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SourcePawn SHA-256

An single-include file that implements a SHA-256 hashing function in native SourcePawn.

Disclaimer

I make no guarantees that this code is even fully functional, let alone bug free.
Any use of this code for security purposes is entirely at your own risk.

Also, do not use SHA-256 for security, doofus. Use a password-specific hashing algorithm like bcrypt.

How to use

/**
 * Generate a SHA-256 hash of a string of input data.
 * Input data can be in UTF-8, hexadecimal or binary.
 *
 * @param input     Input data (UTF-8 text, hexadecimal bytes or binary bytes).
 * @param output    Output buffer.
 * @param size      Size of output buffer.
 * @param mode      How to interpret input data.
 */
stock void SHA256(const char[] input, char[] output, int size, StrInputMode mode = String_UTF8)

char output[HASH_SIZE_256BIT]; // size 65

/* Text (UTF-8) */
SHA256("The quick brown fox jumps over the lazy dog", output, sizeof(output));
// output = "d7a8fbb307d7809469ca9abcb0082e4f8d5651e46d3cdb762d02d0bf37c9e592"
SHA256("The quick brown fox jumps over the lazy dog?", output, sizeof(output));
// output = "f77bc0c0d0779a6b329c7b9e847acb3797734ae531f08cc9d44cb4124d6e2b16"


/* Hexadecimal bytes (Case-insensitive) */
SHA256("AA0066FFDEADBEEF", output, sizeof(output), String_Hex);
// output = "1a61db0b7dc6ba6812d73eb6acdd2e84271c1124b0ec684192aca6f0933045a8"


/* Binary bytes */
SHA256("011000010110001001100011", output, sizeof(output), String_Binary);
// or SHA256("abc", output, sizeof(output), String_UTF8);
// output = "ba7816bf8f01cfea414140de5dae2223b00361a396177a9cb410ff61f20015ad"

How do I know it works?

To test the code, I used some of the tests made freely available by the National Institute of Standards and Technology (NIST--the organisation that originally created the algorithm) via their Cryptographic Algorithm Validation Program (no that doesn't mean this code has been validated).

Included in the repo is a python script generate_nist_tests_sha256.py which can process the SHA256LongMsg.rsp and SHA256ShortMsg.rsp files available under SHA Test Vectors for Hashing Byte-Oriented Messages.

You can just drop the files onto the script and it generates a plugin (called tests_SHA256LongMsg.sp or tests_SHA256ShortMsg.sp) that executes the tests.
Double-check the tests actually generated correctly because my python code is janky.

Hey the '00' (null string) test is failing! Your code sucks!

No, the test is wrong.
You heard me.
That specific test assumes that a null string (length of 0) is the same as a null byte (0x00, length of 1).
I will die on this hill. Null means no data, null byte is just a 0.
Other SHA-256 implementations also have this same quirk (7-Zip for example).