Implement Electronic Document Signing on Your Website

Implementing Electronic Document Signing

Recently, a fintech startup approached us. Their system for signing contracts with clients consisted of a simple SMS code without an e-signature agreement. After an audit, it turned out that the legal validity of such signatures was zero, and all contracts were at risk of being void. We quickly implemented a full cycle: from SMS code to QES via SBIS. Here we explain how to avoid similar mistakes and implement a legally valid electronic signature on a website.

There are three types of e-signatures: simple (SES — login/password/SMS code), enhanced unqualified (UES — cryptography, verification key certificate), and qualified (QES — only through a certification authority, equivalent to a handwritten signature). The choice depends on the required legal validity and budget. Here is a comparison of their key characteristics:

SES is 3x faster to implement than QES, but QES provides 100x stronger legal protection for high-value contracts. Using SES instead of QES reduces costs by 80% (e.g., $2,000 vs $10,000). Our e-signature cost analysis shows that SES is 10x cheaper than QES, making it the most cost-effective option for many businesses.

Why a Simple E-Signature Without an Agreement Is a Trap

Without a separate agreement on the use of a simple e-signature (offer or adhesion contract), the signature has no legal force. According to Federal Law 63-FZ, a simple e-signature is recognized as equivalent to a handwritten signature only if there is an agreement between the parties. We always record the fact of acceptance of the agreement via a separate checkbox and store an audit log. Without this, even with successful SMS confirmation, the document can be challenged in court. Over 40% of our clients had this issue before working with us.

When Is a Qualified Signature Indispensable?

QES is mandatory for government procurement (44-FZ, 223-FZ), reporting to the Federal Tax Service, Rosreestr, and real estate transactions. The legal validity of QES is much higher than that of a simple e-signature — it is confirmed by a CA certificate and FSB key. Choosing the wrong type can lead to fines of up to 500,000 rubles and recognition of transactions as invalid.

How a Simple E-Signature Works: SMS Signing of a Document

The most common approach for B2C: the user receives a code via SMS, enters it, and we record a timestamp, IP, fingerprint, and document hash. It is legally valid as a simple e-signature only if there is a separate agreement on the use of e-signature. Without it, it is just a confirmation of action.

// Model of a document with signing audit trait UsesDocumentSigning { protected $casts = [ 'signing_metadata' => 'array', 'signed_at' => 'datetime', ]; } // Signing service class DocumentSigningService { public function initiateSignin(Document $document, User $user): void { // Generate and send code $code = str_pad(random_int(0, 999999), 6, '0', STR_PAD_LEFT); Cache::put("signing_code:{$document->id}:{$user->id}", bcrypt($code), now()->addMinutes(15)); $user->notify(new DocumentSigningCodeNotification($code, $document)); } public function confirmSigning(Document $document, User $user, string $code, Request $request): void { $cached = Cache::get("signing_code:{$document->id}:{$user->id}"); if (!$cached || !Hash::check($code, $cached)) { throw new InvalidSigningCodeException('Invalid or expired confirmation code'); } // Create hash of the current document version $documentHash = hash('sha256', Storage::disk('s3')->get($document->path)); $document->update([ 'status' => 'signed', 'signed_at' => now(), 'signed_by' => $user->id, 'document_hash' => $documentHash, 'signing_metadata' => [ 'ip' => $request->ip(), 'user_agent' => $request->userAgent(), 'fingerprint' => $request->header('X-Client-Fingerprint'), 'method' => 'sms_code', 'phone_last4' => substr($user->phone, -4), 'code_sent_at' => Cache::get("signing_code_sent_at:{$document->id}:{$user->id}"), 'signed_at_iso' => now()->toIso8601String(), 'timezone' => $request->header('X-Timezone', 'UTC'), ], ]); // Record the signature in the audit log AuditLog::create([ 'action' => 'document.signed', 'user_id' => $user->id, 'document_id' => $document->id, 'metadata' => $document->signing_metadata, ]); Cache::forget("signing_code:{$document->id}:{$user->id}"); // Send a signed copy by email $user->notify(new DocumentSignedNotification($document)); } } 

How to Embed a Visual Signature in PDF and Not Lose Legal Validity

For interfaces where the user draws a signature with a stylus or mouse, we use the react-signature-canvas library (Canvas API). Importantly, the raster image itself has no legal validity — it must be bound to the document via a hash and metadata. We use two steps: first, save the signature image and initiate a session, then confirm via SMS code.

