@xrplf/mpt-crypto

Cryptographic primitives for Confidential MPT (XLS-0096) on the XRP Ledger, exposed as a small hex-in / hex-out TypeScript API over a vendored WebAssembly build of the reference C crypto library.

This package ships as a dependency of xrpl, but it is lazily loaded: the xrpl/confidential builders reach it through a dynamic import, so bundlers code-split its ~2 MB WASM into a separate chunk and apps that never assemble a Confidential MPT transaction never load it. You typically interact with those builders rather than calling this package directly.

What it provides

Confidential MPT replaces a public MPT balance with EC-ElGamal ciphertexts on-ledger and uses zero-knowledge proofs so validators can verify transfers (no overdraft, amounts conserved) without seeing the amounts. This package exposes the building blocks:

• Encryption — encryptAmount, decryptAmount (EC-ElGamal over secp256k1).
• Commitments — getPedersenCommitment, generateBlindingFactor.
• Context hashes — getConvertContextHash, getConvertBackContextHash, getSendContextHash, getClawbackContextHash. Each binds a proof to a specific transaction (account, issuance, sequence, …).
• Proofs — getConvertProof, getConvertBackProof, getConfidentialSendProof, getClawbackProof.
• Constants — the fixed byte sizes (PUBKEY_SIZE, ELGAMAL_TOTAL_SIZE, the per-transaction proof sizes, …) and the bytesToHex / hexToBytes helpers.

Conventions

• Every byte argument and return value is an uppercase, even-length hex string with no 0x prefix (matching the rest of xrpl.js).
• Integer amounts are bigint, to losslessly carry the full uint64_t range.
• Keys are a secp256k1 keypair (32-byte private key, 33-byte compressed public key) — the same curve as a secp256k1 signing key, but a distinct key used only for encryption. Generate one with ripple-keypairs (deriveKeypair(generateSeed({ algorithm: 'ecdsa-secp256k1' }))).
• The WASM module is loaded once and cached on first use, so depending on this package costs nothing until a confidential operation is actually invoked.

Usage

import {
  encryptAmount,
  decryptAmount,
  generateBlindingFactor,
} from '@xrplf/mpt-crypto'

const blinding = await generateBlindingFactor()
const ciphertext = await encryptAmount(1000n, publicKey, blinding)
// `rangeHigh` bounds the discrete-log search; decryption recovers any amount in
// [0, rangeHigh]. Pass the tightest correct bound you know (e.g. the issuance's
// outstanding confidential amount) — cost scales with it.
const amount = await decryptAmount(ciphertext, privateKey, 10_000n) // 1000n

The vendored WASM

wasm/mpt_crypto.{js,mjs,wasm} is an Emscripten build of the reference mpt-crypto C library (XRPLF/mpt-crypto), the same library rippled links. A single .wasm is wrapped by two glues built from it — mpt_crypto.js (CommonJS, for Node / require) and mpt_crypto.mjs (ES module, for bundlers / import) — so the module loads in every environment.

The exact mpt-crypto release these are built from is pinned in MPT_CRYPTO_VERSION. The npm release pipeline downloads that release's WASM bundle and vendors it into wasm/ before publishing (via scripts/fetch-wasm.sh), so the published package always carries the exact WASM for the pinned tag — never fetched at the consumer's install time.

The pinned version must stay in lockstep with the mpt-crypto version that rippled pins — a mismatch produces valid-looking transactions that rippled rejects with tecBAD_PROOF. To update:

1. Find the version rippled pins in its conanfile.py (e.g. mpt-crypto/1.0.2).
2. Set that tag in MPT_CRYPTO_VERSION.
3. Run npm run fetch:wasm to vendor the matching WASM locally (the release pipeline does the same automatically).

fetch-wasm.sh verifies the bundle's SHA256SUMS manifest when the release ships one; integrity of the published npm package is further covered by the npm package hash.