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dex/vendor/gopkg.in/square/go-jose.v2/symmetric.go
2016-07-26 15:51:24 -07:00

349 lines
7.9 KiB
Go

/*-
* Copyright 2014 Square Inc.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package jose
import (
"crypto/aes"
"crypto/cipher"
"crypto/hmac"
"crypto/rand"
"crypto/sha256"
"crypto/sha512"
"crypto/subtle"
"errors"
"hash"
"io"
"gopkg.in/square/go-jose.v2/cipher"
)
// Random reader (stubbed out in tests)
var randReader = rand.Reader
// Dummy key cipher for shared symmetric key mode
type symmetricKeyCipher struct {
key []byte // Pre-shared content-encryption key
}
// Signer/verifier for MAC modes
type symmetricMac struct {
key []byte
}
// Input/output from an AEAD operation
type aeadParts struct {
iv, ciphertext, tag []byte
}
// A content cipher based on an AEAD construction
type aeadContentCipher struct {
keyBytes int
authtagBytes int
getAead func(key []byte) (cipher.AEAD, error)
}
// Random key generator
type randomKeyGenerator struct {
size int
}
// Static key generator
type staticKeyGenerator struct {
key []byte
}
// Create a new content cipher based on AES-GCM
func newAESGCM(keySize int) contentCipher {
return &aeadContentCipher{
keyBytes: keySize,
authtagBytes: 16,
getAead: func(key []byte) (cipher.AEAD, error) {
aes, err := aes.NewCipher(key)
if err != nil {
return nil, err
}
return cipher.NewGCM(aes)
},
}
}
// Create a new content cipher based on AES-CBC+HMAC
func newAESCBC(keySize int) contentCipher {
return &aeadContentCipher{
keyBytes: keySize * 2,
authtagBytes: 16,
getAead: func(key []byte) (cipher.AEAD, error) {
return josecipher.NewCBCHMAC(key, aes.NewCipher)
},
}
}
// Get an AEAD cipher object for the given content encryption algorithm
func getContentCipher(alg ContentEncryption) contentCipher {
switch alg {
case A128GCM:
return newAESGCM(16)
case A192GCM:
return newAESGCM(24)
case A256GCM:
return newAESGCM(32)
case A128CBC_HS256:
return newAESCBC(16)
case A192CBC_HS384:
return newAESCBC(24)
case A256CBC_HS512:
return newAESCBC(32)
default:
return nil
}
}
// newSymmetricRecipient creates a JWE encrypter based on AES-GCM key wrap.
func newSymmetricRecipient(keyAlg KeyAlgorithm, key []byte) (recipientKeyInfo, error) {
switch keyAlg {
case DIRECT, A128GCMKW, A192GCMKW, A256GCMKW, A128KW, A192KW, A256KW:
default:
return recipientKeyInfo{}, ErrUnsupportedAlgorithm
}
return recipientKeyInfo{
keyAlg: keyAlg,
keyEncrypter: &symmetricKeyCipher{
key: key,
},
}, nil
}
// newSymmetricSigner creates a recipientSigInfo based on the given key.
func newSymmetricSigner(sigAlg SignatureAlgorithm, key []byte) (recipientSigInfo, error) {
// Verify that key management algorithm is supported by this encrypter
switch sigAlg {
case HS256, HS384, HS512:
default:
return recipientSigInfo{}, ErrUnsupportedAlgorithm
}
return recipientSigInfo{
sigAlg: sigAlg,
signer: &symmetricMac{
key: key,
},
}, nil
}
// Generate a random key for the given content cipher
func (ctx randomKeyGenerator) genKey() ([]byte, rawHeader, error) {
key := make([]byte, ctx.size)
_, err := io.ReadFull(randReader, key)
if err != nil {
return nil, rawHeader{}, err
}
return key, rawHeader{}, nil
}
// Key size for random generator
func (ctx randomKeyGenerator) keySize() int {
return ctx.size
}
// Generate a static key (for direct mode)
func (ctx staticKeyGenerator) genKey() ([]byte, rawHeader, error) {
cek := make([]byte, len(ctx.key))
copy(cek, ctx.key)
return cek, rawHeader{}, nil
}
// Key size for static generator
func (ctx staticKeyGenerator) keySize() int {
return len(ctx.key)
}
// Get key size for this cipher
func (ctx aeadContentCipher) keySize() int {
return ctx.keyBytes
}
// Encrypt some data
func (ctx aeadContentCipher) encrypt(key, aad, pt []byte) (*aeadParts, error) {
// Get a new AEAD instance
aead, err := ctx.getAead(key)
if err != nil {
return nil, err
}
// Initialize a new nonce
iv := make([]byte, aead.NonceSize())
_, err = io.ReadFull(randReader, iv)
if err != nil {
return nil, err
}
ciphertextAndTag := aead.Seal(nil, iv, pt, aad)
offset := len(ciphertextAndTag) - ctx.authtagBytes
return &aeadParts{
iv: iv,
ciphertext: ciphertextAndTag[:offset],
tag: ciphertextAndTag[offset:],
}, nil
}
// Decrypt some data
func (ctx aeadContentCipher) decrypt(key, aad []byte, parts *aeadParts) ([]byte, error) {
aead, err := ctx.getAead(key)
if err != nil {
return nil, err
}
return aead.Open(nil, parts.iv, append(parts.ciphertext, parts.tag...), aad)
}
// Encrypt the content encryption key.
