# SNIP-43 Unified Bech32m Addresses and Viewing Keys for Starknet
**URL:** https://community.starknet.io/t/snip-43-unified-bech32m-addresses-and-viewing-keys-for-starknet/116001
**Category:** SNIPs
**Created:** [October 8, 2025, 1:22pm UTC](https://community.starknet.io/t/snip-43-unified-bech32m-addresses-and-viewing-keys-for-starknet/116001 "2025-10-08T13:22:18Z")
**Posts on this page:** 2
**Page:** 1
### Author:  [@abdel.1559](https://community.starknet.io/u/abdel.1559)
#### Post date: [October 8, 2025, 1:22pm UTC](https://community.starknet.io/t/snip-43-unified-bech32m-addresses-and-viewing-keys-for-starknet/116001/1 "2025-10-08T13:22:18Z")
[SNIP LINK](https://github.com/starknet-io/SNIPs/blob/main/SNIPS/snip-43.md)
## Abstract
This SNIP defines **Unified Addresses (UA)** for Starknet using **Bech32m** with HRPs:
- `strk` — public address receiver (legacy‑compatible, checksummed)
- `strkx` — shielded receiver (opaque, versioned)
- `strku` — **Unified Address** that _bundles one or more receivers_ and guides senders to the highest‑privacy option they support
It also defines **Unified Viewing Keys** (full/incoming/outgoing) and **Detection Keys** to enable scalable scanning for a future **multi‑asset shielded pool** (MASP). This proposal is **Interface‑only** : on‑chain address/types remain `felt252`. Cryptographic circuit details for the MASP are out of scope and will be specified in a follow‑up Core SNIP.
## Motivation
- **Privacy‑by‑default UX:** Users should share a single address string while wallets automatically choose a shielded receiver when possible.
- **Safety & compatibility:** Bech32m gives robust checksums and HRP scoping; hex remains accepted for backward compatibility.
- **Scalability:** Viewing/Detection Keys let wallets scan at high throughput without trial‑decrypting every output.
- **Multi‑asset reality:** Starknet is multi‑asset; UA avoids per‑asset privacy silos and confusing multiple address formats.
## Specification
> The key words “MUST”, “MUST NOT”, “REQUIRED”, “SHALL”, “SHALL NOT”, “SHOULD”, “SHOULD NOT”, “RECOMMENDED”, “MAY”, and “OPTIONAL” in this document are to be interpreted as described in RFC 2119.
### 1. Encodings and HRPs
All strings use **Bech32m** (separator `'1'`, checksum length 6). Mixed case **MUST** be rejected. Unless otherwise stated:
- **Public** : `strk1` + data (versioned)
- **Shielded** : `strkx1` + data (versioned, opaque)
- **Unified** : `strku1` + data (versioned, TLV list of receivers)
**Length limits** :
- `strk` and `strkx`: **MUST** be ≤ **90** characters.
- `strku`: MAY exceed 90; wallets **SHOULD** display with copy buttons/QRs and line‑wrap when necessary.
All payloads start with a **5‑bit version** `v` followed by kind‑specific bytes encoded with `convertbits(8→5, pad=true)`.
### 2. Public receiver (`hrp = "strk"`, v0)
**Input** : canonical 251‑bit Starknet address `A` (`felt252`, big‑endian).
**Encoding** :
1. Serialize `A` to **32 bytes** big‑endian (left‑pad with zeros).
2. Enforce top 5 bits zero (follows from `A < 2^251`).
3. Data = `v=0 || convertbits(bytes,8→5,pad=true)`.
**Decoding** :
- Verify Bech32m and case.
- Extract `v` (MUST be 0); reconvert to **exactly 32 bytes** ; reject if top 5 bits non‑zero.
This yields a **canonical** textual form for each on‑chain address.
### 3. Shielded receiver (`hrp = "strkx"`, v0)
**Body** : opaque, versioned bytes for a MASP‑style note receiver (e.g., diversifier, pk\_d, network tag, memo policy).
Exact structure is defined in a **separate Core SNIP (MASP)**. This SNIP only defines the **container** :
- Encoding: `v || convertbits(body,8→5,pad=true)`
- Decoding: verify Bech32m; return `v` and raw `body` to higher layers.
Wallets/explorers **MUST NOT** reinterpret `strkx` as public addresses.
### 4. Unified Address (UA) (`hrp = "strku"`, v0)
A UA bundles multiple receivers so senders can pick the most private one they support.
