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PureKit SDK allows developers to protect users' passwords and sensitive personal information in a database from data breaches and both online and offline attacks and make stolen passwords useless even if a database is breached.
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Virgil PureKit .NET/C# SDK

Nuget package Build status GitHub license

Introduction | Features | Register Your Account | Install and configure SDK | Prepare Your Database | Usage Examples | Docs | Support


Virgil Security introduces an implementation of the Password-Hardened Encryption (PHE) protocol – a powerful and revolutionary cryptographic technology that provides stronger and more modern security, that secures users' data and lessens the security risks associated with weak passwords.

Virgil PureKit allows developers interacts with Virgil PHE Service to protect users' passwords and sensitive personal identifiable information (PII data) in a database from offline/online attacks and makes stolen passwords/data useless if your database has been compromised. Neither Virgil nor attackers know anything about users' passwords/data.

This technology can be used within any database or login system that uses a password, so it’s accessible for a company of any industry or size.

Authors of the PHE protocol: Russell W. F. Lai, Christoph Egger, Manuel Reinert, Sherman S. M. Chow, Matteo Maffei and Dominique Schroder.


  • Zero knowledge of users' passwords
  • Passwords & data protection from online attacks
  • Passwords & data protection from offline attacks
  • Instant invalidation of stolen database
  • User data encryption with a personal key

Register Your Account

Before starting practicing with the SDK and usage examples make sure that:

  • you have a registered Virgil Account at Virgil Dashboard
  • you created PURE Application
  • and you got your PureKit application's credentials such as: APP_TOKEN, APP_SECRET_KEY, SERVICE_PUBLIC_KEY

Install and Configure PureKit

The Virgil.PureKit .NET/C# SDK is provided as a package named Virgil.PureKit. The package is distributed via NuGet package management system.

The package is available for .NET Core 2.1

Supported platforms:

  • MacOS
  • Linux
  • Windows

Install PureKit Package

Installing the package using Package Manager Console:

PM> Install-Package Virgil.PureKit -Version 2.0.0

Configure PureKit

Here is an example of how to specify your credentials Protocol class instance:

using Virgil.PureKit;

// here set your PURE App credentials
var context = ProtocolContext.Create(
    appToken: "AT.OSoPhirdopvijQlFPKdlSydN9BUrn5oEuDwf3Hqps",
    servicePublicKey: "PK.1.BFFiWkunWRuVMvJVybtCOZEReUui5V3NmwY21doyxoFlurSYEo1fwSW22mQ8ZPq9pUWVm1rvYhF294wstqu//a4=",
    appSecretKey: "SK.1.YEwMBsXkJ5E5Mb9VKD+pu+gRXOySZXWaRXvkFebRYOc="

var protocol = new Protocol(context);

Prepare Your Database

Virgil.PureKit SDK allows you to easily perform all the necessary operations to create, verify and rotate (update) user's PureRecord.

Pure Record - a user's password that is protected with our PureKit technology. Pure record contains a version, client & server random salts and two values obtained during execution of the PHE protocol.

In order to create and work with user's Pure record you have to set up your database with an additional column.

The column must have the following parameters:

Parameters Type Size (bytes) Description
record bytearray 210 A unique record, namely a user's protected Pure Record.

Usage Examples

Enroll User Record

Use this flow to create a PureRecord in your DB for a user.

Remember, if you already have a database with user passwords, you don't have to wait until a user logs in into your system to implement PHE technology. You can go through your database and enroll (create) a user's Pure Record at any time.

So, in order to create a Pure Record for a new database or available one, go through the following operations:

  • Take a user's password (or its hash or whatever you use) and pass it into the EnrollAccountAsync function in a PureKit on your Server side.
  • PureKit will send a request to PureKit service to get enrollment.
  • Then, PureKit will create a user's Pure Record. You need to store this unique user's Pure Record in your database in associated column.
using Virgil.PureKit;
using Virgil.PureKit.Phe;
using Virgil.PureKit.Utils;

var password = "passw0rd";

// create a new encrypted Pure record using user password or its hash
var enrollResult = await protocol.EnrollAccountAsync(password);
// note that enrollResult.Record is a byte array.

// save encrypted Pure record into your users DB
// you can save encrypted Pure record enrollResult.Record to database as byte array or as base64 string

// encode encrypted password record base64 string
var recordBase64 = Bytes.ToString(enrollResult.Record, StringEncoding.BASE64); 

//use encryption key enrollResult.Key for protecting user data
var phe = new PheCrypto();
var encrypted = phe.Encrypt(data, enrollResult.Key);

When you've created a Pure record for all users in your DB, you can delete the unnecessary column where user passwords were previously stored.

Verify User Record

Use this flow when a user already has his or her own Pure record in your database. This function allows you to verify user's password with the Pure record from your DB every time when the user signs in. You have to pass his or her Pure record from your DB into the VerifyPasswordAsync function:

using Virgil.PureKit;
using Virgil.PureKit.Phe;

// get user's encrypted Pure record from your users DB
var passwordCandidate = "passw0rd";

// check candidate password with encrypted Pure record from your DB
var verifyResult = await protocol.VerifyPasswordAsync(passwordCandidate, record);
// (verifyResult.IsSuccess == false) if passwordCandidate is wrong.

//use verifyResult.Key for decrypting user data
var phe = new PheCrypto();
var decrypted = phe.Decrypt(encrypted, verifyResult.Key);

Encrypt user data in your database

Not only user's password is a sensitive data. In this flow we will help you to protect any Personally identifiable information (PII) in your database.