func (ctx *symmetricKeyCipher) encryptKey(cek []byte, alg KeyAlgorithm) (recipientInfo, error) {
switch alg {
case DIRECT:
return recipientInfo{
header: &rawHeader{},
}, nil
case A128GCMKW, A192GCMKW, A256GCMKW:
aead := newAESGCM(len(ctx.key))
parts, err := aead.encrypt(ctx.key, []byte{}, cek)
if err != nil {
return recipientInfo{}, err
}
return recipientInfo{
header: &rawHeader{
Iv: newBuffer(parts.iv),
Tag: newBuffer(parts.tag),
},
encryptedKey: parts.ciphertext,
}, nil
case A128KW, A192KW, A256KW:
block, err := aes.NewCipher(ctx.key)
if err != nil {
return recipientInfo{}, err
}
jek, err := josecipher.KeyWrap(block, cek)
if err != nil {
return recipientInfo{}, err
}
return recipientInfo{
encryptedKey: jek,
header: &rawHeader{},
}, nil
}
return recipientInfo{}, ErrUnsupportedAlgorithm
}
// Decrypt the content encryption key.
func (ctx *symmetricKeyCipher) decryptKey(headers rawHeader, recipient *recipientInfo, generator keyGenerator) ([]byte, error) {
switch KeyAlgorithm(headers.Alg) {
case DIRECT:
cek := make([]byte, len(ctx.key))
copy(cek, ctx.key)
return cek, nil
case A128GCMKW, A192GCMKW, A256GCMKW:
aead := newAESGCM(len(ctx.key))
parts := &aeadParts{
iv: headers.Iv.bytes(),
ciphertext: recipient.encryptedKey,
tag: headers.Tag.bytes(),
}
cek, err := aead.decrypt(ctx.key, []byte{}, parts)
if err != nil {
return nil, err
}
return cek, nil
case A128KW, A192KW, A256KW:
block, err := aes.NewCipher(ctx.key)
if err != nil {
return nil, err
}
cek, err := josecipher.KeyUnwrap(block, recipient.encryptedKey)
if err != nil {
return nil, err
}
return cek, nil
}
return nil, ErrUnsupportedAlgorithm
}
// Sign the given payload
func (ctx symmetricMac) signPayload(payload []byte, alg SignatureAlgorithm) (Signature, error) {
mac, err := ctx.hmac(payload, alg)
if err != nil {
return Signature{}, errors.New("square/go-jose: failed to compute hmac")
}
return Signature{
Signature: mac,
protected: &rawHeader{},
}, nil
}
// Verify the given payload
func (ctx symmetricMac) verifyPayload(payload []byte, mac []byte, alg SignatureAlgorithm) error {
expected, err := ctx.hmac(payload, alg)
if err != nil {
return errors.New("square/go-jose: failed to compute hmac")
}
if len(mac) != len(expected) {
return errors.New("square/go-jose: invalid hmac")
}
match := subtle.ConstantTimeCompare(mac, expected)
if match != 1 {
return errors.New("square/go-jose: invalid hmac")
}
return nil
}
// Compute the HMAC based on the given alg value
func (ctx symmetricMac) hmac(payload []byte, alg SignatureAlgorithm) ([]byte, error) {
var hash func() hash.Hash
switch alg {
case HS256:
hash = sha256.New
case HS384:
hash = sha512.New384
case HS512:
hash = sha512.New
default:
return nil, ErrUnsupportedAlgorithm
}
hmac := hmac.New(hash, ctx.key)
// According to documentation, Write() on hash never fails
_, _ = hmac.Write(payload)
return hmac.Sum(nil), nil
}