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