rules.js

/*!
 * rules.js - covenant rules for hsd
 * Copyright (c) 2017-2018, Christopher Jeffrey (MIT License).
 * https://github.com/handshake-org/hsd
 */

'use strict';

const assert = require('bsert');
const bio = require('bufio');
const {BufferSet} = require('buffer-map');
const blake2b = require('bcrypto/lib/blake2b');
const sha3 = require('bcrypto/lib/sha3');
const consensus = require('../protocol/consensus');
const reserved = require('./reserved');
const {locked} = require('./locked');
const OwnershipProof = require('./ownership').OwnershipProof;
const AirdropProof = require('../primitives/airdropproof');
const rules = exports;

/** @typedef {import('../types').Amount} AmountValue */
/** @typedef {import('../types').Hash} Hash */
/** @typedef {import('../protocol/network')} Network */
/** @typedef {import('../primitives/tx')} TX */
/** @typedef {import('../coins/coinview')} CoinView */
/** @typedef {import('./ownership').OwnershipProof} OwnershipProof */

/*
 * Constants
 */

const NAME_BUFFER = Buffer.allocUnsafe(63);

const CHARSET = new Uint8Array([
  0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
  0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
  0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 4, 0, 0,
  1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 0, 0, 0, 0, 0, 0,
  0, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2,
  2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 0, 0, 0, 0, 4,
  0, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3,
  3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 0, 0, 0, 0, 0
]);

/**
 * Covenant Types.
 * @enum {Number}
 * @default
 */

rules.types = {
  NONE: 0,
  CLAIM: 1,
  OPEN: 2,
  BID: 3,
  REVEAL: 4,
  REDEEM: 5,
  REGISTER: 6,
  UPDATE: 7,
  RENEW: 8,
  TRANSFER: 9,
  FINALIZE: 10,
  REVOKE: 11
};

const types = rules.types;

/**
 * Covenant types by value.
 * @const {Object}
 */

rules.typesByVal = {
  [types.NONE]: 'NONE',
  [types.CLAIM]: 'CLAIM',
  [types.OPEN]: 'OPEN',
  [types.BID]: 'BID',
  [types.REVEAL]: 'REVEAL',
  [types.REDEEM]: 'REDEEM',
  [types.REGISTER]: 'REGISTER',
  [types.UPDATE]: 'UPDATE',
  [types.RENEW]: 'RENEW',
  [types.TRANSFER]: 'TRANSFER',
  [types.FINALIZE]: 'FINALIZE',
  [types.REVOKE]: 'REVOKE'
};

/**
 * Blacklisted names.
 * @const {Set}
 */

rules.blacklist = new Set([
  'example', // ICANN reserved
  'invalid', // ICANN reserved
  'local', // mDNS
  'localhost', // ICANN reserved
  'test' // ICANN reserved
]);

/**
 * Maximum name size for a TLD.
 * @const {Number}
 * @default
 */

rules.MAX_NAME_SIZE = 63;

/**
 * Maximum resource size.
 * @const {Number}
 * @default
 */

rules.MAX_RESOURCE_SIZE = 512;

/**
 * Consensus name verification flags (used for block validation).
 * @enum {Number}
 * @default
 */

rules.nameFlags = {
  VERIFY_COVENANTS_NONE: 0,
  // Activated when hardening soft fork activates.
  VERIFY_COVENANTS_HARDENED: 1 << 0,
  // Activated when ICANN lockup soft fork activates.
  VERIFY_COVENANTS_LOCKUP: 1 << 1
};

/**
 * Standard verify flags for covenants.
 * @const {NameFlags}
 * @default
 */

rules.nameFlags.MANDATORY_VERIFY_COVENANT_FLAGS = 0;

/**
 * Maximum covenant size.
 * @const {Number}
 * @default
 */

rules.MAX_COVENANT_SIZE = (0
  + 1 + 32
  + 1 + 4
  + 2 + rules.MAX_RESOURCE_SIZE
  + 1 + 32);

