diff --git a/python/.changelog.d/15.added b/python/.changelog.d/15.added
new file mode 100644
index 000000000..70ce443ce
--- /dev/null
+++ b/python/.changelog.d/15.added
@@ -0,0 +1 @@
+Signed Ethereum network and token definitions from host
diff --git a/python/docs/OPTIONS.rst b/python/docs/OPTIONS.rst
index 88de938fe..9fcbe6afc 100644
--- a/python/docs/OPTIONS.rst
+++ b/python/docs/OPTIONS.rst
@@ -251,8 +251,26 @@ Ethereum commands.
 
     Ethereum commands.
 
+    Most Ethereum commands now require the host to specify definition of a network and possibly an
+    ERC-20 token. These definitions can be automatically fetched using the `-a` option.
+
+    You can also specify a custom definition source using the `-d` option. Allowable values are:
+
+    - HTTP or HTTPS URL
+    - path to local directory
+    - path to local tar archive
+    
+
+    For debugging purposes, it is possible to force use a specific network and token definition by
+    using the `--network` and `--token` options. These options accept either a path to a file with a
+    binary blob, or a hex-encoded string.
+
   Options:
-    --help  Show this message and exit.
+    -d, --definitions TEXT  Source for Ethereum definition blobs.
+    -a, --auto-definitions  Automatically download required definitions from trezor.io
+    --network TEXT          Network definition blob.
+    --token TEXT            Token definition blob.
+    --help                  Show this message and exit.
 
   Commands:
     get-address           Get Ethereum address in hex encoding.
diff --git a/python/src/trezorlib/cli/ethereum.py b/python/src/trezorlib/cli/ethereum.py
index 9ddbd4021..13b36a8dd 100644
--- a/python/src/trezorlib/cli/ethereum.py
+++ b/python/src/trezorlib/cli/ethereum.py
@@ -17,7 +17,9 @@
 import json
 import re
 import sys
+import tarfile
 from decimal import Decimal
+from pathlib import Path
 from typing import (
     TYPE_CHECKING,
     Any,
@@ -32,7 +34,8 @@ from typing import (
 
 import click
 
-from .. import ethereum, tools
+from .. import definitions, ethereum, tools
+from ..messages import EthereumDefinitions
 from . import with_client
 
 if TYPE_CHECKING:
@@ -164,14 +167,106 @@ def _format_access_list(
     ]
 
 
+def _hex_or_file(data: str) -> bytes:
+    path = Path(data)
+    if path.is_file():
+        return path.read_bytes()
+
+    if data.startswith("0x"):
+        data = data[2:]
+    try:
+        return bytes.fromhex(data)
+    except ValueError as e:
+        raise click.ClickException(f"Invalid hex or file path: {data}") from e
+
+
+class CliSource(definitions.Source):
+    network: Optional[bytes] = None
+    token: Optional[bytes] = None
+    delegate: definitions.Source = definitions.NullSource()
+
+    def get_network(self, chain_id: int) -> Optional[bytes]:
+        if self.network is not None:
+            return self.network
+        return self.delegate.get_network(chain_id)
+
+    def get_network_by_slip44(self, slip44: int) -> Optional[bytes]:
+        if self.network is not None:
+            return self.network
+        return self.delegate.get_network_by_slip44(slip44)
+
+    def get_token(self, chain_id: int, address: Any) -> Optional[bytes]:
+        if self.token is not None:
+            return self.token
+        return self.delegate.get_token(chain_id, address)
+
+
+DEFINITIONS_SOURCE = CliSource()
+
+
 #####################
 #
 # commands start here
 
 
 @click.group(name="ethereum")
-def cli() -> None:
-    """Ethereum commands."""
+@click.option(
+    "-d", "--definitions", "defs", help="Source for Ethereum definition blobs."
+)
+@click.option(
+    "-a",
+    "--auto-definitions",
+    is_flag=True,
+    help="Automatically download required definitions from trezor.io",
+)
+@click.option("--network", help="Network definition blob.")
+@click.option("--token", help="Token definition blob.")
+def cli(
+    defs: Optional[str],
+    auto_definitions: Optional[bool],
+    network: Optional[str],
+    token: Optional[str],
+) -> None:
+    """Ethereum commands.
+
+    Most Ethereum commands now require the host to specify definition of a network
+    and possibly an ERC-20 token. These definitions can be automatically fetched
+    using the `-a` option.
+
+    You can also specify a custom definition source using the `-d` option. Allowable
+    values are:
+
+    \b
+    - HTTP or HTTPS URL
+    - path to local directory
+    - path to local tar archive
+    \b
+
+    For debugging purposes, it is possible to force use a specific network and token
+    definition by using the `--network` and `--token` options. These options accept
+    either a path to a file with a binary blob, or a hex-encoded string.
+    """
+    if auto_definitions:
+        if defs is not None:
+            raise click.ClickException(
+                "Cannot use --definitions and --auto-definitions at the same time."
+            )
+        DEFINITIONS_SOURCE.delegate = definitions.UrlSource()
+    elif defs is not None:
+        path = Path(defs)
+        if path.is_dir():
+            DEFINITIONS_SOURCE.delegate = definitions.FilesystemSource(path)
+        elif path.is_file() and tarfile.is_tarfile(path):
+            DEFINITIONS_SOURCE.delegate = definitions.TarSource(path)
+        elif defs.startswith("http"):
+            DEFINITIONS_SOURCE.delegate = definitions.UrlSource(defs)
+        else:
+            raise click.ClickException("Unrecognized --definitions value.")
+
+    if network is not None:
+        DEFINITIONS_SOURCE.network = _hex_or_file(network)
+    if token is not None:
+        DEFINITIONS_SOURCE.token = _hex_or_file(token)
 
