Database Reference
In-Depth Information
Table 4.1
Comparison between Symmetric Encryption and Asymmetric Encryption
CONVENTIONAL ENCRYPTION (SYMMETRIC
ENCRYPTION)
PUBLIC-KEY ENCRYPTION (ASYMMETRIC
ENCRYPTION)
Requirements to work:
Requirements to work:
• Use the same algorithm with the same
key for the encryption and the
decryption process.
• One encryption and decryption algorithm is
used for encryption and decryption and two
keys, one for encryption and one for decryption.
• The algorithm and the key should be
shared by the sender and receiver.
• The sender and receiver should have one of
the two keys.
Requirements for security:
Requirements for security:
• The key should be secret.
• The key should be secret.
• It must be impossible to decrypt the
message if no information is available.
• It must be impossible to decrypt the message
if no information is available.
• Discovering the algorithm and
samples of the ciphertext should be
insufficient to determine the key.
• Discovering the algorithm and samples of the
ciphertext should be insufficient to determine
the key.
Most people have chosen to call the first group simply symmetric
key cryptosystems, and the popular name for the second group is just
public key cryptosystems.
4.3.3 Classification according to Percentage of Encrypted Data
The encryption algorithm can be divided into full encryption and
partial encryption according to the percentage of the data encrypted.
4.4 Cryptanalysis
Cryptanalysis is the art of decrypting an encrypted message without
knowing the decryption key [47-50]. Some of the most important
ones, for a system implementer, are described next, and they are sum-
marized in Table 4.2:
In a ciphertext-only attack, the adversary has access only to some
encrypted messages.
A brute-force attack is a kind of ciphertext-only attack. It is based
on a key search and well-designed cryptosystems should be
computationally infeasible to attack.
In a known-plaintext attack, an adversary has some information
about the plaintext and the corresponding given ciphertext.
This may be helpful to determine the decryption key.
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