/**
 * Hash a domain name.
 * @param {String|Buffer} name
 * @returns {Hash}
 */

rules.hashName = function hashName(name) {
  if (Buffer.isBuffer(name))
    return rules.hashBinary(name);
  return rules.hashString(name);
};

/**
 * Hash a domain name.
 * @param {String} name
 * @returns {Hash}
 */

rules.hashString = function hashString(name) {
  assert(typeof name === 'string');
  assert(rules.verifyString(name));

  const slab = NAME_BUFFER;
  const written = slab.write(name, 0, slab.length, 'ascii');

  assert(name.length === written);

  const buf = slab.slice(0, written);

  return rules.hashBinary(buf);
};

/**
 * Hash a domain name.
 * @param {Buffer} name
 * @returns {Buffer}
 */

rules.hashBinary = function hashBinary(name) {
  assert(Buffer.isBuffer(name));
  assert(rules.verifyBinary(name));
  return sha3.digest(name);
};

/**
 * Verify a domain name meets handshake requirements.
 * @param {String|Buffer} name
 * @returns {Boolean}
 */

rules.verifyName = function verifyName(name) {
  if (Buffer.isBuffer(name))
    return rules.verifyBinary(name);
  return rules.verifyString(name);
};

/**
 * Verify a domain name meets handshake requirements.
 * @param {String} str
 * @returns {Boolean}
 */

rules.verifyString = function verifyString(str) {
  assert(typeof str === 'string');

  if (str.length === 0)
    return false;

  if (str.length > rules.MAX_NAME_SIZE)
    return false;

  for (let i = 0; i < str.length; i++) {
    const ch = str.charCodeAt(i);

    // No unicode characters.
    if (ch & 0xff80)
      return false;

    const type = CHARSET[ch];

    switch (type) {
      case 0: // non-printable
        return false;
      case 1: // 0-9
        break;
      case 2: // A-Z
        return false;
      case 3: // a-z
        break;
      case 4: // - and _
        // Do not allow at end or beginning.
        if (i === 0 || i === str.length - 1)
          return false;
        break;
    }
  }

  if (rules.blacklist.has(str))
    return false;

  return true;
};

/**
 * Verify a domain name meets handshake requirements.
 * @param {Buffer} buf
 * @returns {Boolean}
 */

rules.verifyBinary = function verifyBinary(buf) {
  assert(Buffer.isBuffer(buf));

  if (buf.length === 0)
    return false;

  if (buf.length > rules.MAX_NAME_SIZE)
    return false;

  for (let i = 0; i < buf.length; i++) {
    const ch = buf[i];

    // No unicode characters.
    if (ch & 0x80)
      return false;

    const type = CHARSET[ch];

    switch (type) {
      case 0: // non-printable
        return false;
      case 1: // 0-9
        break;
      case 2: // A-Z
        return false;
      case 3: // a-z
        break;
      case 4: // - and _
        // Do not allow at end or beginning.
        if (i === 0 || i === buf.length - 1)
          return false;
        break;
    }
  }

  const str = buf.toString('binary');

  if (rules.blacklist.has(str))
    return false;

  return true;
};

/**
 * Get height and week of name hash rollout.
 * @param {Buffer} nameHash
 * @param {Network} network
 * @returns {Array} [height, week]
 */

rules.getRollout = function getRollout(nameHash, network) {
  assert(Buffer.isBuffer(nameHash) && nameHash.length === 32);
  assert(network && network.names);

  if (network.names.noRollout)
    return [0, 0];

  // Modulo the hash by 52 to get week number.
  const week = modBuffer(nameHash, 52);

  // Multiply result by a number of blocks-per-week.
  const height = week * network.names.rolloutInterval;

  // Add the auction start height to the rollout height.
  return [network.names.auctionStart + height, week];
};

/**
 * Verify a name hash meets the rollout.
 * @param {Buffer} hash
 * @param {Number} height
 * @param {Network} network
 * @returns {Boolean}
 */

rules.hasRollout = function hasRollout(hash, height, network) {
  assert((height >>> 0) === height);
  assert(network);

  const [start] = rules.getRollout(hash, network);

  if (height < start)
    return false;

  return true;
};

