# SHA-256 Final Value Construction and Output

{% embed url="<https://youtu.be/1mge3GDuGOg>" %}

#### From Chaining Variables to Hash Digest

The final step in SHA-256 is to take the **chaining variable values** (produced during the compression step) and **concatenate them** into a single **hexadecimal string**.

In GoLang, this is straightforward:

```
func PrintFinalHashValuesInHex(finalHashValues []uint32) string {
    hashValue := fmt.Sprintf("%x%x%x%x%x%x%x%x",
        finalHashValues[0], finalHashValues[1], finalHashValues[2], finalHashValues[3],
        finalHashValues[4], finalHashValues[5], finalHashValues[6], finalHashValues[7])
    return hashValue
}
```

👉 **Key takeaway:** The eight 32-bit outputs are joined to form the **256-bit SHA-256 digest**.

***

#### Printing the Result

Since our implementation is a **CLI program**, the final hash can be printed to **STDOUT**:

```
func main() {
    fi, _ := os.Stdin.Stat()

    if (fi.Mode() & os.ModeCharDevice) == 0 {
        reader := bufio.NewReader(os.Stdin)
        input, _ := reader.ReadString('\n')
        input = strings.TrimSuffix(input, "\n")
        fmt.Println(GetHash(input))
    } else {
        if len(os.Args) > 1 && len(os.Args) < 3 {
            fmt.Println(GetHash(os.Args[1]))
        } else {
            fmt.Println("Please provide a single input string")
        }
    }
}
```

&#x20;

* If input is piped in via STDIN, the program reads it and prints the hash.
* If run with an argument (e.g., `./sha256 abc`), it hashes that string.
* If no valid input is provided, it prompts the user.

***

#### Example Output

When we run the program with the test input `"abc"`, the result matches the **official output** from the **NIST FIPS 180-4 specification**:

```
"abc" → ba7816bf8f01cfea414140de5dae2223
         b00361a396177a9cb410ff61f20015ad
```

&#x20;

✅ **Summary:**

* The **final chaining variables** are concatenated into a 256-bit hexadecimal digest.
* The program can output the hash via **command-line input** or **STDIN**.
* Test results confirm correctness against the **official SHA-256 standard**.


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