init

.gitignore

+# Compiled Object files, Static and Dynamic libs (Shared Objects)
+*.o
+*.a
+*.so
+
+# Folders
+_obj
+_test
+
+# Architecture specific extensions/prefixes
+*.[568vq]
+[568vq].out
+
+*.cgo1.go
+*.cgo2.c
+_cgo_defun.c
+_cgo_gotypes.go
+_cgo_export.*
+
+_testmain.go
+
+*.exe
+
+*~

LICENSE

+Copyright (c) 2013 Kyle Isom <kyle@tyrfingr.is>
+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
+"AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

README

+# NOTE
+
+This implementation is direct fork of Kylom's implementation. I claim no authorship over this code apart from some minor modifications.
+Please be aware this code **has not yet been reviewed**.
+
+ecies implements the Elliptic Curve Integrated Encryption Scheme.
+
+The package is designed to be compliant with the appropriate NIST
+standards, and therefore doesn't support the full SEC 1 algorithm set.
+
+
+STATUS:
+
+ecies should be ready for use. The ASN.1 support is only complete so
+far as to supported the listed algorithms before.
+
+
+CAVEATS
+
+1. CMAC support is currently not present.
+
+
+SUPPORTED ALGORITHMS
+
+        SYMMETRIC CIPHERS               HASH FUNCTIONS
+             AES128                         SHA-1
+             AES192                        SHA-224
+             AES256                        SHA-256
+                                           SHA-384
+        ELLIPTIC CURVE                     SHA-512
+             P256
+             P384		    KEY DERIVATION FUNCTION
+             P521	       NIST SP 800-65a Concatenation KDF
+
+Curve P224 isn't supported because it does not provide a minimum security
+level of AES128 with HMAC-SHA1. According to NIST SP 800-57, the security
+level of P224 is 112 bits of security. Symmetric ciphers use CTR-mode;
+message tags are computed using HMAC-<HASH> function.
+
+
+CURVE SELECTION
+
+According to NIST SP 800-57, the following curves should be selected:
+
+    +----------------+-------+
+    | SYMMETRIC SIZE | CURVE |
+    +----------------+-------+
+    |     128-bit    |  P256 |
+    +----------------+-------+
+    |     192-bit    |  P384 |
+    +----------------+-------+
+    |     256-bit    |  P521 |
+    +----------------+-------+
+
+
+TODO
+
+1. Look at serialising the parameters with the SEC 1 ASN.1 module.
+2. Validate ASN.1 formats with SEC 1.
+
+
+TEST VECTORS
+
+The only test vectors I've found so far date from 1993, predating AES
+and including only 163-bit curves. Therefore, there are no published
+test vectors to compare to.
+
+
+LICENSE
+
+ecies is released under the same license as the Go source code. See the
+LICENSE file for details.
+
+
+REFERENCES
+
+* SEC (Standard for Efficient Cryptography) 1, version 2.0: Elliptic
+  Curve Cryptography; Certicom, May 2009.
+  http://www.secg.org/download/aid-780/sec1-v2.pdf
+* GEC (Guidelines for Efficient Cryptography) 2, version 0.3: Test
+  Vectors for SEC 1; Certicom, September 1999.
+  http://www.secg.org/collateral/gec2.pdf
+* NIST SP 800-56a: Recommendation for Pair-Wise Key Establishment Schemes
+  Using Discrete Logarithm Cryptography. National Institute of Standards
+  and Technology, May 2007.
+  http://csrc.nist.gov/publications/nistpubs/800-56A/SP800-56A_Revision1_Mar08-2007.pdf
+* Suite B Implementer’s Guide to NIST SP 800-56A. National Security
+  Agency, July 28, 2009.
+  http://www.nsa.gov/ia/_files/SuiteB_Implementer_G-113808.pdf
+* NIST SP 800-57: Recommendation for Key Management – Part 1: General
+  (Revision 3). National Institute of Standards and Technology, July
+  2012.
+  http://csrc.nist.gov/publications/nistpubs/800-57/sp800-57_part1_rev3_general.pdf
+