/**
 * Grind a name for rollout.
 * Used for testing.
 * @param {Number} size
 * @param {Number} height
 * @param {Network} network
 * @returns {String}
 */

rules.grindName = function grindName(size, height, network) {
  assert((size >>> 0) === size);
  assert((height >>> 0) === height);
  assert(network && network.names);

  if (height < network.names.auctionStart)
    height = network.names.auctionStart;

  for (let i = 0; i < 500000; i++) {
    const name = randomString(size);

    if (rules.blacklist.has(name))
      continue;

    const hash = rules.hashName(name);
    const [start] = rules.getRollout(hash, network);

    if (height < start)
      continue;

    if (reserved.has(hash))
      continue;

    return name;
  }

  throw new Error('Could not find available name.');
};

/**
 * Test whether a name is reserved.
 * @param {Buffer} nameHash
 * @param {Number} height
 * @param {Network} network
 * @returns {Boolean}
 */

rules.isReserved = function isReserved(nameHash, height, network) {
  assert(Buffer.isBuffer(nameHash));
  assert((height >>> 0) === height);
  assert(network && network.names);

  if (network.names.noReserved)
    return false;

  if (height >= network.names.claimPeriod)
    return false;

  return reserved.has(nameHash);
};

/**
 * Test whether a name is locked up.
 * ICANNLOCKUP soft fork.
 * @param {Buffer} nameHash
 * @param {Number} height
 * @param {Network} network
 * @returns {Boolean}
 */

rules.isLockedUp = function isLockedUp(nameHash, height, network) {
  assert(Buffer.isBuffer(nameHash));
  assert((height >>> 0) === height);
  assert(network && network.names);

  if (network.names.noReserved)
    return false;

  if (height < network.names.claimPeriod)
    return false;

  const item = locked.get(nameHash);

  if (!item)
    return false;

  // ICANN Names are always LOCKED.
  if (item.root)
    return true;

  // Alexa names will expire after 4 years, after claim period ends.
  if (height < network.names.alexaLockupPeriod)
    return true;

  return false;
};

/**
 * Create a blind bid hash from a value and nonce.
 * @param {AmountValue} value
 * @param {Buffer} nonce
 * @returns {Buffer}
 */

rules.blind = function blind(value, nonce) {
  assert(Number.isSafeInteger(value) && value >= 0);
  assert(Buffer.isBuffer(nonce) && nonce.length === 32);

  const bw = bio.write(40);
  bw.writeU64(value);
  bw.writeBytes(nonce);

  return blake2b.digest(bw.render());
};

/**
 * Test whether a transaction has
 * names contained in the set.
 * @param {TX} tx
 * @param {BufferSet} set
 * @returns {Boolean}
 */

rules.hasNames = function hasNames(tx, set) {
  assert(tx);
  assert(set instanceof BufferSet);

  for (const {covenant} of tx.outputs) {
    if (!covenant.isName())
      continue;

    const nameHash = covenant.getHash(0);

    switch (covenant.type) {
      case types.CLAIM:
      case types.OPEN:
        if (set.has(nameHash))
          return true;
        break;
      case types.BID:
      case types.REVEAL:
      case types.REDEEM:
        break;
      case types.REGISTER:
      case types.UPDATE:
      case types.RENEW:
      case types.TRANSFER:
      case types.FINALIZE:
      case types.REVOKE:
        if (set.has(nameHash))
          return true;
        break;
    }
  }

  return false;
};

/**
 * Add names to set.
 * @param {TX} tx
 * @param {BufferSet} set
 */

rules.addNames = function addNames(tx, set) {
  assert(tx);
  assert(set instanceof BufferSet);

  for (const {covenant} of tx.outputs) {
    if (!covenant.isName())
      continue;

    const nameHash = covenant.getHash(0);

    switch (covenant.type) {
      case types.CLAIM:
      case types.OPEN:
        set.add(nameHash);
        break;
      case types.BID:
      case types.REVEAL:
      case types.REDEEM:
        break;
      case types.REGISTER:
      case types.UPDATE:
      case types.RENEW:
      case types.TRANSFER:
      case types.FINALIZE:
      case types.REVOKE:
        set.add(nameHash);
        break;
    }
  }
};

