Post-Quantum Cryptography

Last Friday evening, I opened my Notes app to find a password I had saved a while ago. Scrolling through the list, I realized: this isn't ideal. I needed a password manager. Sure, there are plenty out there, but what would I actually learn from that? Might as well build something myself.

I started looking into how to encrypt passwords while only remembering one thing: a Master Password. The usual stuff came up: public/private keys, key derivation, encryption. Then I came across Shor's algorithm and Post-Quantum Cryptography (PQC), and that sent me straight down the rabbit hole. Two days later, I was deep into quantum-safe encryption, figuring out how to future-proof passwords.

Scrolling and searching around, I found NIST and Open Quantum Safe. Eventually, I landed on liboqs, but there was a catch - no cross-platform precompiled libraries. I found a few implementations on pub.dev for Flutter, but they looked way too sketchy.

Taking the hard way

Compiling liboqs for iOS and the iOS Simulator (for preview) was a hassle, something I usually try to avoid.

Each target required separate architectures: arm64 for my physical iOS device and arm64 + x86_64 for the simulator

Then came the intricacies of cmake, ninja and openssl, and of course, Xcode being a complete fuck-up in what it does.

Build Process

1. Setup OpenSSL

   shell

   git clone https://github.com/krzyzanowskim/OpenSSL ./openssl

2. Clone and build liboqs

   shell

   git clone https://github.com/open-quantum-safe/liboqs ./liboqs
   cd ./liboqs

   • Build for iOS (arm64)
   shell

   cmake -G Ninja ../ \
       -DCMAKE_SYSTEM_NAME=iOS \
       -DCMAKE_OSX_ARCHITECTURES="arm64" \
       -DCMAKE_OSX_SYSROOT="$(xcrun --sdk iphoneos --show-sdk-path)" \
       -DCMAKE_INSTALL_PREFIX=../iphoneos \
       -DOQS_DIST_BUILD=ON \
       -DOQS_PERMIT_UNSUPPORTED_ARCHITECTURE=ON \
       -DOPENSSL_ROOT_DIR=../openssl/iphoneos \
       -DOPENSSL_CRYPTO_LIBRARY=../openssl/iphoneos/lib/libcrypto.a \
       -DOPENSSL_SSL_LIBRARY=../openssl/iphoneos/lib/libssl.a \
       -DOPENSSL_INCLUDE_DIR=../openssl/iphoneos/include
   
   ninja
   ninja install

   • Build for iOS Simulator (arm64, x86_64)
   shell

   cmake -G Ninja ../ \
      -DCMAKE_SYSTEM_NAME=iOS \
      -DCMAKE_OSX_ARCHITECTURES="x86_64;arm64" \
      -DCMAKE_OSX_SYSROOT="$(xcrun --sdk iphonesimulator --show-sdk-path)" \
      -DCMAKE_INSTALL_PREFIX=../iphonesimulator \
      -DOQS_DIST_BUILD=ON \
      -DOQS_PERMIT_UNSUPPORTED_ARCHITECTURE=ON \
      -DOPENSSL_ROOT_DIR=../openssl/iphonesimulator \
      -DOPENSSL_CRYPTO_LIBRARY=../openssl/iphonesimulator/lib/libcrypto.a \
      -DOPENSSL_INCLUDE_DIR=../openssl/iphonesimulator/include
   
   ninja
   ninja install

   • Create xcframework
   shell

   xcodebuild -create-xcframework \
    -library ./iphoneos/lib/liboqs.a -headers ./iphoneos/include \
    -library ./iphonesimulator/lib/liboqs.a -headers ./iphonesimulator/include \
    -output ./liboqs.xcframework

3. Import liboqs.xcframework into the app
   Once the .xcframework is created, it can be easily integrated into your app.

4. Create a bridging header:

   objective-c

   #ifndef Bridging_Header_h
   #define Bridging_Header_h
   
   // for swift lang
   #include <oqs/oqs.h>
   
   #endif

   Then, specify the Objective-C Bridging Header under
   Targets > Your Target > Objective-C Bridging File > $(PROJECT_DIR)/PATH_TO_FOLDER_IF_NESTED/Bridging_Header.h.

Next Steps

In Part 2, I walk through building a Proof of Concept (POC) app that encrypts and decrypts data using the quantum-safe libraries we set up while also covering the challenges encountered along the way and how they were resolved.