ft_ssl_md5

The ft_ssl_md5 project is a reimplementation of the md5 and sha256 hashing algorithms. It allows you to hash both strings, files (and standard input).

I've tried my best to not use any dynamic allocation in this project, which is why I've used a fixed buffer size of 1024 bytes for reading files and standard input.

Allowed functions

Function	Description	Usage
open	Open a file	To open any file with read permissions
read	Read from a file	To read from a file / stdin
close	Close a file	Close any opened file, to free the file descriptor
write	Write to a file	To write to a file / stdout / stderr
malloc	Dynamic memory allocation	None, don't use it, it's bad.
free	Frees previously allocated memory	-

Compilation

# https
git clone https://github.com/ggmolly/ft_ssl_md5
# ssh
# git clone git@github.com:ggmolly/ft_ssl_md5.git

cd ft_ssl_md5 && make

Usage

Flag	Description
-p	Echo STDIN to STDOUT and append the hash to STDOUT
-q	Quiet mode, prints only the hash
-r	Reverse the format of the output
-s	Print the sum of the given string

# ./ft_ssl [md5|sha256] [-pqr] [-s string] [files ...]

$ ./ft_ssl md5 -s "Hello, World!"
"Hello, World!" (MD5) = 65a8e27d8879283831b664bd8b7f0ad4
$ ./ft_ssl sha256 -s "Hello, World!"
"Hello, World!" (SHA256) = dffd6021bb2bd5b0af676290809ec3a53191dd81c7f70a4b28688a362182986f
$ echo "Hello, World!" | ./ft_ssl md5
(stdin)= bea8252ff4e80f41719ea13cdf007273
$ echo "Hello, World!" | ./ft_ssl sha256 -p
("Hello, World!") = c98c24b677eff44860afea6f493bbaec5bb1c4cbb209c6fc2bbb47f66ff2ad31
$ echo "Hello, World!" | ./ft_ssl sha256 -p -s a empty_file does_not_exists
("Hello, World!") = c98c24b677eff44860afea6f493bbaec5bb1c4cbb209c6fc2bbb47f66ff2ad31
SHA256 ("a") = ca978112ca1bbdcafac231b39a23dc4da786eff8147c4e72b9807785afee48bb
SHA256 (empty_file) = e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855
ft_ssl: file not found: 'does_not_exists'
$ echo "Hello, World!" | ./ft_ssl sha256 -p -r -s "a" empty_file 
("Hello, World!") = c98c24b677eff44860afea6f493bbaec5bb1c4cbb209c6fc2bbb47f66ff2ad31
ca978112ca1bbdcafac231b39a23dc4da786eff8147c4e72b9807785afee48bb "a"
e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855 empty_file

Important

This implementation of SHA-256 only works with little-endian systems.

Fuzzing

I've used a handmade fuzzing tool to test the robustness of my implementation. It checks if the output of my implementation matches the standard implementation of md5 and sha256 for a given input, for random inputs of length 1 to 65535.

The tool requires Python3, and uses hashlib along with subprocess.

Note

The code is not commented, but it works fine.

Modes

• text, passes the input to the -s flag, thus hashing the input as a string.
• file, writes the input to a file, and passes the file to the program, thus hashing the input as a file.
• huge_file, writes the input to a file, and passes the file to the program, file size ranges from 1 KB to 1 GB.

Warning

Both file and huge_file requires Linux, as their data is pulled from /dev/zero.

Usage

$ python3 fuzz.py [md5|sha256] [text|file|huge_file]

References

• RFC 1321
• RFC 6234
• Wikipedia MD5
• Wikipedia SHA-2
• Zunawe's MD5 implementation in C, very helpful to debug my implementation.
• EddieEldridge's SHA-256 implementation in C, also very helpful to debug my implementation.