trezor-firmware/legacy/firmware/ethereum.c

/*
 * This file is part of the TREZOR project, https://trezor.io/
 *
 * Copyright (C) 2016 Alex Beregszaszi <alex@rtfs.hu>
 * Copyright (C) 2016 Pavol Rusnak <stick@satoshilabs.com>
 * Copyright (C) 2016 Jochen Hoenicke <hoenicke@gmail.com>
 *
 * This library is free software: you can redistribute it and/or modify
 * it under the terms of the GNU Lesser General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public License
 * along with this library.  If not, see <http://www.gnu.org/licenses/>.
 */

#include "ethereum.h"
#include "address.h"
#include "crypto.h"
#include "ecdsa.h"
#include "ethereum_networks.h"
#include "ethereum_tokens.h"
#include "fsm.h"
#include "gettext.h"
#include "layout2.h"
#include "memzero.h"
#include "messages.h"
#include "messages.pb.h"
#include "protect.h"
#include "secp256k1.h"
#include "sha3.h"
#include "transaction.h"
#include "util.h"

/* maximum supported chain id.  v must fit in an uint32_t. */
#define MAX_CHAIN_ID 2147483629

static bool ethereum_signing = false;
static uint32_t data_total, data_left;
static EthereumTxRequest msg_tx_request;
static CONFIDENTIAL uint8_t privkey[32];
static uint32_t chain_id;
static uint32_t tx_type;
struct SHA3_CTX keccak_ctx;

static inline void hash_data(const uint8_t *buf, size_t size) {
  sha3_Update(&keccak_ctx, buf, size);
}

/*
 * Push an RLP encoded length to the hash buffer.
 */
static void hash_rlp_length(uint32_t length, uint8_t firstbyte) {
  uint8_t buf[4];
  if (length == 1 && firstbyte <= 0x7f) {
    /* empty length header */
  } else if (length <= 55) {
    buf[0] = 0x80 + length;
    hash_data(buf, 1);
  } else if (length <= 0xff) {
    buf[0] = 0xb7 + 1;
    buf[1] = length;
    hash_data(buf, 2);
  } else if (length <= 0xffff) {
    buf[0] = 0xb7 + 2;
    buf[1] = length >> 8;
    buf[2] = length & 0xff;
    hash_data(buf, 3);
  } else {
    buf[0] = 0xb7 + 3;
    buf[1] = length >> 16;
    buf[2] = length >> 8;
    buf[3] = length & 0xff;
    hash_data(buf, 4);
  }
}

/*
 * Push an RLP encoded list length to the hash buffer.
 */
static void hash_rlp_list_length(uint32_t length) {
  uint8_t buf[4];
  if (length <= 55) {
    buf[0] = 0xc0 + length;
    hash_data(buf, 1);
  } else if (length <= 0xff) {
    buf[0] = 0xf7 + 1;
    buf[1] = length;
    hash_data(buf, 2);
  } else if (length <= 0xffff) {
    buf[0] = 0xf7 + 2;
    buf[1] = length >> 8;
    buf[2] = length & 0xff;
    hash_data(buf, 3);
  } else {
    buf[0] = 0xf7 + 3;
    buf[1] = length >> 16;
    buf[2] = length >> 8;
    buf[3] = length & 0xff;
    hash_data(buf, 4);
  }
}

/*
 * Push an RLP encoded length field and data to the hash buffer.
 */
static void hash_rlp_field(const uint8_t *buf, size_t size) {
  hash_rlp_length(size, buf[0]);
  hash_data(buf, size);
}

/*
 * Push an RLP encoded number to the hash buffer.
 * Ethereum yellow paper says to convert to big endian and strip leading zeros.
 */
static void hash_rlp_number(uint32_t number) {
  if (!number) {
    return;
  }
  uint8_t data[4];
  data[0] = (number >> 24) & 0xff;
  data[1] = (number >> 16) & 0xff;
  data[2] = (number >> 8) & 0xff;
  data[3] = (number)&0xff;
  int offset = 0;
  while (!data[offset]) {
    offset++;
  }
  hash_rlp_field(data + offset, 4 - offset);
}

