@e-sig/core

@e-sig/core — Portable In-Platform E-Signature

Self-contained PKCS#7 PDF signing — no SaaS, no metering, no per-doc fees. Battle-tested in production at opendelphi.org.

This directory is the portable core of the Opendelphi e-signature pipeline. Drop it (plus a tiny adapter you write) into any TypeScript / Node.js project to add real cryptographic signing of PDFs.

What it does

Given an HTML document and a person who wants to sign it, this library:

• Renders the HTML to a PDF (headless Chromium via puppeteer-core; scripting disabled by default).
• Generates or reuses a self-signed RSA-2048 X.509 cert for the signing tenant.
• Embeds a PKCS#7 detached signature under the ETSI.CAdES.detached subfilter, with the ESS signing-certificate-v2 attribute binding the signer cert into the signed data. Pass padesStrict: true for strict PAdES B-B (also drops the PAdES-forbidden signing-time attribute).
• Produces a PDF that opens cleanly in Preview / Adobe Reader with a valid signature panel — any post-signing edit invalidates the signature. verifyPdfSignature() checks this cryptographically (recomputes the digest over the signed ByteRange and RSA-verifies the signature).

Trust vs. validity. The signature is cryptographically valid, but the cert is self-issued — stock Adobe Reader shows "validity unknown" until the cert is trusted (org trust-store import, or plug in an AATL/CA signer). This verifies the signature math and integrity, not third-party trust. See the compliance notes below.

That's the whole thing. It's ~600 lines of TypeScript with zero runtime dependencies on Supabase, Next.js, or any SaaS.

What it does NOT do

By design — these are wrapper concerns:

• Storage of the signed PDF. You decide where (S3, local disk, Supabase Storage, …).
• Auth / authorization. You decide who's allowed to sign.
• UI. You build the signature-capture surface.
• Persistence of the cert pool. Implement the CertStore adapter interface.
• Audit logging. Implement the AuditLogStore adapter interface.

The library gives you crypto + rendering. You bring persistence + UI + auth.

Files

File	Purpose	Project-agnostic?
pem-signer.ts	Custom @signpdf Signer driven by raw PEM key+cert (bypasses node-forge's broken P12 round-trip — see Background below)	✅
cert-issuer.ts	Generate self-signed RSA-2048 X.509; AES-256-GCM-wrap private keys for at-rest storage	✅
render-pdf.ts	HTML → PDF via puppeteer-core; auto-detects Lambda vs local Chrome	✅
sign-pdf.ts	Combine placeholder injection + PKCS#7 sign (ETSI.CAdES)	✅
verify-pdf.ts	Structural verifier (parses /ByteRange + PKCS#7 blob, returns diagnostics)	✅
signature-block.ts	HTML helper to render N signature blocks for multi-party flows	✅
types.ts	Shared TS types (Signer, SigningCertPem, …)	✅
index.ts	Public re-export barrel	✅

Install

npm install \
  @signpdf/signpdf \
  @signpdf/utils \
  @signpdf/placeholder-plain \
  node-forge \
  puppeteer-core \
  @sparticuz/chromium  # only on Lambda; skip for local-only

Plus @types/node-forge if you're using TypeScript.

If you're on Next.js, you MUST externalize the binary-adjacent packages in next.config.ts:

const nextConfig = {
  serverExternalPackages: [
    "@sparticuz/chromium",
    "puppeteer-core",
    "node-forge",
    "@signpdf/signpdf",
    "@signpdf/utils",
    "@signpdf/placeholder-plain",
  ],
  // The chromium binary tarball is a static asset; tell file-tracing to
  // include it in your e-sig route's bundle.
  outputFileTracingIncludes: {
    "/api/your-esig-route": [
      "./node_modules/@sparticuz/chromium/bin/**",
    ],
  },
};

30-second example

import {
  generateSelfSignedCert,
  renderHtmlToPdf,
  signPdf,
  verifyPdfStructure,
} from "@e-sig/core";

// 1. Issue a one-off cert (in real life, persist + reuse).
const cert = generateSelfSignedCert({ subjectName: "Acme Corp" });

