key used for lock of the data. Susan can encrypt a
message using the public key of Bob and Bob use, his private key to decrypt the message Figure 2.2. Anyone from bob co-worker may have access to the
massage that susan encrypt before, but without bob public key the data is not valuableDavid Youd, 1996.
Figure 2.8.3 Encrypt and decrypt message
In another case bob with his private key and the right software, Bob can put digital signatures on documents and other data. A digital signature is a
stamp Bob places on the data which is unique to Bob, and is very difficult to forge. In addition, the signature assures that any changes made to the data that has
been signed can not go undetected.
35 To sign a document, Bobs software will crunch down the data into just a
few lines by a process called hashing. These few lines are called a message digest. It is not possible to change a message digest back into the original data
from which it was created. David Youd , 1996.
Figure 2.8.4 Encrypt digital signature in document
So Bobs software then encrypts the message digest with his private key. The result is the digital signature.
Figure 2.8.5 example digital signature in document
Finally, Bobs software appends the digital signature to document. All of the data that was hashed has been signed.
36
Figure 2.8.6 Digital Signature in document
So it just so happens that Susan works at the companys certificate authority center. Susan can create a digital certificate for Bob simply by signing Bobs
public key as well as some information about Bob. Bob Info:
Name Department
Cubical Number Certificate Info:
Expiration Date Serial Number
Bobs Public Key:
Figure 2.8.7 Digital Signature cerficate in document
2.9 Ron Shamir Adleman RSA Algorithms RSA