/*
 * Calculate the number of bytes needed for an RLP length header.
 * NOTE: supports up to 16MB of data (how unlikely...)
 * FIXME: improve
 */
static int rlp_calculate_length(int length, uint8_t firstbyte) {
  if (length == 1 && firstbyte <= 0x7f) {
    return 1;
  } else if (length <= 55) {
    return 1 + length;
  } else if (length <= 0xff) {
    return 2 + length;
  } else if (length <= 0xffff) {
    return 3 + length;
  } else {
    return 4 + length;
  }
}

static int rlp_calculate_number_length(uint32_t number) {
  if (number <= 0x7f) {
    return 1;
  } else if (number <= 0xff) {
    return 2;
  } else if (number <= 0xffff) {
    return 3;
  } else if (number <= 0xffffff) {
    return 4;
  } else {
    return 5;
  }
}

static void send_request_chunk(void) {
  int progress = 1000 - (data_total > 1000000 ? data_left / (data_total / 800)
                                              : data_left * 800 / data_total);
  layoutProgress(_("Signing"), progress);
  msg_tx_request.has_data_length = true;
  msg_tx_request.data_length = data_left <= 1024 ? data_left : 1024;
  msg_write(MessageType_MessageType_EthereumTxRequest, &msg_tx_request);
}

static int ethereum_is_canonic(uint8_t v, uint8_t signature[64]) {
  (void)signature;
  return (v & 2) == 0;
}

static void send_signature(void) {
  uint8_t hash[32], sig[64];
  uint8_t v;
  layoutProgress(_("Signing"), 1000);

  /* eip-155 replay protection */
  if (chain_id) {
    /* hash v=chain_id, r=0, s=0 */
    hash_rlp_number(chain_id);
    hash_rlp_length(0, 0);
    hash_rlp_length(0, 0);
  }

  keccak_Final(&keccak_ctx, hash);
  if (ecdsa_sign_digest(&secp256k1, privkey, hash, sig, &v,
                        ethereum_is_canonic) != 0) {
    fsm_sendFailure(FailureType_Failure_ProcessError, _("Signing failed"));
    ethereum_signing_abort();
    return;
  }

  memzero(privkey, sizeof(privkey));

  /* Send back the result */
  msg_tx_request.has_data_length = false;

  msg_tx_request.has_signature_v = true;
  if (chain_id > MAX_CHAIN_ID) {
    msg_tx_request.signature_v = v;
  } else if (chain_id) {
    msg_tx_request.signature_v = v + 2 * chain_id + 35;
  } else {
    msg_tx_request.signature_v = v + 27;
  }

  msg_tx_request.has_signature_r = true;
  msg_tx_request.signature_r.size = 32;
  memcpy(msg_tx_request.signature_r.bytes, sig, 32);

  msg_tx_request.has_signature_s = true;
  msg_tx_request.signature_s.size = 32;
  memcpy(msg_tx_request.signature_s.bytes, sig + 32, 32);

  msg_write(MessageType_MessageType_EthereumTxRequest, &msg_tx_request);

  ethereum_signing_abort();
}
/* Format a 256 bit number (amount in wei) into a human readable format
 * using standard ethereum units.
 * The buffer must be at least 25 bytes.
 */
static void ethereumFormatAmount(const bignum256 *amnt, const TokenType *token,
                                 char *buf, int buflen) {
  bignum256 bn1e9;
  bn_read_uint32(1000000000, &bn1e9);
  const char *suffix = NULL;
  int decimals = 18;
  if (token == UnknownToken) {
    strlcpy(buf, "Unknown token value", buflen);
    return;
  } else if (token != NULL) {
    suffix = token->ticker;
    decimals = token->decimals;
  } else if (bn_is_less(amnt, &bn1e9)) {
    suffix = " Wei";
    decimals = 0;
  } else {
    if (tx_type == 1 || tx_type == 6) {
      suffix = " WAN";
    } else {
      ASSIGN_ETHEREUM_SUFFIX(suffix, chain_id);
    }
  }
  bn_format(amnt, NULL, suffix, decimals, 0, false, buf, buflen);
}

static void layoutEthereumConfirmTx(const uint8_t *to, uint32_t to_len,
                                    const uint8_t *value, uint32_t value_len,
                                    const TokenType *token) {
  bignum256 val;
  uint8_t pad_val[32];
  memzero(pad_val, sizeof(pad_val));
  memcpy(pad_val + (32 - value_len), value, value_len);
  bn_read_be(pad_val, &val);

  char amount[32];
  if (token == NULL) {
    if (bn_is_zero(&val)) {
      strcpy(amount, _("message"));
    } else {
      ethereumFormatAmount(&val, NULL, amount, sizeof(amount));
    }
  } else {
    ethereumFormatAmount(&val, token, amount, sizeof(amount));
  }