/**
 * Remove names from set.
 * @param {TX} tx
 * @param {BufferSet} set
 */

rules.removeNames = function removeNames(tx, set) {
  assert(tx);
  assert(set instanceof BufferSet);

  for (const {covenant} of tx.outputs) {
    if (!covenant.isName())
      continue;

    const nameHash = covenant.getHash(0);

    switch (covenant.type) {
      case types.CLAIM:
      case types.OPEN:
        set.delete(nameHash);
        break;
      case types.BID:
      case types.REVEAL:
      case types.REDEEM:
        break;
      case types.REGISTER:
      case types.UPDATE:
      case types.RENEW:
      case types.TRANSFER:
      case types.FINALIZE:
      case types.REVOKE:
        set.delete(nameHash);
        break;
    }
  }
};

/**
 * Count name opens.
 * @param {TX} tx
 * @returns {Number}
 */

rules.countOpens = function countOpens(tx) {
  assert(tx);

  let total = 0;

  for (const {covenant} of tx.outputs) {
    if (covenant.isOpen())
      total += 1;
  }

  return total;
};

/**
 * Count name updates.
 * @param {TX} tx
 * @returns {Number}
 */

rules.countUpdates = function countUpdates(tx) {
  assert(tx);

  let total = 0;

  for (const {covenant} of tx.outputs) {
    switch (covenant.type) {
      case types.NONE:
        break;
      case types.CLAIM:
      case types.OPEN:
        total += 1;
        break;
      case types.BID:
      case types.REVEAL:
      case types.REDEEM:
        break;
      case types.REGISTER:
        break;
      case types.UPDATE:
        total += 1;
        break;
      case types.RENEW:
        break;
      case types.TRANSFER:
        total += 1;
        break;
      case types.FINALIZE:
        break;
      case types.REVOKE:
        total += 1;
        break;
    }
  }

  return total;
};

/**
 * Count name renewals.
 * @param {TX} tx
 * @returns {Number}
 */

rules.countRenewals = function countRenewals(tx) {
  assert(tx);

  let total = 0;

  for (const {covenant} of tx.outputs) {
    switch (covenant.type) {
      case types.REGISTER:
        total += 1;
        break;
      case types.RENEW:
        total += 1;
        break;
      case types.FINALIZE:
        total += 1;
        break;
    }
  }

  return total;
};

/**
 * Check covenant sanity (called from `tx.checkSanity()`).
 * @param {TX} tx
 * @returns {Boolean}
 */

rules.hasSaneCovenants = function hasSaneCovenants(tx) {
  assert(tx);

  // Coinbases are only capable of creating claims.
  if (tx.isCoinbase()) {
    if (tx.inputs.length > tx.outputs.length)
      return false;

    for (let i = 0; i < tx.outputs.length; i++) {
      const output = tx.outputs[i];
      const {covenant} = output;

      switch (covenant.type) {
        case types.NONE: {
          // Just a regular payment.
          if (covenant.items.length !== 0)
            return false;

          // Airdrop proof.
          if (i > 0 && i < tx.inputs.length) {
            const input = tx.inputs[i];
            const {witness} = input;

            // Must have exactly 1 witness item.
            if (witness.items.length !== 1)
              return false;

            let proof;

            try {
              proof = AirdropProof.decode(witness.items[0]);
            } catch (e) {
              return false;
            }

            if (!proof.isSane())
              return false;
          }

          break;
        }

        case types.CLAIM: {
          // Must not be the first input/output.
          if (i === 0)
            return false;

          // Must be linked.
          if (i >= tx.inputs.length)
            return false;

          const input = tx.inputs[i];
          const {witness} = input;

          // Must have exactly 1 witness item.
          if (witness.items.length !== 1)
            return false;

          // Should contain a name hash, height,
          // name, flags, block hash, and block height.
          if (covenant.items.length !== 6)
            return false;

          // Name hash is 32 bytes.
          if (covenant.items[0].length !== 32)
            return false;

