Function deriveP2BKSecretKey

deriveP2BKSecretKey(
    privkey: string | bigint,
    rBlind: string | bigint,
    blindPubkey?: Uint8Array<ArrayBufferLike>,
    naturalPub?: Uint8Array<ArrayBufferLike>,
): null | string
Alpha
Derive a blinded secret key per NUT-26.

Unblinds the pubkey (P = P_ - r·G), verifies x-coord against the naturalPub x(P) == x(p·G), then choose skStd = (p + rᵢ) mod n if parity(P) == parity(p·G), otherwise skNeg = (-p + rᵢ) mod n. Returns skStd if no blindPubkey is provided.
Parameters
- privkey: string | bigint
  Unblinded private key (p), hex or bigint.
- rBlind: string | bigint
  Blinding scalar (r), hex or bigint.
- OptionalblindPubkey: Uint8Array<ArrayBufferLike>
  Optional. Blinded pubkey (P_) to match, 33 byte hex.
- OptionalnaturalPub: Uint8Array<ArrayBufferLike>
  Optional. Pubkey calculated from private key (P = p·G), 33 byte hex.
Returns null | string
Derived blinded secret key as 64 char hex.

Remarks
Security note, this operates on long lived secrets. JavaScript BigInt arithmetic in a JIT is not guaranteed constant time. Do not expose this function on a server that holds private keys.

Throws
If inputs are out of range, or the derived key would be zero.
- Defined in src/crypto/NUT26.ts:112