  char _to1[] = "to 0x__________";
  char _to2[] = "_______________";
  char _to3[] = "_______________?";

  if (to_len) {
    char to_str[41];

    bool rskip60 = false;
    // constants from trezor-common/defs/ethereum/networks.json
    switch (chain_id) {
      case 30:
        rskip60 = true;
        break;
      case 31:
        rskip60 = true;
        break;
    }

    ethereum_address_checksum(to, to_str, rskip60, chain_id);
    memcpy(_to1 + 5, to_str, 10);
    memcpy(_to2, to_str + 10, 15);
    memcpy(_to3, to_str + 25, 15);
  } else {
    strlcpy(_to1, _("to new contract?"), sizeof(_to1));
    strlcpy(_to2, "", sizeof(_to2));
    strlcpy(_to3, "", sizeof(_to3));
  }

  layoutDialogSwipe(&bmp_icon_question, _("Cancel"), _("Confirm"), NULL,
                    _("Send"), amount, _to1, _to2, _to3, NULL);
}

static void layoutEthereumData(const uint8_t *data, uint32_t len,
                               uint32_t total_len) {
  char hexdata[3][17];
  char summary[20];
  uint32_t printed = 0;
  for (int i = 0; i < 3; i++) {
    uint32_t linelen = len - printed;
    if (linelen > 8) {
      linelen = 8;
    }
    data2hex(data, linelen, hexdata[i]);
    data += linelen;
    printed += linelen;
  }

  strcpy(summary, "...          bytes");
  char *p = summary + 11;
  uint32_t number = total_len;
  while (number > 0) {
    *p-- = '0' + number % 10;
    number = number / 10;
  }
  char *summarystart = summary;
  if (total_len == printed) summarystart = summary + 4;

  layoutDialogSwipe(&bmp_icon_question, _("Cancel"), _("Confirm"), NULL,
                    _("Transaction data:"), hexdata[0], hexdata[1], hexdata[2],
                    summarystart, NULL);
}

static void layoutEthereumFee(const uint8_t *value, uint32_t value_len,
                              const uint8_t *gas_price, uint32_t gas_price_len,
                              const uint8_t *gas_limit, uint32_t gas_limit_len,
                              bool is_token) {
  bignum256 val, gas;
  uint8_t pad_val[32];
  char tx_value[32];
  char gas_value[32];

  memzero(tx_value, sizeof(tx_value));
  memzero(gas_value, sizeof(gas_value));

  memzero(pad_val, sizeof(pad_val));
  memcpy(pad_val + (32 - gas_price_len), gas_price, gas_price_len);
  bn_read_be(pad_val, &val);

  memzero(pad_val, sizeof(pad_val));
  memcpy(pad_val + (32 - gas_limit_len), gas_limit, gas_limit_len);
  bn_read_be(pad_val, &gas);
  bn_multiply(&val, &gas, &secp256k1.prime);

  ethereumFormatAmount(&gas, NULL, gas_value, sizeof(gas_value));

  memzero(pad_val, sizeof(pad_val));
  memcpy(pad_val + (32 - value_len), value, value_len);
  bn_read_be(pad_val, &val);

  if (bn_is_zero(&val)) {
    strcpy(tx_value, is_token ? _("token") : _("message"));
  } else {
    ethereumFormatAmount(&val, NULL, tx_value, sizeof(tx_value));
  }

  layoutDialogSwipe(&bmp_icon_question, _("Cancel"), _("Confirm"), NULL,
                    _("Really send"), tx_value, _("paying up to"), gas_value,
                    _("for gas?"), NULL);
}

/*
 * RLP fields:
 * - nonce (0 .. 32)
 * - gas_price (0 .. 32)
 * - gas_limit (0 .. 32)
 * - to (0, 20)
 * - value (0 .. 32)
 * - data (0 ..)
 */

static bool ethereum_signing_check(const EthereumSignTx *msg) {
  if (!msg->has_gas_price || !msg->has_gas_limit) {
    return false;
  }

  size_t tolen = msg->has_to ? strlen(msg->to) : 0;

  if (tolen != 42 && tolen != 40 && tolen != 0) {
    /* Address has wrong length */
    return false;
  }

