blob.h revision 6507c27ab7ea34dd150d7ef9fda41878ed32547c 
1/*
2 * Copyright (C) 2015 The Android Open Source Project
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 *      http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
16
17#ifndef KEYSTORE_BLOB_H_
18#define KEYSTORE_BLOB_H_
19
20#include <stdint.h>
21
22#include <openssl/aes.h>
23#include <openssl/md5.h>
24
25#include <keystore/keystore.h>
26
27#define VALUE_SIZE      32768
28
29/* Here is the file format. There are two parts in blob.value, the secret and
30 * the description. The secret is stored in ciphertext, and its original size
31 * can be found in blob.length. The description is stored after the secret in
32 * plaintext, and its size is specified in blob.info. The total size of the two
33 * parts must be no more than VALUE_SIZE bytes. The first field is the version,
34 * the second is the blob's type, and the third byte is flags. Fields other
35 * than blob.info, blob.length, and blob.value are modified by encryptBlob()
36 * and decryptBlob(). Thus they should not be accessed from outside. */
37
38/* ** Note to future implementors of encryption: **
39 * Currently this is the construction:
40 *   metadata || Enc(MD5(data) || data)
41 *
42 * This should be the construction used for encrypting if re-implementing:
43 *
44 *   Derive independent keys for encryption and MAC:
45 *     Kenc = AES_encrypt(masterKey, "Encrypt")
46 *     Kmac = AES_encrypt(masterKey, "MAC")
47 *
48 *   Store this:
49 *     metadata || AES_CTR_encrypt(Kenc, rand_IV, data) ||
50 *             HMAC(Kmac, metadata || Enc(data))
51 */
52struct __attribute__((packed)) blob {
53    uint8_t version;
54    uint8_t type;
55    uint8_t flags;
56    uint8_t info;
57    uint8_t vector[AES_BLOCK_SIZE];
58    uint8_t encrypted[0]; // Marks offset to encrypted data.
59    uint8_t digest[MD5_DIGEST_LENGTH];
60    uint8_t digested[0]; // Marks offset to digested data.
61    int32_t length; // in network byte order when encrypted
62    uint8_t value[VALUE_SIZE + AES_BLOCK_SIZE];
63};
64
65static const uint8_t CURRENT_BLOB_VERSION = 2;
66
67typedef enum {
68    TYPE_ANY = 0, // meta type that matches anything
69    TYPE_GENERIC = 1,
70    TYPE_MASTER_KEY = 2,
71    TYPE_KEY_PAIR = 3,
72    TYPE_KEYMASTER_10 = 4,
73} BlobType;
74
75class Entropy;
76
77class Blob {
78  public:
79    Blob(const uint8_t* value, size_t valueLength, const uint8_t* info, uint8_t infoLength,
80         BlobType type);
81    Blob(blob b);
82
83    Blob();
84
85    const uint8_t* getValue() const { return mBlob.value; }
86
87    int32_t getLength() const { return mBlob.length; }
88
89    const uint8_t* getInfo() const { return mBlob.value + mBlob.length; }
90    uint8_t getInfoLength() const { return mBlob.info; }
91
92    uint8_t getVersion() const { return mBlob.version; }
93
94    bool isEncrypted() const;
95    void setEncrypted(bool encrypted);
96
97    bool isFallback() const { return mBlob.flags & KEYSTORE_FLAG_FALLBACK; }
98    void setFallback(bool fallback);
99
100    void setVersion(uint8_t version) { mBlob.version = version; }
101    BlobType getType() const { return BlobType(mBlob.type); }
102    void setType(BlobType type) { mBlob.type = uint8_t(type); }
103
104    ResponseCode writeBlob(const char* filename, AES_KEY* aes_key, State state, Entropy* entropy);
105    ResponseCode readBlob(const char* filename, AES_KEY* aes_key, State state);
106
107  private:
108    struct blob mBlob;
109};
110
111#endif  // KEYSTORE_BLOB_H_
112