          // Height must be 4 bytes.
          if (covenant.items[1].length !== 4)
            return false;

          // Name must be valid.
          if (!rules.verifyName(covenant.items[2]))
            return false;

          // Flags must be 1 byte.
          if (covenant.items[3].length !== 1)
            return false;

          // Block hash must be 32 bytes.
          if (covenant.items[4].length !== 32)
            return false;

          // Block height must be 4 bytes.
          if (covenant.items[5].length !== 4)
            return false;

          // Must be a reserved name.
          const nameHash = covenant.items[0];

          if (!reserved.has(nameHash))
            return false;

          // Must match the hash.
          const name = covenant.items[2];
          const key = rules.hashName(name);

          if (!key.equals(nameHash))
            return false;

          /** @type {OwnershipProof} */
          let proof;

          try {
            proof = OwnershipProof.decode(witness.items[0]);
          } catch (e) {
            return false;
          }

          if (!proof.isSane())
            return false;

          if (proof.getName() !== name.toString('binary'))
            return false;

          const flags = covenant.getU8(3);
          const weak = (flags & 1) !== 0;

          if (proof.isWeak() !== weak)
            return false;

          break;
        }

        default: {
          return false;
        }
      }
    }

    return true;
  }

  for (let i = 0; i < tx.outputs.length; i++) {
    const output = tx.outputs[i];
    const {covenant} = output;

    switch (covenant.type) {
      case types.NONE: {
        // Just a regular payment.
        // Can come from a NONE or a REDEEM.
        if (covenant.items.length !== 0)
          return false;

        break;
      }
      case types.CLAIM: {
        // Cannot exist in a non-coinbase.
        return false;
      }
      case types.OPEN: {
        // Has to come from NONE or REDEEM.

        // Should contain a name hash, zero height, and name.
        if (covenant.items.length !== 3)
          return false;

        // Name hash is 32 bytes.
        if (covenant.items[0].length !== 32)
          return false;

        // Height is 4 bytes.
        if (covenant.items[1].length !== 4)
          return false;

        // Height must be zero.
        if (covenant.getU32(1) !== 0)
          return false;

        // Name must be valid.
        if (!rules.verifyName(covenant.items[2]))
          return false;

        const key = rules.hashName(covenant.items[2]);

        if (!key.equals(covenant.items[0]))
          return false;

        break;
      }
      case types.BID: {
        // Has to come from NONE or REDEEM.

        // Should contain a name hash, name, height, and hash.
        if (covenant.items.length !== 4)
          return false;

        // Name hash is 32 bytes.
        if (covenant.items[0].length !== 32)
          return false;

        // Height must be 4 bytes.
        if (covenant.items[1].length !== 4)
          return false;

        // Name must be valid.
        if (!rules.verifyName(covenant.items[2]))
          return false;

        // Hash must be 32 bytes.
        if (covenant.items[3].length !== 32)
          return false;

        const key = rules.hashName(covenant.items[2]);

        if (!key.equals(covenant.items[0]))
          return false;

        break;
      }
      case types.REVEAL: {
        // Has to come from a BID.
        if (i >= tx.inputs.length)
          return false;

        // Should contain name hash, height, and nonce.
        if (covenant.items.length !== 3)
          return false;

        // Name hash must be valid.
        if (covenant.items[0].length !== 32)
          return false;

        // Height must be 4 bytes.
        if (covenant.items[1].length !== 4)
          return false;

        // Nonce must be 32 bytes.
        if (covenant.items[2].length !== 32)
          return false;

        break;
      }
      case types.REDEEM: {
        // Has to come from a REVEAL.
        if (i >= tx.inputs.length)
          return false;

        // Should contain name hash and height.
        if (covenant.items.length !== 2)
          return false;

        // Name hash must be valid.
        if (covenant.items[0].length !== 32)
          return false;

        // Height must be 4 bytes.
        if (covenant.items[1].length !== 4)
          return false;

        break;
      }
      case types.REGISTER: {
        // Has to come from a REVEAL.
        if (i >= tx.inputs.length)
          return false;