  // sending transaction to address 0 (contract creation) without a data field
  if (tolen == 0 && (!msg->has_data_length || msg->data_length == 0)) {
    return false;
  }

  if (msg->gas_price.size + msg->gas_limit.size > 30) {
    // sanity check that fee doesn't overflow
    return false;
  }

  return true;
}

void ethereum_signing_init(EthereumSignTx *msg, const HDNode *node) {
  ethereum_signing = true;
  sha3_256_Init(&keccak_ctx);

  memzero(&msg_tx_request, sizeof(EthereumTxRequest));
  /* set fields to 0, to avoid conditions later */
  if (!msg->has_value) msg->value.size = 0;
  if (!msg->has_data_initial_chunk) msg->data_initial_chunk.size = 0;
  bool toset;
  uint8_t pubkeyhash[20];
  if (msg->has_to && ethereum_parse(msg->to, pubkeyhash)) {
    toset = true;
  } else {
    msg->to[0] = 0;
    toset = false;
    memzero(pubkeyhash, sizeof(pubkeyhash));
  }
  if (!msg->has_nonce) msg->nonce.size = 0;

  /* eip-155 chain id */
  if (msg->has_chain_id) {
    if (msg->chain_id < 1) {
      fsm_sendFailure(FailureType_Failure_DataError,
                      _("Chain Id out of bounds"));
      ethereum_signing_abort();
      return;
    }
    chain_id = msg->chain_id;
  } else {
    chain_id = 0;
  }

  /* Wanchain txtype */
  if (msg->has_tx_type) {
    if (msg->tx_type == 1 || msg->tx_type == 6) {
      tx_type = msg->tx_type;
    } else {
      fsm_sendFailure(FailureType_Failure_DataError, _("Txtype out of bounds"));
      ethereum_signing_abort();
      return;
    }
  } else {
    tx_type = 0;
  }

  if (msg->has_data_length && msg->data_length > 0) {
    if (!msg->has_data_initial_chunk || msg->data_initial_chunk.size == 0) {
      fsm_sendFailure(FailureType_Failure_DataError,
                      _("Data length provided, but no initial chunk"));
      ethereum_signing_abort();
      return;
    }
    /* Our encoding only supports transactions up to 2^24 bytes.  To
     * prevent exceeding the limit we use a stricter limit on data length.
     */
    if (msg->data_length > 16000000) {
      fsm_sendFailure(FailureType_Failure_DataError,
                      _("Data length exceeds limit"));
      ethereum_signing_abort();
      return;
    }
    data_total = msg->data_length;
  } else {
    data_total = 0;
  }
  if (msg->data_initial_chunk.size > data_total) {
    fsm_sendFailure(FailureType_Failure_DataError,
                    _("Invalid size of initial chunk"));
    ethereum_signing_abort();
    return;
  }

  // safety checks
  if (!ethereum_signing_check(msg)) {
    fsm_sendFailure(FailureType_Failure_DataError, _("Safety check failed"));
    ethereum_signing_abort();
    return;
  }

  const TokenType *token = NULL;

  // detect ERC-20 token
  if (toset && msg->value.size == 0 && data_total == 68 &&
      msg->data_initial_chunk.size == 68 &&
      memcmp(msg->data_initial_chunk.bytes,
             "\xa9\x05\x9c\xbb\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00",
             16) == 0) {
    token = tokenByChainAddress(chain_id, pubkeyhash);
  }

  if (token != NULL) {
    layoutEthereumConfirmTx(msg->data_initial_chunk.bytes + 16, 20,
                            msg->data_initial_chunk.bytes + 36, 32, token);
  } else {
    layoutEthereumConfirmTx(pubkeyhash, 20, msg->value.bytes, msg->value.size,
                            NULL);
  }

  if (!protectButton(ButtonRequestType_ButtonRequest_SignTx, false)) {
    fsm_sendFailure(FailureType_Failure_ActionCancelled, NULL);
    ethereum_signing_abort();
    return;
  }

  if (token == NULL && data_total > 0) {
    layoutEthereumData(msg->data_initial_chunk.bytes,
                       msg->data_initial_chunk.size, data_total);
    if (!protectButton(ButtonRequestType_ButtonRequest_SignTx, false)) {
      fsm_sendFailure(FailureType_Failure_ActionCancelled, NULL);
      ethereum_signing_abort();
      return;
    }
  }

  layoutEthereumFee(msg->value.bytes, msg->value.size, msg->gas_price.bytes,
                    msg->gas_price.size, msg->gas_limit.bytes,
                    msg->gas_limit.size, token != NULL);
  if (!protectButton(ButtonRequestType_ButtonRequest_SignTx, false)) {
    fsm_sendFailure(FailureType_Failure_ActionCancelled, NULL);
    ethereum_signing_abort();
    return;
  }

