Android HKDF implementations

This article discusses several open-source implementations of the HKDF scheme for Android. Since HKDF is a relatively simple algorithm, it allows for a good case study of cryptographic code. The primary audience are applied cryptographers and software engineers working on protocols. Key derivation functions (KDFs) are an important building block for practical protocols. They take as input the input keying material (IKM), an optional salt, and a context string (info). Their output is a pseudorandom key of specified length....

2024-04-23 · 12 min · Daniel

Secure remote access to Linux via SSH over Tailscale

This article describes how to securely access a local Linux machine remotely via SSH. The primary audience are engineers and researchers working with dedicated hardware behind a NAT, router, or similar. Researchers often work with dedicated machines that live in the lab or at home. This can be because they need to run experiments which require a lot of compute power or because they need to access hardware that is not available on a cloud server....

2023-04-09 · 6 min · Daniel

Android support for Elliptic Curves (EC) in KeyPairGenerator

This article discusses the support for elliptic curves on Android. Its primary audience are engineers implementing or maintaining cryptographic protocols on Android. It hopefully also shows up as a helpful result when searching for error messages. During a recent cryptography project on Android, I found that only few Elliptic Curves are supported by the built-in key pair generator. The typical error messages I got were along the line of java.security.InvalidAlgorithmParameterException: unknown curve name....

2021-07-10 · 6 min · Daniel

Password hashing on Android

This article explains why password hashing is important and how to do it properly on Android. The primary audience are software engineers working with passwords. Password hashing or password-based key derivation takes a password from the user as input and generates key material as output. This is a helpful thing because many people struggle to memorize 256-bit encryption keys. The standard procedure is to pass the user password through the password hashing function, and then use the derived key for cryptographic operations....

2021-06-14 · 5 min · Daniel