Introduction to Digital Signatures

Digital signatures are a type of electronic signature that ensures the authenticity and integrity of a digital message or document. A digital signature is created using a Public Key Infrastructure (PKI) to encrypt data using a private key. This makes it highly secure and legally binding.

Popular Digital Signature APIs

1. DocuSign API

DocuSign is a widely-used digital signature platform that provides an easy-to-implement API for integrating digital signing capabilities into your application. Below is an example of how to use the DocuSign API to create an envelope.

  import docusign_esign as docusign
  from docusign_esign.rest import ApiException
  
  def create_envelope():
      api_client = docusign.ApiClient()
      api_client.host = 'https://demo.docusign.net/restapi'
      api_client.set_default_header('Authorization', 'Bearer YOUR_ACCESS_TOKEN')
      
      envelope_definition = docusign.EnvelopeDefinition(
          email_subject="Please sign this document",
          documents=[
              docusign.Document(
                  document_base64="BASE64_STRING",
                  name="Sample Document",
                  file_extension="pdf",
                  document_id=1
              )
          ],
          recipients=docusign.Recipients(
              signers=[
                  docusign.Signer(
                      email="signer@example.com",
                      name="John Doe",
                      recipient_id="1",
                      tabs=docusign.Tabs(
                          sign_here_tabs=[
                              docusign.SignHere(
                                  document_id="1",
                                  page_number="1",
                                  recipient_id="1",
                                  tab_label="SignHereTab",
                                  x_position="200",
                                  y_position="300"
                              )
                          ]
                      )
                  )
              ]
          ),
          status="sent"
      )

      envelopes_api = docusign.EnvelopesApi(api_client)
      try:
          envelope_summary = envelopes_api.create_envelope('YOUR_ACCOUNT_ID', envelope_definition=envelope_definition)
          print("Envelope has been sent. Envelope ID: {}".format(envelope_summary.envelope_id))
      except ApiException as e:
          print("Exception when calling EnvelopesApi->create_envelope: %s" % e)

2. HelloSign API

HelloSign, now part of Dropbox, provides a user-friendly API for electronic signatures. Here is an example of creating a signature request using HelloSign API.

  import requests
  
  def send_signature_request(api_key, signer_email, signer_name, file_path):
      url = "https://api.hellosign.com/v3/signature_request/send"
      headers = {
          "Authorization": "Basic " + api_key
      }
      data = {
          "title": "Document Title",
          "subject": "Please sign this document",
          "message": "Please review and sign this document at your earliest convenience.",
          "signers[0][email_address]": signer_email,
          "signers[0][name]": signer_name,
      }
      files = {"file[0]": open(file_path, "rb")}
      
      response = requests.post(url, headers=headers, data=data, files=files)
      if response.status_code == 200:
          print('Signature request sent successfully.')
      else:
          print('Error sending signature request: {}'.format(response.text))

3. Adobe Sign API

Adobe Sign is a part of Adobe’s Document Cloud suite, providing seamless digital signature integrations. Below is an example of using Adobe Sign API to send a document for signing.

  import requests
  
  def send_for_signing(api_access_token, api_agreement_id, signer_email, signer_name):
      headers = {
          'Authorization': 'Bearer {}'.format(api_access_token),
          'Content-Type': 'application/json'
      }
      url = 'https://api.na1.adobesign.com/api/rest/v6/agreements/{}'.format(api_agreement_id)
      
      data = {
          "fileInfos": [{"fileId": api_agreement_id}],
          "name": "Document for Signing",
          "participantSetsInfo": [
              {
                  "memberInfos": [{"email": signer_email}],
                  "order": 1,
                  "role": "SIGNER"
              }
          ],
          "signatureType": "ESIGN",
          "state": "IN_PROCESS"
      }
      
      response = requests.post(url, headers=headers, json=data)
      if response.status_code == 200:
          print('Document sent successfully for signing.')
      else:
          print('Error sending document: {}'.format(response.text))

Example Application with API Integrations

Using the APIs mentioned above, we can create a web application that allows users to upload documents and send them for signing. Below is a simplified example using Flask (a Python web framework) to handle the document upload and signature requests.

  from flask import Flask, request, jsonify
  app = Flask(__name__)

  @app.route('/upload', methods=['POST'])
  def upload_file():
      if 'file' not in request.files:
          return jsonify({'error': 'No file part in the request'}), 400

      file = request.files['file']
      if file.filename == '':
          return jsonify({'error': 'No file selected for uploading'}), 400

      # Save the file locally
      file.save('/path/to/save/' + file.filename)
      
      # Call your signature API functions here (e.g., DocuSign, HelloSign, Adobe Sign)
      # For simplicity, let's say we call send_signature_request()
      success = send_signature_request(api_key='your-api-key', signer_email='signer@example.com', signer_name='John Doe', file_path='/path/to/save/' + file.filename)
      
      if success:
          return jsonify({'message': 'File successfully uploaded and signature request sent'}), 200
      else:
          return jsonify({'error': 'Failed to send signature request'}), 500

  if __name__ == '__main__':
      app.run(debug=True)

In this example, we have a Flask web application with a single route ‘/upload’ that handles file uploads and sends the file for signing using one of the digital signature APIs.

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