        // Should contain name hash, height,
        // record data and block hash.
        if (covenant.items.length !== 4)
          return false;

        // Name hash must be valid.
        if (covenant.items[0].length !== 32)
          return false;

        // Height must be 4 bytes.
        if (covenant.items[1].length !== 4)
          return false;

        // Record data is limited to 512 bytes.
        if (covenant.items[2].length > rules.MAX_RESOURCE_SIZE)
          return false;

        // Must be a block hash.
        if (covenant.items[3].length !== 32)
          return false;

        break;
      }
      case types.UPDATE: {
        // Has to come from a REGISTER, UPDATE, RENEW, or FINALIZE.
        if (i >= tx.inputs.length)
          return false;

        // Should contain name hash, height, and record data.
        if (covenant.items.length !== 3)
          return false;

        // Name hash must be valid.
        if (covenant.items[0].length !== 32)
          return false;

        // Height must be 4 bytes.
        if (covenant.items[1].length !== 4)
          return false;

        // Record data is limited to 512 bytes.
        if (covenant.items[2].length > rules.MAX_RESOURCE_SIZE)
          return false;

        break;
      }
      case types.RENEW: {
        // Has to come from a REGISTER, UPDATE, RENEW, or FINALIZE.
        if (i >= tx.inputs.length)
          return false;

        // Should contain name hash, height,
        // and a block hash.
        if (covenant.items.length !== 3)
          return false;

        // Name hash must be valid.
        if (covenant.items[0].length !== 32)
          return false;

        // Height must be 4 bytes.
        if (covenant.items[1].length !== 4)
          return false;

        // Must be a block hash.
        if (covenant.items[2].length !== 32)
          return false;

        break;
      }
      case types.TRANSFER: {
        // Has to come from a REGISTER, UPDATE, RENEW, or FINALIZE.
        if (i >= tx.inputs.length)
          return false;

        // Should contain the address we
        // _intend_ to transfer to.
        if (covenant.items.length !== 4)
          return false;

        // Name hash must be valid.
        if (covenant.items[0].length !== 32)
          return false;

        // Height must be 4 bytes.
        if (covenant.items[1].length !== 4)
          return false;

        // Version must be 1 byte.
        if (covenant.items[2].length !== 1)
          return false;

        // Must have an address.
        const version = covenant.getU8(2);
        const hash = covenant.items[3];

        // Todo: Add policy rule for high versions.
        if (version > 31)
          return false;

        // Must obey address size limits.
        if (hash.length < 2 || hash.length > 40)
          return false;

        break;
      }
      case types.FINALIZE: {
        // Has to come from a TRANSFER.
        if (i >= tx.inputs.length)
          return false;

        // Should contain name hash and state.
        if (covenant.items.length !== 7)
          return false;

        // Name hash must be valid.
        if (covenant.items[0].length !== 32)
          return false;

        // Must be height.
        if (covenant.items[1].length !== 4)
          return false;

        // Name must be valid.
        if (!rules.verifyName(covenant.items[2]))
          return false;

        // Must be flags byte.
        if (covenant.items[3].length !== 1)
          return false;

        // Must be claim height.
        if (covenant.items[4].length !== 4)
          return false;

        // Must be renewal count.
        if (covenant.items[5].length !== 4)
          return false;

        // Must be a block hash.
        if (covenant.items[6].length !== 32)
          return false;

        const key = rules.hashName(covenant.items[2]);

        if (!key.equals(covenant.items[0]))
          return false;

        break;
      }
      case types.REVOKE: {
        // Has to come from a REGISTER, UPDATE, RENEW, or FINALIZE.
        if (i >= tx.inputs.length)
          return false;

        // Should contain name hash and height.
        if (covenant.items.length !== 2)
          return false;

        // Name hash must be valid.
        if (covenant.items[0].length !== 32)
          return false;

        // Must be height.
        if (covenant.items[1].length !== 4)
          return false;

        break;
      }
      default: {
        // Unknown covenant.
        // Don't enforce anything other than DoS limits.
        if (covenant.items.length > consensus.MAX_SCRIPT_STACK)
          return false;

        if (covenant.getSize() > rules.MAX_COVENANT_SIZE)
          return false;

        break;
      }
    }
  }

  return true;
};

