All three types of cryptography schemes have unique function mapping to specific applications. For example, the
symmetric key cryptography approach is typically used for the encryption of data providing confidentiality,
whereas asymmetric key cryptography is mainly used in key exchange and nonrepudiation, thereby providing
confidentiality and authentication. The hash algorithm (noncryptic), on the other hand, does not provide
confidentiality but provides message integrity, and cryptographic hash algorithms provide message integrity and
identity of peers during transport over insecure channels.
Symmetric Key Cryptography
A symmetric key cryptography, also known as a secret-key or preshared key algorithm, is an approach that
uses a single key for both encryption and decryption. Symmetric key cryptography is typically used to encrypt
the contents of a message to provide data confidentiality.
Figure 14-3 depicts how the symmetric key encryption process works in using the same single key on both
ends. The key must be known to both ends. The sender (Bob) uses a secret key to encrypt the plaintext
message and thereby produce the ciphertext, and the receiver (Alice) uses the same secret key to decrypt the
ciphertext, thereby producing the original plaintext message.
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