 
 @cli.command()
@@ -181,7 +276,8 @@ def cli() -> None:
 def get_address(client: "TrezorClient", address: str, show_display: bool) -> str:
     """Get Ethereum address in hex encoding."""
     address_n = tools.parse_path(address)
-    return ethereum.get_address(client, address_n, show_display)
+    network = ethereum.network_from_address_n(address_n, DEFINITIONS_SOURCE)
+    return ethereum.get_address(client, address_n, show_display, network)
 
 
 @cli.command()
@@ -306,8 +402,11 @@ def sign_tx(
         click.echo("Can't send tokens and custom data at the same time")
         sys.exit(1)
 
+    encoded_network = DEFINITIONS_SOURCE.get_network(chain_id)
     address_n = tools.parse_path(address)
-    from_address = ethereum.get_address(client, address_n)
+    from_address = ethereum.get_address(
+        client, address_n, encoded_network=encoded_network
+    )
 
     if token:
         data = _erc20_contract(token, to_address, amount)
@@ -315,8 +414,14 @@ def sign_tx(
         amount = 0
 
     if data:
+        # use token definition regardless of whether the data is an ERC-20 transfer
+        # -- this might prove useful in the future
+        encoded_token = DEFINITIONS_SOURCE.get_token(chain_id, to_address)
         data_bytes = ethereum.decode_hex(data)
     else:
+        # force use provided token definition even if no data (that is what the user
+        # seems to want)
+        encoded_token = DEFINITIONS_SOURCE.token
         data_bytes = b""
 
     if gas_limit is None:
@@ -335,6 +440,11 @@ def sign_tx(
     assert gas_limit is not None
     assert nonce is not None
 
+    defs = EthereumDefinitions(
+        encoded_network=encoded_network,
+        encoded_token=encoded_token,
+    )
+
     if is_eip1559:
         assert max_gas_fee is not None
         assert max_priority_fee is not None
@@ -350,6 +460,7 @@ def sign_tx(
             max_gas_fee=max_gas_fee,
             max_priority_fee=max_priority_fee,
             access_list=access_list,
+            definitions=defs,
         )
     else:
         if gas_price is None:
@@ -366,6 +477,7 @@ def sign_tx(
             value=amount,
             data=data_bytes,
             chain_id=chain_id,
+            definitions=defs,
         )
 
