Suggestions of standards added to openpgp/Gnupg/LibrePgp

[Hakun_the_eril]

Hi!
As the Baochip-x1 has the hardware to do a lot of cryptographic functions
like active zeroisation, Ed25519 signed boot, Glitch sensors, security
mesh, PV sensor, ECC-protected RAM,Algorithm-agnostic engine etc I think
that these could be added to standards.
.
I suggest:
# Authenticated Ephemeral ECDH Session Protocol and Cipher Profile Encoding
## Abstract

This document specifies a **binary authenticated ephemeral ECDH handshake**
(InitMessage and ResponseMessage), **HKDF-SHA256** key derivation with
fixed UTF-8 labels, and a **compact binary encoding** for **named cipher
profiles** (ECDHE curve, ordered AEAD layers, Shamir threshold metadata).
The handshake provides **forward secrecy** for session keys: long-term keys
authenticate ephemeral keys; ECDH uses ephemeral key pairs only. The format
is intended for submission to the OpenPGP working group as an extension
compatible in spirit with [RFC 9580](https://www.rfc-editor.org/rfc/rfc9580)
algorithm and notation registries, without reusing OpenPGP packet syntax
for the handshake octets themselves.

---

## 1. Introduction

OpenPGP ([RFC 9580](https://www.rfc-editor.org/rfc/rfc9580)) specifies
message formats, public-key encryption, signatures, and AEAD payloads. It
does **not** define a standalone **ephemeral-ephemeral ECDH** session
establishment with **mutual** authentication of ephemeral keys via
**long-term** Brainpool signing keys. This document fills that gap for
toolchains that require **forward secrecy** at the session layer while
binding identity to existing long-term OpenPGP-compatible key material
(fingerprint binding).

**Cipher profiles** name a policy: **ECDHE curve**, **ordered list of
symmetric AEAD layers** (encrypt order; decrypt reverse), and **Shamir (k,
n)** metadata for long-term key handling. Profiles serialise to a
**deterministic octet string** for storage and negotiation.

This specification is written for **interoperability** among independent
implementations that adopt the same octet layouts and labels.

---

## 2. Terminology

The key words **MUST**, **MUST NOT**, **REQUIRED**, **SHALL**, **SHALL
NOT**, **SHOULD**, **SHOULD NOT**, **RECOMMENDED**, **NOT RECOMMENDED**,
**MAY**, and **OPTIONAL** are to be interpreted as described in BCP 14
([RFC 2119](https://www.rfc-editor.org/rfc/rfc2119)) ([RFC 8174](
https://www.rfc-editor.org/rfc/rfc8174)) when, and only when, they appear
in all capitals, as shown here.

**Initiator:** The party that sends `InitMessage`.
**Responder:** The party that sends `ResponseMessage`.
**Long-term fingerprint:** SHA-256 digest (32 octets) over the uncompressed
SEC1 encoding of the long-term **verifying** public key, represented on the
wire as 64 ASCII hexadecimal digits.

---

## 3. Conventions

- All multi-octet integers are **big-endian** unless stated otherwise.
- **Curve public keys** are **uncompressed SEC1** points ([SEC 1](
https://www.secg.org/sec1-v2.pdf)).
- **ECDSA** signatures on the wire are **DER**-encoded ([RFC 5480](
https://www.rfc-editor.org/rfc/rfc5480)-style ECDSA-Sig-Value).
- **HKDF** follows [RFC 5869](https://www.rfc-editor.org/rfc/rfc5869) with
**HMAC-SHA256**.

---

## 4. Protocol and encodings

### 4.1 Protocol version

Implementations MUST support protocol version byte `0x01` for both
`InitMessage` and `ResponseMessage`. Parsers MUST reject other version
values unless a later specification defines them.

### 4.2 Curve identifiers (`curve_id`)

| `curve_id` | Curve | SEC1 uncompressed length (octets) |
|------------|--------|-----------------------------------|
| `0x01` | brainpoolP256r1 [RFC 5639](https://www.rfc-editor.org/rfc/rfc5639)
| 65 |
| `0x02` | brainpoolP384r1 | 97 |
| `0x03` | brainpoolP512r1 | 129 |

Senders MUST set `curve_id` to one of these values. Receivers MUST verify
that the ephemeral public key length field matches this table for the
received `curve_id`.

