这是我刚写的维吉尼亚密码的算法，要求输入明文和密钥，输出密文和解密后的明文。
然而输出结果相差甚远，求好心的大牛有空查看一下我写的出现了什么问题。
源代码:
//实现维吉尼亚密码的算法
include
include
char plaintext[100],key[20],ciphertext[100],decry_plaintext[100];
void encryption();//加密函数
void decryption();//解密函数
void encryption()
{
int length_plain,length_cipher,i = 0,j = 0;
length_plain = strlen(plaintext);//明文长度
length_cipher = strlen(ciphertext);//密文长度
if(length_plain > length_cipher)//明文长度大于密钥长度
{
for(i = 0;i < length_plain;i++)
{
ciphertext[i] = (plaintext[i] + key[j]) % 26 + 97 - 32;//小写字母转化为大写字母
printf("%c",ciphertext[i]);
j++;
if(j >= length_cipher){
j = 0;
}
}
}
else
{
for(i = 0;i < length_plain;i++)
{
ciphertext[i] = (plaintext[i] + key[j]) % 26 + 97 - 32;
printf("%c",ciphertext[i]);
j++;
}
}
printf("\n");
}
void decryption()
{
int length_plain,length_cipher,i = 0,j = 0;
length_plain = strlen(plaintext);
length_cipher = strlen(ciphertext);
if(length_plain > length_cipher)
{
for(i = 0;i < length_plain;i++)
{
decry_plaintext[i] = (ciphertext[i] - key[j]) % 26 + 97;
printf("%c",decry_plaintext[i]);
j++;
if(j >= length_plain){
j = 0;
}
}
}
else
{
for(i = 0;i < length_cipher;i++)
{
decry_plaintext[i] = (ciphertext[i] - key[j]) % 26 + 97;
printf("%c",decry_plaintext[i]);
j++;
}
}
printf("\n");
}
int main()
{
printf("Please input the plaintext:\n");
gets(plaintext);//输入明文
printf("Please input the key:\n");
gets(key);//输入密钥
puts(ciphertext);
encryption();
printf("Please output the decry_plaintext:\n");
decryption();
puts(decry_plaintext);
return 0;
}