     to = ethereum.decode_hex(to_address)
@@ -420,7 +532,8 @@ def sign_tx(
 def sign_message(client: "TrezorClient", address: str, message: str) -> Dict[str, str]:
     """Sign message with Ethereum address."""
     address_n = tools.parse_path(address)
-    ret = ethereum.sign_message(client, address_n, message)
+    network = ethereum.network_from_address_n(address_n, DEFINITIONS_SOURCE)
+    ret = ethereum.sign_message(client, address_n, message, network)
     output = {
         "message": message,
         "address": ret.address,
@@ -448,9 +561,15 @@ def sign_typed_data(
     - recursive structs
     """
     address_n = tools.parse_path(address)
+    network = ethereum.network_from_address_n(address_n, DEFINITIONS_SOURCE)
+    defs = EthereumDefinitions(encoded_network=network)
     data = json.loads(file.read())
     ret = ethereum.sign_typed_data(
-        client, address_n, data, metamask_v4_compat=metamask_v4_compat
+        client,
+        address_n,
+        data,
+        metamask_v4_compat=metamask_v4_compat,
+        definitions=defs,
     )
     output = {
         "address": ret.address,
@@ -490,7 +609,10 @@ def sign_typed_data_hash(
     address_n = tools.parse_path(address)
     domain_hash = ethereum.decode_hex(domain_hash_hex)
     message_hash = ethereum.decode_hex(message_hash_hex) if message_hash_hex else None
-    ret = ethereum.sign_typed_data_hash(client, address_n, domain_hash, message_hash)
+    network = ethereum.network_from_address_n(address_n, DEFINITIONS_SOURCE)
+    ret = ethereum.sign_typed_data_hash(
+        client, address_n, domain_hash, message_hash, network
+    )
     output = {
         "domain_hash": domain_hash_hex,
         "message_hash": message_hash_hex,
diff --git a/python/src/trezorlib/definitions.py b/python/src/trezorlib/definitions.py
new file mode 100644
index 000000000..2960678c3
--- /dev/null
+++ b/python/src/trezorlib/definitions.py
@@ -0,0 +1,145 @@
+import logging
+import tarfile
+import typing as t
+from pathlib import Path
+
+import construct as c
+import requests
+from construct_classes import Struct, subcon
+
+from . import cosi, merkle_tree
+from .messages import EthereumDefinitionType
+from .tools import EnumAdapter
+
+LOG = logging.getLogger(__name__)
+
+FORMAT_MAGIC = b"trzd1"
+DEFS_BASE_URL = "https://data.trezor.io/firmware/eth-definitions/"
+
+DEFINITIONS_DEV_SIGS_REQUIRED = 1
+DEFINITIONS_DEV_PUBLIC_KEYS = [
+    bytes.fromhex(key)
+    for key in ("db995fe25169d141cab9bbba92baa01f9f2e1ece7df4cb2ac05190f37fcc1f9d",)
+]
+
+DEFINITIONS_SIGS_REQUIRED = 2
+DEFINITIONS_PUBLIC_KEYS = [
+    bytes.fromhex(key)
+    for key in (
+        "4334996343623e462f0fc93311fef1484ca23d2ff1eec6df1fa8eb7e3573b3db",
+        "a9a22cc265a0cb1d6cb329bc0e60bc45df76b9ab28fb87b61136feaf8d8fdc96",
+        "b8d2b21de27124f0511f903ae7e60e07961810a0b8f28ea755fa50367a8a2b8b",
+    )
+]
+
+
+ProofFormat = c.PrefixedArray(c.Int8ul, c.Bytes(32))
+
+
+class DefinitionPayload(Struct):
+    magic: bytes
+    data_type: EthereumDefinitionType
+    timestamp: int
+    data: bytes
+
+    SUBCON = c.Struct(
+        "magic" / c.Const(FORMAT_MAGIC),
+        "data_type" / EnumAdapter(c.Int8ul, EthereumDefinitionType),
+        "timestamp" / c.Int32ul,
+        "data" / c.Prefixed(c.Int16ul, c.GreedyBytes),
+    )
+
+
+class Definition(Struct):
+    payload: DefinitionPayload = subcon(DefinitionPayload)
+    proof: t.List[bytes]
+    sigmask: int
+    signature: bytes
+
+    SUBCON = c.Struct(
+        "payload" / DefinitionPayload.SUBCON,
+        "proof" / ProofFormat,
+        "sigmask" / c.Int8ul,
+        "signature" / c.Bytes(64),
+    )
+
+    def verify(self, dev: bool = False) -> None:
+        payload = self.payload.build()
+        root = merkle_tree.evaluate_proof(payload, self.proof)
+        cosi.verify(
+            self.signature,
+            root,
+            DEFINITIONS_DEV_SIGS_REQUIRED,
+            DEFINITIONS_DEV_PUBLIC_KEYS,
+            self.sigmask,
+        )
+
+
+class Source:
+    def fetch_path(self, *components: str) -> t.Optional[bytes]:
+        raise NotImplementedError
+
+    def get_network_by_slip44(self, slip44: int) -> t.Optional[bytes]:
+        return self.fetch_path("slip44", str(slip44), "network.dat")
+
+    def get_network(self, chain_id: int) -> t.Optional[bytes]:
+        return self.fetch_path("chain-id", str(chain_id), "network.dat")
+
+    def get_token(self, chain_id: int, address: t.AnyStr) -> t.Optional[bytes]:
+        if isinstance(address, bytes):
+            address_str = address.hex()
+        elif address.startswith("0x"):
+            address_str = address[2:]
+        else:
+            address_str = address
+
+        address_str = address_str.lower()
+
+        return self.fetch_path("chain-id", f"{chain_id}", f"token-{address_str}.dat")
+
+
+class NullSource(Source):
+    def fetch_path(self, *components: str) -> t.Optional[bytes]:
+        return None
+
+
+class FilesystemSource(Source):
+    def __init__(self, root: Path) -> None:
+        self.root = root
+
+    def fetch_path(self, *components: str) -> t.Optional[bytes]:
+        path = self.root.joinpath(*components)
+        if not path.exists():
+            LOG.info("Requested definition at %s was not found", path)
+            return None
+        LOG.info("Reading definition from %s", path)
+        return path.read_bytes()
+
+
+class UrlSource(Source):
+    def __init__(self, base_url: str = DEFS_BASE_URL) -> None:
+        self.base_url = base_url
+
+    def fetch_path(self, *components: str) -> t.Optional[bytes]:
+        url = self.base_url + "/".join(components)
+        LOG.info("Downloading definition from %s", url)
+        r = requests.get(url)
+        if r.status_code == 404:
+            LOG.info("Requested definition at %s was not found", url)
+            return None
+        r.raise_for_status()
+        return r.content
+
+
+class TarSource(Source):
+    def __init__(self, path: Path) -> None:
+        self.archive = tarfile.open(path)
+
+    def fetch_path(self, *components: str) -> t.Optional[bytes]:
+        inner_name = "/".join(components)
+        LOG.info("Extracting definition from %s:%s", self.archive.name, inner_name)
+        try:
+            return self.archive.extractfile(inner_name).read()  # type: ignore [not a known member]
+        except Exception:
+            LOG.info("Requested definition at %s was not found", inner_name)
+            return None
diff --git a/python/src/trezorlib/ethereum.py b/python/src/trezorlib/ethereum.py
index 01a9d543c..92c1c2395 100644
--- a/python/src/trezorlib/ethereum.py
+++ b/python/src/trezorlib/ethereum.py
@@ -17,8 +17,8 @@
 import re
 from typing import TYPE_CHECKING, Any, AnyStr, Dict, List, Optional, Tuple
 
-from . import exceptions, messages
-from .tools import expect, prepare_message_bytes, session
+from . import definitions, exceptions, messages
+from .tools import expect, prepare_message_bytes, session, unharden
 
 if TYPE_CHECKING:
     from .client import TrezorClient
@@ -141,15 +141,39 @@ def encode_data(value: Any, type_name: str) -> bytes:
     raise ValueError(f"Unsupported data type for direct field encoding: {type_name}")
 
 
+def network_from_address_n(
+    address_n: "Address",
+    source: definitions.Source,
+) -> Optional[bytes]:
+    """Get network definition bytes based on address_n.
+
+    Tries to extract the slip44 identifier and lookup the network definition.
+    Returns None on failure.
+    """
+    if len(address_n) < 2:
+        return None
+
+    # unharden the slip44 part if needed
+    slip44 = unharden(address_n[1])
+    return source.get_network_by_slip44(slip44)
+
+
 # ====== Client functions ====== #
 
