Explanation/Reference:
Explanation:
Hybrid cryptography is the combined use of symmetric and asymmetric algorithms where the symmetric key encrypts data and an asymmetric key encrypts the symmetric key.
A digital envelope is another term used to describe hybrid cryptography.
When a message is encrypted with a symmetric key (secret key) and the symmetric key is encrypted with an asymmetric key, it is collectively known as a digital envelope.
Incorrect Answers:
A: A message that is encrypted and signed with a digital certificate is not the correct definition of a digital envelope. The message would have to be encrypted with a symmetric key and the symmetric key is encrypted with an asymmetric key to be a digital envelope. This answer does not specify what type of encryption is used.
B: A message that is signed with a secret key and encrypted with the sender's private key is not the correct definition of a digital envelope. A private key is an asymmetric key. In a digital envelope, the message is encrypted with a symmetric key and the symmetric key is encrypted with an asymmetric key.
D: A message that is encrypted with the recipient's public key and signed with the sender's private key is not the correct definition of a digital envelope. A public key is an asymmetric key. In a digital envelope, the message is encrypted with a symmetric key and the symmetric key is encrypted with an asymmetric key.
References:
Harris, Shon, All In One CISSP Exam Guide, 6th Edition, McGraw-Hill, 2013, p. 811