#### 4.1 UA payload layout (v0)
```bash
ua_v0 := flags (1 byte) || receiver_list
receiver_list := receiver_entry || receiver_entry || ...
receiver_entry := type (1 byte) || length (2 bytes, big-endian) || value (length bytes)
```
- `flags` (bitfield):
- bit 0 (PUBLIC\_FALLBACK\_ALLOWED): if 0, wallets MUST prompt before using any public receiver.
- other bits **MUST** be zero for v0 and **MUST** be ignored if unknown.
- `type` (receiver type codes, v0):
- `0x01` — **Shielded MASP v0** (`strkx` payload bytes)
- `0x00` — **Public v0** (32‑byte canonical Starknet address)
- A UA **MAY** contain multiple shielded receivers (future pools/versions) and optionally a public receiver for compatibility.
**Bech32m data** : `v=0 || convertbits(ua_v0,8→5,pad=true)`.
#### 4.2 Receiver selection rules (normative)
Given a UA, a sender wallet:
1. Builds a **capability set** of receivers it supports for the **asset being sent**.
2. Sorts supported receivers by **priority** (highest first):
**Shielded MASP v0** \> **Public v0**.
1. Picks the first supported receiver.
- If the first supported is **public** and UA `PUBLIC_FALLBACK_ALLOWED == 0`, the wallet **MUST** prompt for explicit consent before proceeding.
Wallets **MUST** ignore unknown `type` values (future‑proofing) while preserving them when re‑serializing UAs.
### 5. Viewing Keys & Detection Keys
To enable scalable scanning and optional audits, define the following textual containers (Bech32m):
- **Unified Full Viewing Key** : `strkvu1` + data
Contains one or more per‑receiver viewing keys (TLV list mirroring UA). Grants read access to **incoming + outgoing** metadata needed for full accounting.
- **Unified Incoming Viewing Key** : `strkvi1` + data
Allows detection and decryption of **incoming** notes only (no spend).
- **Detection Key** : `strkdk1` + data
A lightweight key (derived from the incoming viewing key) that lets light clients filter outputs using short **detection tags** without trial decryption.
**Notes** :
- Exact key derivation (KDFs, PRFs, domain sep) and ciphertext formats are defined in the MASP Core SNIP.
- Detection tags MUST be **unlinking** and short (e.g., 1–2 bytes) to bound false positives while keeping privacy; the tag computation function is normative in the MASP SNIP.
### 6. MASP Hooks (non‑normative sketch; to be specified in Core SNIP)
- **Assets** : each ERC‑20‑like asset has a 32‑byte `asset_id` (Poseidon‑based or equivalent) preventing collisions across networks/classes.
- **Notes** : commitments include `(diversifier, pk_d, value, asset_id, rho, r, …)`.
- **Nullifiers** : derived from a nullifier key and note position; unique on spend.
- **Actions** : transactions carry spends/outputs, encrypted payloads, detection tags, and a fee action.
- **Fees** : default in STRK; optionally any asset (allow‑list).
- **Relaying/AA** : define a “private paymaster” flow where a ZK proof authorizes gas sponsorship without linking to the sender; optionally include Privacy‑Pools‑style innocence proofs.
This SNIP references these concepts only to shape the **interfaces** above.
### 7. RPC & SDK Changes
**Parsing & formatting:**
- All endpoints that accept “addresses” **MUST** accept:
- canonical hex `0x…` (legacy)
- `strk…`, `strkx…`, or `strku…` (Bech32m)
- Add optional request/response parameter `encoding: "hex" | "bech32m"`; default **SHOULD** remain hex in responses for backward compatibility.
**Discovery:**
- Add `starknet_parseAddress(string)` →
```bash
{
kind: "public" | "shielded" | "unified",
hrp: "strk" | "strkx" | "strku",
version: 0,
// for public:
hex: "0x…",
// for shielded:
payload: "0x…", // opaque bytes
// for unified:
flags: 0|1,
receivers: [
{ type: "masp0", payload: "0x…" },
{ type: "public0", hex: "0x…" }
]
}
```
- SDKs **SHOULD** expose UA builders and selection logic as a shared utility.
**Explorers/Indexers:**
- Dual search index (hex ↔ Bech32m).
- Display Bech32m by default with a “copy‑as‑hex” fallback.
### 8. Backwards Compatibility
- Protocol/consensus unchanged; on‑chain still uses `felt252`.
- Hex continues to work everywhere.
