encryption and decryption of text files

[vermarajeev]

Hi guys,
I have some text files. I need to encrypt the files and then decrypt it again. This is my first experience in encryption and decryption. I want some suggestions about how this can be achieved in best way. I need it for my project.

The encryption and decryption solution should be perfect such that nobody others should be able to break the key unless he/she know it( security measures)

thanks in advance

[hirak1984]

Your question is not clear.

If you want to know only how to encrypt a file,the easiest way is to AND/OR each character present with a special key.
Then only performing reverse operation on the chars with that key can decrypt the file.
But if you want to encrypt file to make it verrrrrrrrry secure,go through some documents regarding encryption,there you will find advanced keys,and algorithms.

Hi guys,
I have some text files. I need to encrypt the files and then decrypt it again. This is my first experience in encryption and decryption. I want some suggestions about how this can be achieved in best way. I need it for my project.

The encryption and decryption solution should be perfect such that nobody others should be able to break the key unless he/she know it( security measures)

thanks in advance

[Ganon11]

Out of curiosity, what type of data is in the file to be encrypted?

[hirak1984]

Ya I should have asked that also,
my suggestion will work for only text or doc files.

Out of curiosity, what type of data is in the file to be encrypted?

[vermarajeev]

Hmmm! Interesting,
Thanks for your replies....

The file contains only human understable characters... And yes I want the encryption and decryption to be very secure such that nobody should be able to hack my files.


Thanks

[hirak1984]

Just consuder the ascii values of the chars and do some mathematical operations.It will serve ur purpose

Hmmm! Interesting,
Thanks for your replies....

The file contains only human understable characters... And yes I want the encryption and decryption to be very secure such that nobody should be able to hack my files.


Thanks

[Ganon11]

The most basic encryption method I could think of would be to take each character and add a certain value to it - 37, or 60, or some random number. Make sure to cast the result back to a char value, so that the encrypted text will look like a bunch of garbage text.

During decryption, take each character and subtract the same value from it, resulting in the original character.

Unfortunately, this is a very simple encryption method, and anyone who is able to study your encrypted file long enough or catch a glimpse of the code will be able to figure it out.

Another possibility would be to pick a key word, such as "house". Get the first character of the file to be encrypted, and add to it the integer value of 'h' - the first letter in house. Write the new character to the coded file. Next, get the second character from the input file, add add to it the value of 'o' - the second letter in house. Repeat this process until the 'e' is house, then loop back to the h and repeat. This will be a slightly more hidden process, but just as easily reversable.

[vermarajeev]

The most basic encryption method I could think of would be to take each character and add a certain value to it - 37, or 60, or some random number. Make sure to cast the result back to a char value, so that the encrypted text will look like a bunch of garbage text.

During decryption, take each character and subtract the same value from it, resulting in the original character.

Unfortunately, this is a very simple encryption method, and anyone who is able to study your encrypted file long enough or catch a glimpse of the code will be able to figure it out.

Another possibility would be to pick a key word, such as "house". Get the first character of the file to be encrypted, and add to it the integer value of 'h' - the first letter in house. Write the new character to the coded file. Next, get the second character from the input file, add add to it the value of 'o' - the second letter in house. Repeat this process until the 'e' is house, then loop back to the h and repeat. This will be a slightly more hidden process, but just as easily reversable.

Hi thanks for your reply....It sounds interesting. I have done a sample program.Please let me know if you meant the same

#include <iostream>
#include <fstream>
using namespace std;
 
void encryptFile( ifstream& ifs, ofstream& ofs, string encryptKey )
{
    char line[256];    
    while( !ifs.eof() )
    {
        ifs.getline( line, sizeof(line) );        
 
        string strLine = line;
        unsigned int j=0;
        for(unsigned int i=0; i<strLine.length(); ++i)
        {    
            strLine[i] += encryptKey[j++];            
            ofs.put( strLine[i] );
            if( j >= encryptKey.length() )
                j = 0;
        }
        cout<<"Encrypted data"<<endl;
        cout<<strLine.data()<<endl;
    }
}
 
