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private key that obtained by using two layers of
encryption can guarantee the security of messages. Figure
3 illustrates the encryption process of the digital envelope.
First, the plaintext is encrypted by symmetric key, and
then symmetric key is encrypted by receiver’s public key
so as to obtain digital envelop, that is, the data ciphertext
and key ciphertext. [1]
C. Signed Digital Envelope
The conventional digital envelope can ensure the
confidentiality of the data, but its adoption of the public
key encryption makes it possible for malicious user to
destroy the data, so the integrity and undeniability of the
data can not be guaranteed. However, signed digital
envelope can make it up for conventional digital envelope
due to its adoption of private key encryption. And a new
and improved encryption scheme is born by combining
digital envelope with digital signature
Figure 4 illustrates the improved scheme. First, the
digital signature is obtained by signing plaintext data with
sender’s private key, and then plaintext data are
encrypted by symmetric key, and after that, both the
signature and the symmetric key are encrypted by
sender’s public key. In this way, only the authorized
receiver has access to the initial data that can not be
altered by malicious user. Figure 5 illustrates the process
that the authorized user receives the data and has them
verified.
Ⅲ. SECURE COMMUNICATION BASED ON SIGNED DIGITAL
ENVELOPE
The .Net provides all the developers with first-class
encryption model which has great scalability and doesn’t
have to resort to that obscure function from the
unmanaged class. Therefore, .Net was chosen as the
development environment to bring about a new scheme in
this paper.
A. Methods for Symmetric Encryption and Decryption
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The steps of symmetric encryption are shown as
follows:
(1)Creating encryption key
TripleDESCryptoServiceProvider crypt = new
TripleDESCryptoServiceProvider();
……
……
crypt.GenerateKey();//creating symmetric key
(2)Creating encrypted object and memory stream
MemoryStream ms = new MemoryStream();
……
(3)Packing the memory stream with CrytoStream
and encrypting it.
CryptoStream cs = new CrytoStream
( ms,crypt.CreateEncryptor (), CryptoStreamMode.
Write ) ; // packing the memory stream with
CrytoStream
StreamWriter sw = new StreamWriter(cs);
sw.WriteLine (“plaintext”);// importing plaintext data
sw.Flush();
cs.FlushFinalBlock();
……
Both decryption and encryption need to pack memory
with CryoStream, but in this regard, CreateDecrytor
proves itself better than CreateEncyptor in practice.
B. Methods for Public Key Encryption and Decryption
Being similar with digital signature, here we can use
RSACryptoServiceProvider class and
DSACryptoServiceProvider. But digital signature is to
use one’s own private key to encrypt the data, and what is
known as asymmetric encryption, in most cases, refers to
the use of counterpart’s public key to encrypt the data.
Different encryption keys can be applied to different
circumstances.
The steps of public key encryption are shown as
follows:
(1)Creating key pair
RSACryptoServiceProvider crypt = new
RSACryptoServiceProvider();
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