Encryption

This is a discussion on Encryption within the C Programming forums, part of the General Programming Boards category; Dear Everyone, Can someone give me a simple example for encrypt the "Hello", I've download the "encrypt.c", but so hard ...

  1. #1
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    Mar 2002
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    Smile Encryption

    Dear Everyone,

    Can someone give me a simple example for encrypt the "Hello",
    I've download the "encrypt.c", but so hard for me,
    please who can give me the simple one.

    Thanks.


    /*
    * File: encrypt.c
    * Date: 8 May 1999
    * Author: Bret Taylor (bstaylor@stanford.edu)
    * -------------------------------------------
    * This is the implementation for the encrypt.h library. This
    * library uses bit manipulation to consistently map characters
    * to an unreadable format that is also 8 bits in length. It does
    * so with the bitwise XOR operator (^), which returns which bits
    * are on in the first operand, but not in both. The useful thing
    * about this operator is that a variable XOR'd with another can be
    * returned to its original state simply by XORing it with that
    * variable again. Hence, this library (internally, anyway) doesn't
    * even make a distinction between encrypting and decrypting (both
    * simply require XORing each character in the input file)!
    */

    #include "encrypt.h"
    #include <assert.h>


    /* Private Function Prototypes */
    static void ApplyKeyToFile(FILE *in, FILE *out, unsigned char key);


    /*
    * Public Function: EncodeFile
    * ---------------------------
    * This function is simply a wrapper function for the ApplyKeyToFile
    * decoder/encoder function.
    */
    void EncodeFile(FILE *textFile, FILE *outputFile, unsigned char key)
    {
    assert(textFile && outputFile);
    ApplyKeyToFile(textFile, outputFile, key);
    }


    /*
    * Public Function: DecodeFile
    * ---------------------------
    * This function is simply a wrapper function for the ApplyKeyToFile
    * decoder/encoder function.
    */
    void DecodeFile(FILE *encodedFile, FILE *outputFile, unsigned char key)
    {
    assert(encodedFile && outputFile);
    ApplyKeyToFile(encodedFile, outputFile, key);
    }


    /*
    * Function: ApplyKeyToFile
    * ------------------------
    * This function reads in characters from the in file, applying
    * the bitwise XOR operator on each. It then writes those characters
    * to out. Read this file's comments for a detailed explanation why
    * this function makes no distinction between "encoding" and
    * "decoding".
    */
    static void ApplyKeyToFile(FILE *in, FILE *out, unsigned char key)
    {
    int ch;

    while ((ch = getc(in)) != EOF)
    putc(ch ^ key, out);
    }

  2. #2
    ATH0 quzah's Avatar
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    All this does is take a character and XOR it with a value. It does this with every charater in the file. If you understand how a bitwise XOR works, then you can understand this function.

    Quzah.
    Hope is the first step on the road to disappointment.

  3. #3
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    Oct 2001
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    197
    Here is something else about the XOR-encryption and its application.

    klausi
    When I close my eyes nobody can see me...

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