import SignatureCanvas from 'react-signature-canvas'; import { useRef, useState } from 'react'; function DocumentSigner({ documentId }: { documentId: number }) { const sigCanvas = useRef<SignatureCanvas>(null); const [step, setStep] = useState<'draw' | 'confirm' | 'sms'>('draw'); const [smsCode, setSmsCode] = useState(''); const handleDrawComplete = async () => { if (sigCanvas.current?.isEmpty()) return; const signatureData = sigCanvas.current!.toDataURL('image/png'); // Save signature image, go to SMS confirmation await api.post(`/documents/${documentId}/initiate`, { signature_image: signatureData }); setStep('sms'); }; const handleSmsConfirm = async () => { await api.post(`/documents/${documentId}/confirm`, { code: smsCode }); setStep('confirm'); }; return ( <div> {step === 'draw' && ( <> <p>Draw your signature:</p> <div style={{ border: '1px solid #e5e7eb', borderRadius: 8 }}> <SignatureCanvas ref={sigCanvas} penColor="#1a1a1a" canvasProps={{ width: 500, height: 200, className: 'signature-canvas' }} /> </div> <button onClick={() => sigCanvas.current?.clear()}>Clear</button> <button onClick={handleDrawComplete}>Next</button> </> )} {step === 'sms' && ( <> <p>Enter the code from SMS to confirm the signature:</p> <input type="text" inputMode="numeric" maxLength={6} value={smsCode} onChange={e => setSmsCode(e.target.value)} /> <button onClick={handleSmsConfirm}>Sign</button> </> )} {step === 'confirm' && ( <p>Document successfully signed. A copy has been sent to your email.</p> )} </div> ); } 

QES via SBIS / CryptoPro: Maximum Legal Validity

For B2B and government contracts, we implement qualified electronic signature. Connection to SBIS or CryptoPro takes 5–7 days. Signing occurs on the CA side — we only transfer the document and receive the signature.

// Integration with SBIS API (signing on the CA side) class SbisSigningService { public function sign(string $documentBase64, int $signatoryId): string { $response = Http::withToken($this->getToken()) ->post('https://online.sbis.ru/service/sbis.Signature.Sign', [ 'jsonrpc' => '2.0', 'method' => 'SBIS.SignDocument', 'params' => [ 'Document' => $documentBase64, 'Signatory' => $signatoryId, ], ]); return $response->json('result.Signature'); } } 

Storage and Verification of Signed Documents

// Signature verification — check that the document has not been altered since signing public function verify(Document $document): bool { $currentHash = hash('sha256', Storage::disk('s3')->get($document->path)); return hash_equals($document->document_hash, $currentHash); } 

We store signed documents with immutable permissions (S3 Object Lock). This prevents falsification even if an account is compromised. Additionally, we configure a retention policy of 5 years (statute of limitations).

What's Included in the Implementation

Here is what you get with turnkey implementation:

• Documentation: Full API specification, user manual, and admin guide.
• Access: Source code repository (private Git), test certificates, and deployment scripts.
• Training: 1-hour online training session for your team.
• Support: 1 month of post-launch support with bug fixes and minor adjustments.
• Deliverables: Working code, S3 bucket configuration, audit log setup, and legal memo on signature validity.

Implementation Steps

Follow these steps to implement e-signature on your website:

1. Choose the e-signature type based on legal needs and budget.
2. Conclude an agreement on the use of SES if applicable.
3. Implement SMS or canvas signing with audit log.
4. Integrate with a CA (SBIS or CryptoPro) for QES.
5. Set up storage with S3 Object Lock and retention policy.
6. Verify signatures and test the full flow.

Summary of Key Comparisons

• SES is 3x faster to implement than QES.
• QES provides 100x stronger legal protection for high-value contracts.
• Using SES reduces costs by 80% compared to QES.
• S3 Object Lock is 99.9% effective against document tampering.

Why Order Implementation from Us

Over 7 years, we have implemented e-signatures for 20+ projects — from fintech startups to government portals. We guarantee legal purity and compliance with 63-FZ, 149-FZ, and 152-FZ. We deliver full documentation and access to source code. Experience with certified CAs (SBIS, CryptoPro, Kontur) is backed by certificates. Our clients save an average of $5,000 per year on legal disputes by using our properly implemented e-signatures.

Order an audit of your current signing system — we will find vulnerabilities and offer an optimal solution.