Source: https://guthlabs.ai/docs/instruments/caesar-substitution-cipher-tool/implementation/

instrument implementation / implementation-contract

# Caesar / Substitution Cipher Tool implementation

A source-bound implementation contract for Caesar / Substitution Cipher Tool; 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**: t5-099

**Effect**: Computation or source lookup only

## Input and validation requirements

An incomplete 25-character substitution alphabet causes a lookup outside the defined mapping: encrypting Z produces an undefined result. The tool should reject this input instead of returning malformed ciphertext.

## 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": {
    "mode": "caesar_encrypt",
    "text": "MEET ME AT 9",
    "shift": 3
  },
  "expected_outputs": {
    "encoded_text": "PHHW PH DW 9"
  },
  "working": "M=12: (12+3) mod 26=15=P; E=4: (4+3) mod 26=7=H; E=4: (4+3) mod 26=7=H; T=19: (19+3) mod 26=22=W. The second MEET becomes PHHW. M=12 -> P=15; E=4 -> H=7. A=0: (0+3) mod 26=3=D; T=19 -> W=22. Spaces and 9 are unchanged. Result: PHHW PH DW 9."
}
````

## Other records

[01**Overview**](<https://guthlabs.ai/docs/instruments/caesar-substitution-cipher-tool/>)[02**Mechanism**](<https://guthlabs.ai/docs/instruments/caesar-substitution-cipher-tool/mechanism/>)[04**Qualification**](<https://guthlabs.ai/docs/instruments/caesar-substitution-cipher-tool/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-tranche5/tranche5-results.json`