(C#) Aadhaar Paperless Offline e-kyc

Opens an encrypted .zip containing Aadhaar Paperless Offline e-KYC XML. Gets the XML and validates the digital signature. Then computes the hash for the mobile number and Email ID.

For more information, see https://uidai.gov.in/ecosystem/authentication-devices-documents/about-aadhaar-paperless-offline-e-kyc.html

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// This example requires the Chilkat API to have been previously unlocked.
// See Global Unlock Sample for sample code.

// Open the .zip containing the Aadhaar Paperless Offline e-KYC XML.
// The .zip is encrypted using the "Share Phrase".
Chilkat.Zip zip = new Chilkat.Zip();
bool success = zip.OpenZip("qa_data/xml_dsig/offline_paperless_kyc.zip");
if (success == false) {
    Debug.WriteLine(zip.LastErrorText);
    return;
}

// The .zip should contain 1 XML file.
Chilkat.ZipEntry entry = zip.GetEntryByIndex(0);
if (zip.LastMethodSuccess == false) {
    Debug.WriteLine(zip.LastErrorText);
    return;
}

// To get the contents, we need to specify the Share Phrase.
string sharePhrase = "Lock@487";
zip.DecryptPassword = sharePhrase;

Chilkat.BinData bdXml = new Chilkat.BinData();
// The XML file will be unzipped into the bdXml object.
success = entry.UnzipToBd(bdXml);
if (success == false) {
    Debug.WriteLine(entry.LastErrorText);

    return;
}

// First verify the XML digital signature.
Chilkat.XmlDSig dsig = new Chilkat.XmlDSig();
success = dsig.LoadSignatureBd(bdXml);
if (success != true) {
    Debug.WriteLine(dsig.LastErrorText);
    return;
}

// The UIDAI XML signature does not contain the KeyInfo, so we must load the uidai certificate
// and indicate that its public key is to be used for verifying the signature.
Chilkat.Cert cert = new Chilkat.Cert();
success = cert.LoadFromFile("qa_data/xml_dsig/uidai_auth_sign_prod_2023.cer");
if (success != true) {
    Debug.WriteLine(cert.LastErrorText);
    return;
}

// Get the certificate's public key.
Chilkat.PublicKey pubKey = cert.ExportPublicKey();
success = dsig.SetPublicKey(pubKey);

// The XML in this example contains only 1 signature.
bool bVerifyReferenceDigests = true;
bool bVerified = dsig.VerifySignature(bVerifyReferenceDigests);
if (bVerified == false) {
    Debug.WriteLine(dsig.LastErrorText);
    Debug.WriteLine("The signature was not valid.");
    return;
}

Debug.WriteLine("The XML digital signature is valid.");

// Let's compute the hash for the Mobile Number.

// 	Hashing logic for Mobile Number :
// 	Sha256(Sha256(Mobile+SharePhrase))*number of times last digit of Aadhaar number
// 	(Ref ID field contains last 4 digits).
// 
// 	Example :
// 	Mobile: 1234567890
// 	Aadhaar Number:XXXX XXXX 3632
// 	Passcode : Lock@487
// 	Hash: Sha256(Sha256(1234567890Lock@487))*2
// 	In case of Aadhaar number ends with Zero we will hashed one time.

Chilkat.Crypt2 crypt = new Chilkat.Crypt2();
crypt.HashAlgorithm = "sha256";
crypt.EncodingMode = "hexlower";

string strToHash = "1234567890Lock@487";
Chilkat.BinData bdHash = new Chilkat.BinData();
success = bdHash.AppendString(strToHash,"utf-8");

// Hash a number of times equal to the last digit of your Aadhaar number.
// If the Aadhaar number ends with 0, then hash one time.
// For this example, we'll just set the number of times to hash
// for the case where an Aadhaar number ends in "9"
int numTimesToHash = 9;
int i;
for (i = 1; i <= numTimesToHash; i++) {
    string tmpStr = crypt.HashBdENC(bdHash);
    bdHash.Clear();
    bdHash.AppendString(tmpStr,"utf-8");
}

Debug.WriteLine("Computed Mobile hash = " + bdHash.GetString("utf-8"));

// Let's get the mobile hash stored in the XML and compare it with our computed hash.
Chilkat.Xml xml = new Chilkat.Xml();
success = xml.LoadBd(bdXml,true);
string m_hash = xml.ChilkatPath("UidData|Poi|(m)");

Debug.WriteLine("Stored Mobile hash   = " + m_hash);

// Now do the same thing for the email hash:

strToHash = "abc@gm.comLock@487";
bdHash.Clear();
success = bdHash.AppendString(strToHash,"utf-8");

for (i = 1; i <= numTimesToHash; i++) {
    string tmpStr = crypt.HashBdENC(bdHash);
    bdHash.Clear();
    bdHash.AppendString(tmpStr,"utf-8");
}

Debug.WriteLine("Computed Email hash = " + bdHash.GetString("utf-8"));

string e_hash = xml.ChilkatPath("UidData|Poi|(e)");
Debug.WriteLine("Stored Email hash   = " + e_hash);