 
 @expect(messages.EthereumAddress, field="address", ret_type=str)
 def get_address(
-    client: "TrezorClient", n: "Address", show_display: bool = False
+    client: "TrezorClient",
+    n: "Address",
+    show_display: bool = False,
+    encoded_network: Optional[bytes] = None,
 ) -> "MessageType":
     return client.call(
-        messages.EthereumGetAddress(address_n=n, show_display=show_display)
+        messages.EthereumGetAddress(
+            address_n=n,
+            show_display=show_display,
+            encoded_network=encoded_network,
+        )
     )
 
 
@@ -174,6 +198,7 @@ def sign_tx(
     data: Optional[bytes] = None,
     chain_id: Optional[int] = None,
     tx_type: Optional[int] = None,
+    definitions: Optional[messages.EthereumDefinitions] = None,
 ) -> Tuple[int, bytes, bytes]:
     if chain_id is None:
         raise exceptions.TrezorException("Chain ID cannot be undefined")
@@ -187,6 +212,7 @@ def sign_tx(
         to=to,
         chain_id=chain_id,
         tx_type=tx_type,
+        definitions=definitions,
     )
 
     if data is None:
@@ -231,6 +257,7 @@ def sign_tx_eip1559(
     max_gas_fee: int,
     max_priority_fee: int,
     access_list: Optional[List[messages.EthereumAccessList]] = None,
+    definitions: Optional[messages.EthereumDefinitions] = None,
 ) -> Tuple[int, bytes, bytes]:
     length = len(data)
     data, chunk = data[1024:], data[:1024]
@@ -246,6 +273,7 @@ def sign_tx_eip1559(
         access_list=access_list,
         data_length=length,
         data_initial_chunk=chunk,
+        definitions=definitions,
     )
 
     response = client.call(msg)
@@ -265,11 +293,16 @@ def sign_tx_eip1559(
 
 @expect(messages.EthereumMessageSignature)
 def sign_message(
-    client: "TrezorClient", n: "Address", message: AnyStr
+    client: "TrezorClient",
+    n: "Address",
+    message: AnyStr,
+    encoded_network: Optional[bytes] = None,
 ) -> "MessageType":
     return client.call(
         messages.EthereumSignMessage(
-            address_n=n, message=prepare_message_bytes(message)
+            address_n=n,
+            message=prepare_message_bytes(message),
+            encoded_network=encoded_network,
         )
     )
 
@@ -281,6 +314,7 @@ def sign_typed_data(
     data: Dict[str, Any],
     *,
     metamask_v4_compat: bool = True,
+    definitions: Optional[messages.EthereumDefinitions] = None,
 ) -> "MessageType":
     data = sanitize_typed_data(data)
     types = data["types"]
@@ -289,6 +323,7 @@ def sign_typed_data(
         address_n=n,
         primary_type=data["primaryType"],
         metamask_v4_compat=metamask_v4_compat,
+        definitions=definitions,
     )
     response = client.call(request)
 