### 4.3 InitMessage (normative layout)

Serialisation order (concatenation):

| Field | Size | Description |
|-------|------|-------------|
| `version` | 1 | MUST be `0x01`. |
| `curve_id` | 1 | As in Section 4.2. |
| `epk_len` | 1 | Length of initiator ephemeral public key; MUST equal SEC1
length for `curve_id`. |
| `epk` | `epk_len` | Uncompressed SEC1 initiator ephemeral public key. |
| `fp_len` | 1 | Length of fingerprint field; MUST be `64` when fingerprint
is hex-encoded SHA-256. |
| `fingerprint` | `fp_len` | 64 ASCII hex digits (`0-9`, `a-f` preferred;
parsers MUST accept `A-F`). |
| `sig_len` | 2 | Big-endian; length of DER signature. |
| `signature` | `sig_len` | ECDSA-SHA256 over initiator **preimage**
(Section 4.5). |

The total serialised size MUST NOT exceed **512** octets.

### 4.4 ResponseMessage (normative layout)

Fields 1–8 are identical in structure to InitMessage for `version`,
`curve_id`, responder `epk_len`, responder `epk`, `fp_len`, responder
long-term `fingerprint`, and `sig_len` / `signature` for the **responder**
preimage. Additional fields:

| Field | Size | Description |
|-------|------|-------------|
| (same as Init through responder signature) | | |
| `iepk_len` | 1 | MUST equal initiator ephemeral length for `curve_id`. |
| `initiator_epk_copy` | `iepk_len` | **Copy** of initiator ephemeral
public key from InitMessage. |
| `sig_len_r` | 2 | Big-endian; length of responder DER signature. |
| `signature_r` | `sig_len_r` | ECDSA-SHA256 over responder **preimage**
(Section 4.5). |

The initiator MUST compare `initiator_epk_copy` to its own sent ephemeral
key using a **constant-time** equality check.

### 4.5 Signature preimages (ECDSA-SHA256)

Hash input is **raw concatenation** (no length prefixes except where
lengths are fixed by `curve_id`):

- **Initiator preimage:** `version || curve_id ||
initiator_ephemeral_sec1_uncompressed`
- **Responder preimage:** `version || curve_id || responder_ephemeral_sec1
|| initiator_ephemeral_sec1`

The hash function is **SHA-256**; ECDSA is Brainpool with the long-term
signing key associated with the fingerprint.

### 4.6 ECDH shared secret and HKDF

1. **ECDH** is performed on the agreed curve; the shared secret is the
**x**-coordinate of the resulting point, packed to a fixed width per curve;
**interoperating peers MUST use identical packing** (see Appendix A for
conformance vectors).
2. **HKDF-Extract** salt: lexicographic ordering of the two ephemeral
public key byte strings: if `epk_initiator <= epk_responder` (lexicographic
octet compare), salt = `epk_initiator || epk_responder`; else salt =
`epk_responder || epk_initiator`. If the salt is empty in a helper,
implementations MUST use 32 zero octets as HMAC key per [RFC 5869](
https://www.rfc-editor.org/rfc/rfc5869) empty-salt handling where
applicable.
3. **HKDF-Expand** with **SHA-256**; output length **32** octets per
derived key unless a profile specifies otherwise.

**HKDF `info` labels (UTF-8, exact octets):**

| Label (exact) | Derived key role |
|---------------|------------------|
| `openpgp-ephemeral-session/payload-i2r/v1` | Payload AEAD, initiator to
responder |
| `openpgp-ephemeral-session/payload-r2i/v1` | Payload AEAD, responder to
initiator |
| `openpgp-ephemeral-session/gdss-mask/v1` | Optional GDSS masking stream |
| `openpgp-ephemeral-session/gdss-sync/v1` | Optional GDSS sync |
| `openpgp-ephemeral-session/gdss-timing/v1` | Optional GDSS timing |
| `openpgp-ephemeral-session/mac/v1` | Optional HMAC key |

Implementations MUST NOT reuse labels for distinct key roles. Changing any
label octet breaks interoperability.

