JS实现维吉尼亚加解密

JS实现维吉尼亚加解密

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一、原理：

二、加密方法：

加密公式：C = (P + K)%26

C：密文

P：原文

K：第几套加密方式

使用第几套加密方式是通过约定一个规则来确定的，这个规则就是“密钥”。

解密方法：

解密公式：P = (C - K)%26

C：密文

P：原文

K：第几套加密方式

如果P<0,P+26取得正序

三、代码实践

一、加密：

	//加密
	function wiginiya_encrypt() {
		//C = P + K (mod 26). 获取偏移量索引
		let key = document.wiginiya.key.value;
		let plaintext = document.wiginiya.plaintext.value;
		let ciphertext = "";
		// do the encoding
		let kpos = 0;
		for( let i = 0; i < plaintext.length; i ++ ) {
			let Kcode = key.charCodeAt( kpos % key.length );
			let Pcode = plaintext.charCodeAt( i );
			let Ccode = Pcode;
			if ( Pcode >= 65 && Pcode <= 90 ) {
				if ( Kcode >= 65 && Kcode <= 90 ) {
					Ccode = ( ( Kcode - 65 ) + ( Pcode - 65 ) ) % 26 + 65;
				}
				if ( Kcode >= 97 && Kcode <= 122 ) {
					Ccode = ( ( Kcode - 97 ) + ( Pcode - 65 ) ) % 26 + 65;
				}
				kpos ++;	//伴随长度变化
			}
			if ( Pcode >= 97 && Pcode <= 122 ) {
				if ( Kcode >= 65 && Kcode <= 90 ) {
					Ccode = ( ( Kcode - 65 ) + ( Pcode - 97 ) ) % 26 + 97;
				}
				if ( Kcode >= 97 && Kcode <= 122 ) {
					Ccode = ( ( Kcode - 97 ) + ( Pcode - 97 ) ) % 26 + 97;
				}
				kpos ++;
			}
		ciphertext += String.fromCharCode(Ccode);
		}
		document.wiginiya.ciphertext.value = ciphertext;
	}

二、解密： 

	//解密
	function wiginiya_decrypt() {
	//P = C - K (mod 26). 模逆运算求索引
    let key = document.wiginiya.key.value;
    let ciphertext = document.wiginiya.ciphertext.value;
    let plaintext = "";
    // do the encoding
    let kpos = 0;
    for( let i = 0; i < ciphertext.length; i ++ ) {
        let Kcode = key.charCodeAt( kpos % key.length );
        var Ccode = ciphertext.charCodeAt( i );
        var Pcode = Ccode;
        if ( Ccode >= 65 && Ccode <= 90 ) {
            if (Kcode >= 65 && Kcode <= 90) {
                Pcode = ( ( Ccode - 65 ) - ( Kcode - 65 ) + 26 ) % 26 + 65;
            }
            if ( Kcode >= 97 && Kcode <= 122 ) {
                Pcode = ( ( Ccode - 65 ) - ( Kcode - 97 ) + 26 ) % 26 + 65;
            }
            kpos ++;
        }
        if ( Ccode >= 97 && Ccode <= 122 ) {
            if ( Kcode >= 65 && Kcode <= 90 ) {
                Pcode = ( ( Ccode - 97 ) - ( Kcode - 65 ) + 26 ) % 26 + 97;
            }
            if ( Kcode >= 97 && Kcode <= 122) {
                Pcode = ( ( Ccode - 97 ) - ( Kcode - 97 ) + 26 ) % 26 + 97;
            }
            kpos ++;
        }
        plaintext += String.fromCharCode(Pcode);
		}
		document.wiginiya.plaintext.value = plaintext;
	}