/**
 * Perform contextual verification for covenants.
 * Called from `tx.checkInputs()`.
 * @param {TX} tx
 * @param {CoinView} view
 * @param {Number} height
 * @param {Network} network
 * @returns {Number}
 */

rules.verifyCovenants = function verifyCovenants(tx, view, height, network) {
  assert(tx && view);
  assert(network && network.names);

  if (tx.isCoinbase()) {
    let conjured = 0;

    for (let i = 1; i < tx.inputs.length; i++) {
      const {witness} = tx.inputs[i];
      const output = tx.output(i);
      const covenant = tx.covenant(i);

      assert(output && covenant);

      // Airdrop Proof.
      if (!covenant.isClaim()) {
        assert(covenant.isNone());

        if (witness.items.length !== 1)
          return -1;

        let proof;
        try {
          proof = AirdropProof.decode(witness.items[0]);
        } catch (e) {
          return -1;
        }

        assert(proof.isSane());

        const value = proof.getValue();

        if (output.value !== value - proof.fee)
          return -1;

        if (output.address.version !== proof.version)
          return -1;

        if (!output.address.hash.equals(proof.address))
          return -1;

        conjured += value;

        if (conjured > consensus.MAX_MONEY)
          return -1;

        continue;
      }

      // DNSSEC Ownership Proof.
      if (covenant.getU32(1) !== height)
        return -1;

      if (witness.items.length !== 1)
        return -1;

      /** @type {OwnershipProof} */
      let proof;
      try {
        proof = OwnershipProof.decode(witness.items[0]);
      } catch (e) {
        return -1;
      }

      const data = proof.getData(network);

      if (!data)
        return -1;

      if (output.address.version !== data.version)
        return -1;

      if (!output.address.hash.equals(data.hash))
        return -1;

      if (!covenant.getHash(4).equals(data.commitHash))
        return -1;

      if (covenant.getU32(5) !== data.commitHeight)
        return -1;

      if (output.value !== data.value - data.fee)
        return -1;

      if (data.commitHeight === 0) // Fail early.
        return -1;

      if (height >= network.deflationHeight) {
        if (data.commitHeight === 1) {
          if (data.fee > 1000 * consensus.COIN)
            return -1;

          conjured += data.value;
        } else {
          conjured += output.value;
        }
      } else {
        conjured += data.value;
      }

      if (conjured > consensus.MAX_MONEY)
        return -1;
    }

    return conjured;
  }

  for (let i = 0; i < tx.inputs.length; i++) {
    const {prevout} = tx.inputs[i];
    const entry = view.getEntry(prevout);
    assert(entry);

    // coin is the UTXO being consumed as an input
    const coin = entry.output;
    const uc = coin.covenant;
    // output is the UTXO being created by the tx
    const output = tx.output(i);
    const covenant = tx.covenant(i);

    switch (uc.type) {
      case types.NONE:
      case types.OPEN:
      case types.REDEEM: {
        // Can go nowhere, does not need to be linked.
        if (!output)
          break;

        // Can only go to a NONE, OPEN, or BID.
        switch (covenant.type) {
          case types.NONE:
            break;
          case types.OPEN:
            break;
          case types.BID:
            break;
          default:
            return -1;
        }

        break;
      }
      case types.BID: {
        // Must be be linked.
        if (!output)
          return -1;

        // Bid has to go to a reveal.
        if (!covenant.isReveal())
          return -1;

        // Names must match.
        if (!covenant.getHash(0).equals(uc.getHash(0)))
          return -1;

        // Heights must match.
        if (covenant.getU32(1) !== uc.getU32(1))
          return -1;

        const nonce = covenant.getHash(2);
        const blind = rules.blind(output.value, nonce);

        // The value and nonce must match the
        // hash they presented in their bid.
        if (!blind.equals(uc.getHash(3)))
          return -1;

