Method and apparatus for encrypting message for maintaining message integrity, and method and apparatus for decrypting message for maintaining message integrity

A method of encrypting a message of an encryption apparatus, the method comprising:

• generating a plurality of message blocks by dividing the message;
• generating a random number and encrypting the plurality of message blocks in a cipher block chaining (CBC) mode of the advanced encryption standard (AES) by using the random number;
• generating an encryption key by using a part of the plurality of encrypted message blocks and a shared key;
• generating a first ciphertext by combining the plurality of encrypted message blocks;
• generating a second ciphertext by encrypting the random number by using the encryption key;
• and
• combining the first ciphertext and the second ciphertext.

A method of decrypting an encrypted message, the method comprising:

• receiving the encrypted message that comprises a first ciphertext and a second ciphertext, wherein the first ciphertext is obtained by encrypting a message by using a random number, and wherein the second ciphertext is obtained by encrypting the random number by using an encryption key that is generated by using a hash value of the first ciphertext and a shared key;
• separating the first ciphertext and the second ciphertext and calculating the hash value of the first ciphertext;
• generating a decryption key by using the hash value of the first ciphertext and the shared key;
• extracting the random number by decrypting the second ciphertext by using the decryption key;
• and
• decrypting the first ciphertext by using the random number.

A method of decrypting an encrypted message, the method comprising:

• receiving the encrypted message comprising a first ciphertext and a second ciphertext, wherein the first ciphertext comprises a plurality of encrypted message blocks obtained by encrypting a plurality of message blocks by using a random number in a cipher block chaining (CBC) mode of the advanced encryption standard (AES), and wherein the second ciphertext is generated by encrypting the random number by using an encryption key;
• separating the first ciphertext and the second ciphertext and generating a decryption key by using a part of the plurality of encrypted message blocks and a shared key;
• extracting the random number by decrypting the second ciphertext by using the decryption key;
• and
• decrypting the first ciphertext by using the random number and generating a decrypted message by combining a plurality of decrypted message blocks,
• wherein the encryption key is generated by using the part of the plurality of encrypted message blocks and the shared key.