ecies.go

+package ecies
+
+import (
+	"crypto/cipher"
+	"crypto/ecdsa"
+	"crypto/elliptic"
+	"crypto/hmac"
+	"crypto/subtle"
+	"fmt"
+	"hash"
+	"io"
+	"math/big"
+)
+
+var (
+	ErrImport           = fmt.Errorf("ecies: failed to import key")
+	ErrInvalidCurve     = fmt.Errorf("ecies: invalid elliptic curve")
+	ErrInvalidParams    = fmt.Errorf("ecies: invalid ECIES parameters")
+	ErrInvalidPublicKey = fmt.Errorf("ecies: invalid public key")
+	ErrSharedKeyTooBig  = fmt.Errorf("ecies: shared key is too big")
+)
+
+// PublicKey is a representation of an elliptic curve public key.
+type PublicKey struct {
+	X *big.Int
+	Y *big.Int
+	elliptic.Curve
+	Params *ECIESParams
+}
+
+// Export an ECIES public key as an ECDSA public key.
+func (pub *PublicKey) ExportECDSA() *ecdsa.PublicKey {
+	return &ecdsa.PublicKey{pub.Curve, pub.X, pub.Y}
+}
+
+// Import an ECDSA public key as an ECIES public key.
+func ImportECDSAPublic(pub *ecdsa.PublicKey) *PublicKey {
+	return &PublicKey{
+		X:      pub.X,
+		Y:      pub.Y,
+		Curve:  pub.Curve,
+		Params: ParamsFromCurve(pub.Curve),
+	}
+}
+
+// PrivateKey is a representation of an elliptic curve private key.
+type PrivateKey struct {
+	PublicKey
+	D *big.Int
+}
+
+// Export an ECIES private key as an ECDSA private key.
+func (prv *PrivateKey) ExportECDSA() *ecdsa.PrivateKey {
+	pub := &prv.PublicKey
+	pubECDSA := pub.ExportECDSA()
+	return &ecdsa.PrivateKey{*pubECDSA, prv.D}
+}
+
+// Import an ECDSA private key as an ECIES private key.
+func ImportECDSA(prv *ecdsa.PrivateKey) *PrivateKey {
+	pub := ImportECDSAPublic(&prv.PublicKey)
+	return &PrivateKey{*pub, prv.D}
+}
+
+// Generate an elliptic curve public / private keypair. If params is nil,
+// the recommended default paramters for the key will be chosen.
+func GenerateKey(rand io.Reader, curve elliptic.Curve, params *ECIESParams) (prv *PrivateKey, err error) {
+	pb, x, y, err := elliptic.GenerateKey(curve, rand)
+	if err != nil {
+		return
+	}
+	prv = new(PrivateKey)
+	prv.PublicKey.X = x
+	prv.PublicKey.Y = y
+	prv.PublicKey.Curve = curve
+	prv.D = new(big.Int).SetBytes(pb)
+	if params == nil {
+		params = ParamsFromCurve(curve)
+	}
+	prv.PublicKey.Params = params
+	return
+}
+
+// MaxSharedKeyLength returns the maximum length of the shared key the
+// public key can produce.
+func MaxSharedKeyLength(pub *PublicKey) int {
+	return (pub.Curve.Params().BitSize + 7) / 8
+}
+
+// ECDH key agreement method used to establish secret keys for encryption.
+func (prv *PrivateKey) GenerateShared(pub *PublicKey, skLen, macLen int) (sk []byte, err error) {
+	if prv.PublicKey.Curve != pub.Curve {
+		err = ErrInvalidCurve
+		return
+	}
+	x, _ := pub.Curve.ScalarMult(pub.X, pub.Y, prv.D.Bytes())