  /* Stage 1: Calculate total RLP length */
  uint32_t rlp_length = 0;

  layoutProgress(_("Signing"), 0);

  rlp_length += rlp_calculate_length(msg->nonce.size, msg->nonce.bytes[0]);
  rlp_length +=
      rlp_calculate_length(msg->gas_price.size, msg->gas_price.bytes[0]);
  rlp_length +=
      rlp_calculate_length(msg->gas_limit.size, msg->gas_limit.bytes[0]);
  rlp_length += rlp_calculate_length(toset ? 20 : 0, pubkeyhash[0]);
  rlp_length += rlp_calculate_length(msg->value.size, msg->value.bytes[0]);
  rlp_length +=
      rlp_calculate_length(data_total, msg->data_initial_chunk.bytes[0]);
  if (tx_type) {
    rlp_length += rlp_calculate_number_length(tx_type);
  }
  if (chain_id) {
    rlp_length += rlp_calculate_number_length(chain_id);
    rlp_length += rlp_calculate_length(0, 0);
    rlp_length += rlp_calculate_length(0, 0);
  }

  /* Stage 2: Store header fields */
  hash_rlp_list_length(rlp_length);

  layoutProgress(_("Signing"), 100);

  if (tx_type) {
    hash_rlp_number(tx_type);
  }
  hash_rlp_field(msg->nonce.bytes, msg->nonce.size);
  hash_rlp_field(msg->gas_price.bytes, msg->gas_price.size);
  hash_rlp_field(msg->gas_limit.bytes, msg->gas_limit.size);
  hash_rlp_field(pubkeyhash, toset ? 20 : 0);
  hash_rlp_field(msg->value.bytes, msg->value.size);
  hash_rlp_length(data_total, msg->data_initial_chunk.bytes[0]);
  hash_data(msg->data_initial_chunk.bytes, msg->data_initial_chunk.size);
  data_left = data_total - msg->data_initial_chunk.size;

  memcpy(privkey, node->private_key, 32);

  if (data_left > 0) {
    send_request_chunk();
  } else {
    send_signature();
  }
}

void ethereum_signing_txack(const EthereumTxAck *tx) {
  if (!ethereum_signing) {
    fsm_sendFailure(FailureType_Failure_UnexpectedMessage,
                    _("Not in Ethereum signing mode"));
    layoutHome();
    return;
  }

  if (tx->data_chunk.size > data_left) {
    fsm_sendFailure(FailureType_Failure_DataError, _("Too much data"));
    ethereum_signing_abort();
    return;
  }

  if (data_left > 0 && (!tx->has_data_chunk || tx->data_chunk.size == 0)) {
    fsm_sendFailure(FailureType_Failure_DataError,
                    _("Empty data chunk received"));
    ethereum_signing_abort();
    return;
  }

  hash_data(tx->data_chunk.bytes, tx->data_chunk.size);

  data_left -= tx->data_chunk.size;

  if (data_left > 0) {
    send_request_chunk();
  } else {
    send_signature();
  }
}

void ethereum_signing_abort(void) {
  if (ethereum_signing) {
    memzero(privkey, sizeof(privkey));
    layoutHome();
    ethereum_signing = false;
  }
}

static void ethereum_message_hash(const uint8_t *message, size_t message_len,
                                  uint8_t hash[32]) {
  struct SHA3_CTX ctx;
  sha3_256_Init(&ctx);
  sha3_Update(&ctx, (const uint8_t *)"\x19" "Ethereum Signed Message:\n", 26);
  uint8_t c;
  if (message_len >= 1000000000) {
    c = '0' + message_len / 1000000000 % 10;
    sha3_Update(&ctx, &c, 1);
  }
  if (message_len >= 100000000) {
    c = '0' + message_len / 100000000 % 10;
    sha3_Update(&ctx, &c, 1);
  }
  if (message_len >= 10000000) {
    c = '0' + message_len / 10000000 % 10;
    sha3_Update(&ctx, &c, 1);
  }
  if (message_len >= 1000000) {
    c = '0' + message_len / 1000000 % 10;
    sha3_Update(&ctx, &c, 1);
  }
  if (message_len >= 100000) {
    c = '0' + message_len / 100000 % 10;
    sha3_Update(&ctx, &c, 1);
  }
  if (message_len >= 10000) {
    c = '0' + message_len / 10000 % 10;
    sha3_Update(&ctx, &c, 1);
  }
  if (message_len >= 1000) {
    c = '0' + message_len / 1000 % 10;
    sha3_Update(&ctx, &c, 1);
  }
  if (message_len >= 100) {
    c = '0' + message_len / 100 % 10;
    sha3_Update(&ctx, &c, 1);
  }
  if (message_len >= 10) {
    c = '0' + message_len / 10 % 10;
    sha3_Update(&ctx, &c, 1);
  }
  c = '0' + message_len % 10;
  sha3_Update(&ctx, &c, 1);
  sha3_Update(&ctx, message, message_len);
  keccak_Final(&ctx, hash);
}