- Migration path:
1. Ship libraries + test vectors.
2. Wallets/SDKs accept both; display Bech32m by default.
3. Explorers adopt dual indexing.
4. RPC opt‑in for Bech32m outputs.
### 9. Security Considerations
- **Checksum & case discipline** : Bech32m rejects mixed case and detects typos; wallets MUST surface checksum errors prominently.
- **HRP spoofing** : UIs MUST highlight HRP prominently; never auto‑coerce `strku`→`strk` or `strkx` without explicit consent.
- **Public fallback** : UA’s `PUBLIC_FALLBACK_ALLOWED` defaults to **0** ; wallets MUST prompt before sending publicly.
- **Key scope** : Viewing/Detection Keys MUST be derivable in a way that prevents spend authority; documentation MUST make scopes explicit.
- **Network binding** : Implementations MUST bind HRPs to the active network (e.g., mainnet vs testnet HRPs in a future SNIP) to avoid cross‑network misuse.
- **P2P/Mempool surfaces** : When a MASP is introduced, client/network‑layer hardening (timing obfuscation, relays) is REQUIRED; tracked in the Core SNIP.
### 10. Test Cases
The following **v0** examples are provided for interoperability testing. (All are valid Bech32m strings; round‑trips MUST pass.)
#### 10.1 Public address round‑trip
- Input hex: `0x12235445`
- `strk` (v0) **encode →**
```bash
strk1qqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqy3r23zsp63rc2
```
- **Decode →** hex `0x0000000000000000000000000000000000000000000000000000000012235445`
(top 5 bits zero; interpret as `< 2^251`)
#### 10.2 Shielded receiver (opaque, sample payload)
- `strkx` (v0) **example →**
```bash
strkx1q8yxgcltjgu6zekqspuhk7acdvht8pevwqdga3t5wfah2cdp0cgcm0vy8zm4nlsfgj6uky7qkyjz
```
- Decoding yields `version = 0` and opaque bytes (length 43 in this sample).
#### 10.3 Unified Address with shielded + public
- `strku` (v0) **example (line‑wrapped for readability)** →
```bash
strku1qqqqsq2eepjx86uj8xskdsyq09ahhwrt96ecwtrsr28v2arj0d6krg
t7zxxmmppckavluz2ykh93qqqpqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqq
qqqqqqqqqqqqy3r23zsgnztfs
```
- Contains two receivers (in TLV):
- `type=0x01` MASP v0 (opaque 43‑byte payload)
- `type=0x00` Public v0 (32‑byte canonical address for fallback)
- `flags=0x00` → public fallback **requires explicit consent**.
#### 10.4 Negative tests
- Change any single character in the strings above → checksum **MUST** fail.
- Mixed case (e.g., `Strk1…`) → **reject**.
- For `strk` v0: if decoded 32‑byte payload has any top‑5 bits set → **reject**.
(Reference vectors for more addresses, UA permutations, and mutated strings SHOULD be added under `assets/snip-xxx/`.)
## Rationale
- **Why Bech32m?** Strong checksum and forward compatibility for non‑legacy payloads; fits HRP namespace and QR‑friendly UX.
- **Why UA?** Prevents the “too many address formats” problem. Senders don’t need to understand pool versions; they just use the best receiver they support.
- **Why TLV?** Extensible and minimally prescriptive; unknown receiver types can be kept and forwarded.
- **Length rule for UA:** Real‑world UAs exceed 90 chars; we explicitly allow longer strings and require wallets to handle them ergonomically.
- **Viewing/Detection Keys:** Essential for practical light‑client UX; they keep scanning cost sublinear while maintaining privacy boundaries.
## Reference Implementation (outline)
Language‑agnostic utilities (~200 LOC typical):
- `convertbits(in: bytes, 8→5, pad=true)` and inverse
- Bech32m encode/decode (constant `0x2bc830a3`)
- UA TLV encoder/decoder and selection logic
- Public v0 canonicalizer (32‑byte big‑endian; top‑bit checks)
Cairo is **not required** (encoding is off‑chain), but a Cairo library MAY be provided for test tooling.
## Backwards Compatibility
This proposal introduces **additional** encodings only. Hex `0x…` continues to be accepted. No consensus or on‑chain ABI changes are required.
---
### Author:  [@nibed86328](https://community.starknet.io/u/nibed86328)
#### Post date: [October 21, 2025, 1:54am UTC](https://community.starknet.io/t/snip-43-unified-bech32m-addresses-and-viewing-keys-for-starknet/116001/2 "2025-10-21T01:54:19Z")
A question regarding the backwards compatibility, will this change the way v3 transactions work? Will argent’s regular hex address still exist for each account?