PII is a data that could potentially identify a specific individual, and PII can be sensitive. Sensitive PII is information which, when disclosed, could result in harm to the individual whose privacy has been breached. Sensitive PII should therefore be encrypted in transit and when data is at rest. Such information includes biometric information, medical information, personally identifiable financial information (PIFI) and unique identifiers such as passport or Social Security numbers.

PureKit service allows you to protect user's PII (personal data) with a user's encryptionKey that is obtained from EnrollAccount or VerifyPassword functions. The encryptionKey will be the same for both functions.

In addition, this key is unique to a particular user and won't be changed even after rotating (updating) the user's PureRecord. The encryptionKey will be updated after user changes own password.

Here is an example of data encryption/decryption with an encryptionKey:

using Virgil.PureKit;
using Virgil.PureKit.Phe;
using Virgil.PureKit.Utils;

var phe = new PheCrypto();
var data = Bytes.FromString("Personal data", StringEncoding.UTF8);

//verifyResult.Key is obtained from protocol.EnrollAccountAsync()
// or protocol.VerifyPasswordAsync() calls
var ciphertext = phe.Encrypt(data, verifyResult.Key);
var decrypted = phe.Decrypt(ciphertext, verifyResult.Key);

//use decrypted data

Encryption is performed using AES256-GCM with key & nonce derived from the user's encryptionKey using HKDF and random 256-bit salt.

Virgil Security has Zero knowledge about a user's encryptionKey, because the key is calculated every time when you execute EnrollAccountAsync or VerifyPasswordAsync functions at your server side.

Rotate app keys and user PureRecord

There can never be enough security, so you should rotate your sensitive data regularly (about once a week). Use this flow to get an UPDATE_TOKEN for updating user's PureRecord in your database and to get a new APP_SECRET_KEY and SERVICE_PUBLIC_KEY of a specific application.

Also, use this flow in case your database has been COMPROMISED!

This action doesn't require to create an additional table or to modify scheme of existing table. When a user needs to change his or her own password, use the EnrollAccount function to replace user's oldRecord in your DB with a newRecord.

There is how it works:

Step 1. Get your UPDATE_TOKEN

Navigate to Virgil Dashboard, open your pure application panel and press "Show update token" button to get the UPDATE_TOKEN.

Step 2. Initialize PureKit with the UPDATE_TOKEN Move to Virgil.PureKit SDK configuration file and specify your UPDATE_TOKEN:

using Virgil.PureKit;

// here set your PURE App credentials
var context = ProtocolContext.Create(
    appToken: "AT.OSoPhirdopvijQlFPKdlSydN9BUrn5oEuDwf3Hqps",
    servicePublicKey: "PK.1.BFFiWkunWRuVMvJVybtCOZEReUui5V3NmwY21doyxoFlurSYEo1fwSW22mQ8ZPq9pUWVm1rvYhF294wstqu//a4=",
    appSecretKey: "SK.1.YEwMBsXkJ5E5Mb9VKD+pu+gRXOySZXWaRXvkFebRYOc=",
    updateToken: "UT.2.00000000+0000000000000000000008UfxXDUU2FGkMvKhIgqjxA+hsAtf17K5j11Cnf07jB6uVEvxMJT0lMGv00000="

var protocol = new Protocol(context);

Step 3. Start migration. Use the new RecordUpdater("UPDATE_TOKEN") SDK function to create an instance of class that will update your old records to new ones (you don't need to ask your users to create a new password). The Update() function requires user's old Pure record from your DB:

using Virgil.PureKit;
using Virgil.PureKit.Utils;

var updater = new RecordUpdater("UPDATE_TOKEN");

//for each record get old record from the database as a byte array
//if you keep old record as a base64 string, get byte array from it:
var oldRecord = Bytes.FromString(oldRecordBase64, StringEncoding.BASE64)

//update old record
var newRecord = updater.Update(oldRecord);
//a WrongVersionException will be raised if "UPDATE_TOKEN" has wrong version.

//save new record to the database

So, run the Update() function and save user's new Pure record into your database.

Since the PureKit is able to work simultaneously with two versions of user's PureRecords (new Pure record and old Pure record), this will not affect the backend or users. This means, if a user logs into your system when you do the migration, the Virgil PureKit will verify his password without any problems because PureKit can work with both user's Pure Records (new and old).

Step 4. Get a new APP_SECRET_KEY and SERVICE_PUBLIC_KEY of a specific application

Use Virgil CLI update-keys command and your UPDATE_TOKEN to update the APP_SECRET_KEY and SERVICE_PUBLIC_KEY:

// FreeBSD / Linux / Mac OS
./virgil pure update-keys <service_public_key> <app_secret_key> <update_token>

// Windows OS
virgil pure update-keys <service_public_key> <app_secret_key> <update_token>

Step 5. Move to Virgil.PureKit SDK configuration file and replace your previous APP_SECRET_KEY, SERVICE_PUBLIC_KEY with a new one (APP_TOKEN will be the same). Delete previous APP_SECRET_KEY, SERVICE_PUBLIC_KEY and UPDATE_TOKEN.

using Virgil.PureKit;

// here set your PURE App credentials
var context = ProtocolContext.Create(
    appToken: "APP_TOKEN_HERE",
    servicePublicKey: "NEW_SERVICE_PUBLIC_KEY_HERE",
    appSecretKey: "NEW_APP_SECRET_KEY_HERE",

var protocol = new Protocol(context);



This library is released under the 3-clause BSD License.


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