+	if x == nil || (x.BitLen()+7)/8 < (skLen+macLen) {
+		err = ErrSharedKeyTooBig
+		return
+	}
+	sk = x.Bytes()[:skLen+macLen]
+	return
+}
+
+var (
+	ErrKeyDataTooLong = fmt.Errorf("ecies: can't supply requested key data")
+	ErrSharedTooLong  = fmt.Errorf("ecies: shared secret is too long")
+	ErrInvalidMessage = fmt.Errorf("ecies: invalid message")
+)
+
+var (
+	big2To32   = new(big.Int).Exp(big.NewInt(2), big.NewInt(32), nil)
+	big2To32M1 = new(big.Int).Sub(big2To32, big.NewInt(1))
+)
+
+func incCounter(ctr []byte) {
+	if ctr[3]++; ctr[3] != 0 {
+		return
+	} else if ctr[2]++; ctr[2] != 0 {
+		return
+	} else if ctr[1]++; ctr[1] != 0 {
+		return
+	} else if ctr[0]++; ctr[0] != 0 {
+		return
+	}
+	return
+}
+
+// NIST SP 800-56 Concatenation Key Derivation Function (see section 5.8.1).
+func concatKDF(hash hash.Hash, z, s1 []byte, kdLen int) (k []byte, err error) {
+	if s1 == nil {
+		s1 = make([]byte, 0)
+	}
+
+	reps := ((kdLen + 7) * 8) / (hash.BlockSize() * 8)
+	if big.NewInt(int64(reps)).Cmp(big2To32M1) > 0 {
+		fmt.Println(big2To32M1)
+		return nil, ErrKeyDataTooLong
+	}
+
+	counter := []byte{0, 0, 0, 1}
+	k = make([]byte, 0)
+
+	for i := 0; i <= reps; i++ {
+		hash.Write(counter)
+		hash.Write(z)
+		hash.Write(s1)
+		k = append(k, hash.Sum(nil)...)
+		hash.Reset()
+		incCounter(counter)
+	}
+
+	k = k[:kdLen]
+	return
+}
+
+// messageTag computes the MAC of a message (called the tag) as per
+// SEC 1, 3.5.
+func messageTag(hash func() hash.Hash, km, msg, shared []byte) []byte {
+	if shared == nil {
+		shared = make([]byte, 0)
+	}
+	mac := hmac.New(hash, km)
+	mac.Write(msg)
+	tag := mac.Sum(nil)
+	return tag
+}
+
+// Generate an initialisation vector for CTR mode.
+func generateIV(params *ECIESParams, rand io.Reader) (iv []byte, err error) {
+	iv = make([]byte, params.BlockSize)
+	_, err = io.ReadFull(rand, iv)
+	return
+}
+
+// symEncrypt carries out CTR encryption using the block cipher specified in the
+// parameters.
+func symEncrypt(rand io.Reader, params *ECIESParams, key, m []byte) (ct []byte, err error) {
+	c, err := params.Cipher(key)
+	if err != nil {
+		return
+	}
+
+	iv, err := generateIV(params, rand)
+	if err != nil {
+		return
+	}
+	ctr := cipher.NewCTR(c, iv)
+
+	ct = make([]byte, len(m)+params.BlockSize)
+	copy(ct, iv)
+	ctr.XORKeyStream(ct[params.BlockSize:], m)
+	return
+}
+
+// symDecrypt carries out CTR decryption using the block cipher specified in
+// the parameters
+func symDecrypt(rand io.Reader, params *ECIESParams, key, ct []byte) (m []byte, err error) {
+	c, err := params.Cipher(key)
+	if err != nil {
+		return
+	}
+
+	ctr := cipher.NewCTR(c, ct[:params.BlockSize])
+
+	m = make([]byte, len(ct)-params.BlockSize)
