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feat: Add support for X25519 key wrapping in ECDH Tink key
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This change also removes redundant ECDH key templates who
were originally intended to include KW primitive logic but
is not necessary since KW is executed outside of the Tink
key.

closes hyperledger-archives#2445

Signed-off-by: Baha Shaaban <[email protected]>
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Baha Shaaban committed Jan 22, 2021
1 parent 1f1d38c commit bd4aa11
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Showing 44 changed files with 1,713 additions and 2,288 deletions.
6 changes: 4 additions & 2 deletions pkg/crypto/api.go
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Original file line number Diff line number Diff line change
Expand Up @@ -42,7 +42,8 @@ type Crypto interface {

// WrapKey will execute key wrapping of cek using apu, apv and recipient public key 'recPubKey'.
// 'opts' allows setting the option sender key handle using WithSender() option. It allows ECDH-1PU key wrapping
// (aka Authcrypt). The absence of this option uses ECDH-ES key wrapping (aka Anoncrypt).
// (aka Authcrypt). The absence of this option uses ECDH-ES key wrapping (aka Anoncrypt). Another option that can
// be used is WithXC20PKW() to instruct the WrapKey to use XC20P key wrapping instead of the default A256GCM.
// returns:
// RecipientWrappedKey containing the wrapped cek value
// error in case of errors
Expand All @@ -51,7 +52,8 @@ type Crypto interface {

// UnwrapKey unwraps a key in recWK using recipient private key kh.
// 'opts' allows setting the option sender key handle using WithSender() option. It allows ECDH-1PU key unwrapping
// (aka Authcrypt). The absence of this option uses ECDH-ES key unwrapping (aka Anoncrypt).
// (aka Authcrypt). The absence of this option uses ECDH-ES key unwrapping (aka Anoncrypt). There is no need to
// use WithXC20PKW() for UnwrapKey since the function will use the wrapping algorithm based on recWK.Alg.
// returns:
// unwrapped key in raw bytes
// error in case of errors
Expand Down
90 changes: 36 additions & 54 deletions pkg/crypto/tinkcrypto/crypto.go
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Original file line number Diff line number Diff line change
Expand Up @@ -11,10 +11,8 @@ SPDX-License-Identifier: Apache-2.0
package tinkcrypto

import (
"crypto/ecdsa"
"errors"
"fmt"
"math/big"

"github.com/google/tink/go/aead"
aeadsubtle "github.com/google/tink/go/aead/subtle"
Expand All @@ -32,6 +30,10 @@ const (
ECDHESA256KWAlg = "ECDH-ES+A256KW"
// ECDH1PUA256KWAlg is the ECDH-1PU with AES-GCM 256 key wrapping algorithm.
ECDH1PUA256KWAlg = "ECDH-1PU+A256KW"
// ECDHESXC20PKWAlg is the ECDH-ES with XChacha20Poly1305 key wrapping algorithm.
ECDHESXC20PKWAlg = "ECDH-ES+XC20PKW"
// ECDH1PUXC20PKWAlg is the ECDH-1PU with XChacha20Poly1305 key wrapping algorithm.
ECDH1PUXC20PKWAlg = "ECDH-1PU+XC20PKW"
)

var errBadKeyHandleFormat = errors.New("bad key handle format")
Expand All @@ -43,12 +45,13 @@ var errBadKeyHandleFormat = errors.New("bad key handle format")

// Crypto is the default Crypto SPI implementation using Tink.
type Crypto struct {
kw keyWrapper
ecKW keyWrapper
okpKW keyWrapper
}

// New creates a new Crypto instance.
func New() (*Crypto, error) {
return &Crypto{kw: &keyWrapperSupport{}}, nil
return &Crypto{ecKW: &ecKWSupport{}, okpKW: &okpKWSupport{}}, nil
}

// Encrypt will encrypt msg using the implementation's corresponding encryption key and primitive in kh of a public key.
Expand Down Expand Up @@ -203,11 +206,13 @@ func (t *Crypto) VerifyMAC(macBytes, data []byte, kh interface{}) error {
}

// WrapKey will do ECDH (ES or 1PU) key wrapping of cek using apu, apv and recipient public key 'recPubKey'.
// The optional 'wrapKeyOpts' specifies the sender kh for 1PU key wrapping.
// This function is used with the following parameters:
// - Key Wrapping: ECDH-ES (no options)/ECDH-1PU (using crypto.WithSender() option) over A256KW as
// per https://tools.ietf.org/html/rfc7518#appendix-A.2
// - KDF: Concat KDF as per https://tools.ietf.org/html/rfc7518#section-4.6
// - Key Wrapping: `ECDH-ES` (no options) or `ECDH-1PU` (using crypto.WithSender() option in wrapKeyOpts) over either
// `A256KW` alg (AES256-GCM, default with no options) as per https://tools.ietf.org/html/rfc7518#appendix-A.2 or
// `XC20PKW` alg (XChacha20Poly1305, using crypto.WithXC20PKW() option in wrapKeyOpts).
// - KDF (based on recPubKey.Curve): `Concat KDF` as per https://tools.ietf.org/html/rfc7518#section-4.6 (for recPubKey
// with NIST P curves) or `Curve25519`+`Concat KDF` as per https://tools.ietf.org/html/rfc7748#section-6.1 (for
// recPubKey with X25519 curve).
// returns the resulting key wrapping info as *composite.RecipientWrappedKey or error in case of wrapping failure.
func (t *Crypto) WrapKey(cek, apu, apv []byte, recPubKey *cryptoapi.PublicKey,
wrapKeyOpts ...cryptoapi.WrapKeyOpts) (*cryptoapi.RecipientWrappedKey, error) {
Expand All @@ -221,34 +226,34 @@ func (t *Crypto) WrapKey(cek, apu, apv []byte, recPubKey *cryptoapi.PublicKey,
opt(pOpts)
}

