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Ed25519 digital signature algorithm

Ed25519 digital signature algorithm is described in RFC8032. This repository aims to provide modularized implementation of this algorithm.

Originally Ed25519 consists of three modules:

  • digital signature algorithm itself
  • SHA512 hash function
  • random number generator, to generate keypairs

This repository offers at least two different C implementations for every module. Every implementation is tested and can be replaced with other at link-time. New implementations can be added as well.

During CMake time, users are able to choose any of these implementations using cmake definitions:

  • EDIMPL
    • ref10 - portable C implementation.
    • amd64-64-24k-pic - optimized C and ASM implementation, works only on Linux amd64. Has fixes in ASM files, to allow position independent code (-fPIC) builds.
  • HASH
    • sha2_openssl
    • sha2_sphlib
    • sha3_brainhub - default
  • RANDOM
    • rand_openssl
    • dev_urandom - default
    • dev_random
    • bcryptgen (windows only)
  • BUILD
    • STATIC
    • SHARED - build ed25519 library as shared library (default)

Example: We want to build shared library with fast amd64 implementation, SHA3 and PRNG, which reads entropy from /dev/urandom:

$ cmake .. -DEDIMPL=amd64-64-24k-pic -DHASH=sha3_brainhub -DRANDOM=dev_urandom -DBUILD=SHARED                   bogdan@Bogdans-MacBook-Pro
-- [hunter] Calculating Toolchain-SHA1
-- [hunter] Calculating Config-SHA1
-- [hunter] HUNTER_ROOT: /Users/bogdan/.hunter
-- [hunter] [ Hunter-ID: 1c7aaff | Toolchain-ID: 9e23df5 | Config-ID: 997ea55 ]
-- [hunter] GTEST_ROOT: /Users/bogdan/.hunter/_Base/1c7aaff/9e23df5/997ea55/Install (ver.: 1.8.0-hunter-p11)
-- EDIMPL=amd64-64-24k-pic is selected (Ed25519 implementation)
-- HASH=sha3_brainhub is selected (SHA implementation)
-- RANDOM=dev_urandom is selected (RNG implementation)
-- BUILD=SHARED is selected (library build type)
-- [ed25519] Target RANDOM=bcryptgen is not supported on your platform
-- Configuring done
-- Generating done
-- Build files have been written to: /Users/bogdan/tools/iroha-ed25519/build

Note: only those targets (including tests) will be built, which are specified in EDIMPL, HASH, RANDOM variables.

API

Modules

ed25519 digital signature algorithm

  • ref10 - portable but relatively slow C implementation, originally copied from supercop-20171020. Its API was redesigned to separate signature data from the signed message content.
  • amd64-64-24k-pic - fast (4x ref10) but non-portable C and ASM implementation, only for AMD64. Copied from supercop-20171020. Adopted to be included as a module. Has Position Independent Code (-fPIC) fixes by @l4l.

SHA512 has function as a dependency of ed25519

  • sha2_openssl - implementation of FIPS 180-4 SHA2 512 hash function, which uses openssl underneath
  • sha2_sphlib - implementation of FIPS 180-4 SHA2 512 hash function, which was taken from supercop-20190110
  • sha3_brainhub - implementation of FIPS 202 SHA3 512 hash function taken from brainhub repository. Repository consists of a single C file, which was adopted to be included in a project as a module.

PRNG implementation as a dependency of ed25519

To generate keypair ed25519 needs a source of randomness (entropy).

This repository offers 4 implementations:

  • rand_openssl uses RAND_bytes from openssl
  • dev_urandom reads entropy from /dev/urandom
  • dev_random reads entropy from /dev/random (blocking call, uses busy waiting when user asks for more entropy than device can offer)
  • bcryptgen reads entropy from windows preferred entropy source.