+	ctr.XORKeyStream(m, ct[params.BlockSize:])
+	return
+}
+
+// Encrypt encrypts a message using ECIES as specified in SEC 1, 5.1. If
+// the shared information parameters aren't being used, they should be
+// nil.
+func Encrypt(rand io.Reader, pub *PublicKey, m, s1, s2 []byte) (ct []byte, err error) {
+	params := pub.Params
+	if params == nil {
+		if params = ParamsFromCurve(pub.Curve); params == nil {
+			err = ErrUnsupportedECIESParameters
+			return
+		}
+	}
+	R, err := GenerateKey(rand, pub.Curve, params)
+	if err != nil {
+		return
+	}
+
+	hash := params.Hash()
+	z, err := R.GenerateShared(pub, params.KeyLen, params.KeyLen)
+	if err != nil {
+		return
+	}
+	K, err := concatKDF(hash, z, s1, params.KeyLen+params.KeyLen)
+	if err != nil {
+		return
+	}
+	Ke := K[:params.KeyLen]
+	Km := K[params.KeyLen:]
+	hash.Write(Km)
+	Km = hash.Sum(nil)
+	hash.Reset()
+
+	em, err := symEncrypt(rand, params, Ke, m)
+	if err != nil || len(em) <= params.BlockSize {
+		return
+	}
+
+	d := messageTag(params.Hash, Km, em, s2)
+
+	Rb := elliptic.Marshal(pub.Curve, R.PublicKey.X, R.PublicKey.Y)
+	ct = make([]byte, len(Rb)+len(em)+len(d))
+	copy(ct, Rb)
+	copy(ct[len(Rb):], em)
+	copy(ct[len(Rb)+len(em):], d)
+	return
+}
+
+// Decrypt decrypts an ECIES ciphertext.
+func (prv *PrivateKey) Decrypt(rand io.Reader, c, s1, s2 []byte) (m []byte, err error) {
+	if c == nil || len(c) == 0 {
+		err = ErrInvalidMessage
+		return
+	}
+	params := prv.PublicKey.Params
+	if params == nil {
+		if params = ParamsFromCurve(prv.PublicKey.Curve); params == nil {
+			err = ErrUnsupportedECIESParameters
+			return
+		}
+	}
+	hash := params.Hash()
+
+	var (
+		rLen   int
+		hLen   int = hash.Size()
+		mStart int
+		mEnd   int
+	)
+
+	switch c[0] {
+	case 2, 3, 4:
+		rLen = ((prv.PublicKey.Curve.Params().BitSize + 7) / 4)
+		if len(c) < (rLen + hLen + 1) {
+			err = ErrInvalidMessage
+			return
+		}
+	default:
+		err = ErrInvalidPublicKey
+		return
+	}
+
+	mStart = rLen
+	mEnd = len(c) - hLen
+
+	R := new(PublicKey)
+	R.Curve = prv.PublicKey.Curve
+	R.X, R.Y = elliptic.Unmarshal(R.Curve, c[:rLen])
+	if R.X == nil {
+		err = ErrInvalidPublicKey
+		return
+	}
+
+	z, err := prv.GenerateShared(R, params.KeyLen, params.KeyLen)
+	if err != nil {
+		return
+	}
+
+	K, err := concatKDF(hash, z, s1, params.KeyLen+params.KeyLen)
+	if err != nil {
+		return
+	}
+
+	Ke := K[:params.KeyLen]
+	Km := K[params.KeyLen:]
+	hash.Write(Km)
+	Km = hash.Sum(nil)
+	hash.Reset()
+
+	d := messageTag(params.Hash, Km, c[mStart:mEnd], s2)
+	if subtle.ConstantTimeCompare(c[mEnd:], d) != 1 {
+		err = ErrInvalidMessage
+		return
+	}
+
+	m, err = symDecrypt(rand, params, Ke, c[mStart:mEnd])
+	return
+}