        // If they lied to us, they can
        // never redeem their money.
        if (coin.value < output.value)
          return -1;

        break;
      }
      case types.CLAIM:
      case types.REVEAL: {
        // Must be be linked.
        if (!output)
          return -1;

        // Reveal has to go to a REGISTER, or
        // a REDEEM (in the case of the loser).
        switch (covenant.type) {
          case types.REGISTER: {
            // Names must match.
            if (!covenant.getHash(0).equals(uc.getHash(0)))
              return -1;

            // Heights must match.
            if (covenant.getU32(1) !== uc.getU32(1))
              return -1;

            // Addresses must match.
            if (!output.address.equals(coin.address))
              return -1;

            // Note: We use a vickrey auction.
            // Output value must match the second
            // highest bid. This will be checked
            // elsewhere.

            break;
          }
          case types.REDEEM: {
            // Names must match.
            if (!covenant.getHash(0).equals(uc.getHash(0)))
              return -1;

            // Heights must match.
            if (covenant.getU32(1) !== uc.getU32(1))
              return -1;

            if (uc.isClaim())
              return -1;

            break;
          }
          default: {
            return -1;
          }
        }

        break;
      }
      case types.REGISTER:
      case types.UPDATE:
      case types.RENEW:
      case types.FINALIZE: {
        // Must be be linked.
        if (!output)
          return -1;

        // Money is now locked up forever.
        if (output.value !== coin.value)
          return -1;

        // Addresses must match.
        if (!output.address.equals(coin.address))
          return -1;

        // Can only send to an UPDATE, RENEW, TRANSFER, or REVOKE.
        switch (covenant.type) {
          case types.UPDATE:
          case types.RENEW:
          case types.TRANSFER:
          case types.REVOKE: {
            // Names must match.
            if (!covenant.getHash(0).equals(uc.getHash(0)))
              return -1;

            // Heights must match.
            if (covenant.getU32(1) !== uc.getU32(1))
              return -1;

            break;
          }
          default: {
            return -1;
          }
        }

        break;
      }
      case types.TRANSFER: {
        // Must be be linked.
        if (!output)
          return -1;

        // Money is now locked up forever.
        if (output.value !== coin.value)
          return -1;

        // Can only send to an UPDATE, RENEW, FINALIZE, or REVOKE.
        switch (covenant.type) {
          case types.UPDATE:
          case types.RENEW:
          case types.REVOKE: {
            // Names must match.
            if (!covenant.getHash(0).equals(uc.getHash(0)))
              return -1;

            // Heights must match.
            if (covenant.getU32(1) !== uc.getU32(1))
              return -1;

            // Addresses must match.
            if (!output.address.equals(coin.address))
              return -1;

            break;
          }
          case types.FINALIZE: {
            // Names must match.
            if (!covenant.getHash(0).equals(uc.getHash(0)))
              return -1;

            // Heights must match.
            if (covenant.getU32(1) !== uc.getU32(1))
              return -1;

            // Address must match the one committed
            // to in the original transfer covenant.
            if (output.address.version !== uc.getU8(2))
              return -1;

            if (!output.address.hash.equals(uc.get(3)))
              return -1;

            break;
          }
          default: {
            return -1;
          }
        }

        break;
      }
      case types.REVOKE: {
        // Revocations are perma-burned.
        return -1;
      }
      default: {
        // Unknown covenant.
        // Don't enforce anything.
        if (covenant.isName())
          return -1;
        break;
      }
    }
  }

  return 0;
};

/*
 * Helpers
 */

function randomString(len) {
  assert((len >>> 0) === len);

  let s = '';

  for (let i = 0; i < len; i++) {
    const n = Math.random() * (0x7b - 0x61) + 0x61;
    const c = Math.floor(n);

    s += String.fromCharCode(c);
  }

  return s;
}

function modBuffer(buf, num) {
  assert(Buffer.isBuffer(buf));
  assert((num & 0xff) === num);
  assert(num !== 0);

  const p = 256 % num;

  let acc = 0;

  for (let i = 0; i < buf.length; i++)
    acc = (p * acc + buf[i]) % num;

  return acc;
}