void decryptFile( ifstream& ifs, string encryptKey )
{
    char line[256];    
    while( !ifs.eof() )
    {
        ifs.getline( line, sizeof(line) );
        string strLine = line;
        unsigned j=0;
        for(unsigned i=0; i<strLine.length(); ++i)
        {    
            strLine[i] -= encryptKey[j++];            
            if( j >= encryptKey.length() )
                j = 0;
        }
        cout<<"Decrypted data"<<endl;
        cout<<strLine.data()<<endl;
    }
}
 
int main()
{
    ifstream ifs("test.txt");
    if( ifs.fail() )
        return 0;
 
    ofstream ofs("coded.txt");
    if( ofs.fail() )
        return 0;
 
    string encryptKey = "house";    
    encryptFile( ifs, ofs, encryptKey );
 
    ofs.close();
    ifs.close();
 
    ifstream ifstm("coded.txt");
    if( !ifstm )
        return 0;
 
    decryptFile( ifstm, encryptKey );    
 
    ifstm.close();
 
    return 0;
}

[nmadct]

It's not clear whether you just want results -- to keep your data safe -- or you want to actually implement encryption yourself. Encryption is tricky to do and, being a beginner, what you write will not be very secure until you've gotten to the point where you know what you're doing. If your goal is simply to add security into an app that you're writing, I recommend that you go download one of the various free encryption libraries that are available online and use the functions from that library to encrypt your data. If you want to learn about cryptography, more power to you, I recommend you go read a book on it first.

[vermarajeev]

It's not clear whether you just want results -- to keep your data safe -- or you want to actually implement encryption yourself. Encryption is tricky to do and, being a beginner, what you write will not be very secure until you've gotten to the point where you know what you're doing. If your goal is simply to add security into an app that you're writing, I recommend that you go download one of the various free encryption libraries that are available online and use the functions from that library to encrypt your data. If you want to learn about cryptography, more power to you, I recommend you go read a book on it first.

Yes i want to actually implement encryption myself.

"Encryption is tricky to do"
"I recommend you go read a book on it first"
--->Where can I find the best resources??????


"I recommend that you go download one of the various free encryption libraries that are available online and use the functions from that library to encrypt your data."
--->Please suggest some links such that I can get how it is implemented

Is there any problem with the solution that I have written?????

Please let me know about my queries.
Thanks

[vermarajeev]

Yes i want to actually implement encryption myself.

"Encryption is tricky to do"
"I recommend you go read a book on it first"
--->Where can I find the best resources??????


"I recommend that you go download one of the various free encryption libraries that are available online and use the functions from that library to encrypt your data."
--->Please suggest some links such that I can get how it is implemented

Is there any problem with the solution that I have written?????

Please let me know about my queries.
Thanks

I also want the file to be password protected.
The explanation is as follows:
Present scenario
--------------------------------
I have three models in my project 1) MODEL1 2) MODEL2 3) MODEL3

Suppose
MODEL1 creates a text file called model1.txt with human understandable characters

This model1.txt is given to MODEL2 which performs operation using that model1.txt, then generates model2.txt( with different contents different from model1.txt)

model2.txt is given to MODEL3 to view the results.

To be done scenario
--------------------------------
MODEL1 creates a text file called model1.txt with human understandable characters which should be encrypted with password protected

This encrypted file model1.txt is given to MODEL2 who knows the password, enters the password known and then decrypts the information in that file(if the password is correct), which performs operation using that model1.txt, this MODEL2 then generates model2.txt( with different contents different from model1.txt) again with the same password protected same as MODEL1

model2.txt is given to MODEL3 who knows the password, enters the correct password then decrypts the file to view the results.

this is want I want
Thanks

[Ganon11]

