int DeviceKey::generate_derived_key(const unsigned char *salt, size_t isalt_size, unsigned char *output,
uint16_t ikey_type)
{
uint32_t key_buff[DEVICE_KEY_32BYTE / sizeof(uint32_t)];
size_t actual_size = DEVICE_KEY_32BYTE;
if (DEVICE_KEY_16BYTE != ikey_type && DEVICE_KEY_32BYTE != ikey_type) {
return DEVICEKEY_INVALID_KEY_TYPE;
}
actual_size = DEVICE_KEY_16BYTE != ikey_type ? DEVICE_KEY_32BYTE : DEVICE_KEY_16BYTE;
//First try to read the key from KVStore
int ret = read_key_from_kvstore(key_buff, actual_size);
if (DEVICEKEY_SUCCESS != ret && DEVICEKEY_NOT_FOUND != ret) {
return ret;
}
//If the key was not found in KVStore we will create it by using random generation and then save it to KVStore
if (DEVICEKEY_NOT_FOUND == ret) {
ret = generate_key_by_random(key_buff, actual_size);
if (DEVICEKEY_SUCCESS != ret) {
return ret;
}
ret = device_inject_root_of_trust(key_buff, actual_size);
if (DEVICEKEY_SUCCESS != ret) {
return ret;
}
}
ret = get_derived_key(key_buff, actual_size, salt, isalt_size, output, ikey_type);
return ret;
}
/*
* encrypted_read - format and copy the encrypted data to userspace
*
* The resulting datablob format is:
* <master-key name> <decrypted data length> <encrypted iv> <encrypted data>
*
* On success, return to userspace the encrypted key datablob size.
*/
static long encrypted_read(const struct key *key, char __user *buffer,
size_t buflen)
{
struct encrypted_key_payload *epayload;
struct key *mkey;
const u8 *master_key;
size_t master_keylen;
char derived_key[HASH_SIZE];
char *ascii_buf;
size_t asciiblob_len;
int ret;
epayload = rcu_dereference_key(key);
/* returns the hex encoded iv, encrypted-data, and hmac as ascii */
asciiblob_len = epayload->datablob_len + ivsize + 1
+ roundup(epayload->decrypted_datalen, blksize)
+ (HASH_SIZE * 2);
if (!buffer || buflen < asciiblob_len)
return asciiblob_len;
mkey = request_master_key(epayload, &master_key, &master_keylen);
if (IS_ERR(mkey))
return PTR_ERR(mkey);
ret = get_derived_key(derived_key, ENC_KEY, master_key, master_keylen);
if (ret < 0)
goto out;
ret = derived_key_encrypt(epayload, derived_key, sizeof derived_key);
if (ret < 0)
goto out;
ret = datablob_hmac_append(epayload, master_key, master_keylen);
if (ret < 0)
goto out;
ascii_buf = datablob_format(epayload, asciiblob_len);
if (!ascii_buf) {
ret = -ENOMEM;
goto out;
}
up_read(&mkey->sem);
key_put(mkey);
if (copy_to_user(buffer, ascii_buf, asciiblob_len) != 0)
ret = -EFAULT;
kfree(ascii_buf);
return asciiblob_len;
out:
up_read(&mkey->sem);
key_put(mkey);
return ret;
}
static int encrypted_key_decrypt(struct encrypted_key_payload *epayload,
const char *format, const char *hex_encoded_iv)
{
struct key *mkey;
u8 derived_key[HASH_SIZE];
const u8 *master_key;
u8 *hmac;
const char *hex_encoded_data;
unsigned int encrypted_datalen;
size_t master_keylen;
size_t asciilen;
int ret;
encrypted_datalen = roundup(epayload->decrypted_datalen, blksize);
asciilen = (ivsize + 1 + encrypted_datalen + HASH_SIZE) * 2;
if (strlen(hex_encoded_iv) != asciilen)
return -EINVAL;
hex_encoded_data = hex_encoded_iv + (2 * ivsize) + 2;
ret = hex2bin(epayload->iv, hex_encoded_iv, ivsize);
if (ret < 0)
return -EINVAL;
ret = hex2bin(epayload->encrypted_data, hex_encoded_data,
encrypted_datalen);
if (ret < 0)
return -EINVAL;
hmac = epayload->format + epayload->datablob_len;
ret = hex2bin(hmac, hex_encoded_data + (encrypted_datalen * 2),
HASH_SIZE);
if (ret < 0)
return -EINVAL;
mkey = request_master_key(epayload, &master_key, &master_keylen);
if (IS_ERR(mkey))
return PTR_ERR(mkey);
ret = datablob_hmac_verify(epayload, format, master_key, master_keylen);
if (ret < 0) {
pr_err("encrypted_key: bad hmac (%d)\n", ret);
goto out;
}
ret = get_derived_key(derived_key, ENC_KEY, master_key, master_keylen);
if (ret < 0)
goto out;
ret = derived_key_decrypt(epayload, derived_key, sizeof derived_key);
if (ret < 0)
pr_err("encrypted_key: failed to decrypt key (%d)\n", ret);
out:
up_read(&mkey->sem);
key_put(mkey);
return ret;
}
static int datablob_hmac_append(struct encrypted_key_payload *epayload,
const u8 *master_key, size_t master_keylen)
{
u8 derived_key[HASH_SIZE];
u8 *digest;
int ret;
ret = get_derived_key(derived_key, AUTH_KEY, master_key, master_keylen);
if (ret < 0)
goto out;
digest = epayload->format + epayload->datablob_len;
ret = calc_hmac(digest, derived_key, sizeof derived_key,
epayload->format, epayload->datablob_len);
if (!ret)
dump_hmac(NULL, digest, HASH_SIZE);
out:
return ret;
}
/* verify HMAC before decrypting encrypted key */
static int datablob_hmac_verify(struct encrypted_key_payload *epayload,
const u8 *format, const u8 *master_key,
size_t master_keylen)
{
u8 derived_key[HASH_SIZE];
u8 digest[HASH_SIZE];
int ret;
char *p;
unsigned short len;
ret = get_derived_key(derived_key, AUTH_KEY, master_key, master_keylen);
if (ret < 0)
goto out;
len = epayload->datablob_len;
if (!format) {
p = epayload->master_desc;
len -= strlen(epayload->format) + 1;
} else
p = epayload->format;
ret = calc_hmac(digest, derived_key, sizeof derived_key, p, len);
if (ret < 0)
goto out;
ret = memcmp(digest, epayload->format + epayload->datablob_len,
sizeof digest);
if (ret) {
ret = -EINVAL;
dump_hmac("datablob",
epayload->format + epayload->datablob_len,
HASH_SIZE);
dump_hmac("calc", digest, HASH_SIZE);
}
out:
return ret;
}