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title: "Building a Cryptographic Hash Function from Scratch in Rust (part 2)" date: "2026-02-15" description: "I gave TorqueHash the ability to stream data using Rust's Write trait — turning it from a byte-slice toy into a composable I/O component with a real CLI." tags: ["rust", "cryptography", "systems-programming", "web3"] author: "Khusniddin Fakhritdinov" slug: "building-a-cryptographic-hash-function-from-scratch-in-rust-part-2"

Building a Cryptographic Hash Function from Scratch in Rust (part 2)

In part 1, I built TorqueHash — a minimal cryptographic hash function using sponge construction and ARX operations. It worked. You fed it a byte slice, it scrambled the bits through 24 rounds of permutations, and out came a 256-bit digest.

But it had a limitation: the only way to use it was to call update() with a &[u8]. Want to hash a file? You'd have to read the entire thing into memory first. That's not how real tools work. sha256sum doesn't load a 4GB file into RAM - it streams data through the hash function in chunks.

This time, I wanted TorqueHash to plug into Rust's I/O ecosystem - the same way a file, a network socket, or stdout does.

The full source code is on GitHub: github.com/hfmuzb/torque_hash

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The Write Trait: Turning a Hasher into a Byte Sink

Rust's standard library has a trait called std::io::Write. Anything that implements it can receive bytes - files, TCP streams, buffered writers, even stdout. The trait requires just two methods:

fn write(&mut self, buf: &[u8]) -> std::io::Result<usize>;
fn flush(&mut self) -> std::io::Result<()>;

A hasher is, at its core, a sink for bytes. You pour data in and it absorbs it. So implementing Write for TorqueHash is natural:

impl Write for TorqueHash {
    fn write(&mut self, buf: &[])  std::io::<> {
        .(buf);
        (buf.())
    }

     (& )  std::io::<()> {
        (())
    }
}