#include <iostream>
#include <fstream>
using namespace std;
 
void encryptFile( ifstream& ifs, ofstream& ofs, string encryptKey )
{
    char line[256];    
    while( !ifs.eof() )
    {
        ifs.getline( line, sizeof(line) );        
 
        string strLine = line;
        unsigned int j=0;
        for(unsigned int i=0; i<strLine.length(); ++i)
        {    
            strLine[i] += encryptKey[j++];            
            ofs.put( strLine[i] );
            if( j >= encryptKey.length() )
                j = 0;
        }
        cout<<"Encrypted data"<<endl;
        cout<<strLine.data()<<endl;
    }
}
 
void decryptFile( ifstream& ifs, string encryptKey )
{
    char line[256];    
    while( !ifs.eof() )
    {
        ifs.getline( line, sizeof(line) );
        string strLine = line;
        unsigned j=0;
        for(unsigned i=0; i<strLine.length(); ++i)
        {    
            strLine[i] -= encryptKey[j++];            
            if( j >= encryptKey.length() )
                j = 0;
        }
        cout<<"Decrypted data"<<endl;
        cout<<strLine.data()<<endl;
    }
}
 
int main()
{
    ifstream ifs("test.txt");
    if( ifs.fail() )
        return 0;
 
    ofstream ofs("coded.txt");
    if( ofs.fail() )
        return 0;
 
    string encryptKey = "house";    
    encryptFile( ifs, ofs, encryptKey );
 
    ofs.close();
    ifs.close();
 
    ifstream ifstm("coded.txt");
    if( !ifstm )
        return 0;
 
    decryptFile( ifstm, encryptKey );    
 
    ifstm.close();
 
    return 0;
}

This code looks good. The only think I'll point out is that, when adding and subtracting encryptKey, there is a possibility of going out of character bounds. A single character may be ASCII value 240 when you add a letter to it with ASCII value 65, making 305 - a number out of bounds for a char. You should use % to keep the number between 0 and 255.

The same will happen when subtracting encryptKey from the encoded string. In the above example, when properly bounded, the char ASCII value would be 50. But when you subtract 65 from it, you will get -15, which is out of bounds. You will need to find a way to keep that between 0 and 255 (Instead of subtracting, try adding 256 - that char value).

[nmadct]

Yes i want to actually implement encryption myself.

"Encryption is tricky to do"
"I recommend you go read a book on it first"
--->Where can I find the best resources??????


"I recommend that you go download one of the various free encryption libraries that are available online and use the functions from that library to encrypt your data."
--->Please suggest some links such that I can get how it is implemented

Is there any problem with the solution that I have written?????

Please let me know about my queries.
Thanks

There's an online book about cryptography here:

http://www.cacr.math.uwaterloo.ca/hac/

Some resources with brief reviews:

http://www.youdzone.com/cryptobooks_Programming.html

It's good that you want to implement cryptography yourself, it's good as a programming exercise. However, I wanted to dispell the illusion that you're getting strong security from it. The kind of techniques being discussed here can easily be defeated by an attack that analyzes the frequency of letters and letter sequences in the text. I'm guessing such attacks would probably not even take very long on modern computers, ranging from seconds to minutes to crack your code. (This assumes that the data is text in a human language; arbitrary data would be hard to analyze in this way.)

If you want to use a freely available crypto library, have a look at this page:

http://www.homeport.org/~adam/crypto/

Another alternative is to use a stand-alone program like GnuPG to do the encryption, and simply invoke it from your program with the proper parameters.

[vermarajeev]

There's an online book about cryptography here:

http://www.cacr.math.uwaterloo.ca/hac/

Some resources with brief reviews:

http://www.youdzone.com/cryptobooks_Programming.html

It's good that you want to implement cryptography yourself, it's good as a programming exercise. However, I wanted to dispell the illusion that you're getting strong security from it. The kind of techniques being discussed here can easily be defeated by an attack that analyzes the frequency of letters and letter sequences in the text. I'm guessing such attacks would probably not even take very long on modern computers, ranging from seconds to minutes to crack your code. (This assumes that the data is text in a human language; arbitrary data would be hard to analyze in this way.)

If you want to use a freely available crypto library, have a look at this page:

http://www.homeport.org/~adam/crypto/

Another alternative is to use a stand-alone program like GnuPG to do the encryption, and simply invoke it from your program with the proper parameters.

I just tried using the crypto library but believe me I'm not getting anything...Can someone help me with this....

I have a text file, how can I encrypt it using crypto++ with password protected as discussed above....If you want any links please refer above threads...