// 2. Render HTML → unsigned PDF.
const unsigned = await renderHtmlToPdf({
  html: `<h1>Service Agreement</h1><p>Signed by Jane Doe at ${new Date().toISOString()}.</p>`,
});

// 3. Sign it.
const { signedPdf } = await signPdf({
  pdf: unsigned,
  keyPem: cert.keyPem,
  certPem: cert.certPem,
  reason: "Service Agreement acceptance",
  location: "https://acme.example",
  contactInfo: "[e-mail]",
  name: "Jane Doe",
});

// 4. Verify the result cryptographically (also exported as verifyPdfSignature).
//    ok === true only when structure + document digest + RSA signature all pass;
//    a single flipped byte under the signature makes ok=false / digestValid=false.
const verify = verifyPdfStructure(signedPdf);
console.log(verify.ok, verify.digestValid, verify.signatureValid, verify.signerCommonName);
// → true, true, true, "E-sig (Acme Corp)"

// 5. Persist + serve. Up to you.
require("fs").writeFileSync("./signed.pdf", signedPdf);

That's it. Open signed.pdf in Preview — signature panel shows valid (self-signed).

RFC 3161 trusted timestamps (CAdES-T)

Pass a tsa transport to signPdf to embed an RFC 3161 TimeStampToken, upgrading the signature from CAdES-B to CAdES-T. The token is added as the id-aa-timeStampToken unsigned attribute (OID 1.2.840.113549.1.9.16.2.14) computed over the SignerInfo signatureValue (RFC 3161 §2.4.1).

The package performs no network egress — you inject the POST so the package stays dependency-free. The TSA only ever receives a SHA-256 hash, never the document or any PHI:

import type { TsaTransport } from "@e-sig/core";

const tsa: TsaTransport = {
  required: false, // false = degrade to CAdES-B on TSA failure; true = throw
  fetch: async (reqDerBytes) => {
    const res = await fetch("http://timestamp.digicert.com", {
      method: "POST",
      headers: { "Content-Type": "application/timestamp-query" },
      body: reqDerBytes,
    });
    return new Uint8Array(await res.arrayBuffer());
  },
};

const { signedPdf, timestamped, tsaError } = await signPdf({
  pdf, keyPem, certPem,
  reason: "DUA acceptance", location: "opendelphi.org",
  contactInfo: "[e-mail]", name: "Acme Research Institute",
  tsa,
});

const v = verifyPdfStructure(signedPdf);
// v.timestamped, v.timestampTime (ISO), v.tsaCommonName
// v.ok is false if the §2.4.2 binding check fails (imprint != sha256(sigValue))

Notes:

• Budget: when tsa is supplied and signatureLength is omitted, the /Contents placeholder budget defaults to 30720 (vs 8192 without a TSA) to fit the TimeStampToken plus the TSA certificate chain. An overflow is rejected, never silently truncated.
• Degradation: with required: false (default), a TSA error produces a valid CAdES-B signature and sets tsaError; with required: true the error is rethrown.
• Verification enforces the RFC 3161 §2.4.2 binding: the token's messageImprint must equal sha256(SignerInfo.signature), else ok:false.

See CONSUMING.md for the full consumer guide.

Persisting certs + audit logs across requests

For real usage you need to:

• Cache certs per tenant so you don't regenerate on every sign.
• Encrypt private keys at rest so a DB leak doesn't compromise signing authority.
• Log every sign for ESIGN / UETA / 21 CFR §11 compliance evidence.

The library provides adapter interfaces (CertStore, AuditLogStore — see ../adapters/types.ts). Implement them against your DB.

A reference Supabase implementation lives at ../adapters/supabase.ts (~150 lines). It works against any schema with these two tables — copy the migration from supabase/migrations/00106_esig_self_contained.sql for the canonical shape, or write your own.

