Home | History | Annotate | Download | only in keystore
      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  */
     52 struct __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 
     65 static const uint8_t CURRENT_BLOB_VERSION = 2;
     66 
     67 typedef 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 
     75 class Entropy;
     76 
     77 class 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