h5p9sl / hmac_sha256

Minimal HMAC-SHA256 implementation in C / C++

hmac_sha256

Minimal HMAC-SHA256 implementation in C / C++

This repository provides minimal HMAC-Sha256 code you can copy into your own projects. The hmac_sha256 function looks like this:

size_t // Returns the number of bytes written to `out`
hmac_sha256(
    // [in]: The key and its length.
    //      Should be at least 32 bytes long for optimal security.
    const void* key, const size_t keylen,

    // [in]: The data to hash alongside the key.
    const void* data, const size_t datalen,

    // [out]: The output hash.
    //      Should be 32 bytes long. If it's less than 32 bytes,
    //      the resulting hash will be truncated to the specified length.
    void* out, const size_t outlen
);

Contributing

All contributions are welcome, feature requests, or issues. I aim to tailor this code not only for myself, but for other's use cases too.

Usage Example (C++)

hmac_sha256/examples/simple_example.cpp

Lines 13 to 26 in 79a57d2

	const std::string str_data = "Hello World!";
	const std::string str_key = "super-secret-key";
	std::stringstream ss_result;
	// Allocate memory for the HMAC
	std::vector<uint8_t> out(SHA256_HASH_SIZE);
	// Call hmac-sha256 function
	hmac_sha256(
	str_key.data(), str_key.size(),
	str_data.data(), str_data.size(),
	out.data(), out.size()
	);

Sha256 Implementation

Big thank you to WjCryptLib for providing the Sha256 implementation of which this project is based off. If you need more public domain cryptographic functions in C (sha, aes, md5), check them out.

hmac_sha256's Issues

The result is incorrect , when the first value of the key is "00"

Hi,

Please try with these data:

{
/* Test with my golden data. */
"\x00\x01\x02\x03\x04\x05\x06\x07\x08\x09\x0a\x0b\x0c\x0d\x0e\x0f",
"\xd6\x36\xff\x79",
"f92a28969656d325bbf23b622bb3cd1815413a80f968a42e8e92bafa0f652896",
},

You will get incorrect result, I tried several key/data pair and found that when the first key value is \x00, then the result becomes incorrect.

I am using : https://cryptii.com/pipes/hmac calculator to check your result.

Thanks,
Bhavik

hmac_sha256 is dangerous

Use hmac_sha256 with caution, H allocates up to datalen + SHA256_BLOCK_SIZE bytes of memory and cannot be used with data streams. The sample code for MD5 in the appendix of RFC 2104 is a better starting point for those looking to implement a streaming-capable version that does not consume all system memory.

Issue with hmac_sha256.c

Hi, thanks for posting your code. When trying to compile I noticed that the hmac_sha256.c file has a problem in the function definition at line 76:

const size_t buflen = xlen + ylen;
uint8_t buf[buflen];

buflen is not a real const, or at least that's how the visual studio compiler sees it.

Please document license and copyright

Documenting License and Copyright will allow the actual use of your code (which is "All rights Reserved" by default).

Thanks.

Getting error running your code

Hi,
Thanks vm for posting this code. When I compiled and ran your code (had to make a small adjustment in concat_and_hash:
uint8_t* buf;
buf = calloc(destlen + srclen, sizeof(uint8_t));
it compiles and works, but the assert throws an error:
Message: Hello World!
HMAC: acde3f64ec328ad72d496afcc86de01509eac15505a4517471b6ed47d1b218dd
Assertion failed: ss_result.str() == "4b393abced1c497f8048860ba1ede46a23f1ff5209b18e9c428bddfbb690aad8", file C:\dev\HMACTest\HMACTest.cpp, line 43

Do you have any idea what is causing this?
Thanks
Jerome