Pure Java and JNI backed Curve25519 implementation.
Clone or download
Fetching latest commit…
Cannot retrieve the latest commit at this time.
Permalink
Failed to load latest commit information.
android
common
gradle/wrapper
j2me
java
tests
.gitignore
LICENSE
README.md
build.gradle
gradlew
gradlew.bat
settings.gradle

README.md

curve25519-java

A Java Curve25519 implementation that is backed by native code when available, and pure Java when a native library is not available. There is also a J2ME build variant.

Installing

To use on Android:

dependencies {
  compile 'org.whispersystems:curve25519-android:(latest version number here)'
}

To use from pure Java:

<dependency>
  <groupId>org.whispersystems</groupId>
  <artifactId>curve25519-java</artifactId>
  <version>(latest version number here)</version>
</dependency>

To use from J2ME:

<dependency>
  <groupId>org.whispersystems</groupId>
  <artifactId>curve25519-j2me</artifactId>
  <version>(latest version number here)</version>
</dependency>

The Android artifact is an AAR that contains an NDK-backed native implementation, while the Java artifact is a JAR that only contains the pure-Java Curve25519 provider.

Using

Obtaining an instance

The caller needs to specify a provider when obtaining a Curve25519 instance. There are four built in providers:

  1. Curve25519.NATIVE -- This is a JNI backed provider.
  2. Curve25519.JAVA -- This is a pure Java 7 backed provider.
  3. Curve25519.J2ME -- This is a J2ME compatible provider.
  4. Curve25519.BEST -- This is a provider that attempts to use NATIVE, but falls back to JAVA if the former is unavailable.

The caller specifies a provider during instance creation:

Curve25519 cipher = Curve25519.getInstance(Curve25519.BEST);

Since J2ME doesn't have built-in SecureRandom support, J2ME users need to supply their own source of SecureRandom by implementing the SecureRandomProvider interface and passing it in:

Curve25519 cipher = Curve25519.getInstance(Curve25519.J2ME, new MySecureRandomProvider());

Generating a Curve25519 keypair:

Curve25519KeyPair keyPair = Curve25519.getInstance(Curve25519.BEST).generateKeyPair();

Calculating a shared secret:

Curve25519 cipher       = Curve25519.getInstance(Curve25519.BEST);
byte[]     sharedSecret = cipher.calculateAgreement(publicKey, privateKey);

Calculating a signature:

Curve25519 cipher    = Curve25519.getInstance(Curve25519.BEST);
byte[]     signature = cipher.calculateSignature(secureRandom, privateKey, message);

Verifying a signature:

Curve25519 cipher         = Curve25519.getInstance(Curve25519.BEST);
boolean    validSignature = cipher.verifySignature(publicKey, message, signature);

License

Copyright 2015 Open Whisper Systems

Licensed under the GPLv3: http://www.gnu.org/licenses/gpl-3.0.html