h2c

README

Hashing to Elliptic Curves

This is just for testing.

IETF Data Tracker: draft-irtf-cfrg-hash-to-curve

Internet-Draft: git repository

This document specifies a number of algorithms that may be used to encode or hash an arbitrary string to a point on an elliptic curve.

Reference Implementation

The purpose of this implementation is for generating test vectors and enabling cross compatibility with other implementations.

This implementation is for reference only. It MUST NOT be used in production systems.

Other implementations

• Sage

Contact

Feel free to open a github issue for anything related to the implementation, otherwise e-mail authors of the draft.

Documentation

Overview

Package h2c provides implementations of hashing functions that take arbitrary-length byte strings and output a point on an elliptic curve.

These methods follow the current work-in-progress standardization effort at IETF https://datatracker.ietf.org/doc/draft-irtf-cfrg-hash-to-curve.

Version: draft-irtf-cfrg-hash-to-curve-05

Index

• type Expander
• type ExpanderType
• type HashToPoint
• type SuiteID
  • func (id SuiteID) Get(dst []byte) (HashToPoint, error)

Types

type Expander

type Expander struct {
	Ty ExpanderType
	ID uint // This id is converted to crytpo.Hash or to xof.Xof
}

Expander identifies the type of expander function.

type ExpanderType

type ExpanderType int

ExpanderType is

const (
	// XMD denotes an expander based on a Merkle-Damgard hash function.
	XMD ExpanderType = iota
	// XOF denotes an expander based on an extendable output function.
	XOF
	// OTHER is reserved for user-designed expander functions.
	OTHER
)

type HashToPoint

type HashToPoint interface {
	// IsRandomOracle returns true if the output distribution is
	// indifferentiable from a random oracle.
	IsRandomOracle() bool
	// Hash returns a point on an elliptic curve given a byte string.
	Hash(in []byte) C.Point
	// GetCurve returns the destination elliptic curve.
	GetCurve() C.EllCurve
}

HashToPoint represents a complete and secure function for hashing strings to points.

type SuiteID

type SuiteID string

SuiteID is the identifier of supported hash to curve suites.

const (
	P256_XMDSHA256_SSWU_NU_         SuiteID = "P256_XMD:SHA-256_SSWU_NU_"
	P256_XMDSHA256_SSWU_RO_         SuiteID = "P256_XMD:SHA-256_SSWU_RO_"
	P256_XMDSHA256_SVDW_NU_         SuiteID = "P256_XMD:SHA-256_SVDW_NU_"
	P256_XMDSHA256_SVDW_RO_         SuiteID = "P256_XMD:SHA-256_SVDW_RO_"
	P384_XMDSHA512_SSWU_NU_         SuiteID = "P384_XMD:SHA-512_SSWU_NU_"
	P384_XMDSHA512_SSWU_RO_         SuiteID = "P384_XMD:SHA-512_SSWU_RO_"
	P384_XMDSHA512_SVDW_NU_         SuiteID = "P384_XMD:SHA-512_SVDW_NU_"
	P384_XMDSHA512_SVDW_RO_         SuiteID = "P384_XMD:SHA-512_SVDW_RO_"
	P521_XMDSHA512_SSWU_NU_         SuiteID = "P521_XMD:SHA-512_SSWU_NU_"
	P521_XMDSHA512_SSWU_RO_         SuiteID = "P521_XMD:SHA-512_SSWU_RO_"
	P521_XMDSHA512_SVDW_NU_         SuiteID = "P521_XMD:SHA-512_SVDW_NU_"
	P521_XMDSHA512_SVDW_RO_         SuiteID = "P521_XMD:SHA-512_SVDW_RO_"
	Curve25519_XMDSHA256_ELL2_NU_   SuiteID = "curve25519_XMD:SHA-256_ELL2_NU_"
	Curve25519_XMDSHA256_ELL2_RO_   SuiteID = "curve25519_XMD:SHA-256_ELL2_RO_"
	Curve25519_XMDSHA512_ELL2_NU_   SuiteID = "curve25519_XMD:SHA-512_ELL2_NU_"
	Curve25519_XMDSHA512_ELL2_RO_   SuiteID = "curve25519_XMD:SHA-512_ELL2_RO_"
	Edwards25519_XMDSHA256_ELL2_NU_ SuiteID = "edwards25519_XMD:SHA-256_ELL2_NU_"
	Edwards25519_XMDSHA256_ELL2_RO_ SuiteID = "edwards25519_XMD:SHA-256_ELL2_RO_"
	Edwards25519_XMDSHA512_ELL2_NU_ SuiteID = "edwards25519_XMD:SHA-512_ELL2_NU_"
	Edwards25519_XMDSHA512_ELL2_RO_ SuiteID = "edwards25519_XMD:SHA-512_ELL2_RO_"
	Curve448_XMDSHA512_ELL2_NU_     SuiteID = "curve448_XMD:SHA-512_ELL2_NU_"
	Curve448_XMDSHA512_ELL2_RO_     SuiteID = "curve448_XMD:SHA-512_ELL2_RO_"
	Edwards448_XMDSHA512_ELL2_NU_   SuiteID = "edwards448_XMD:SHA-512_ELL2_NU_"
	Edwards448_XMDSHA512_ELL2_RO_   SuiteID = "edwards448_XMD:SHA-512_ELL2_RO_"
	Secp256k1_XMDSHA256_SSWU_NU_    SuiteID = "secp256k1_XMD:SHA-256_SSWU_NU_"
	Secp256k1_XMDSHA256_SSWU_RO_    SuiteID = "secp256k1_XMD:SHA-256_SSWU_RO_"
	Secp256k1_XMDSHA256_SVDW_NU_    SuiteID = "secp256k1_XMD:SHA-256_SVDW_NU_"
	Secp256k1_XMDSHA256_SVDW_RO_    SuiteID = "secp256k1_XMD:SHA-256_SVDW_RO_"
	BLS12381G1_XMDSHA256_SSWU_NU_   SuiteID = "BLS12381G1_XMD:SHA-256_SSWU_NU_"
	BLS12381G1_XMDSHA256_SSWU_RO_   SuiteID = "BLS12381G1_XMD:SHA-256_SSWU_RO_"
	BLS12381G1_XMDSHA256_SVDW_NU_   SuiteID = "BLS12381G1_XMD:SHA-256_SVDW_NU_"
	BLS12381G1_XMDSHA256_SVDW_RO_   SuiteID = "BLS12381G1_XMD:SHA-256_SVDW_RO_"
)

func (SuiteID) Get

func (id SuiteID) Get(dst []byte) (HashToPoint, error)

Get returns a HashToPoint based on the SuiteID, otherwise returns an error if the SuiteID is not supported or invalid.