1-2 Oracle Fusion Middleware Reference for Oracle Security Developer Tools
original text is present, its appearance changes into a form that is unintelligible if intercepted. The message recipient likewise uses a cryptographic tool to decrypt the
ciphertext into its original readable format.
Cryptography secures communications over a network such as the internet by providing:
■
Authentication, which assures the receiver that the information is coming from a trusted source. Authentication is commonly achieved through the use of a
Message Authentication Code
MAC ,
digital signature , and
digital certificate .
■
Confidentiality, which ensures that only the intended receiver can read a message. Confidentiality is commonly attained through encryption.
■
Integrity, which ensures that the received message has not been altered from the original. Integrity is commonly ensured by using a cryptographic hash function.
■
Non-repudiation, which is a way to prove that a given sender actually sent a particular message. Non-repudiation is typically achieved through the use of
digital signatures.
1.1.1 Types of Cryptographic Algorithms
The mathematical operations used to map between plaintext and ciphertext are identified by a
cryptographic algorithm also known as a cipher. Cryptographic
algorithms require the text to be mapped, and, at a minimum, require some value which controls the mapping process. This value is called a
key .
Essentially, there are three types of cryptographic algorithms which can be categorized by the number of keys used for encryption and decryption, and by their application
and usage. The basic types of cryptographic algorithms are:
■
Symmetric Cryptographic Algorithms
■
Asymmetric Cryptographic Algorithms
■
Hash Functions Each type is optimized for certain applications. Hash functions are suited for ensuring
data integrity. Symmetric cryptography is ideally suited for encrypting messages. Asymmetric cryptography is used for the secure exchange of keys, authentication, and
non-repudiation. Asymmetric cryptography could also be used to encrypt messages, although this is rarely done. Symmetric cryptography operates about 1000 times faster,
and is better suited for encryption than asymmetric cryptography.
1.1.1.1 Symmetric Cryptographic Algorithms
A symmetric cryptography
algorithm also known as secret key cryptography
uses a single key for both encryption and decryption. The sender uses the key to encrypt the
plaintext and sends the ciphertext to the receiver. The receiver applies the same key to decrypt the message and recover the plaintext. The key must be known to both the
sender and receiver. The biggest problem with symmetric cryptography is the secure distribution of the key.
Symmetric cryptography schemes are generally categorized as being either a block
cipher or
stream cipher . A block cipher encrypts one fixed-size block of data usually
64 bits at a time using the same key on each block. Some common block ciphers used today include
Blowfish ,
AES ,
DES , and
3DES .
Stream ciphers operate on a single bit at a time and implement some form of feedback mechanism so that the key is constantly changing.
RC4 is an example of a stream
cipher that is used for secure communications using the SSL protocol.
Introduction to Oracle Security Developer Tools 1-3
1.1.1.2 Asymmetric Cryptographic Algorithms
An asymmetric cryptography
algorithm also known as public key cryptography
uses one key to encrypt the plaintext and another key to decrypt the ciphertext. It does not matter which key is applied first, but both keys are required for the process to
work.
In asymmetric cryptography, one of the keys is designated the public key
and is made widely available. The other key is designated the
private key and is never revealed to
another party. To send messages under this scheme, the sender encrypts some information using the receiver’s public key. The receiver then decrypts the ciphertext
using her private key. This method can also be used to prove who sent a message non-repudiation. The sender can encrypt some plaintext with her private key, and
when the receiver decrypts the message with the sender’s public key, the receiver knows that the message was indeed sent by that sender.
Some of the common asymmetric algorithms in use today are RSA
, DSA
, and
Diffie-Hellman .
1.1.1.3 Hash Functions
