{
  "$schema": "../../schema/test-vector.schema.json",
  "name": "SHA-256 ACK CRC Computation",
  "spec_ref": "src/04-payload-ack.md",
  "protocol_version": 0,
  "description": "Tests MeshCore ACK CRC computation: SHA-256(timestamp_le || txt_type_attempt || text || sender_pub_key)[0..3]. Each vector presents the full ACK packet that would be returned, along with the crypto_context showing the plaintext fed to SHA-256. Vectors ack-crc-001..004 share timestamp/text/pub_key and differ only in the attempt nibble of txt_type_attempt, demonstrating that each retry produces a distinct ACK CRC.",
  "vectors": [
    {
      "id": "ack-crc-001",
      "description": "ACK CRC for TXT_MSG 'hello', ts=0x12345678, attempt=0, zero pubkey",
      "type": "encode_decode",
      "structured": {
        "header": {
          "version": 0,
          "payload_type": "ack",
          "route_type": "flood"
        },
        "path": {
          "hash_size": 1,
          "hash_count": 0,
          "hashes": []
        },
        "payload": {
          "ack_crc": "B2EC0C9E"
        }
      },
      "binary": "0D 00 9E0CECB2",
      "crypto_context": {
        "plaintext": "78563412 00 68656C6C6F",
        "sender_public_key": "0000000000000000000000000000000000000000000000000000000000000000"
      },
      "notes": "SHA-256(timestamp(4) || txt_type_attempt(1) || text || sender_pub_key(32))[0..3] = 9E0CECB2 (LE). Displayed ack_crc field is the uint32 value 0xB2EC0C9E."
    },
    {
      "id": "ack-crc-002",
      "description": "Same message as ack-crc-001 but attempt=1 — distinct CRC",
      "type": "encode_decode",
      "structured": {
        "header": {
          "version": 0,
          "payload_type": "ack",
          "route_type": "flood"
        },
        "path": {
          "hash_size": 1,
          "hash_count": 0,
          "hashes": []
        },
        "payload": {
          "ack_crc": "13F08151"
        }
      },
      "binary": "0D 00 5181F013",
      "crypto_context": {
        "plaintext": "78563412 01 68656C6C6F",
        "sender_public_key": "0000000000000000000000000000000000000000000000000000000000000000"
      },
      "notes": "txt_type_attempt=0x01 (TXT_TYPE_PLAIN<<2 | attempt=1). Confirms attempt increment changes ACK CRC."
    },
    {
      "id": "ack-crc-003",
      "description": "Same message as ack-crc-001 but attempt=2 — distinct CRC",
      "type": "encode_decode",
      "structured": {
        "header": {
          "version": 0,
          "payload_type": "ack",
          "route_type": "flood"
        },
        "path": {
          "hash_size": 1,
          "hash_count": 0,
          "hashes": []
        },
        "payload": {
          "ack_crc": "4AD71DDF"
        }
      },
      "binary": "0D 00 DF1DD74A",
      "crypto_context": {
        "plaintext": "78563412 02 68656C6C6F",
        "sender_public_key": "0000000000000000000000000000000000000000000000000000000000000000"
      }
    },
    {
      "id": "ack-crc-004",
      "description": "Same message as ack-crc-001 but attempt=3 — distinct CRC (max attempt)",
      "type": "encode_decode",
      "structured": {
        "header": {
          "version": 0,
          "payload_type": "ack",
          "route_type": "flood"
        },
        "path": {
          "hash_size": 1,
          "hash_count": 0,
          "hashes": []
        },
        "payload": {
          "ack_crc": "1A537B8F"
        }
      },
      "binary": "0D 00 8F7B531A",
      "crypto_context": {
        "plaintext": "78563412 03 68656C6C6F",
        "sender_public_key": "0000000000000000000000000000000000000000000000000000000000000000"
      },
      "notes": "attempt=3 is the maximum value representable in the 2-bit attempt field."
    }
  ]
}