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Signed Data Standard

ERC 191. Martin Holst Swende , Nick Johnson.

ERC 191, Signed Data Standard. We propose the following format for signed_data 0x19 .

Status in the source: Final. A reading of the public specification, not a copy of it and not a certification.

Signed Data Standard is worth reading for the rule it actually adds: We propose the following format for signed_data 0x19 .
Evidence
Primary paper
Re-measured
No
Assumptions
3
Records linked
3

Code

Source, repository, and what is actually hosted

  • ERC 191https://eips.ethereum.org/EIPS/eip-191
  • The source URL is not a GitHub repository. No code remote is invented.
  • Full text is not mirrored. Public availability is not a licence to copy the file onto this site.
  • Add to a reading list

01 Claim ledger

What the paper is allowed to say

Each row is a sentence already in the study. The status is the same on every row: a model claim, not a live measurement.

  1. Claim 01 · Paper model

    The rule

    We propose the following format for signed_data 0x19 .

  2. Claim 02 · Paper model

    What was already failing

    A signature that does not commit to what the user saw can be replayed into a different spend, a different chain, or a different message.

  3. Claim 03 · Paper model

    What the number does not mean

    The source marks this final. That is a statement about the text, not a promise that every wallet or node has shipped it.

  4. Claim 04 · Paper model

    What a builder should be able to point at

    An implementation either constrains signed_data, RLP, personal_sign or it is a different design.

02 Three cuts

Observation, model, falsifier

A desk does not stop at the summary. Each claim is cut three ways, using only this study's own assumptions and checks. Nothing here is a new figure.

  1. 01 The rule

    Observation

    What the study says

    We propose the following format for signed_data 0x19 .

    Model

    What has to hold

    The object that has to change is signed_data, RLP, personal_sign. A neighbouring document with a similar name is not this one.

    Falsifier

    What would retire it

    What is covered by the signed bytes in Signed Data Standard?

  2. 02 What was already failing

    Observation

    What the study says

    A signature that does not commit to what the user saw can be replayed into a different spend, a different chain, or a different message.

    Model

    What has to hold

    The object that has to change is signed_data, RLP, personal_sign. A neighbouring document with a similar name is not this one.

    Falsifier

    What would retire it

    Can the same signature be replayed on another chain, account, or message?

  3. 03 What the number does not mean

    Observation

    What the study says

    The source marks this final. That is a statement about the text, not a promise that every wallet or node has shipped it.

    Model

    What has to hold

    You are implementing ERC 191 at the status the text itself states: Final.

    Falsifier

    What would retire it

    Which primitive does the text require: signed_data, RLP, personal_sign?

  4. 04 What a builder should be able to point at

    Observation

    What the study says

    An implementation either constrains signed_data, RLP, personal_sign or it is a different design.

    Model

    What has to hold

    The object that has to change is signed_data, RLP, personal_sign. A neighbouring document with a similar name is not this one.

    Falsifier

    What would retire it

    What is covered by the signed bytes in Signed Data Standard?

03 Sequence

One action, as an operating tape

  1. 01Open ERC 191 and read the status line before the examples.
  2. 02Write down the rule in one sentence. A fair version of that sentence is: We propose the following format for signed_data 0x19 .
  3. 03Name the object that changes: signed_data, RLP, personal_sign.
  4. 04Ask what an old client, an old contract, or an offline counterparty does. If the document is silent, the silence is part of the design.

04 Load-bearing

The argument, and where a pitch drops it

  1. What the text is allowed to settle

    The cut

    Ethereum Request for Comment 191 can settle the shape of Signed Data Standard. It cannot settle whether a later client, a later fork, or a later wallet still does this.

    Why it carries weight

    If this cut is skipped, the paper's name is being used without the mechanism that makes the name mean anything.

    Where it is dropped

    Wallet support is not the same as consensus validity.

  2. What this page will not pretend

    The cut

    There is no benchmark, no adoption number, and no claim that the mechanism is safe outside the assumptions written in the source.

    Why it carries weight

    If this cut is skipped, the paper's name is being used without the mechanism that makes the name mean anything.

    Where it is dropped

    The source marks this final. That is a statement about the text, not a promise that every wallet or node has shipped it.

05 Register

What has to be true

  • Model · Not re-measured

    You are implementing ERC 191 at the status the text itself states: Final.

  • Data · Not re-measured

    The object that has to change is signed_data, RLP, personal_sign. A neighbouring document with a similar name is not this one.

  • Model · Not re-measured

    Wallet support is not the same as consensus validity.

06 Divergence

What happened after the paper

The source marks this final. That is a statement about the text, not a promise that every wallet or node has shipped it. Later documents can narrow, replace, or ignore this one. Cite the number you mean.

A later client, parameter set, or reward formula is a different object. Cite this paper for the mechanism. Cite a primary release for the network. This desk has not re-run the proof.

07 Pre-mortem

What to check before you use the idea

  4. 0 of 3 marked on this browser. A mark is a reading note, not a pass, a rating, or a recommendation.

08 Anatomy

The paper, in the order a builder needs

The problem it names

A signature that does not commit to what the user saw can be replayed into a different spend, a different chain, or a different message.

What the design proposes

  • We propose the following format for signed_data 0x19 .
  • The initial 0x19 byte is intended to ensure that the signed_data is not valid RLP.
  • > For a single byte whose value is in the [0x00, 0x7f] range, that byte is its own RLP encoding.

How the mechanism is specified

  • Taken from the specification, the next constraint is: The initial 0x19 byte is intended to ensure that the signed_data is not valid RLP.
  • Locate signed_data, RLP, personal_sign in ERC 191 and apply it to one transaction or call.
  • Then check the failure the class of rule always has: a node that did not upgrade, a reverted call, a replayed signature, or a peer that does not speak the message.

What this page does not treat as proven

  • A signature scheme is not a privacy system. It hides the signer only if the protocol says so.
  • Wallet support is not the same as consensus validity.
  • The source marks this final. That is a statement about the text, not a promise that every wallet or node has shipped it.

Why the desk still reads it

Use ERC 191 when a pitch says 'Signed Data Standard' without saying whether the rule is consensus, policy, or an interface. The number is the citation. The pitch is not.

09 Lexicon

Terms, opened into the record

ERC 191
The public text titled Signed Data Standard.
Final
The document's own label for how finished the text is. It is not a market fact.

10 Repository

Every linked record on this page

Underlined words open a page that already exists: a concept, a protocol profile, a failure record, or another paper. If a word is not underlined, this desk does not have a record for it.

Protocols

This is Blockchain Lab's reading of a public design paper. It is not the paper, not a copy of it, and not an offer of tokens, equity, custody or a partnership. Later network behaviour can diverge from the text. Nothing here is investment, legal or technical advice.

Research status: Design paper. Last reviewed: 1 October 2026. This is a reading of a public paper, not investment, legal or security advice.