PQHD: Post-Quantum Hierarchical Deterministic Wallet

Status: Live on mainnet.

PQHD replaces BIP-32 for PQ signature schemes. BIP-32’s non-hardened derivation is catastrophic under quantum attack (an exposed xpub is equivalent to an exposed xpriv, and no NIST PQ scheme supports the homomorphic public-key derivation BIP-32 requires). PQHD uses hardened-only derivation with hash-based key material and scheme-specific domain separation.

This page is the protocol specification overview. Wallet commands and operator examples live in Wallets / Using PQHD and RPC Reference.

Path structure


m / purpose' / coin_type' / scheme' / account' / change' / index'

All path elements are hardened. PQHD does not support BIP32-style public child derivation.

Field	Value	Meaning
`purpose'`	`10007'`	Tidecoin PQHD purpose.
`coin_type'`	`6868'`	Tidecoin coin type.
`scheme'`	Scheme prefix	Registered PQ signature scheme.
`account'`	User-controlled	Wallet account namespace.
`change'`	`0'` or `1'`	Receive or change branch.
`index'`	User-controlled	Address/key index.

Derivation pipeline

PQHD v1 derives leaf key material from a 32-byte master seed:

Compute SeedID32 = SHA256("Tidecoin PQHD seedid v1" || master_seed).
Create the master node using HMAC-SHA-512 from the 32-byte master seed.
Derive hardened children with HMAC-SHA-512 over parent secret material.
Extract scheme-separated leaf material with HKDF.
Convert leaf material into a deterministic PQ keypair.

Falcon key generation uses the first 48 bytes of derived stream material. ML-DSA key generation uses the first 32 bytes.

Domain separation

The implementation uses explicit Tidecoin PQHD labels:

Label	Purpose
`Tidecoin PQHD seedid v1`	Seed identifier computation.
`Tidecoin PQHD seed`	Master node derivation.
`Tidecoin PQHD hkdf v1`	HKDF salt/domain.
`Tidecoin PQHD stream key v1`	Leaf stream key derivation.
`Tidecoin PQHD rng v1`	Deterministic keygen stream blocks.

Scheme registry

The scheme' path element uses the same prefix byte as serialized public keys:

Prefix	Scheme
`7`	Falcon-512
`8`	Falcon-1024
`9`	ML-DSA-44
`10`	ML-DSA-65
`11`	ML-DSA-87

Mainnet activation matters: Falcon-512 is live on mainnet; the other schemes are implemented but gated by AuxPoW activation.

Descriptor integration

Tidecoin descriptor wallets use pqhd(...) expressions:


wpkh(pqhd(<seedid32>)/10007h/6868h/7h/0h/0h/*h)

Parser rules:

SEEDID32 is 32 bytes encoded as 64 hex characters.
The path has exactly six hardened elements after pqhd(SEEDID32).
The wildcard form, when used, must be the final hardened element.
purpose must be 10007.
coin_type must be 6868.
change must be 0 or 1.
BIP32 xpub / xprv expressions are intentionally unsupported.

PSBT integration

Tidecoin PSBT support can include proprietary PQHD origin records using identifier tidecoin and subtype 0x01. Wallet RPCs default to suppressing PQHD origin metadata for privacy; integrations can request it with include_pqhd_origins when offline signing requires origin data.

Security properties

PQHD avoids xpub-style public derivation, so publishing derivation metadata does not create a public-key-to-private-key shortcut.
All child derivation is hardened.
Secret material is cleansed from short-lived buffers where the implementation owns those buffers.
Wallet storage, encryption, and backup remain operational responsibilities.

Backup boundary

Descriptors describe scripts and derivation intent. They do not replace wallet secret material. A recoverable wallet needs the wallet backup, PQHD seed, or wallet-specific recovery material.