CertStore interface

interface CertStore {
  findActive(tenantId: string): Promise<StoredCert | null>;
  insert(input: { tenantId; generated; keyPemEncrypted; rotatedFromId? }): Promise<StoredCert>;
  deactivate(id: string): Promise<void>;
  findExpiring(withinDays: number): Promise<StoredCert[]>;
}

AuditLogStore interface

interface AuditLogStore {
  insert(entry: AuditLogEntry): Promise<AuditLogRow>;
}

Then use the convenience helper ensureActiveCert from ../adapters/supabase.ts as a template:

const result = await ensureActiveCert({
  store: new YourCertStore(...),
  tenantId: "acme-corp",
  subjectName: "Acme Corp",
  passphrase: process.env.ESIG_CERT_PASSPHRASE!,
});
// result.certPem + result.keyPem ready to feed into signPdf()

Compliance posture

The Opendelphi production wire-up uses this library for HIPAA-bound Data Use Agreements and is mapped against:

• ESIGN Act § 7001 (R1–R5) — Intent, Consent to electronic, Attribution, Integrity, Retention. R4 Integrity is fully covered by the crypto core; R1/R2/R3/R5 are wrapper concerns.
• UETA § 9 + § 13 — Attribution + system attribution log.
• 21 CFR § 11.50 / § 11.70 — FDA-grade requirements where applicable.

See .planning/phases/19-esig-primitives-spike/19-04-ESIGN-GAPS.md for the full mapping.

Not legal advice. Talk to your lawyer about whether this satisfies the regulatory framework for your specific use case.

Background — why this exists

Why not DocuSign / DocuSeal / Documenso?

Per-document metering (~$0.20/sig) made the unit economics painful at scale. And every signed PDF flowed through a third-party processor — making HIPAA + GDPR compliance harder than it had to be.

This library is what you reach for when "no SaaS, no metering, no fees" is a hard requirement.

Why not pdf-lib?

pdf-lib is the most popular Node PDF library, but it hasn't shipped a release since 2021. Documenso uses @libpdf/core instead — same conclusion here. (Neither is actually used by this core — we drive puppeteer for rendering and @signpdf + node-forge for signing, both actively maintained.)

Why not PKCS#12?

We tried. node-forge.pkcs12.toPkcs12Asn1 produces P12 bundles whose MAC neither node-forge nor openssl can verify. Looks like a long-standing BMPString-password-derivation bug. We bypass it entirely — the PemSigner takes raw PEM and drives forge.pkcs7 directly.

Bugs to avoid (we hit these so you don't have to)

• Don't use node-forge.pkcs12.toPkcs12Asn1 — see above.
• ASCII-only cert subject names — forge.pki.certificateFromPem mis-counts bytes for non-ASCII (em-dash in OU breaks PEM round-trip with "Too few bytes to parse DER").
• @signpdf/signpdf v3 ESM default import is opaque — use the named export: import { SignPdf } from "@signpdf/signpdf" and new SignPdf().sign(...).
• @sparticuz/chromium is Lambda-only — locally, use system Chrome via the executablePath override.
• Storing key + cert in one PEM file is fragile — forge.pem.decode extracts blocks correctly, but re-encoding the cert block from a multi-block buffer doesn't survive certificateFromPem round-trip. Store them as separate files / DB columns.

Performance

End-to-end on Vercel Lambda (cold start), tested against opendelphi.org in production:

• Render HTML → unsigned PDF: ~2.5 s (cold) / ~0.5 s (warm)
• Generate cert (first sign per tenant): ~0.8 s (RSA-2048 keygen dominates)
• PKCS#7 sign: ~0.1 s
• Upload + audit + DB row flip: ~0.3 s
• Total cold-start round-trip: ~4.5 s

Subsequent signs reuse the cached cert → ~1–1.5 s warm.

License

Same as the parent project. The core/ directory is intentionally self-contained so it can be vendored under your own license.

Acknowledgments

• @signpdf for the PKCS#7 placeholder + signing infrastructure.
• node-forge for the X.509 + PKCS#7 + crypto primitives.
• Documenso + DocuSeal CE as reference implementations (read-only — no code copied — see .planning/phases/19-esig-primitives-spike/19-02-PATTERNS-OBSERVED.md for the lessons borrowed).