Source: https://guthlabs.ai/docs/instruments/sha-256-hash-function-demo/implementation/

instrument implementation / implementation-contract

# SHA-256 / Hash Function Demo implementation

A source-bound implementation contract for SHA-256 / Hash Function Demo; deployment and executable qualification remain separate.

Status: **VERIFIED_CLEAN**Lifecycle: **implementation-contract**

## Binding contract

This record describes what an executable surface must bind and validate. It does not claim that a public calculator, package, or production route is deployed.

**Record owner**: Guth Instruments

**Lifecycle**: verified-clean

**Evidence ID**: t4-064

**Effect**: Computation or source lookup only

## Input and validation requirements

The extreme-length vector reaches the SHA-256 domain limit and must be rejected; otherwise the 64-bit length field wraps to zero and the result is not standard SHA-256. The specification also leaves hex-letter case unspecified, creating a representation-compatibility hazard.

## Required corrections

No binding erratum is attached to this unique-name record. Implementers must still preserve the declared units, domain, and failure behavior.

## Inspectable interface fixture

The sample below is evidence for interface and validation tests, not a production implementation.

````
{
  "inputs": {
    "algorithm": "SHA-256",
    "text": ""
  },
  "expected_outputs": {
    "hex_digest": "e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855"
  },
  "working": "1. UTF-8 bytes: 0 bytes. 2. Bit length: 0 x 8 = 0 bits. 3. Pad one 0x80 byte, then 55 zero bytes, then append the 64-bit big-endian length 0x0000000000000000: 1 + 55 + 8 = 64 bytes, so there is one 512-bit block. 4. Initialize the standard SHA-256 state and apply the 64 compression rounds to that block. 5. Add the resulting working words to the initial state modulo 2^32. 6. Concatenate the eight final 32-bit words: e3b0c442 || 98fc1c14 || 9afbf4c8 || 996fb924 || 27ae41e4 || 649b934c || a495991b || 7852b855 = e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855."
}
````

## Other records

[01**Overview**](<https://guthlabs.ai/docs/instruments/sha-256-hash-function-demo/>)[02**Mechanism**](<https://guthlabs.ai/docs/instruments/sha-256-hash-function-demo/mechanism/>)[04**Qualification**](<https://guthlabs.ai/docs/instruments/sha-256-hash-function-demo/qualification/>)

## Sources and evidence

These pointers bind the page to evidence. They do not grant authority or collapse verification into deployment.

- `VERIFIED_LEDGER.json`

- `evidence-tranche4/tranche4-results.json`