params.go

+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"
+	"fmt"
+	"hash"
+)
+
+// The default curve for this package is the NIST P256 curve, which
+// provides security equivalent to AES-128.
+var DefaultCurve = elliptic.P256()
+
+var (
+	ErrUnsupportedECDHAlgorithm   = fmt.Errorf("ecies: unsupported ECDH algorithm")
+	ErrUnsupportedECIESParameters = fmt.Errorf("ecies: unsupported ECIES parameters")
+)
+
+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
+	ECIES_AES256_SHA256 *ECIESParams
+	ECIES_AES256_SHA384 *ECIESParams
+	ECIES_AES256_SHA512 *ECIESParams
+)
+
+func init() {
+	ECIES_AES128_SHA256 = &ECIESParams{
+		Hash:      sha256.New,
+		hashAlgo:  crypto.SHA256,
+		Cipher:    aes.NewCipher,
+		BlockSize: aes.BlockSize,
+		KeyLen:    16,
+	}
+
+	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{
+	elliptic.P256(): ECIES_AES128_SHA256,
+	elliptic.P384(): ECIES_AES256_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 P256, P384, and P512 are supported.
+func ParamsFromCurve(curve elliptic.Curve) (params *ECIESParams) {
+	return paramsFromCurve[curve]
+
+	/*
+		switch curve {
+		case elliptic.P256():
+			return ECIES_AES128_SHA256
+		case elliptic.P384():
+			return ECIES_AES256_SHA384
+		case elliptic.P521():
+			return ECIES_AES256_SHA512
+		default:
+			return nil
+		}
+	*/
+}
+
+// ASN.1 encode the ECIES parameters relevant to the encryption operations.
+func paramsToASNECIES(params *ECIESParams) (asnParams asnECIESParameters) {
+	if nil == params {
+		return
+	}
+	asnParams.KDF = asnNISTConcatenationKDF
+	asnParams.MAC = hmacFull
+	switch params.KeyLen {
+	case 16:
+		asnParams.Sym = aes128CTRinECIES
+	case 24:
+		asnParams.Sym = aes192CTRinECIES
+	case 32:
+		asnParams.Sym = aes256CTRinECIES
+	}
+	return
+}
+
+// ASN.1 encode the ECIES parameters relevant to ECDH.
+func paramsToASNECDH(params *ECIESParams) (algo asnECDHAlgorithm) {
+	switch params.hashAlgo {
+	case crypto.SHA224:
+		algo = dhSinglePass_stdDH_sha224kdf
+	case crypto.SHA256:
+		algo = dhSinglePass_stdDH_sha256kdf
+	case crypto.SHA384:
+		algo = dhSinglePass_stdDH_sha384kdf
+	case crypto.SHA512:
+		algo = dhSinglePass_stdDH_sha512kdf
+	}
+	return
+}
+
+// ASN.1 decode the ECIES parameters relevant to the encryption stage.
+func asnECIEStoParams(asnParams asnECIESParameters, params *ECIESParams) {
+	if !asnParams.KDF.Cmp(asnNISTConcatenationKDF) {
+		params = nil
+		return
+	} else if !asnParams.MAC.Cmp(hmacFull) {
+		params = nil
+		return
+	}
+
+	switch {
+	case asnParams.Sym.Cmp(aes128CTRinECIES):
+		params.KeyLen = 16
+		params.BlockSize = 16
+		params.Cipher = aes.NewCipher
+	case asnParams.Sym.Cmp(aes192CTRinECIES):
+		params.KeyLen = 24
+		params.BlockSize = 16
+		params.Cipher = aes.NewCipher
+	case asnParams.Sym.Cmp(aes256CTRinECIES):
+		params.KeyLen = 32
+		params.BlockSize = 16
+		params.Cipher = aes.NewCipher
+	default:
+		params = nil
+	}
+}
+
+// ASN.1 decode the ECIES parameters relevant to ECDH.
+func asnECDHtoParams(asnParams asnECDHAlgorithm, params *ECIESParams) {
+	if asnParams.Cmp(dhSinglePass_stdDH_sha224kdf) {
+		params.hashAlgo = crypto.SHA224
+		params.Hash = sha256.New224
+	} else if asnParams.Cmp(dhSinglePass_stdDH_sha256kdf) {
+		params.hashAlgo = crypto.SHA256
+		params.Hash = sha256.New
+	} else if asnParams.Cmp(dhSinglePass_stdDH_sha384kdf) {
+		params.hashAlgo = crypto.SHA384
+		params.Hash = sha512.New384
+	} else if asnParams.Cmp(dhSinglePass_stdDH_sha512kdf) {
+		params.hashAlgo = crypto.SHA512
+		params.Hash = sha512.New
+	} else {
+		params = nil
+	}
+}