### 4.7 Cipher profile compact encoding

A **cipher profile** serialises as:

| Field | Size | Description |
|-------|------|-------------|
| `name_len` | 1 | Length of `name`; MUST be ≤ 64. |
| `name` | `name_len` | UTF-8 profile identifier (e.g. `standard`,
`conservative-shamir`). |
| `desc_len` | 1 | Length of description; MUST be ≤ 128. |
| `description` | `desc_len` | UTF-8 human-readable text. |
| `curve_id` | 1 | Same as Section 4.2 (ECDHE curve for session). |
| `layer_count` | 1 | Number of AEAD layers; MUST be 1–4. |
| `layer_id` × `layer_count` | each 1 | Symmetric layer type (see below). |
| `shamir_k` | 1 | Shamir threshold **k** (1–255). |
| `shamir_n` | 1 | Shamir total **n** (1–255); MUST satisfy `k ≤ n`. |

**Layer type IDs (`layer_id`):**

| `layer_id` | Algorithm |
|------------|-----------|
| `0x01` | AES-256-GCM |
| `0x02` | ChaCha20-Poly1305 [RFC 8439](
https://www.rfc-editor.org/rfc/rfc8439) |
| `0x03` | Twofish-256 (EtM construction as in implementation) |
| `0x04` | Serpent-256 (EtM construction as in implementation) |

**Encryption order:** layers are applied **in array order** (first layer =
innermost plaintext); **decryption** applies **reverse** order.
**Authentication** MUST be verified at each layer; failure MUST abort
decryption.

---

## 5. Security Considerations

**Threat model:** The handshake aims for **confidentiality** and
**integrity** of session keys against passive and active network attackers,
under the assumption that long-term signing keys remain uncompromised
during the handshake. **Forward secrecy** holds for past sessions if
ephemeral private keys are destroyed after use.

**Limitations:**

- This document does **not** specify transport binding to TLS or OpenPGP;
bindings are application-defined.
- **Side-channel** resistance of ECDH and ECDSA depends on the
cryptographic library and hardware.
- **Downgrade** of `curve_id` or profile MUST be prevented by policy at a
higher layer if multiple options are offered.
- **GDSS** optional keys are product-specific; implementations MAY omit
derivation of those labels.

**Guidance:** Implementations SHOULD use constant-time comparison for
`initiator_epk_copy`. Implementations MUST zeroise ephemeral private keys
after ECDH.

---

## 6. IANA Considerations

This document requests IANA to create or extend registries under the
**OpenPGP** umbrella (exact registry names subject to IESG and IANA review):

| Registry | Request |
|----------|---------|
| **Ephemeral ECDH extension `curve_id`** (or sub-registry of Experimental
/ Private Use) | Reserve `0x01`–`0x03` as in Section 4.2; future values via
IETF Review or Specification Required. |
| **Cipher profile `layer_id`** | Reserve `0x01`–`0x04` as in Section 4.7. |
| **HKDF info labels** | Register the six UTF-8 strings in Section 4.6 as
**well-known** `info` labels for this protocol (reference: this document). |
| **Notation names** (optional OpenPGP binding) | Register `
openpgp-cipher-profile at ietf.org` (example) for embedding profile
fingerprints in signature notations if WG desires OpenPGP message binding. |

Until IANA assigns numbers, private experimentation MAY use
implementation-defined prefixes with **no** guarantee of global uniqueness.

---

## 7. References

### 7.1 Normative References

| ID | Reference |
|----|-----------|
| RFC2119 | Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997. |
| RFC5639 | Lochter, M. and Merkle, J., "Elliptic Curve Cryptography (ECC)
Brainpool Standard Curves and Curve Generation", RFC 5639, March 2010. |
| RFC5869 | Krawczyk, H. and Eronen, P., "HMAC-based Extract-and-Expand Key
Derivation Function (HKDF)", RFC 5869, May 2010. |
| RFC8174 | Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key
Words", BCP 14, RFC 8174, May 2017. |
| RFC8439 | Nir, Y. and Langley, A., "ChaCha20 and Poly1305 for IETF
Protocols", RFC 8439, June 2018. |
| SEC1 | SECG, "Elliptic Curve Cryptography", SEC 1, Version 2.0. |

### 7.2 Informative References

| ID | Reference |
|----|-----------|
| RFC9580 | Wussler, S., et al., "OpenPGP", RFC 9580, July 2024. |

---

## Appendix A. Interoperability test anchors

Implementations MUST demonstrate interoperability using **fixed test
vectors** (to be published in a future revision of this document or a
companion **Implementation Techniques** note). Until those vectors are
published, conformance tests SHOULD cover:

- Handshake serialisation round-trip for `InitMessage` and
`ResponseMessage` per Sections 4.3–4.4.
- HKDF label distinctness (no two roles share the same `info` string).
- Brainpool ECDH and ECDSA with [RFC 5639](
https://www.rfc-editor.org/rfc/rfc5639) test vectors where applicable.
- Side-channel review of comparison and scalar paths
(implementation-dependent).



