空密码

空密码，也称为隐藏密码，是一种古老的加密形式，其中明文与大量非密码材料混合。今天它被认为是一种简单的隐写术形式，可以用来隐藏密文。
使用Null Cipher有多种选择。在这里，我们依次取每个单词的第一个字母。可以选择该模式以增加加密级别其他选项可以是：

从每个单词中取出最后一个字母。
从特定位置取信
使用模式（1、2、3、1、2、3 [每个单词中的每个字母]）。您也可以使用其他一些模式。
将重要字母放置在标点符号或特定字符旁边或以一定间隔放置。

Null Cipher 依次取每个单词的第一个字母

更多包含空密码的消息示例：

Input will be one paragraph or sentence without any newline.

Input : News Eight Weather: Tonight increasing snow.
        Unexpected precipitation smothers eastern
        towns. Be extremely cautious and use snowtires
        especially heading east. The [highway is not]
        knowingly slippery. Highway evacuation is 
        suspected. Police report emergency situations
        in downtown ending near Tuesday.

Explanation:
Taking the first letter in each word successively yields
the real message.
Here we are converting decoded message to lowercase.

News Eight Weather: Tonight Increasing Snow.
Unexpected Precipitation Smothers Eastern
Towns. Be Extremely Cautious And Use Snowtires
Especially Heading East. The [Highway Is Not]
Knowingly Slippery. Highway Evacuation Is
Suspected. Police Report Emergency Situations
In Downtown Ending Near Tuesday.

Output :
After Deciphered : newtisupsetbecausehethinksheispresident

After breaking the words manually the output will be:
  Newt is upset because he thinks he is President

C++

// CPP program to decode NULL CIPHER
#include 
using namespace std;
string decode(string str)
{
    // Store the decoded string.
    string res = "";
    // found variable is used to tell that the encoded
    // encoded character is found in that particular word.
    bool found = false;
 
    for (int i = 0; i < str.size(); i++)
    {
        // Set found variable to false whenever we find
        // whitespace, meaning that encoded character for
        // new word is not found
        if (str[i] == ' ')
        {
            found = false;
            continue;
        }
        if (!found)
        {
            if (str[i] >= 'A' && str[i] <= 'Z')
            {
                res += str[i] + 32;
                found = true;
            }
            else if (str[i] >= 'a' && str[i] <= 'z')
            {
                res += str[i];
                found = true;
            }
        }
    }
    return res;
}
// Driver code
int main()
{
    string in;
    in = "A Step by Step Guide for Placement Preparation by GeeksforGeeks";
 
    cout << "Enciphered Message: ";
 
    // Function call
    cout << decode(in) << endl;
    return 0;
}

Java

// Java program to decode NULL CIPHER
class GFG
{
 
    // Function to decode the message.
    static String decode(String str)
    {
        // Store the decoded string
        String res = "";
 
        // found variable is used
        // to tell that the encoded
        // encoded character is
        // found in that particular word.
        boolean found = false;
        for (int i = 0; i < str.length(); i++)
        {
            // Set found variable to false
            // whenever we find
            // whitespace, meaning that
            // encoded character for
            // new word is not found
            if (str.charAt(i) == ' ')
            {
                found = false;
                continue;
            }
            if (!found)
            {
                if ((str.charAt(i) >= 'A' && str.charAt(i) <= 'Z') ||
                    (str.charAt(i) >= 'a' && str.charAt(i) <= 'z'))
                {
                    res += Character.toString(str.charAt(i));
                    found = true;
                }
            }
        }
        return res.toLowerCase();
    }
 
    // Driver Code
    public static void main(String[] args)
    {
        String in;
        in = "A Step by Step Guide for Placement Preparation by GeeksforGeeks";
        System.out.println("Enciphered Message: " + decode(in));
    }
}
 
// This code is contributed by Vivek Kumar Singh

Python3

# Python program to decode NULL CIPHER
 
# Function to decode the message.
def decode(string):
     
    # Store the decoded string
    res = ""
 
    # found variable is used
    # to tell that the encoded
    # encoded character is
    # found in that particular word.
    found = False
 
    for character in string:
 
        # Set found variable to false
        # whenever we find
        # whitespace, meaning that
        # encoded character for
        # new word is not found
        if character == ' ':
            found = False
            continue
 
        if not found:
            if character>='A' and character<='Z' or character>='a' and character<='z':
                res += character
                found = True
 
    return res.lower()
 
# Driver code
if __name__ == "__main__":
    input = "A Step by Step Guide for Placement Preparation by GeeksforGeeks"
    print("Enciphered Message:",decode(input))
 
# This code is contributed by Vivek Kumar Singh

C#

// A C# program to decode NULL CIPHER
using System;
     
class GFG
{
 
    // Function to decode the message.
    static String decode(String str)
    {
        // Store the decoded string
        String res = "";
 
        // found variable is used
        // to tell that the encoded
        // encoded character is
        // found in that particular word.
        Boolean found = false;
        for (int i = 0; i < str.Length; i++)
    {
        // Set found variable to false whenever we find
        // whitespace, meaning that encoded character for
        // new word is not found
        if (str[i] == ' ')
        {
            found = false;
            continue;
        }
        if (!found)
        {
            if (str[i] >= 'A' && str[i] <= 'Z')
            {
                res += (char)(str[i] + 32);
                found = true;
            }
            else if (str[i] >= 'a' && str[i] <= 'z')
            {
                res += (char)str[i];
                found = true;
            }
        }
    }
    return res;
    }
 
    // Driver Code
    public static void Main(String[] args)
    {
        String str;
        str = "A Step by Step Guide for Placement Preparation by GeeksforGeeks";
        Console.WriteLine("Enciphered Message: " + decode(str));
    }
}
 
// This code has been contributed by 29AjayKumar

Javascript

输出：

Enciphered Message: asbsgfppbg