A multi-threaded file encryptor which applies the Caesar cipher to an input file and outputs the result to a specified output file. To reduce predicatability, the encryption module randomly resets itself with a new encryption key.
Five threads exist: main, encryption, reader, writer, input counter and output counter. Several semaphores are defined to control syncronization among these threads to avoid race conditions.
- Obtains the input and output files as command line arguments. If the number of command line arguments is incorrect, it exits after displaying a message about correct usage.
- Calls init( ) with the input and output file names.
- Prompts the user for the input and output buffer sizes N and M. The buffers may be any size >1.
- Initialize shared variables. This includes allocating appropriate data structures for the input (N characters) and output (M characters) buffers.
- Creates the other threads.
- Waits for all threads to complete.
- Displays the number of occurrences of each letter in the input and output files.
Consumes one character at a time from the input buffer, encrypts it (using caesar_encrypt()), and places it in the output buffer. The encryption thread may need to wait for an item to
become available in the input buffer, and for a slot to become available in the output buffer. A character in the output buffer cannot be overwritten until the writer thread and the output
counter thread have processed the character. The encryption thread continues until all characters of the input file have been encrypted.
Reads from the input file one character at a time (using read_input()), and places the characters in the input buffer. Each buffer item corresponds to a character. The reader thread may
need to block until other threads have consumed data from the input buffer. Specifically, a character in the input buffer cannot be overwritten until the encryptor thread and the input
counter thread have processed the character. The reader continues until the end of the input file is reached.
Writes the encrypted characters in the output buffer to the output file (using write_output). It will block until an encrypted character is available in the buffer. The writer
continues until it has written the last encrypted character.
Counts occurrences of each letter (using count_input()) in the input file by looking at each character in the input buffer. It will block if no characters are available in the input buffer.
Counts occurrences of each letter (using count_output()) in the output file by looking at each character in the output buffer. It will block if no characters are available in the output buffer.
To reduce predicatability, the encryption module randomly resets itself with a new encryption key.
When this happens, the input and output counts are reset to zero. Before it performs a reset, it
will inform the application by calling reset_requested(). After a reset is complete, it will call
reset_finished().These function calls are used to print the input and output counts before the
reset, to ensure the correct behavior of the system during and after the reset. Only the
characters encrypted using a particular key would be counted together and there would be no
characters that go uncounted.
nikababtsov@LAPTOP-VGHR5LTP:/mnt/c/Users/Nika/file_encryptor$ make
gcc -c encrypt-module.c
gcc -c encrypt-module.h
gcc -pthread encrypt-module.o -o encrypt352 -lm
nikababtsov@LAPTOP-VGHR5LTP:/mnt/c/Users/Nika/file_encryptor$ ./encrypt352 input.txt output.txt
Enter a read buffer size: 4
Enter a write buffer size: 4
Reset requested
Total input count with current key is 265
A:16 B:0 C:2 D:2 E:23 F:3 G:7 H:9 I:16 J:0 K:2 L:6 M:8 N:14 O:11 P:2 Q:0 R:11 S:11 T:19 U:10 V:7 W:0 X:1 Y:7 Z:0
Total output count with current key is 265
A:0 B:16 C:0 D:2 E:2 F:23 G:3 H:7 I:9 J:16 K:0 L:2 M:6 N:8 O:14 P:11 Q:2 R:0 S:11 T:11 U:19 V:10 W:7 X:0 Y:1 Z:7
Reset finished
Total input count with current key is 32
A:3 B:0 C:0 D:1 E:3 F:2 G:0 H:1 I:3 J:0 K:0 L:0 M:1 N:1 O:1 P:0 Q:0 R:2 S:0 T:2 U:1 V:1 W:0 X:0 Y:2 Z:0
Total output count with current key is 32
A:0 B:1 C:3 D:2 E:0 F:1 G:3 H:0 I:0 J:0 K:1 L:1 M:1 N:0 O:0 P:2 Q:0 R:2 S:1 T:1 U:0 V:0 W:2 X:0 Y:3 Z:0
End of file reached
input and resulting output file can be viewed under file_encryptor/input.txt and file_encrypter/output.txt
input.txt
Seven :
"I've spent the last three years struggling to regain my Humanity. I'm afraid I may have lost it again in that arena."
Tuvok :
"You are experiencing difficult emotions."
Seven :
"Guilt, shame, remorse."
Tuvok :
"Then you haven't lost your Humanity. You have reaffirmed it."
output.txt
Tfwfo :
"J'wf tqfou uif mbtu uisff zfbst tusvhhmjoh up sfhbjo nz Ivnbojuz. J'n bgsbje J nbz ibwf mptu ju bhbjo jo uibu bsfob."
Uvwpl :
"Zpv bsf fyqfsjfodjoh ejggjdvmu fnpujpot."
Tfwfo :
"Hvjmu, tibnf, sfnpstf."
Uvwpl :
"Uifo zpv ibwfo'u mptu zpvs Ivnylgrw. Wms fytc pcyddgpkcb gr."