# Shamir Secret Sharing for OpenPGP-Adjacent Key Material: Share Format and
Field Arithmetic
## Abstract

This document specifies **Shamir’s Secret Sharing** over **GF(256)** for
secrets of **16 to 64 octets**, including **share index** and **share
value** layout, **K-of-N** metadata, a **textual armour** format (**OPENPGP
SHAMIR SHARE**), and **HKDF** labelling for post-recovery key derivation.
It is intended for interoperability with hardware tokens and host tools
that split or recover OpenPGP-relevant signing material. The format
complements [RFC 9580](https://www.rfc-editor.org/rfc/rfc9580) OpenPGP
messages by defining a **container** for shares that MAY be transported
inside experimental packets or as standalone files.

---

## 1. Introduction

Shamir’s method (1979) splits a secret into **N** shares such that any
**K** shares suffice for reconstruction. This document **normatively**
defines the **field**, **byte-wise sharing** construction, **wire
formats**, and **armour** using **GF(256)** arithmetic compatible with the
**AES** field (see `vsss_rs::Gf256` or equivalent **bit-identical**
implementation).

OpenPGP ([RFC 9580](https://www.rfc-editor.org/rfc/rfc9580)) does not
define threshold splits of long-term private key material. This
specification provides a **concrete** format implementors can adopt pending
WG adoption of OpenPGP-native packet types.

---

## 2. Terminology

The key words **MUST**, **MUST NOT**, **REQUIRED**, **SHALL**, **SHALL
NOT**, **SHOULD**, **SHOULD NOT**, **RECOMMENDED**, **NOT RECOMMENDED**,
**MAY**, and **OPTIONAL** are to be interpreted as described in BCP 14
([RFC 2119](https://www.rfc-editor.org/rfc/rfc2119)) ([RFC 8174](
https://www.rfc-editor.org/rfc/rfc8174)) when, and only when, they appear
in all capitals.

**K:** Threshold number of shares required to reconstruct.
**N:** Total number of shares generated.
**Share index:** Non-zero octet in `1..=255` identifying the polynomial
evaluation point.

---

## 3. Conventions

- **Field:** GF(256) with the **same** reduction polynomial as the AES
block field; implementations MUST produce **bit-identical** results to a
**reference** `vsss_rs::Gf256` (or equivalent) definition across all split
and recover operations.
- **Secret length:** `L` octets where **16 ≤ L ≤ 64**. All shares for one
split MUST use the same `L`.
- **Threshold:** Integers **K** and **N** MUST satisfy **1 ≤ K ≤ N ≤ 255**.

---

## 4. Mathematical construction (normative)

For each byte position **j** in `0..L` independently:

1. Let **s[j]** be the secret byte at position **j** (treated as an element
of GF(256)).
2. Construct a polynomial **P** of degree **K − 1** with coefficients in
GF(256): the constant term is **s[j]**; coefficients **1..K−1** MUST be
sampled uniformly at random using a cryptographically secure RNG.
3. For share index **i** (1 ≤ **i** ≤ **N**), the share byte at position
**j** is **P(i)** evaluated in GF(256) with **i** mapped to the field
element **i**.

**Recovery:** Given **K** distinct shares with indices **i_1…i_K** and
matching value vectors, the secret byte **s[j]** is **P(0)** computed via
Lagrange interpolation in GF(256).

Implementations MUST reject duplicate share indices during recovery.
Implementations MUST NOT infer **K** solely from the number of shares
without explicit parameter matching.

---

## 5. Binary share payload (normative minimum)

A **share value** in memory or binary transport is:

| Field | Size (octets) | Description |
|-------|----------------|-------------|
| `index` | 1 | Share index **i**, MUST be in `1..=255`. |
| `value` | `L` | **16 ≤ L ≤ 64**; polynomial evaluation bytes aligned with
Section 4. |

The tuple `(index, value)` together with known **K**, **N**, and secret
length **L** are REQUIRED for recovery.

---

## 6. OPENPGP SHAMIR SHARE armour (normative text format)

Armour is **ASCII** and MUST use the following structure:

1. Line: `-----BEGIN OPENPGP SHAMIR SHARE-----`
2. Line: `Version: 1`
3. Line: `Profile: ` + UTF-8 profile name (policy label).
4. Line: `Threshold: ` + decimal **K**.
5. Line: `Total: ` + decimal **N**.
6. Line: `Index: ` + decimal share index **i**.
7. Line: `Fingerprint: ` + hexadecimal fingerprint of associated long-term
key (implementation-defined encoding).
8. Line: `Created: ` + RFC 3339 timestamp.
9. Empty line.
10. Base64 ([RFC 4648](https://www.rfc-editor.org/rfc/rfc4648)) body
encoding **only** the **`value`** octets (not the index).
11. Line: `-----END OPENPGP SHAMIR SHARE-----`

Parsers MUST verify Base64 and length constraints. The **index** in the
header MUST match the share; implementations MUST treat mismatch as fatal.

