New Pluralsight Course: ASP.NET Authentication - The Big Picture

09 September 2019 Authentication
Pluralsight Logo

If you are looking to get an understanding of the various approaches to user authentication, how they rank up, and what libraries to use to implement it in ASP.NET Core, then check out my new Pluralsight course: “ASP.NET Authentication – The Big Picture”.

I have designed this course so that you can either watch it end to end or pick the parts that matter to you; with the aim to give you both a pragmatic overview of modern authentication, along with a practitioner’s recommendation of useful libraries with which to implement them.

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JWT Signing using RSASSA-PSS in .NET Core

29 July 2019 C#

As of version 5.5, Microsoft’s IdentityModel library now supports the signing of JSON Web Tokens using the RSASSA-PSS (Probabilistic Signature Scheme) digital signature algorithm. This is great news if you’re looking to start building .NET Core systems that implement OpenID’s Financial-grade API and Open Banking, where PS256 should be used for signing.

You can find the full list of support for various .NET targets on GitHub, but the exciting thing is that PS256, PS384, and PS512 are now supported on .NET Core.

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Implementing Sign In with Apple in ASP.NET Core

08 June 2019 OpenID Connect
.NET Core

Sign in with Apple was recently released as part of Apple’s WWDC 2019 conference. They’ve essentially weighed into the identity provider space with the username and password being handled by Apple ID and 2FA handled by your registered Apple devices.

Sign In with Apple gives us a new alternative to other social login providers such as Google and Facebook. However, unlike those services, it seems to be more aimed at identity and authentication, rather than access to services such as Google calendar.

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Secure Remote Password (SRP) in C# and .NET Core

31 May 2019 PAKE

Password Authenticated Key Exchange (PAKE) is one of those odd protocols that sounds like a great idea, but one that no one seems to be using. Even then, it seems no one can agree upon a good implementation. Secure Remote Password (SRP) is the most common implementation, found in use by Apple and 1Password; however, it is far from perfect.

I’m underqualified to explain any of those sweeping statements, so I’m going to leave it to cryptographer Matthew Green, who has two excellent articles on both PAKE and SRP. I highly recommend reading at least the first one before implementing PAKE in your application.

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Encrypting Identity Tokens in IdentityServer4

10 April 2019 Identity Server

I previously wrote an article on how to use Proof-Key for Code Exchange (PKCE) in a server-side ASP.NET Core application. In the IdentityServer world authorization code with PKCE now replaces OpenID Connect's (OIDC) hybrid flow as our most secure authorization method; however, not all client libraries or even OpenID Providers support PKCE yet. An alternative approach that gives a comparatively high level of assurance is to use the OIDC hybrid flow in combination with encrypted identity tokens via JSON Web Encryption (JWE).

Using the hybrid flow with encrypted identity tokens allows us to validate the authorization response (via identity token validation), ensure that the authorization code was intended for us (via c_hash validation), and prevent PII passing via the browser (thanks to JWE).

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Generating a Crypto Random String in Dart

31 March 2019 Dart
.NET Core

To help a 10% project at work, the Rock Solid Knowledge IdentityServer team has been creating a basic OpenID Connect library for a Flutter application. After poking around in Dart over the weekend, I found that Dart did not have a straightforward way to create a cryptographically random string suitable for OAuth/OpenID Connect values such as state, nonce, or PKCE’s code challenge. So, in this article, I’m going to share a straightforward way to generate one.

Dart’s Random Number Generator

Luckily, Dart does have a cryptographically secure random number generator that we can use, found in the dart:math library.

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Solving the Cryptopals Crypto Challenges in C#

11 February 2019 Cryptopals

I’ve recently started the cryptopals crypto challenges, and, frankly, even the basics are kicking my ass. However, I seem to be enjoying them, and I’m finally starting to understand some of the Computer Science topics I really should have listened to at University. If you are like me and prefer learning by getting your hands dirty and hacking some code together, then I highly recommend working through some of these challenges.

If you have not heard about cryptopals before, then I'll leave it to the creators to explain:

“We've built a collection of 48 exercises that demonstrate attacks on real-world crypto.

This is a different way to learn about crypto than taking a class or reading a book. We give you problems to solve. They're derived from weaknesses in real-world systems and modern cryptographic constructions. We give you enough info to learn about the underlying crypto concepts yourself. When you're finished, you'll not only have learned a good deal about how cryptosystems are built, but you'll also understand how they're attacked.”

The cryptopals crypto challenges
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Challenge 1: Base64 Encoding

11 February 2019 Cryptopals

We’ve all used Convert.ToBase64String() but what is it actually happening under the covers? Sure, it’s taking a value and representing it using only characters from a range of 64 characters, but how exactly does it do that? Up until now, I probably couldn’t have told you.

My favorite example for understanding how Base64 encoding works is actually from Wikipedia...

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Challenges 2-6: Caesar and Vigenère Ciphers

11 February 2019 Cryptopals

The next few challenges cover implementing and then breaking the Caesar and Vigenère ciphers. These ciphers usually serve as the introduction to most cryptography books, as a history lesson of what we used to use and how easy they are to break. However, with cryptopals, we take this academic knowledge and turn it into practice.

Peter Paul Rubens - Julius Caesar
Peter Paul Rubens Julius Caesar. Photo taken by Ralf Roletschek
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Ktor using OAuth 2.0 and IdentityServer4

01 February 2019 Kotlin

This article will show you how to configure a Kotlin Ktor application to get access tokens from IdentityServer4 using OAuth 2.0. These tokens can then be used to access an API on behalf of a user. We’ll be using JWTs as our access tokens. To find out how to authorize access to a Ktor API using JWTs, check out my past article “JSON Web Token Verification in Ktor using Kotlin and Java-JWT”.

Kotlin logo
Ktor logo
IdentityServer logo

Ktor OAuth Support

Currently, Ktor only supports OAuth which means our Ktor application can receive access tokens to talk to an API on behalf of the user, but it cannot find out who the user is. If we wanted to find out who the user is and to receive identity tokens, we would need OpenID Connect, which is currently unsupported...

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