EdDSA-Java

This is an implementation of EdDSA in Java. Structurally, it is based on the ref10 implementation in SUPERCOP (see https://ed25519.cr.yp.to/software.html).

There are two internal implementations:

• A port of the radix-2^51 operations in ref10 - fast and constant-time, but only useful for Ed25519.
• A generic version using BigIntegers for calculation - a bit slower and not constant-time, but compatible with any EdDSA parameter specification.

To use

Download the latest .jar from the releases tab and place it in your classpath.

Gradle users:

compile 'net.i2p.crypto:eddsa:0.3.0'

Java 7 and above are supported.

The JUnit4 tests require the Hamcrest library hamcrest-all.jar.

This code is released to the public domain and can be used for any purpose. See LICENSE.txt for details.

Disclaimer

There are no guarantees that this is secure for all cases, and users should review the code themselves before depending on it. PRs that fix bugs or improve reviewability are very welcome. Additionally:

• The unit test suite includes tests against the data from the original Python implementation.
• The code (as of 97cea3f0d910fc627c7b57b1bc4d783cdd0c2a4a) was reviewed by an independent developer.
• The code (as of dc9f58f2c874463c15465326efc040d17a627b3a) was audited by an independent third party, and the one issue found was fixed.

Code comparison

For ease of following, here are the main methods in ref10 and their equivalents in this codebase:

EdDSA Operation	ref10 function	Java function
Generate keypair	crypto_sign_keypair	EdDSAPrivateKeySpec constructor
Sign message	crypto_sign	EdDSAEngine.engineSign
Verify signature	crypto_sign_open	EdDSAEngine.engineVerify

EdDSA point arithmetic	ref10 function	Java function
R = b * B	ge_scalarmult_base	GroupElement.scalarMultiply
R = a*A + b*B	ge_double_scalarmult_vartime	GroupElement.doubleScalarMultiplyVariableTime
R = 2 * P	ge_p2_dbl	GroupElement.dbl
R = P + Q	ge_madd, ge_add	GroupElement.madd, GroupElement.add
R = P - Q	ge_msub, ge_sub	GroupElement.msub, GroupElement.sub

Important changes

0.3.0

• The library has been extensively profiled for contention issues in a multi-threaded environment. The only remaining potential contention is in EdDSANamedCurveTable.defineCurve(), which will be rarely called.
• The public constant for the curve name has returned as ED_25519, and the curve specification has a public constant ED_25519_CURVE_SPEC to avoid repeated lookups when converting to and from encoded form for the public or private keys.
• GroupElement is now completely immutable, and all fields final, to avoid the need for synchronized blocks over mutable fields. This required some new constructors and paths to construction.
• EdDSAPublicKeySpec.getNegativeA() and EdDSAPublicKey.getNegativeA() now evaluate lazily, taking advantage of the immutability of GroupElement.negate(). This boosts the performance of the public key constructor when the key is just being passed around rather than used.
• Support for X509Key wrapped EdDSA public keys.

0.2.0

• Ed25519 is now named Ed25519 in EdDSANamedCurveTable, and the previous public constant (containing the older inaccurate name) has been removed.

Credits

• The Ed25519 class was originally ported by k3d3 from the Python Ed25519 reference implementation.
• Useful comments and tweaks were found in the GNUnet implementation of Ed25519 (based on k3d3's class).
• BloodyRookie reviewed the code, adding many useful comments, unit tests and literature.