Basic string encrypthion and decryption

[|HBO|]

is there a function (except base64) for this?I meant the string has to be encrypt then decrypt.
thanks in advanced

[matsp]

Encrypting/decrypting for what purpose. Base64 not really encryption, it is basicly a way to encode non-printable characters as printable ones, by encoding 6 bits at a time into one printable character.

Encryption in my vocabulary means changing something from clear-text to "unreadable" by preforming some sort of translation of the characters. These range from a simple "shuffle the alphabet" (e.g. A => B, B => C, C => D, and so on, to Z => A). So "HELLO" becomes "IFMMP". This is relatively easy to implement in a computer, but also very easy to decrypt without actually knowing the key.

There are encryption algorithms that are MUCH more complex and "intrusion proof".

--
Mats

[|HBO|]

Encryption in my vocabulary means changing something from clear-text to "unreadable" by preforming some sort of translation of the characters. These range from a simple "shuffle the alphabet" (e.g. A => B, B => C, C => D, and so on, to Z => A). So "HELLO" becomes "IFMMP". This is relatively easy to implement in a computer, but also very easy to decrypt without actually knowing the key.
Mats

This is exactly what i am looking for.Any ideas or funcs name or funcss will be appreciated.

[matsp]

Well, there isn't, as far as I know, any standard function that does this. There are plenty of algorithms about if you google for "encryption algorithm". There is also, I'm certain without looking, a collection of encryption/decryption libraries around in places like www.sourceforge.org or such. These will contain the encryption methods in a way that you can use in your application.

--
Mats

[|HBO|]

anyway..
i have a func like:

 int i=0,j=0;
 while(i < strlen(source)) {
  from[i] += 1;
  i++; j++;
  if (j == strlen(destination)-1) j=0;
  }

But this contains all ascii s.but i want just to use letter.s.(not others)
How can i do it?

[matsp]

So you mean if you have "1234ABC12" it should be converted to "1234BCD12"?

Try using "isalpha()", it will return true for letters, nothing else.

--
Mats

[|HBO|]

So you mean if you have "1234ABC12" it should be converted to "1234BCD12"?

Try using "isalpha()", it will return true for letters, nothing else.

--
Mats

Not really.I meant if the string is "HBO" then the output must be "ICP" but if the string contains "z" things getting complicated because of after 'z' there is a '{'.I want to use just letters.

[matsp]

Not really.I meant if the string is "HBO" then the output must be "ICP" but if the string contains "z" things getting complicated because of after 'z' there is a '{'.I want to use just letters.

Ok, so you could build a table that contains your translation, so you index it by "current letter", and at that index, you get the "translated letter".

char encode[26] = "BCDEFGHIJKLMNOPQRSTUVWXYZA";
char decode[26] = "ZABCDEFGHIJKLMNOPQRSTUVWYXY";

--
Mats

[|HBO|]

Ok, so you could build a table that contains your translation, so you index it by "current letter", and at that index, you get the "translated letter".

char encode[26] = "BCDEFGHIJKLMNOPQRSTUVWXYZA";
char decode[26] = "ZABCDEFGHIJKLMNOPQRSTUVWYXY";

--
Mats

But this is the thing that i am confused about .How ?
Besides thanks for your concern.

[matsp]

Assuming above arrays:

char encodechar(char c)
{
   return encode[c - 'A'];
}

Decode is obviously same but using decode array.

This assumes that your incoming letter is an upper-case in the range 'A'..'Z' - anything else will have a undefined result.

--
Mats

[ssharish2005]

even u could use just this way as well

if(str[i] == 'z' || str[i] == 'Z')
      str[i] -= 25;
else
      str[i] += 1;

ssharish2005

[saman007uk]

Or, you could do something like (assuming strings always end with a '\0'):

//Buffer size incudes '\0'
#define BUFFER_SIZE 255

int encrypt(char *source, char *encrypted){
	int i;
	for (i=0; source[i]!='\0' && i <BUFFER_SIZE -1 ; i++){
		encrypted[i]= source[i]+ (long long int) ( i+ tan(i) + exp(i) + pow(i+2,8)) ;
	};
	encrypted[i]='\0';
	return 0;
}

int decrypt(char *encrypted, char *decrypted){
	int i;
	for (i=0; encrypted[i]!='\0' && i < BUFFER_SIZE - 1; i++){
		decrypted[i]= encrypted[i] - (long long int) ( i+ tan(i) + exp(i) + pow(i+2,8));
	};
	decrypted[i]='\0';
	return 0;
}

[|HBO|]

Or, you could do something like (assuming strings always end with a '\0'):

//Buffer size incudes '\0'
#define BUFFER_SIZE 255

int encrypt(char *source, char *encrypted){
	int i;
	for (i=0; source[i]!='\0' && i <BUFFER_SIZE -1 ; i++){
		encrypted[i]= source[i]+ (long long int) ( i+ tan(i) + exp(i) + pow(i+2,8)) ;
	};
	encrypted[i]='\0';
	return 0;
}

int decrypt(char *encrypted, char *decrypted){
	int i;
	for (i=0; encrypted[i]!='\0' && i < BUFFER_SIZE - 1; i++){
		decrypted[i]= encrypted[i] - (long long int) ( i+ tan(i) + exp(i) + pow(i+2,8));
	};
	decrypted[i]='\0';
	return 0;
}

Thank you but it is not working.
for encryption:

        char buf2[128];
        char *buf1 = "hbo";
        encrypt(buf1, buf2);
        printf("Encrypted: %s\n", buf2);

./encrypt
Encrypted: v

[saman007uk]

Try this:

#include <stdio.h>
#include <math.h>
#define BUFFER_SIZE 256
//Buffer size incudes '\0'

int encrypt(char *source, char *encrypted){
	int i;
	for (i=0; source[i]!='\0' && i <BUFFER_SIZE -1 ; i++){
		encrypted[i]= source[i]+ (long long int) ( i*8 -i+ 100*cos(i) + exp(i) + pow(i+2,8)) ;
	};
	encrypted[i]='\0';
	return 0;
}

int decrypt(char *encrypted, char *decrypted){
	int i;
	for (i=0; encrypted[i]!='\0' && i <BUFFER_SIZE -1 ; i++){
		decrypted[i]= encrypted[i]- (long long int) ( i*8 -i+ 100*cos(i) + exp(i) + pow(i+2,8)) ;
	};
	decrypted[i]='\0';
	return 0;
}

int main(void){
	char source[BUFFER_SIZE]={"TestingTesting ..."};
	char encrypted[BUFFER_SIZE]={0}, decrypted[BUFFER_SIZE]={0};
	encrypt(source, encrypted);
	
	printf("Encrypted String\n");
	printf("################\n");
	printf("&#37;s\n", encrypted); fflush(stdout);
	printf("################\n\n");
	
	printf("Decrypted String\n");
	printf("################\n");
	decrypt(encrypted, decrypted);
	printf("%s\n", decrypted);fflush(stdout);
	printf("################\n\n");
	return 0;
}

Note that I had to chage the functions a bit (as tan(i) tending to -/+infinity can cause problems).

Output:

Encrypted String
################
U�}}�;;��ׄp55�
################

Decrypted String
################
TestingTesting ...
################

Note that blank spaces and new lines can also be part of the encrypted string!

[|HBO|]

Thank you very much.

Encrypted String
################
U�}}�;;��ׄp55�
################

But this is the thing i am dealing with.I don't wanna it contains punctuation mark.(i meant the output must be isalnum char.)
Regards.