(3)Other cryptography approaches
Another approach to cryptography is “session key cryptography,” which
combines the approaches of common key cryptography and public key
cryptography. It is also referred to as a “hybrid cryptography” approach.
The session key cryptography takes advantage of the fast encryption speed
of common key cryptography, and the ease of key management under public key cryptography, combining the approaches to provide a more practical approach to encryption.
The framework and characteristics of communications using session key
cryptography are summarized below.
Sender encrypts plaintext using a common key.
A “digital signature” refers to information
that is appended in order to attest to the
validity of electromagnetic records (digital documents). A digital signature has
the same effect as a seal or signature
that is used to attest validity in daily life.
A digital signature is achieved through
the combined use of a message digest
and common key cryptography.
The characteristics of a digital signature
are summarized below.
• Sender uses a secret key for encryption so that it is possible to attest that
it is the sender.
• The message digest is compared to
attest that the data has not been falsified.
Reference
The recipient decrypts the common key using their own secret key.
The recipient decrypts the ciphertext using the common key.
●Characteristics
• Uses common key cryptography for fast encryption and decryption speed.
• Uses public key cryptography to enable confidential notification of common keys.
Sender
A “message digest” is compact data
that contains a summary of the original
plaintext. A hash function is used to
summarize the original plaintext. It is
not possible to generate the original
plaintext from the message digest,
while even a single change in the original plaintext completely changes the
values of the message digest. Therefore, the message digest before transmission and after transmission can be
compared to attest that the data has not
been falsified.
Technology element
Message digest
Chapter 9
Sender transmits the common key that has been encrypted using the
recipient’s public key.
Reference
Digital signature
Recipient
Transmit
Encryption
Decryption
Common key
Common key
Decryption using
recipient’s secret key
Encryption using
recipient’s public key
Transmit
Encryption
Plaintext
Decryption
Ciphertext
Ciphertext
Ciphertext
Plaintext
Common key
Common key
Same key
300