@@ -369,11 +404,13 @@ def sign_typed_data_hash(
     n: "Address",
     domain_hash: bytes,
     message_hash: Optional[bytes],
+    encoded_network: Optional[bytes] = None,
 ) -> "MessageType":
     return client.call(
         messages.EthereumSignTypedHash(
             address_n=n,
             domain_separator_hash=domain_hash,
             message_hash=message_hash,
+            encoded_network=encoded_network,
         )
     )
diff --git a/python/src/trezorlib/merkle_tree.py b/python/src/trezorlib/merkle_tree.py
new file mode 100755
index 000000000..117382eda
--- /dev/null
+++ b/python/src/trezorlib/merkle_tree.py
@@ -0,0 +1,178 @@
+# This file is part of the Trezor project.
+#
+# Copyright (C) 2012-2022 SatoshiLabs and contributors
+#
+# This library is free software: you can redistribute it and/or modify
+# it under the terms of the GNU Lesser General Public License version 3
+# as published by the Free Software Foundation.
+#
+# 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 License along with this library.
+# If not, see <https://www.gnu.org/licenses/lgpl-3.0.html>.
+
+import typing as t
+from hashlib import sha256
+
+from typing_extensions import Protocol
+
+
+def leaf_hash(value: bytes) -> bytes:
+    """Calculate a hash of a leaf node based on its value.
+
+    See documentation for `MerkleTree` for details.
+    """
+    return sha256(b"\x00" + value).digest()
+
+
+def internal_hash(left: bytes, right: bytes) -> bytes:
+    """Calculate a hash of an internal node based on its child nodes.
+
+    See documentation for `MerkleTree` for details.
+    """
+    hash_a = min(left, right)
+    hash_b = max(left, right)
+    return sha256(b"\x01" + hash_a + hash_b).digest()
+
+
+class NodeType(Protocol):
+    """Merkle tree node."""
+
+    tree_hash: bytes
+    """Merkle root hash of the subtree rooted at this node."""
+
+    def add_to_proof_list(self, proof_entry: bytes) -> None:
+        """Add a proof entry to the proof list of this node."""
+        ...
+
+
+class Leaf:
+    """Leaf of a Merkle tree."""
+
+    def __init__(self, value: bytes) -> None:
+        self.tree_hash = leaf_hash(value)
+        self.proof: t.List[bytes] = []
+
+    def add_to_proof_list(self, proof_entry: bytes) -> None:
+        self.proof.append(proof_entry)
+
+
+class Node:
+    """Internal node of a Merkle tree.
+
+    Does not have its own proof, but helps to build the proof of its children by passing
+    the respective proof entries to them.
+    """
+
+    def __init__(self, left: NodeType, right: NodeType) -> None:
+        self.left = left
+        self.right = right
+        self.left.add_to_proof_list(self.right.tree_hash)
+        self.right.add_to_proof_list(self.left.tree_hash)
+        self.tree_hash = internal_hash(self.left.tree_hash, self.right.tree_hash)
+
+    def add_to_proof_list(self, proof_entry: bytes) -> None:
+        self.left.add_to_proof_list(proof_entry)
+        self.right.add_to_proof_list(proof_entry)
+
+
+class MerkleTree:
+    """Merkle tree for a list of byte values.
+
+    The tree is built up as follows:
+
+    1. Order the leaves by their hash.
+    2. Build up the next level up by pairing the leaves in the current level from left
+       to right.
+    3. Any left-over odd node at the current level gets pushed to the next level.
+    4. Repeat until there is only one node left.
+
+    Values are not saved in the tree, only their hashes. This allows us to construct a
+    tree with very large values without having to keep them in memory.
+
+    Semantically, the tree operates as a set, but this implementation does not check for
+    duplicates. If the same value is added multiple times, the resulting tree will be
+    different from a tree with only one instance of the value. In addition, only one of
+    the several possible proofs for the repeated value is retrievable.
+
+    Proof hashes are constructed as follows:
+
+    - Leaf node entries are hashes of b"\x00" + value.
+    - Internal node entries are hashes of b"\x01" + min(left, right) + max(left, right).
+
+    The prefixes function to distinguish leaf nodes from internal nodes. This prevents
+    two attacks:
+
+    (a) An attacker cannot misuse a proof for an internal node to claim that
+        <internal-node-entry> is a member of the tree.
+    (b) An attacker cannot insert a leaf node in the format of <internal-node-entry>
+        that is itself an internal node of a different tree. This would allow the
+        attacker to expand the tree with their own subtree.
+
+    Ordering the internal node entry as min(left, right) + max(left, right) simplifies
+    the proof format and verifier code: when constructing the internal entry, the
+    verifier does not need to distinguish between left and right subtree.
+    """
+
+    entries: t.Dict[bytes, Leaf]
+    """Map of leaf hash -> leaf node.
+
+    Use `leaf_hash` to calculate the hash of a value, or use `get_proof(value)`
+    to access the proof directly.
+    """
+    root: NodeType
+    """Root node of the tree."""
+
+    def __init__(self, values: t.Iterable[bytes]) -> None:
+        leaves = [Leaf(value) for value in values]
+        leaves.sort(key=lambda leaf: leaf.tree_hash)
+
+        if not leaves:
+            raise ValueError("Merkle tree must have at least one value")
+
+        self.entries = {leaf.tree_hash: leaf for leaf in leaves}
+
+        # build the tree
+        current_level = leaves
+        while len(current_level) > 1:
+            # build one level of the tree
+            next_level = []
+            while len(current_level) >= 2:
+                left, right, *current_level = current_level
+                next_level.append(Node(left, right))
+
+            # add the remaining one or zero nodes to the next level
+            next_level.extend(current_level)
+
+            # switch levels and continue
+            current_level = next_level
+
+        assert len(current_level) == 1, "Tree must have exactly one root node"
+        # save the root
+        self.root = current_level[0]
+
+    def get_root_hash(self) -> bytes:
+        return self.root.tree_hash
+
+    def get_proof(self, value: bytes) -> t.List[bytes]:
+        """Get the proof for a given value."""
+        try:
+            return self.entries[leaf_hash(value)].proof
+        except KeyError:
+            raise KeyError("Value not found in Merkle tree") from None
+
+
+def evaluate_proof(value: bytes, proof: t.List[bytes]) -> bytes:
+    """Evaluate the provided proof of membership.
+
+    Reconstructs the Merkle root hash for a tree that contains `value` as a leaf node,
+    proving membership in a Merkle tree with the given root hash. The result can be
+    compared to a statically known root hash, or a signature of it can be verified.
+    """
+    hash = leaf_hash(value)
+    for proof_entry in proof:
+        hash = internal_hash(hash, proof_entry)
+    return hash
diff --git a/python/src/trezorlib/messages.py b/python/src/trezorlib/messages.py
index a9ecc2810..7eab11392 100644
--- a/python/src/trezorlib/messages.py
+++ b/python/src/trezorlib/messages.py
@@ -492,6 +492,11 @@ class DebugButton(IntEnum):
     INFO = 2
 
 
+class EthereumDefinitionType(IntEnum):
+    NETWORK = 0
+    TOKEN = 1
+
+
 class EthereumDataType(IntEnum):
     UINT = 1
     INT = 2
@@ -4555,12 +4560,79 @@ class EosActionUnknown(protobuf.MessageType):
         self.data_chunk = data_chunk
 