**Note:** The index appears in the header; the **value** is Base64-only.
Implementations MAY alternatively encode `index || value` in Base64 in a
future version—**Version: 1** as specified ties index to header fields.

---

## 7. HKDF after recovery

When expanding recovered material into operational keys, implementations
**MUST** use [RFC 5869](https://www.rfc-editor.org/rfc/rfc5869) with
**SHA-512** and `info` exactly:

`openpgp-shamir/vault-recovery/v1` (UTF-8 octets)

This label MUST NOT be reused for unrelated derivations.

---

## 8. Mapping to OpenPGP (informative operations)

Implementations MAY:

- Wrap armour in a **MIME** part or **file** attachment.
- Place a **notation** on a signature: e.g. name
`shamir-share-digest at openpgp.example` with a SHA-256 digest of the armour
body (policy-specific).
- Encapsulate binary payloads in **Private/Experimental** OpenPGP packets
([RFC 9580](https://www.rfc-editor.org/rfc/rfc9580) private packet
conventions) once IANA assigns packet tags (Section 10).

This document **does not** require OpenPGP implementations to parse shares
inside literal data packets; it defines the **share format** independent of
OpenPGP framing.

---

## 9. Security Considerations

**Threat model:** Shares protect against single-point loss of the full
secret only if **K** shares are required and **custody** is separated. An
attacker with **K** shares reconstructs the secret.

**Limitations:**

- **GF(256)** Shamir is **not** post-quantum for the share reconstruction
math; long-term risk is the same class as symmetric key recovery.
- **RNG** quality for polynomial coefficients MUST be CSPRNG-backed.
- **Armour** is **not encrypted**; implementations SHOULD encrypt shares at
rest (e.g. OpenPGP-encrypted file) when distributed.
- **Fingerprint** binding does not prevent substitution unless the
fingerprint is verified out-of-band.

**Guidance:** Implementations MUST zeroise recovered secrets after use.
Implementations SHOULD use **constant-time** comparison where comparing
share metadata to secrets.

---

## 10. IANA Considerations

This document requests:

| Item | Action |
|------|--------|
| **OpenPGP Packet Tag** | Assign an **Experimental** or **Private** packet
tag for **OPENPGP-SHAMIR-SHARE** binary blob (optional encapsulation of
Sections 5–6), or reserve from private-use range per [RFC 9580](
https://www.rfc-editor.org/rfc/rfc9580) IANA procedures. |
| **Notation name** | Register `openpgp-shamir-share-v1 at ietf.org` (example)
for signature notations pointing to external share custody. |
| **HKDF info registry** | Register `openpgp-shamir/vault-recovery/v1` as a
well-known `info` label for Shamir recovery KDF. |
| **Media type** (optional) | `application/vnd.openpgp.shamir-share` for
armour files. |

Exact numbers are **TBD** pending IESG and IANA review.

---

## 11. References

### 11.1 Normative References

| ID | Reference |
|----|-----------|
| RFC2119 | Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119. |
| RFC4648 | Josefsson, S., "The Base16, Base32, and Base64 Data Encodings",
RFC 4648. |
| RFC5869 | Krawczyk, H. and Eronen, P., "HKDF", RFC 5869. |
| RFC8174 | Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key
Words", BCP 14, RFC 8174. |
| SHAMIR79 | Shamir, A., "How to share a secret", Communications of the
ACM, 1979. |

### 11.2 Informative References

| ID | Reference |
|----|-----------|
| RFC9580 | "OpenPGP", RFC 9580. |

---

## Appendix A. Interoperability test anchors

Implementations MUST validate split/recover using **published test
vectors** (to be added in a future revision). Conformance tests SHOULD
include:

- Round-trip split and recover for fixed K, N, L.
- Rejection of duplicate `index` values.
- Boundary checks for L in {16, 64}.
- **Fuzz** and timing-hardening (implementation-dependent).

---

## Document history

| Version | Notes |
|---------|--------|
| 00 | Initial proposal: GF(256) Shamir, binary share payload, OPENPGP
SHAMIR SHARE armour Version 1. |
The baochips specs can be found here: https://www.baochip.com/   Or here:
https://github.com/Supermagnum/Baochip-1x-firmware
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