# Walkthrough Implementation of SHA-256 in Golang

<figure><img src="https://hub.bsvblockchain.org/~gitbook/image?url=https%3A%2F%2F2147185133-files.gitbook.io%2F%7E%2Ffiles%2Fv0%2Fb%2Fgitbook-x-prod.appspot.com%2Fo%2Fspaces%252FWtK4ab0ntyPZBmGoKq4t%252Fuploads%252Fgit-blob-055fb62103fb8c9757cf427a939578a226471ae8%252FBSVA-HashFunctions_Ch3L1_DA1.gif%3Falt%3Dmedia&#x26;width=768&#x26;dpr=4&#x26;quality=100&#x26;sign=ab5961ce&#x26;sv=2" alt=""><figcaption></figcaption></figure>

#### Why Look at the Code?

You don’t need to know the low-level workings of SHA-256 to understand how **Bitcoin or BSV functions**. But examining an implementation is useful because many of the **concepts and operations** inside SHA-256 also appear elsewhere in BSV:

* The **XOR (exclusive OR)** bit operation is used in both **digital signatures** and **Bitcoin Script**.
* The way **binary values are combined, shifted, and mixed** shows up in transaction verification and script execution.

⚠️ **Note:** The following example is **for learning only**. It has **not been optimized or rigorously tested**. For real-world systems, always use **official, vetted libraries**.

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#### Example Implementation in GoLang

Our simple SHA-256 implementation in Go follows three main stages:

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**1. Input and Preprocessing**

* **Input**: Take the raw message.
* **Message Block Construction**: Break the input into fixed-size blocks.
* **Message Schedule Construction**: Expand the message into a sequence of words for use in the compression step.

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**2. Compression**

* **Initialize Working Variables**: Set up registers with predefined constants.
* **Compute Temporary Words**: Perform logical functions, rotations, and modular additions.
* **Mutate Variables**: Update the working variables across multiple rounds of computation.
* **Integrate**: Mix the mutated values with the initial state.

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**3. Final Value and Output**

* **Concatenate Final State**: Combine the registers after all rounds.
* **Output Digest**: Produce the **256-bit hash value**, usually expressed in hexadecimal.

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✅ **Summary:** This walkthrough demonstrates how SHA-256 processes input into a secure digest. While the Go code itself is mainly illustrative, the underlying operations mirror those used in **digital signatures, scripts, and transaction verification** across the BSV system.


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