c, err := t.kw.getCurve(recPubKey.Curve)
wk, err := t.deriveKEKAndWrap(cek, apu, apv, pOpts.SenderKey(), recPubKey, pOpts.UseXC20PKW())
if err != nil {
return nil, fmt.Errorf("wrapKey: failed to get curve of recipient key: %w", err)
return nil, fmt.Errorf("wrapKey: %w", err)
}

pubKey := &ecdsa.PublicKey{
Curve: c,
X: new(big.Int).SetBytes(recPubKey.X),
Y: new(big.Int).SetBytes(recPubKey.Y),
}

ephemeralPriv, err := t.kw.generateKey(pubKey.Curve)
if err != nil {
return nil, fmt.Errorf("wrapKey: failed to generate EPK: %w", err)
}

return t.deriveKEKAndWrap(cek, apu, apv, pOpts.SenderKey(), ephemeralPriv, pubKey, recPubKey.KID)
return wk, nil
}

// UnwrapKey unwraps a key in recWK using ECDH (ES or 1PU) with recipient private key kh.
// The optional 'wrapKeyOpts' specifies the sender kh for 1PU key unwrapping.
// Note, if the option was used in WrapKey(), then it must be set here as well for a successful unwrapping.
// This function is used with the following parameters:
// - Key Unwrapping: ECDH-ES (no options)/ECDH-1PU (using crypto.WithSender() option) over A256KW as
// per https://tools.ietf.org/html/rfc7518#appendix-A.2
// - KDF: Concat KDF as per https://tools.ietf.org/html/rfc7518#section-4.6
// - Key Unwrapping: `ECDH-ES` (no options) or `ECDH-1PU` (using crypto.WithSender() option in wrapKeyOpts) over either
// `A256KW` alg (AES256-GCM, when recWK.alg is either ECDH-ES+A256KW or ECDH-1PU+A256KW) as per
// https://tools.ietf.org/html/rfc7518#appendix-A.2 or
// `XC20PKW` alg (XChacha20Poly1305, when recWK.alg is either ECDH-ES+XC20PKW or ECDH-1PU+XC20PKW).
// - KDF (based on recWk.EPK.KeyType): `Concat KDF` as per https://tools.ietf.org/html/rfc7518#section-4.6 (for type
// value as EC) or `Curve25519`+`Concat KDF` as per https://tools.ietf.org/html/rfc7748#section-6.1 (for type value
// as OKP, ie X25519 key).
// returns the resulting unwrapping key or error in case of unwrapping failure.
func (t *Crypto) UnwrapKey(recWK *cryptoapi.RecipientWrappedKey, kh interface{},
//
// Notes:
// 1- if the crypto.WithSender() option was used in WrapKey(), then it must be set here as well for successful key
// unwrapping.
// 2- unwrapping a key with recWK.alg value set as either `ECDH-1PU+A256KW` or `ECDH-1PU+XC20PKW` requires the use of
// crypto.WithSender() option (containing the sender public key) in order to execute ECDH-1PU derivation.
// 3- the ephemeral key in recWK.EPK must have the same KeyType as the recipientKH and the same Curve for NIST P
// curved keys. Unwrapping a key with non matching types/curves will result in unwrapping failure.
// 4- recipientKH must contain the private key since unwrapping is usually done on the recipient side.
func (t *Crypto) UnwrapKey(recWK *cryptoapi.RecipientWrappedKey, recipientKH interface{},
wrapKeyOpts ...cryptoapi.WrapKeyOpts) ([]byte, error) {
if recWK == nil {
return nil, fmt.Errorf("unwrapKey: RecipientWrappedKey is empty")
Expand All @@ -260,34 +265,11 @@ func (t *Crypto) UnwrapKey(recWK *cryptoapi.RecipientWrappedKey, kh interface{},
opt(pOpts)
}

privKey, ok := kh.(*keyset.Handle)
if !ok {
return nil, fmt.Errorf("unwrapKey: %w", errBadKeyHandleFormat)
}

recipientPrivateKey, err := extractPrivKey(privKey)
key, err := t.deriveKEKAndUnwrap(recWK.Alg, recWK.EncryptedCEK, recWK.APU, recWK.APV, &recWK.EPK, pOpts.SenderKey(),
recipientKH)
if err != nil {
return nil, fmt.Errorf("unwrapKey: %w", err)
}

// TODO: add support for 25519 key wrapping https://github.com/hyperledger/aries-framework-go/issues/2445
recPrivKey := hybridECPrivToECDSAKey(recipientPrivateKey)

epkCurve, err := t.kw.getCurve(recWK.EPK.Curve)
if err != nil {
return nil, fmt.Errorf("unwrapKey: failed to GetCurve: %w", err)
}

if recipientPrivateKey.PublicKey.Curve != epkCurve {
return nil, errors.New("unwrapKey: recipient and epk keys are not on the same curve")
}

epkPubKey := &ecdsa.PublicKey{
Curve: epkCurve,
X: new(big.Int).SetBytes(recWK.EPK.X),
Y: new(big.Int).SetBytes(recWK.EPK.Y),
}

return t.deriveKEKAndUnwrap(recWK.Alg, recWK.EncryptedCEK, recWK.APU, recWK.APV, pOpts.SenderKey(),
epkPubKey, recPrivKey)
return key, nil
}
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