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package jose
import (
"crypto/ecdsa"
"crypto/elliptic"
"crypto/rand"
"crypto/sha256"
"errors"
"fmt"
"github.com/dvsekhvalnov/jose2go/arrays"
"github.com/dvsekhvalnov/jose2go/base64url"
"github.com/dvsekhvalnov/jose2go/kdf"
"github.com/dvsekhvalnov/jose2go/keys/ecc"
"github.com/dvsekhvalnov/jose2go/padding"
"math/big"
)
func init() {
RegisterJwa(&Ecdh{directAgreement: true})
}
// Elliptic curve Diffie–Hellman key management (key agreement) algorithm implementation
type Ecdh struct {
directAgreement bool
}
func (alg *Ecdh) Name() string {
return ECDH_ES
}
func (alg *Ecdh) WrapNewKey(cekSizeBits int, key interface{}, header map[string]interface{}) (cek []byte, encryptedCek []byte, err error) {
if pubKey, ok := key.(*ecdsa.PublicKey); ok {
if _, ok := header[alg.idHeader()].(string); !ok {
return nil, nil, errors.New(fmt.Sprintf("Ecdh.WrapNewKey(): expected '%v' param in JWT header, but was not found.", alg.idHeader()))
}
var d []byte
var x, y *big.Int
if d, x, y, err = elliptic.GenerateKey(pubKey.Curve, rand.Reader); err != nil {
return nil, nil, err
}
ephemeral := ecc.NewPrivate(x.Bytes(), y.Bytes(), d)
xBytes := padding.Align(x.Bytes(), pubKey.Curve.Params().BitSize)
yBytes := padding.Align(y.Bytes(), pubKey.Curve.Params().BitSize)
epk := map[string]string{
"kty": "EC",
"x": base64url.Encode(xBytes),
"y": base64url.Encode(yBytes),
"crv": name(pubKey.Curve),
}
header["epk"] = epk
return alg.deriveKey(pubKey, ephemeral, cekSizeBits, header), nil, nil
}
return nil, nil, errors.New("Ecdh.WrapNewKey(): expected key to be '*ecdsa.PublicKey'")
}
func (alg *Ecdh) Unwrap(encryptedCek []byte, key interface{}, cekSizeBits int, header map[string]interface{}) (cek []byte, err error) {
if privKey, ok := key.(*ecdsa.PrivateKey); ok {
var epk map[string]interface{}
if epk, ok = header["epk"].(map[string]interface{}); !ok {
return nil, errors.New("Ecdh.Unwrap(): expected 'epk' param in JWT header, but was not found.")
}
if _, ok := header[alg.idHeader()].(string); !ok {
return nil, errors.New(fmt.Sprintf("Ecdh.Unwrap(): expected '%v' param in JWT header, but was not found.", alg.idHeader()))
}
var x, y, crv string
var xBytes, yBytes []byte
if x, ok = epk["x"].(string); !ok {
return nil, errors.New("Ecdh.Unwrap(): expects 'epk' key to contain 'x','y' and 'crv' fields, but 'x' was not found.")
}
if y, ok = epk["y"].(string); !ok {
return nil, errors.New("Ecdh.Unwrap(): expects 'epk' key to contain 'x','y' and 'crv' fields, but 'y' was not found.")
}
if crv, ok = epk["crv"].(string); !ok {
return nil, errors.New("Ecdh.Unwrap(): expects 'epk' key to contain 'x','y' and 'crv' fields, but 'crv' was not found.")
}
if crv != "P-256" && crv != "P-384" && crv != "P-521" {
return nil, errors.New(fmt.Sprintf("Ecdh.Unwrap(): unknown or unsupported curve %v", crv))
}
if xBytes, err = base64url.Decode(x); err != nil {
return nil, err
}
if yBytes, err = base64url.Decode(y); err != nil {
return nil, err
}
pubKey := ecc.NewPublic(xBytes, yBytes)
if !privKey.Curve.IsOnCurve(pubKey.X, pubKey.Y) {
return nil, errors.New(fmt.Sprintf("Ephemeral public key received in header is invalid for reciever's private key."))
}
return alg.deriveKey(pubKey, privKey, cekSizeBits, header), nil
}
return nil, errors.New("Ecdh.Unwrap(): expected key to be '*ecdsa.PrivateKey'")
}
func (alg *Ecdh) deriveKey(pubKey *ecdsa.PublicKey, privKey *ecdsa.PrivateKey, keySizeBits int, header map[string]interface{}) []byte {
var enc, apv, apu []byte
var err error
enc = []byte(header[alg.idHeader()].(string))
if a, ok := header["apv"].(string); !ok {
if apv, err = base64url.Decode(a); err != nil {
apv = nil
}
}
if a, ok := header["apu"].(string); !ok {
if apu, err = base64url.Decode(a); err != nil {
apu = nil
}
}
z, _ := pubKey.Curve.ScalarMult(pubKey.X, pubKey.Y, privKey.D.Bytes())
zBytes := padding.Align(z.Bytes(), privKey.Curve.Params().BitSize)
return kdf.DeriveConcatKDF(keySizeBits, zBytes, prependDatalen(enc), prependDatalen(apu), prependDatalen(apv), arrays.UInt32ToBytes(uint32(keySizeBits)), nil, sha256.New())
}
func (alg *Ecdh) idHeader() string {
if alg.directAgreement {
return "enc"
}
return "alg"
}
func name(curve elliptic.Curve) string {
return fmt.Sprintf("P-%v", curve.Params().BitSize)
}
func prependDatalen(bytes []byte) []byte {
return arrays.Concat(arrays.UInt32ToBytes(uint32(len(bytes))), bytes)
}
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