[hirak1984]

ABOUT PASSWORD PROTECTED FILES:

well say,there is a exe file "a.exe" which does some operation with a text file "b.txt".
Now if you double click on a.exe it will ask for password to open b.txt.
Writing code for this type of operation is easy.
But if we directly open b.txt using any text editor it will show content.
one cant password protect this file by writing any c code,because every code needs to be executed,which is irrelevant here.
what one can do is to hide b.txt in some other drive or encrypt it,or use some ready made software to password protect it.
if anyone can make the file b.txt password protected using c codes,please let me know.

[nmadct]

I just tried using the crypto library but believe me I'm not getting anything...Can someone help me with this....

I have a text file, how can I encrypt it using crypto++ with password protected as discussed above....If you want any links please refer above threads...

I don't have time to write a program and test it, but I think you wanna do something like this:

int block_size = Twofish::BlockSize();
char input[block_size];
char output[block_size];
// copy your data into input
TwofishEncryption enc("mypassword");
enc.ProcessBlock(input,output);
// output is now filled with the encrypted version of input
char original[block_size];
Twofish::Decryption dec("mypassword");
dec.ProcessBlock(output,original);
// original now contains the same text as input
 

Note that the encryption/decryption only works on one block of data at a time, in order to encrypt your whole file, you'll need to loop until it's done.

[RedSon]

The easiest and most secure encryption method is to XOR your data with a random key. To decrypt it you must also have the same random key. All you do is XOR it again and your text appears. This is known as a one-time-pad or method.

It looks like some of the guys are telling you about some variations of a Cesar cipher like a polyalphabetic cipher or just a strait substitution cipher. But most of these methods are vulnerable to a statistical analysis attack. If you are serious about encryption and protecting your data, either use the XOR operation provided in c/c++ or use a crypto api. Your crypto api must be one that has been reviewed and throughly tested.

You must also consider how your OS manages your application's data. If you are really serious about protecting your data you must be sure that no key information remains in unprotected areas of memory or on the stack.

One last thing about XOR, no matter what you do never, ever, ever use the same key twice and never use a key that is at all similar to any other previous key that you have used. This is critical! If you use a key that is the same or similar it will be a simple matter to decrypt your message.

[hirak1984]

Hi RedSon,
basically there are hundred methods of encryption-decryption.
Where we were struggling was if we can make a file password protected in such a way that while double clicking over it in windows,it will ask for password for opening.
And the code should be in c/c++.
Can you please throw some light on the matter?

The easiest and most secure encryption method is to XOR your data with a random key. To decrypt it you must also have the same random key. All you do is XOR it again and your text appears. This is known as a one-time-pad or method.

It looks like some of the guys are telling you about some variations of a Cesar cipher like a polyalphabetic cipher or just a strait substitution cipher. But most of these methods are vulnerable to a statistical analysis attack. If you are serious about encryption and protecting your data, either use the XOR operation provided in c/c++ or use a crypto api. Your crypto api must be one that has been reviewed and throughly tested.

You must also consider how your OS manages your application's data. If you are really serious about protecting your data you must be sure that no key information remains in unprotected areas of memory or on the stack.

One last thing about XOR, no matter what you do never, ever, ever use the same key twice and never use a key that is at all similar to any other previous key that you have used. This is critical! If you use a key that is the same or similar it will be a simple matter to decrypt your message.

[sicarie]

vermarajeev-

I believe you will find this link interesting: it is MIT's Cryptography Course that they opened to the public. As well, they have an Advanced Crypto Class. I don't know what levels they start at (I haven't gotten to them yet) - so I included both.

[vermarajeev]

Hi guys,

I'm feel happy that there are many people to clarify doubts.

I'm just going through the documents provided as a link.

If any problems I'll let you know....

Kudous to you all guys

[RedSon]

Hi RedSon,
basically there are hundred methods of encryption-decryption.
Where we were struggling was if we can make a file password protected in such a way that while double clicking over it in windows,it will ask for password for opening.
And the code should be in c/c++.
Can you please throw some light on the matter?

Let there be light... http://msdn2.microsoft.com/en-us/library/aa365005.aspx