 
+class EthereumNetworkInfo(protobuf.MessageType):
+    MESSAGE_WIRE_TYPE = None
+    FIELDS = {
+        1: protobuf.Field("chain_id", "uint64", repeated=False, required=True),
+        2: protobuf.Field("symbol", "string", repeated=False, required=True),
+        3: protobuf.Field("slip44", "uint32", repeated=False, required=True),
+        4: protobuf.Field("name", "string", repeated=False, required=True),
+    }
+
+    def __init__(
+        self,
+        *,
+        chain_id: "int",
+        symbol: "str",
+        slip44: "int",
+        name: "str",
+    ) -> None:
+        self.chain_id = chain_id
+        self.symbol = symbol
+        self.slip44 = slip44
+        self.name = name
+
+
+class EthereumTokenInfo(protobuf.MessageType):
+    MESSAGE_WIRE_TYPE = None
+    FIELDS = {
+        1: protobuf.Field("address", "bytes", repeated=False, required=True),
+        2: protobuf.Field("chain_id", "uint64", repeated=False, required=True),
+        3: protobuf.Field("symbol", "string", repeated=False, required=True),
+        4: protobuf.Field("decimals", "uint32", repeated=False, required=True),
+        5: protobuf.Field("name", "string", repeated=False, required=True),
+    }
+
+    def __init__(
+        self,
+        *,
+        address: "bytes",
+        chain_id: "int",
+        symbol: "str",
+        decimals: "int",
+        name: "str",
+    ) -> None:
+        self.address = address
+        self.chain_id = chain_id
+        self.symbol = symbol
+        self.decimals = decimals
+        self.name = name
+
+
+class EthereumDefinitions(protobuf.MessageType):
+    MESSAGE_WIRE_TYPE = None
+    FIELDS = {
+        1: protobuf.Field("encoded_network", "bytes", repeated=False, required=False, default=None),
+        2: protobuf.Field("encoded_token", "bytes", repeated=False, required=False, default=None),
+    }
+
+    def __init__(
+        self,
+        *,
+        encoded_network: Optional["bytes"] = None,
+        encoded_token: Optional["bytes"] = None,
+    ) -> None:
+        self.encoded_network = encoded_network
+        self.encoded_token = encoded_token
+
+
 class EthereumSignTypedData(protobuf.MessageType):
     MESSAGE_WIRE_TYPE = 464
     FIELDS = {
         1: protobuf.Field("address_n", "uint32", repeated=True, required=False, default=None),
         2: protobuf.Field("primary_type", "string", repeated=False, required=True),
         3: protobuf.Field("metamask_v4_compat", "bool", repeated=False, required=False, default=True),
+        4: protobuf.Field("definitions", "EthereumDefinitions", repeated=False, required=False, default=None),
     }
 
     def __init__(
@@ -4569,10 +4641,12 @@ class EthereumSignTypedData(protobuf.MessageType):
         primary_type: "str",
         address_n: Optional[Sequence["int"]] = None,
         metamask_v4_compat: Optional["bool"] = True,
+        definitions: Optional["EthereumDefinitions"] = None,
     ) -> None:
         self.address_n: Sequence["int"] = address_n if address_n is not None else []
         self.primary_type = primary_type
         self.metamask_v4_compat = metamask_v4_compat
+        self.definitions = definitions
 
 
 class EthereumTypedDataStructRequest(protobuf.MessageType):
@@ -4710,6 +4784,7 @@ class EthereumGetAddress(protobuf.MessageType):
     FIELDS = {
         1: protobuf.Field("address_n", "uint32", repeated=True, required=False, default=None),
         2: protobuf.Field("show_display", "bool", repeated=False, required=False, default=None),
+        3: protobuf.Field("encoded_network", "bytes", repeated=False, required=False, default=None),
     }
 
     def __init__(
@@ -4717,9 +4792,11 @@ class EthereumGetAddress(protobuf.MessageType):
         *,
         address_n: Optional[Sequence["int"]] = None,
         show_display: Optional["bool"] = None,
+        encoded_network: Optional["bytes"] = None,
     ) -> None:
         self.address_n: Sequence["int"] = address_n if address_n is not None else []
         self.show_display = show_display
+        self.encoded_network = encoded_network
 
 
 class EthereumAddress(protobuf.MessageType):
@@ -4752,6 +4829,7 @@ class EthereumSignTx(protobuf.MessageType):
         8: protobuf.Field("data_length", "uint32", repeated=False, required=False, default=0),
         9: protobuf.Field("chain_id", "uint64", repeated=False, required=True),
         10: protobuf.Field("tx_type", "uint32", repeated=False, required=False, default=None),
+        12: protobuf.Field("definitions", "EthereumDefinitions", repeated=False, required=False, default=None),
     }
 
     def __init__(
@@ -4767,6 +4845,7 @@ class EthereumSignTx(protobuf.MessageType):
         data_initial_chunk: Optional["bytes"] = b'',
         data_length: Optional["int"] = 0,
         tx_type: Optional["int"] = None,
+        definitions: Optional["EthereumDefinitions"] = None,
     ) -> None:
         self.address_n: Sequence["int"] = address_n if address_n is not None else []
         self.gas_price = gas_price
@@ -4778,6 +4857,7 @@ class EthereumSignTx(protobuf.MessageType):
         self.data_initial_chunk = data_initial_chunk
         self.data_length = data_length
         self.tx_type = tx_type
+        self.definitions = definitions
 
 
 class EthereumSignTxEIP1559(protobuf.MessageType):
@@ -4794,6 +4874,7 @@ class EthereumSignTxEIP1559(protobuf.MessageType):
         9: protobuf.Field("data_length", "uint32", repeated=False, required=True),
         10: protobuf.Field("chain_id", "uint64", repeated=False, required=True),
         11: protobuf.Field("access_list", "EthereumAccessList", repeated=True, required=False, default=None),
+        12: protobuf.Field("definitions", "EthereumDefinitions", repeated=False, required=False, default=None),
     }
 
