To ensure message integrity, confidentiality and non-repudiation between two parties, the MOST effective method would be to create a message digest by applying a cryptographic hashing algorithm against:

A. the entire message, enciphering the message digest using the senders private key, enciphering the message with a symmetric key and enciphering the key by using the receivers public key.

B. any part of the message, enciphering the message digest using the senders private key, enciphering the message with a symmetric key and enciphering the key using the receivers public key.

C. the entire message, enciphering the message digest using the senders private key, enciphering the message with a symmetric key and enciphering both the encrypted message and digest using the receivers public key.

D. the entire message, enciphering the message digest using the senders private key and enciphering the message using the receivers public key.

Explanation:

Applying a cryptographic hashing algorithm against the entire message addresses the message integrity issue. Enciphering the message digest using the senders private key addresses non repudiation. Encrypting the message with a symmetric key, thereafter allowing the key to be enciphered using the receivers public key, most efficiently addresses the confidentiality of the message as well as the receivers non repudiation. The other choices would address only a portion of the requirements.