验证数字签名

If you have data for which a digital signature was generated, you can verify the authenticity of the signature. To do so, you need

• the data
• the signature
• the public key corresponding to the private key used to sign the data

In this example you write a VerSig program to verify the signature generated by the GenSig program. This demonstrates the steps required to verify the authenticity of an alleged signature.

VerSig imports a public key and a signature that is alleged to be the signature of a specified data file and then verifies the authenticity of the signature. The public key, signature, and data file names are specified on the command line.

The steps to create the VerSig sample program to import the files and to verify the signature are the following.

1. 准备初始程序结构

   Create a text file named VerSig.java. Type in the initial program structure (import statements, class name, main method, and so on).

2. 输入和转换编码的公钥字节

   Import the encoded public key bytes from the file specified as the first command line argument and convert them to a PublicKey.

3. 输入签名字节

   Input the signature bytes from the file specified as the second command line argument.

4. 验证签名

   Get a Signature object and initialize it with the public key for verifying the signature. Supply it with the data whose signature is to be verified (from the file specified as the third command line argument), and verify the signature.

5. 编译并运行程序