     def __init__(
@@ -4810,6 +4891,7 @@ class EthereumSignTxEIP1559(protobuf.MessageType):
         access_list: Optional[Sequence["EthereumAccessList"]] = None,
         to: Optional["str"] = '',
         data_initial_chunk: Optional["bytes"] = b'',
+        definitions: Optional["EthereumDefinitions"] = None,
     ) -> None:
         self.address_n: Sequence["int"] = address_n if address_n is not None else []
         self.access_list: Sequence["EthereumAccessList"] = access_list if access_list is not None else []
@@ -4822,6 +4904,7 @@ class EthereumSignTxEIP1559(protobuf.MessageType):
         self.chain_id = chain_id
         self.to = to
         self.data_initial_chunk = data_initial_chunk
+        self.definitions = definitions
 
 
 class EthereumTxRequest(protobuf.MessageType):
@@ -4866,6 +4949,7 @@ class EthereumSignMessage(protobuf.MessageType):
     FIELDS = {
         1: protobuf.Field("address_n", "uint32", repeated=True, required=False, default=None),
         2: protobuf.Field("message", "bytes", repeated=False, required=True),
+        3: protobuf.Field("encoded_network", "bytes", repeated=False, required=False, default=None),
     }
 
     def __init__(
@@ -4873,9 +4957,11 @@ class EthereumSignMessage(protobuf.MessageType):
         *,
         message: "bytes",
         address_n: Optional[Sequence["int"]] = None,
+        encoded_network: Optional["bytes"] = None,
     ) -> None:
         self.address_n: Sequence["int"] = address_n if address_n is not None else []
         self.message = message
+        self.encoded_network = encoded_network
 
 
 class EthereumMessageSignature(protobuf.MessageType):
@@ -4921,6 +5007,7 @@ class EthereumSignTypedHash(protobuf.MessageType):
         1: protobuf.Field("address_n", "uint32", repeated=True, required=False, default=None),
         2: protobuf.Field("domain_separator_hash", "bytes", repeated=False, required=True),
         3: protobuf.Field("message_hash", "bytes", repeated=False, required=False, default=None),
+        4: protobuf.Field("encoded_network", "bytes", repeated=False, required=False, default=None),
     }
 
     def __init__(
@@ -4929,10 +5016,12 @@ class EthereumSignTypedHash(protobuf.MessageType):
         domain_separator_hash: "bytes",
         address_n: Optional[Sequence["int"]] = None,
         message_hash: Optional["bytes"] = None,
+        encoded_network: Optional["bytes"] = None,
     ) -> None:
         self.address_n: Sequence["int"] = address_n if address_n is not None else []
         self.domain_separator_hash = domain_separator_hash
         self.message_hash = message_hash
+        self.encoded_network = encoded_network
 
 
 class EthereumTypedDataSignature(protobuf.MessageType):
diff --git a/python/tests/test_merkle_tree.py b/python/tests/test_merkle_tree.py
new file mode 100644
index 000000000..3f441d4c8
--- /dev/null
+++ b/python/tests/test_merkle_tree.py
@@ -0,0 +1,108 @@
+# This file is part of the Trezor project.
+#
+# Copyright (C) 2012-2022 SatoshiLabs and contributors
+#
+# This library is free software: you can redistribute it and/or modify
+# it under the terms of the GNU Lesser General Public License version 3
+# as published by the Free Software Foundation.
+#
+# 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 License along with this library.
+# If not, see <https://www.gnu.org/licenses/lgpl-3.0.html>.
+
+import pytest
+
+import typing as t
+
+from trezorlib.merkle_tree import (
+    MerkleTree,
+    Leaf,
+    Node,
+    leaf_hash,
+    internal_hash,
+    evaluate_proof,
+)
+
+
+NODE_VECTORS = (  # node, expected_hash
+    (  # leaf node
+        Leaf(b"hello"),
+        "8a2a5c9b768827de5a9552c38a044c66959c68f6d2f21b5260af54d2f87db827",
+    ),
+    (  # node with leaf nodes
+        Node(left=Leaf(b"hello"), right=Leaf(b"world")),
+        "24233339aadcedf287d262413f03c028eb8db397edd32a2878091151b99bf20f",
+    ),
+    (  # asymmetric node with leaf hanging on second level
+        Node(left=Node(left=Leaf(b"hello"), right=Leaf(b"world")), right=Leaf(b"!")),
+        "c3727420dc97c0dbd89678ee195957e44cfa69f5759b395a07bc171b21468633",
+    ),
+)
+
+
+MERKLE_TREE_VECTORS = (
+    (  # one value
+        # values
+        [b"Merkle"],
+        # expected root hash
+        leaf_hash(b"Merkle"),
+        # expected dict of proof lists
+        {
+            b"Merkle": [],
+        },
+    ),
+    (  # two values
+        # values
+        [b"Haber", b"Stornetta"],
+        # expected root hash
+        internal_hash(
+            leaf_hash(b"Haber"),
+            leaf_hash(b"Stornetta"),
+        ),
+        # expected dict of proof lists
+        {
+            b"Haber": [leaf_hash(b"Stornetta")],
+            b"Stornetta": [leaf_hash(b"Haber")],
+        },
+    ),
+    (  # three values
+        # values
+        [b"Andersen", b"Wuille", b"Maxwell"],
+        # expected root hash
+        internal_hash(
+            internal_hash(
+                leaf_hash(b"Maxwell"),
+                leaf_hash(b"Wuille"),
+            ),
+            leaf_hash(b"Andersen"),
+        ),
+        # expected dict of proof lists
+        {
+            b"Andersen": [internal_hash(leaf_hash(b"Maxwell"), leaf_hash(b"Wuille"))],
+            b"Maxwell": [leaf_hash(b"Wuille"), leaf_hash(b"Andersen")],
+            b"Wuille": [leaf_hash(b"Maxwell"), leaf_hash(b"Andersen")],
+        },
+    ),
+)
+
+
+@pytest.mark.parametrize("node, expected_hash", NODE_VECTORS)
+def test_node(node: t.Union[Node, Leaf], expected_hash: str) -> None:
+    assert node.tree_hash.hex() == expected_hash
+
+
+@pytest.mark.parametrize("values, root_hash, proofs", MERKLE_TREE_VECTORS)
+def test_tree(
+    values: t.List[bytes],
+    root_hash: bytes,
+    proofs: t.Dict[bytes, t.List[bytes]],
+) -> None:
+    mt = MerkleTree(values)
+    assert mt.get_root_hash() == root_hash
+    for value, proof in proofs.items():
+        assert mt.get_proof(value) == proof
+        assert evaluate_proof(value, proof) == root_hash
diff --git a/tools/snippets/README.md b/tools/snippets/README.md
index 29e2180fd..11119d52a 100644
--- a/tools/snippets/README.md
+++ b/tools/snippets/README.md
@@ -17,3 +17,7 @@ These scripts do not need to have a high standard, but each of those should have
 
