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cryptfs: Clarify sizing of intermediate key

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Some parts of the code were intermingling constants for the master
key and the intermediate key.  That works at the moment because
these are the same size.  But we'll be introducing logic allowing
different sized master keys, while keeping the intermediate the
same.  To aid that introduction, we use separate constants for
the intermediate key.

Bug: 73079191
Test: Build
Change-Id: I22b1dbf18aff2f76229df1c898fc606d6c1af3ca
This commit is contained in:
Greg Kaiser 2018-02-14 20:05:54 -08:00
parent b802078adc
commit c0de9c7dba
1 changed files with 23 additions and 14 deletions
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37
cryptfs.cpp
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@ -73,7 +73,15 @@ extern "C" {
#define HASH_COUNT 2000
#define KEY_LEN_BYTES 16
#define IV_LEN_BYTES 16
constexpr size_t INTERMEDIATE_KEY_LEN_BYTES = 16;
constexpr size_t INTERMEDIATE_IV_LEN_BYTES = 16;
constexpr size_t INTERMEDIATE_BUF_SIZE =
(INTERMEDIATE_KEY_LEN_BYTES + INTERMEDIATE_IV_LEN_BYTES);
// SCRYPT_LEN is used by struct crypt_mnt_ftr for its intermediate key.
static_assert(INTERMEDIATE_BUF_SIZE == SCRYPT_LEN,
"Mismatch of intermediate key sizes");
#define KEY_IN_FOOTER "footer"
@ -1043,7 +1051,7 @@ static int pbkdf2(const char *passwd, const unsigned char *salt,
/* Turn the password into a key and IV that can decrypt the master key */
return PKCS5_PBKDF2_HMAC_SHA1(passwd, strlen(passwd), salt, SALT_LEN,
HASH_COUNT, KEY_LEN_BYTES + IV_LEN_BYTES,
HASH_COUNT, INTERMEDIATE_BUF_SIZE,
ikey) != 1;
}
@ -1061,7 +1069,7 @@ static int scrypt(const char *passwd, const unsigned char *salt,
/* Turn the password into a key and IV that can decrypt the master key */
crypto_scrypt((const uint8_t*)passwd, strlen(passwd),
salt, SALT_LEN, N, r, p, ikey,
KEY_LEN_BYTES + IV_LEN_BYTES);
INTERMEDIATE_BUF_SIZE);
return 0;
}
@ -1082,21 +1090,21 @@ static int scrypt_keymaster(const char *passwd, const unsigned char *salt,
rc = crypto_scrypt((const uint8_t*)passwd, strlen(passwd),
salt, SALT_LEN, N, r, p, ikey,
KEY_LEN_BYTES + IV_LEN_BYTES);
INTERMEDIATE_BUF_SIZE);
if (rc) {
SLOGE("scrypt failed");
return -1;
}
if (keymaster_sign_object(ftr, ikey, KEY_LEN_BYTES + IV_LEN_BYTES,
if (keymaster_sign_object(ftr, ikey, INTERMEDIATE_BUF_SIZE,
&signature, &signature_size)) {
SLOGE("Signing failed");
return -1;
}
rc = crypto_scrypt(signature, signature_size, salt, SALT_LEN,
N, r, p, ikey, KEY_LEN_BYTES + IV_LEN_BYTES);
N, r, p, ikey, INTERMEDIATE_BUF_SIZE);
free(signature);
if (rc) {
@ -1112,7 +1120,7 @@ static int encrypt_master_key(const char *passwd, const unsigned char *salt,
unsigned char *encrypted_master_key,
struct crypt_mnt_ftr *crypt_ftr)
{
unsigned char ikey[32+32] = { 0 }; /* Big enough to hold a 256 bit key and 256 bit IV */
unsigned char ikey[INTERMEDIATE_BUF_SIZE] = { 0 };
EVP_CIPHER_CTX e_ctx;
int encrypted_len, final_len;
int rc = 0;
@ -1147,7 +1155,8 @@ static int encrypt_master_key(const char *passwd, const unsigned char *salt,
/* Initialize the decryption engine */
EVP_CIPHER_CTX_init(&e_ctx);
if (! EVP_EncryptInit_ex(&e_ctx, EVP_aes_128_cbc(), NULL, ikey, ikey+KEY_LEN_BYTES)) {
if (! EVP_EncryptInit_ex(&e_ctx, EVP_aes_128_cbc(), NULL, ikey,
ikey+INTERMEDIATE_KEY_LEN_BYTES)) {
SLOGE("EVP_EncryptInit failed\n");
return -1;
}
@ -1178,7 +1187,7 @@ static int encrypt_master_key(const char *passwd, const unsigned char *salt,
int r = 1 << crypt_ftr->r_factor;
int p = 1 << crypt_ftr->p_factor;
rc = crypto_scrypt(ikey, KEY_LEN_BYTES,
rc = crypto_scrypt(ikey, INTERMEDIATE_KEY_LEN_BYTES,
crypt_ftr->salt, sizeof(crypt_ftr->salt), N, r, p,
crypt_ftr->scrypted_intermediate_key,
sizeof(crypt_ftr->scrypted_intermediate_key));
@ -1199,7 +1208,7 @@ static int decrypt_master_key_aux(const char *passwd, unsigned char *salt,
unsigned char** intermediate_key,
size_t* intermediate_key_size)
{
unsigned char ikey[32+32] = { 0 }; /* Big enough to hold a 256 bit key and 256 bit IV */
unsigned char ikey[INTERMEDIATE_BUF_SIZE] = { 0 };
EVP_CIPHER_CTX d_ctx;
int decrypted_len, final_len;
@ -1212,7 +1221,7 @@ static int decrypt_master_key_aux(const char *passwd, unsigned char *salt,
/* Initialize the decryption engine */
EVP_CIPHER_CTX_init(&d_ctx);
if (! EVP_DecryptInit_ex(&d_ctx, EVP_aes_128_cbc(), NULL, ikey, ikey+KEY_LEN_BYTES)) {
if (! EVP_DecryptInit_ex(&d_ctx, EVP_aes_128_cbc(), NULL, ikey, ikey+INTERMEDIATE_KEY_LEN_BYTES)) {
return -1;
}
EVP_CIPHER_CTX_set_padding(&d_ctx, 0); /* Turn off padding as our data is block aligned */
@ -1231,10 +1240,10 @@ static int decrypt_master_key_aux(const char *passwd, unsigned char *salt,
/* Copy intermediate key if needed by params */
if (intermediate_key && intermediate_key_size) {
*intermediate_key = (unsigned char*) malloc(KEY_LEN_BYTES);
*intermediate_key = (unsigned char*) malloc(INTERMEDIATE_KEY_LEN_BYTES);
if (*intermediate_key) {
memcpy(*intermediate_key, ikey, KEY_LEN_BYTES);
*intermediate_key_size = KEY_LEN_BYTES;
memcpy(*intermediate_key, ikey, INTERMEDIATE_KEY_LEN_BYTES);
*intermediate_key_size = INTERMEDIATE_KEY_LEN_BYTES;
}
}