Question

.

Please write a function that will do the following

Decryption of a message encrypted with a substitution cipher given cipher text only without any key

Please provide comments on each line of code outlining what that line is doing.

Note: Only the Function is to be written, all user inputs i.e the text to be decrypted will be entered earlier in the program.

Code must be written in C and be able to be compiled using GCC

If any questions need to be asked before attempting please do so

Answer 1

void sub_decrypt()
{
printf("Enter a text to Decrypt substitution cipher (without substitutions/key): \n");   
                scanf(" %[^\n]s", text);      
                printf("\nDecrypted Text: ");
  
                for(n=0; text[n]!='\0'; n++)
                {
                     if(text[n] >= 'a' && text[n] <= 'z')
                     {
                        text[n] = text[n] - 32;
                     }
                    if(text[n] < 'A' || text[n] > 'Z')
                    {
                        printf("%c", text[n]);
                    }
          
                    for(i=0; i<26; i++)
                    {
                        if(substitution[i] >= 'a' && substitution[i] <= 'z')
                        {
                            substitution[i] = substitution[i] - 32;
                        }
                        if (text[n] == substitution[i])
                        {
                            printf("%c", ALPHABET[i]);
                        }
                    }
                }
return 0;
}