crypto/ecies/params.go

// Copyright (c) 2013 Kyle Isom <[email protected]>
// Copyright (c) 2012 The Go Authors. All rights reserved.
//
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions are
// met:
//
//    * Redistributions of source code must retain the above copyright
// notice, this list of conditions and the following disclaimer.
//    * Redistributions in binary form must reproduce the above
// copyright notice, this list of conditions and the following disclaimer
// in the documentation and/or other materials provided with the
// distribution.
//    * Neither the name of Google Inc. nor the names of its
// contributors may be used to endorse or promote products derived from
// this software without specific prior written permission.
//
// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

package ecies

// This file contains parameters for ECIES encryption, specifying the
// symmetric encryption and HMAC parameters.

import (
	"crypto"
	"crypto/aes"
	"crypto/cipher"
	"crypto/elliptic"
	"crypto/sha256"
	"crypto/sha512"
	"errors"
	"fmt"
	"hash"

	"github.com/luxfi/crypto/secp256k1"
)

// DefaultCurve is secp256k1 — the value, not the brand. The fact that
// EVM address derivation hashes secp256k1 pubkeys with Keccak does not
// make secp256k1 an Ethereum primitive; it predates and is consumed by
// many systems. Importing the curve via its primitive package keeps
// the dependency name aligned with what the code does (secp256k1 curve
// operations) rather than which downstream brand happens to use it.
var (
	DefaultCurve                  = secp256k1.S256()
	ErrUnsupportedECDHAlgorithm   = errors.New("ecies: unsupported ECDH algorithm")
	ErrUnsupportedECIESParameters = errors.New("ecies: unsupported ECIES parameters")
	ErrInvalidKeyLen              = fmt.Errorf("ecies: invalid key size (> %d) in ECIESParams", maxKeyLen)
)

// KeyLen is limited to prevent overflow of the counter
// in concatKDF. While the theoretical limit is much higher,
// no known cipher uses keys larger than 512 bytes.
const maxKeyLen = 512

type ECIESParams struct {
	Hash      func() hash.Hash // hash function
	hashAlgo  crypto.Hash
	Cipher    func([]byte) (cipher.Block, error) // symmetric cipher
	BlockSize int                                // block size of symmetric cipher
	KeyLen    int                                // length of symmetric key
}

// Standard ECIES parameters:
// * ECIES using AES128 and HMAC-SHA-256-16
// * ECIES using AES256 and HMAC-SHA-256-32
// * ECIES using AES256 and HMAC-SHA-384-48
// * ECIES using AES256 and HMAC-SHA-512-64

var (
	ECIES_AES128_SHA256 = &ECIESParams{
		Hash:      sha256.New,
		hashAlgo:  crypto.SHA256,
		Cipher:    aes.NewCipher,
		BlockSize: aes.BlockSize,
		KeyLen:    16,
	}

	ECIES_AES192_SHA384 = &ECIESParams{
		Hash:      sha512.New384,
		hashAlgo:  crypto.SHA384,
		Cipher:    aes.NewCipher,
		BlockSize: aes.BlockSize,
		KeyLen:    24,
	}

	ECIES_AES256_SHA256 = &ECIESParams{
		Hash:      sha256.New,
		hashAlgo:  crypto.SHA256,
		Cipher:    aes.NewCipher,
		BlockSize: aes.BlockSize,
		KeyLen:    32,
	}

	ECIES_AES256_SHA384 = &ECIESParams{
		Hash:      sha512.New384,
		hashAlgo:  crypto.SHA384,
		Cipher:    aes.NewCipher,
		BlockSize: aes.BlockSize,
		KeyLen:    32,
	}

	ECIES_AES256_SHA512 = &ECIESParams{
		Hash:      sha512.New,
		hashAlgo:  crypto.SHA512,
		Cipher:    aes.NewCipher,
		BlockSize: aes.BlockSize,
		KeyLen:    32,
	}
)

var paramsFromCurve = map[elliptic.Curve]*ECIESParams{
	secp256k1.S256(): ECIES_AES128_SHA256,
	elliptic.P256():  ECIES_AES128_SHA256,
	elliptic.P384():  ECIES_AES192_SHA384,
	elliptic.P521():  ECIES_AES256_SHA512,
}

func AddParamsForCurve(curve elliptic.Curve, params *ECIESParams) {
	paramsFromCurve[curve] = params
}

// ParamsFromCurve selects parameters optimal for the selected elliptic curve.
// Only the curves secp256k1, P256, P384, and P521 are supported.
func ParamsFromCurve(curve elliptic.Curve) (params *ECIESParams) {
	if curve == nil {
		return nil
	}
	// Fast path: exact instance match.
	if p := paramsFromCurve[curve]; p != nil {
		return p
	}
	// Fallback: match by curve parameters. Wrapper types (e.g. the
	// crypto package's btCurve, which wraps secp256k1 but is a distinct
	// type) break instance-identity map lookups; matching on the field
	// prime P uniquely identifies the curve and is wrapper-agnostic.
	cp := curve.Params()
	if cp == nil || cp.P == nil {
		return nil
	}
	for c, p := range paramsFromCurve {
		if cc := c.Params(); cc != nil && cc.P != nil && cc.P.Cmp(cp.P) == 0 {
			return p
		}
	}
	return nil
}

func pubkeyParams(key *PublicKey) (*ECIESParams, error) {
	params := key.Params
	if params == nil {
		if params = ParamsFromCurve(key.Curve); params == nil {
			return nil, ErrUnsupportedECIESParameters
		}
	}
	if params.KeyLen > maxKeyLen {
		return nil, ErrInvalidKeyLen
	}
	return params, nil
}