1 /*
2  * Copyright (C) 2010 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 /* This structure starts 16,384 bytes before the end of a hardware
18  * partition that is encrypted, or in a separate partition.  It's location
19  * is specified by a property set in init.<device>.rc.
20  * The structure allocates 48 bytes for a key, but the real key size is
21  * specified in the struct.  Currently, the code is hardcoded to use 128
22  * bit keys.
23  * The fields after salt are only valid in rev 1.1 and later stuctures.
24  * Obviously, the filesystem does not include the last 16 kbytes
25  * of the partition if the crypt_mnt_ftr lives at the end of the
26  * partition.
27  */
28 
29 #include <stdbool.h>
30 #include <cutils/properties.h>
31 
32 /* The current cryptfs version */
33 #define CURRENT_MAJOR_VERSION 1
34 #define CURRENT_MINOR_VERSION 3
35 
36 #define CRYPT_FOOTER_OFFSET 0x4000
37 #define CRYPT_FOOTER_TO_PERSIST_OFFSET 0x1000
38 #define CRYPT_PERSIST_DATA_SIZE 0x1000
39 
40 #define MAX_CRYPTO_TYPE_NAME_LEN 64
41 
42 #define MAX_KEY_LEN 48
43 #define SALT_LEN 16
44 #define SCRYPT_LEN 32
45 
46 /* definitions of flags in the structure below */
47 #define CRYPT_MNT_KEY_UNENCRYPTED 0x1 /* The key for the partition is not encrypted. */
48 #define CRYPT_ENCRYPTION_IN_PROGRESS 0x2 /* Encryption partially completed,
49                                             encrypted_upto valid*/
50 #define CRYPT_INCONSISTENT_STATE 0x4 /* Set when starting encryption, clear when
51                                         exit cleanly, either through success or
52                                         correctly marked partial encryption */
53 #define CRYPT_DATA_CORRUPT 0x8 /* Set when encryption is fine, but the
54                                   underlying volume is corrupt */
55 
56 /* Allowed values for type in the structure below */
57 #define CRYPT_TYPE_PASSWORD 0 /* master_key is encrypted with a password
58                                * Must be zero to be compatible with pre-L
59                                * devices where type is always password.*/
60 #define CRYPT_TYPE_DEFAULT  1 /* master_key is encrypted with default
61                                * password */
62 #define CRYPT_TYPE_PATTERN  2 /* master_key is encrypted with a pattern */
63 #define CRYPT_TYPE_PIN      3 /* master_key is encrypted with a pin */
64 #define CRYPT_TYPE_MAX_TYPE 3 /* type cannot be larger than this value */
65 
66 #define CRYPT_MNT_MAGIC 0xD0B5B1C4
67 #define PERSIST_DATA_MAGIC 0xE950CD44
68 
69 #define SCRYPT_PROP "ro.crypto.scrypt_params"
70 #define SCRYPT_DEFAULTS { 15, 3, 1 }
71 
72 /* Key Derivation Function algorithms */
73 #define KDF_PBKDF2 1
74 #define KDF_SCRYPT 2
75 /* Algorithms 3 & 4 deprecated before shipping outside of google, so removed */
76 #define KDF_SCRYPT_KEYMASTER 5
77 
78 /* Maximum allowed keymaster blob size. */
79 #define KEYMASTER_BLOB_SIZE 2048
80 
81 /* __le32 and __le16 defined in system/extras/ext4_utils/ext4_utils.h */
82 #define __le8  unsigned char
83 
84 #if !defined(SHA256_DIGEST_LENGTH)
85 #define SHA256_DIGEST_LENGTH 32
86 #endif
87 
88 struct crypt_mnt_ftr {
89   __le32 magic;         /* See above */
90   __le16 major_version;
91   __le16 minor_version;
92   __le32 ftr_size;      /* in bytes, not including key following */
93   __le32 flags;         /* See above */
94   __le32 keysize;       /* in bytes */
95   __le32 crypt_type;    /* how master_key is encrypted. Must be a
96                          * CRYPT_TYPE_XXX value */
97   __le64 fs_size;	/* Size of the encrypted fs, in 512 byte sectors */
98   __le32 failed_decrypt_count; /* count of # of failed attempts to decrypt and
99                                   mount, set to 0 on successful mount */
100   unsigned char crypto_type_name[MAX_CRYPTO_TYPE_NAME_LEN]; /* The type of encryption
101                                                                needed to decrypt this
102                                                                partition, null terminated */
103   __le32 spare2;        /* ignored */
104   unsigned char master_key[MAX_KEY_LEN]; /* The encrypted key for decrypting the filesystem */
105   unsigned char salt[SALT_LEN];   /* The salt used for this encryption */
106   __le64 persist_data_offset[2];  /* Absolute offset to both copies of crypt_persist_data
107                                    * on device with that info, either the footer of the
108                                    * real_blkdevice or the metadata partition. */
109 
110   __le32 persist_data_size;       /* The number of bytes allocated to each copy of the
111                                    * persistent data table*/
112 
113   __le8  kdf_type; /* The key derivation function used. */
114 
115   /* scrypt parameters. See www.tarsnap.com/scrypt/scrypt.pdf */
116   __le8  N_factor; /* (1 << N) */
117   __le8  r_factor; /* (1 << r) */
118   __le8  p_factor; /* (1 << p) */
119   __le64 encrypted_upto; /* If we are in state CRYPT_ENCRYPTION_IN_PROGRESS and
120                             we have to stop (e.g. power low) this is the last
121                             encrypted 512 byte sector.*/
122   __le8  hash_first_block[SHA256_DIGEST_LENGTH]; /* When CRYPT_ENCRYPTION_IN_PROGRESS
123                                                     set, hash of first block, used
124                                                     to validate before continuing*/
125 
126   /* key_master key, used to sign the derived key which is then used to generate
127    * the intermediate key
128    * This key should be used for no other purposes! We use this key to sign unpadded
129    * data, which is acceptable but only if the key is not reused elsewhere. */
130   __le8 keymaster_blob[KEYMASTER_BLOB_SIZE];
131   __le32 keymaster_blob_size;
132 
133   /* Store scrypt of salted intermediate key. When decryption fails, we can
134      check if this matches, and if it does, we know that the problem is with the
135      drive, and there is no point in asking the user for more passwords.