 ## [monero_unused_functions](./monero_unused_functions.py)
 - Find functions from Monero cryptography that are not used.
+
+## [eth_defs_unpack.py](./eth_defs_unpack.py)
+- Unpacks the definitions from a `definitions-sparse.zip` that does not contain the
+  Merkle proofs for space-saving. This format is not currently distributed.
diff --git a/tools/snippets/eth_defs_unpack.py b/tools/snippets/eth_defs_unpack.py
new file mode 100755
index 000000000..ea96c4812
--- /dev/null
+++ b/tools/snippets/eth_defs_unpack.py
@@ -0,0 +1,107 @@
+#!/usr/bin/env python3
+
+# This file is part of the Trezor project.
+#
+# Copyright (C) 2012-2022 SatoshiLabs and contributors
+#
+# This library is free software: you can redistribute it and/or modify
+# it under the terms of the GNU Lesser General Public License version 3
+# as published by the Free Software Foundation.
+#
+# 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 License along with this library.
+# If not, see <https://www.gnu.org/licenses/lgpl-3.0.html>.
+from __future__ import annotations
+
+import click
+import requests
+import zipfile
+from pathlib import Path
+
+from trezorlib import definitions, merkle_tree
+
+ZIP_FILENAME = "definitions-sparse.zip"
+
+TOPDIRS = ("chain-id", "slip44")
+
+
+class SparseZipSource(definitions.Source):
+    def __init__(self, zip: Path | zipfile.ZipFile) -> None:
+        if isinstance(zip, Path):
+            self.zip = zipfile.ZipFile(zip)
+        else:
+            self.zip = zip
+
+        # extract signature
+        self.signature = self.read_bytes("signature.dat")
+        self.root_hash = self.read_bytes("root.dat")
+
+        # construct a Merkle tree
+        entries = []
+        for name in self.zip.namelist():
+            if name.startswith("chain-id/"):
+                entries.append(self.read_bytes(name))
+        entries.sort()
+        self.merkle_tree = merkle_tree.MerkleTree(entries)
+
+        if self.root_hash != self.merkle_tree.get_root_hash():
+            raise ValueError("Failed to reconstruct the correct Merkle tree")
+
+    def read_bytes(self, path: str | Path) -> bytes:
+        with self.zip.open(str(path)) as f:
+            return f.read()
+
+    def fetch_path(self, *components: str) -> bytes | None:
+        path = "/".join(components)
+        data = self.read_bytes(path)
+        proof = self.merkle_tree.get_proof(data)
+        proof_bytes = definitions.ProofFormat.build(proof)
+        return data + proof_bytes + self.signature
+
+
+@click.command()
+@click.option(
+    "-z",
+    "--definitions-zip",
+    type=click.Path(exists=True, dir_okay=False, resolve_path=True, path_type=Path),
+    help="Local zip file with stored definitions.",
+)
+@click.argument(
+    "outdir",
+    type=click.Path(resolve_path=True, file_okay=False, writable=True, path_type=Path),
+)
+def unpack_definitions(definitions_zip: Path, outdir: Path) -> None:
+    """Script that unpacks and completes (insert missing Merkle Tree proofs
+    into the definitions) the Ethereum definitions (networks and tokens).
+
+    If no local zip is provided, the latest one will be downloaded from trezor.io.
+    """
+    if definitions_zip is None:
+        result = requests.get(definitions.DEFS_BASE_URL + ZIP_FILENAME)
+        result.raise_for_status()
+        zip = zipfile.ZipFile(result.raw)
+    else:
+        zip = zipfile.ZipFile(definitions_zip)
+
+    source = SparseZipSource(zip)
+
+    if not outdir.exists():
+        outdir.mkdir()
+
+    for name in zip.namelist():
+        if name == "signature.dat" or not name.endswith(".dat"):
+            continue
+
+        local_path = outdir / name
+        local_path.parent.mkdir(parents=True, exist_ok=True)
+        data = source.fetch_path(name)
+        assert data is not None, f"Could not read data for: {name}"
+        local_path.write_bytes(data)
+
+
+if __name__ == "__main__":
+    unpack_definitions()