Ed25519 ported to Java
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README.md

ed25519-java

This is an implementation of EdDSA in Java. Structurally, it is based on the ref10 implementation in SUPERCOP (see http://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:0.1.0'

The code requires Java 6 (for e.g. the Arrays.copyOfRange() calls in EdDSAEngine.engineVerify()).

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 uses. All unit tests are passing, including tests against the data from the Python implementation, and the code has been reviewed by an independent developer, but it has not yet been audited by a professional cryptographer. In particular, the constant-time signing properties of ref10 may not have been completely retained (although this is the eventual goal for the Ed25519-specific implementation).

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

Credits