void ethereum_message_sign(const EthereumSignMessage *msg, const HDNode *node,
                           EthereumMessageSignature *resp) {
  uint8_t pubkeyhash[20];
  if (!hdnode_get_ethereum_pubkeyhash(node, pubkeyhash)) {
    return;
  }

  resp->has_address = true;
  resp->address[0] = '0';
  resp->address[1] = 'x';
  ethereum_address_checksum(pubkeyhash, resp->address + 2, false, 0);
  // ethereum_address_checksum adds trailing zero

  uint8_t hash[32];
  ethereum_message_hash(msg->message.bytes, msg->message.size, hash);

  uint8_t v;
  if (ecdsa_sign_digest(&secp256k1, node->private_key, hash,
                        resp->signature.bytes, &v, ethereum_is_canonic) != 0) {
    fsm_sendFailure(FailureType_Failure_ProcessError, _("Signing failed"));
    return;
  }

  resp->has_signature = true;
  resp->signature.bytes[64] = 27 + v;
  resp->signature.size = 65;
  msg_write(MessageType_MessageType_EthereumMessageSignature, resp);
}

int ethereum_message_verify(const EthereumVerifyMessage *msg) {
  if (msg->signature.size != 65) {
    fsm_sendFailure(FailureType_Failure_DataError, _("Malformed signature"));
    return 1;
  }

  uint8_t pubkeyhash[20];
  if (!ethereum_parse(msg->address, pubkeyhash)) {
    fsm_sendFailure(FailureType_Failure_DataError, _("Malformed address"));
    return 1;
  }

  uint8_t pubkey[65];
  uint8_t hash[32];

  ethereum_message_hash(msg->message.bytes, msg->message.size, hash);

  /* v should be 27, 28 but some implementations use 0,1.  We are
   * compatible with both.
   */
  uint8_t v = msg->signature.bytes[64];
  if (v >= 27) {
    v -= 27;
  }
  if (v >= 2 || ecdsa_recover_pub_from_sig(
                    &secp256k1, pubkey, msg->signature.bytes, hash, v) != 0) {
    return 2;
  }

  struct SHA3_CTX ctx;
  sha3_256_Init(&ctx);
  sha3_Update(&ctx, pubkey + 1, 64);
  keccak_Final(&ctx, hash);

  /* result are the least significant 160 bits */
  if (memcmp(pubkeyhash, hash + 12, 20) != 0) {
    return 2;
  }
  return 0;
}

bool ethereum_parse(const char *address, uint8_t pubkeyhash[20]) {
  memzero(pubkeyhash, 20);
  size_t len = strlen(address);
  if (len == 40) {
    // do nothing
  } else if (len == 42) {
    // check for "0x" prefix and strip it when required
    if (address[0] != '0') return false;
    if (address[1] != 'x' && address[1] != 'X') return false;
    address += 2;
    len -= 2;
  } else {
    return false;
  }
  for (size_t i = 0; i < len; i++) {
    if (address[i] >= '0' && address[i] <= '9') {
      pubkeyhash[i / 2] |= (address[i] - '0') << ((1 - (i % 2)) * 4);
    } else if (address[i] >= 'a' && address[i] <= 'f') {
      pubkeyhash[i / 2] |= ((address[i] - 'a') + 10) << ((1 - (i % 2)) * 4);
    } else if (address[i] >= 'A' && address[i] <= 'F') {
      pubkeyhash[i / 2] |= ((address[i] - 'A') + 10) << ((1 - (i % 2)) * 4);
    } else {
      return false;
    }
  }
  return true;
}