136 
137      Note that if any part of this structure is corrupt, this will not match and
138      we will continue to believe the user entered the wrong password. In that
139      case the only solution is for the user to enter a password enough times to
140      force a wipe.
141 
142      Note also that there is no need to worry about migration. If this data is
143      wrong, we simply won't recognise a right password, and will continue to
144      prompt. On the first password change, this value will be populated and
145      then we will be OK.
146    */
147   unsigned char scrypted_intermediate_key[SCRYPT_LEN];
148 };
149 
150 /* Persistant data that should be available before decryption.
151  * Things like airplane mode, locale and timezone are kept
152  * here and can be retrieved by the CryptKeeper UI to properly
153  * configure the phone before asking for the password
154  * This is only valid if the major and minor version above
155  * is set to 1.1 or higher.
156  *
157  * This is a 4K structure.  There are 2 copies, and the code alternates
158  * writing one and then clearing the previous one.  The reading
159  * code reads the first valid copy it finds, based on the magic number.
160  * The absolute offset to the first of the two copies is kept in rev 1.1
161  * and higher crypt_mnt_ftr structures.
162  */
163 struct crypt_persist_entry {
164   char key[PROPERTY_KEY_MAX];
165   char val[PROPERTY_VALUE_MAX];
166 };
167 
168 /* Should be exactly 4K in size */
169 struct crypt_persist_data {
170   __le32 persist_magic;
171   __le32 persist_valid_entries;
172   __le32 persist_spare[30];
173   struct crypt_persist_entry persist_entry[0];
174 };
175 
176 #define DATA_MNT_POINT "/data"
177 
178 /* Return values for cryptfs_crypto_complete */
179 #define CRYPTO_COMPLETE_NOT_ENCRYPTED  1
180 #define CRYPTO_COMPLETE_ENCRYPTED      0
181 #define CRYPTO_COMPLETE_BAD_METADATA  -1
182 #define CRYPTO_COMPLETE_PARTIAL       -2
183 #define CRYPTO_COMPLETE_INCONSISTENT  -3
184 #define CRYPTO_COMPLETE_CORRUPT       -4
185 
186 /* Return values for cryptfs_enable_inplace*() */
187 #define ENABLE_INPLACE_OK 0
188 #define ENABLE_INPLACE_ERR_OTHER -1
189 #define ENABLE_INPLACE_ERR_DEV -2  /* crypto_blkdev issue */
190 
191 /* Return values for cryptfs_getfield */
192 #define CRYPTO_GETFIELD_OK                   0
193 #define CRYPTO_GETFIELD_ERROR_NO_FIELD      -1
194 #define CRYPTO_GETFIELD_ERROR_OTHER         -2
195 #define CRYPTO_GETFIELD_ERROR_BUF_TOO_SMALL -3
196 
197 /* Return values for cryptfs_setfield */
198 #define CRYPTO_SETFIELD_OK                    0
199 #define CRYPTO_SETFIELD_ERROR_OTHER          -1
200 #define CRYPTO_SETFIELD_ERROR_FIELD_TOO_LONG -2
201 #define CRYPTO_SETFIELD_ERROR_VALUE_TOO_LONG -3
202 
203 /* Return values for persist_del_key */
204 #define PERSIST_DEL_KEY_OK                 0
205 #define PERSIST_DEL_KEY_ERROR_OTHER       -1
206 #define PERSIST_DEL_KEY_ERROR_NO_FIELD    -2
207 
208 #ifdef __cplusplus
209 extern "C" {
210 #endif
211 
212   int wait_and_unmount(const char *mountpoint, bool kill);
213 
214   typedef int (*kdf_func)(const char *passwd, const unsigned char *salt,
215                           unsigned char *ikey, void *params);
216 
217   int cryptfs_crypto_complete(void);
218   int cryptfs_check_passwd(char *pw);
219   int cryptfs_verify_passwd(char *newpw);
220   int cryptfs_restart(void);
221   int cryptfs_enable(char *flag, int type, char *passwd, int allow_reboot);
222   int cryptfs_changepw(int type, const char *newpw);
223   int cryptfs_enable_default(char *flag, int allow_reboot);
224   int cryptfs_setup_ext_volume(const char* label, const char* real_blkdev,
225           const unsigned char* key, int keysize, char* out_crypto_blkdev);
226   int cryptfs_revert_ext_volume(const char* label);
227   int cryptfs_enable_file();
228   int cryptfs_getfield(const char *fieldname, char *value, int len);
229   int cryptfs_setfield(const char *fieldname, const char *value);
230   int cryptfs_mount_default_encrypted(void);
231   int cryptfs_get_password_type(void);
232   const char* cryptfs_get_password(void);
233   void cryptfs_clear_password(void);
234 
235   // Functions for file encryption to use to inherit our encryption logic
236   int cryptfs_create_default_ftr(struct crypt_mnt_ftr* ftr, int key_length);
237   int cryptfs_get_master_key(struct crypt_mnt_ftr* ftr, const char* password,
238                              unsigned char* master_key);
239   int cryptfs_set_password(struct crypt_mnt_ftr* ftr, const char* password,
240                            const unsigned char* master_key);
241 #ifdef __cplusplus
242 }
243 #endif
244