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#Encrypting Issue
near basinBOT
stiff oyster
Here is the code:
unsigned char *Crypt(unsigned char *data, int datalength, unsigned int initialValue){
// error handleing checks
if(data == nullptr){ // checking data is valid input
throw invalid_argument("Error: Null pointer for input data");
}
if(datalength <0) { // checking datalength negative and greater than 1 byte
throw out_of_range("Error: datalength out of valid range [0, 8]");
}
if(initialValue < 0 ){ // valid input range
throw out_of_range("Error: initialValue out of valid range [0, 255]");
}
unsigned int feedback_value = 0x87654321; // This is the F value
unsigned char* key_stream = new unsigned char[datalength];
unsigned char* output = new unsigned char[datalength] ;
if(output == nullptr){
throw bad_alloc(); // memory allocation failure
}
// Using the LFSR algo to produce a key stream
for(int i = 0; i <8; i++){
if(initialValue %2 == 0){
initialValue = initialValue >> 1;
} else{
initialValue = (initialValue >> 1) ^ feedback_value;
}
}
key_stream[0] = initialValue & 0xFF;
// obtaining the keystream with reinterpret_cast is not making it possible, so need to use another method
// - this interprets the entire unsigned int as an array of unsigned char
// key_stream = reinterpret_cast<unsigned char*>(&initialValue); // concerned about using this.
// so far it is alright, but don't know issues about it
for(size_t i = 0; i < datalength; i++){
output[i] = data[i] ^ key_stream[i]; // does the XOR with length of bytes
}
delete[] key_stream;
return output;
}
And the main function:
nt main(int argc, char const *argv[])
{
// Run excample of the LFSR cipher and XOR cipher
const char* str= "apple";
unsigned char* data = (unsigned char*) str;
unsigned int initialValue = 0x12345678; // this is the current state: initial
int datalength = 5;
// We need to deal with extreme cases to run algorithmn better
// like str ="pineapple", datalength = 10
unsigned char *lfsr_encryption = Crypt(data,datalength,initialValue);
// print the encrypted data
for(size_t i = 0; i < datalength; ++i){
cout << "\\x" << setw(2) << setfill('0') << hex << static_cast<int>(lfsr_encryption[i]);
if(i < datalength - 1){
cout << "|";
}
}
// initialValue = initialValue >> 1;
// hex is 0xCD01EFD730
// for (size_t i = 0; i < datalength; i++) {
// cout << hex<< static_cast<int>(lfsr_encryption[i]); // also use printf("%c", data[i]);
// }
// Now do the reverse and get back the message
cout << endl;
data = lfsr_encryption;
unsigned char *lfsr_decryption = Crypt(data,datalength,initialValue);
for (int i = 0; lfsr_decryption[i] != '\0'; i++) {
cout << (char)lfsr_decryption[i]; // also use printf("%c", data[i]);
}
return 0;
}
lavish jacinth
@stiff oyster have you tried stepping through the code with a debugger?
stiff oyster
<@505989297820925952> have you tried stepping through the code with a debugger?
I haven’t yet. I definitely would need to tho.
lavish jacinth
alright then, have fun!
stiff oyster
I was able to step through the code with gdb and got this as the outputs after running the function.
(gdb) print initialValue
$4 = 700264620
(gdb) print key_stream
$5 = (unsigned char *) 0x55555556aeb0 "\254"
(gdb) print output
$6 = (unsigned char *) 0x55555556aed0 "\315pple"
(gdb)
Before the function, I got the initial defined output.
So far, I don't understand the issue as I never really used gdb extensively before.
stiff oyster
@lavish jacinth
stiff oyster
I think it ha to deal with the key_stream definition as only a single character is being encrypted. Which in return cause the output to be incorrect.
I am still a bit confused on how to change it such that the encryption is possible. Even with reinterpret_cast<unsigned char> the issue is still there. Don't get where I am missing the logic.
near basinBOT
near basinBOT