[PATCH v5 1/2] fscrypt-crypt-util: add HCTR2 implementation

Nathan Huckleberry
2022-08-03T22:41:45Z

This patch adds an implementation of HCTR2 to the fscrypt testing
utility.

More information on HCTR2 can be found here: "Length-preserving
encryption with HCTR2": https://ia.cr/2021/1441

Signed-off-by: Nathan Huckleberry <nhuck@google.com>
---
common/encrypt | 2 +
src/fscrypt-crypt-util.c | 358 ++++++++++++++++++++++++++++++++-------
2 files changed, 303 insertions(+), 57 deletions(-)

diff --git a/common/encrypt b/common/encrypt
index f90c4ef0..937bb914 100644
--- a/common/encrypt
+++ b/common/encrypt
@@ -767,6 +767,7 @@ FSCRYPT_MODE_AES_256_CTS=4
FSCRYPT_MODE_AES_128_CBC=5
FSCRYPT_MODE_AES_128_CTS=6
FSCRYPT_MODE_ADIANTUM=9
+FSCRYPT_MODE_AES_256_HCTR2=10

FSCRYPT_POLICY_FLAG_DIRECT_KEY=0x04
FSCRYPT_POLICY_FLAG_IV_INO_LBLK_64=0x08
@@ -785,6 +786,7 @@ _fscrypt_mode_name_to_num()
AES-128-CBC-ESSIV) echo $FSCRYPT_MODE_AES_128_CBC ;;
AES-128-CTS-CBC) echo $FSCRYPT_MODE_AES_128_CTS ;;
Adiantum) echo $FSCRYPT_MODE_ADIANTUM ;;
+ AES-256-HCTR2) echo $FSCRYPT_MODE_AES_256_HCTR2 ;;
*) _fail "Unknown fscrypt mode: $name" ;;
esac
}
diff --git a/src/fscrypt-crypt-util.c b/src/fscrypt-crypt-util.c
index 03cc3c4a..11009da7 100644
--- a/src/fscrypt-crypt-util.c
+++ b/src/fscrypt-crypt-util.c
@@ -37,7 +37,8 @@
/*
* Define to enable the tests of the crypto code in this file. If enabled, you
* must link this program with OpenSSL (-lcrypto) v1.1.0 or later, and your
- * kernel needs CONFIG_CRYPTO_USER_API_SKCIPHER=y and CONFIG_CRYPTO_ADIANTUM=y.
+ * kernel needs CONFIG_CRYPTO_USER_API_SKCIPHER=y, CONFIG_CRYPTO_ADIANTUM=y, and
+ * CONFIG_CRYPTO_HCTR2=y.
*/
#undef ENABLE_ALG_TESTS

@@ -54,7 +55,8 @@ static void usage(FILE *fp)
"resulting ciphertext (or plaintext) to stdout.\n"
"\n"
"CIPHER can be AES-256-XTS, AES-256-CTS-CBC, AES-128-CBC-ESSIV, AES-128-CTS-CBC,\n"
-"or Adiantum. MASTER_KEY must be a hex string long enough for the cipher.\n"
+"Adiantum, or AES-256-HCTR2. MASTER_KEY must be a hex string long enough for\n"
+"the cipher.\n"
"\n"
"WARNING: this program is only meant for testing, not for \"real\" use!\n"
"\n"
@@ -268,7 +270,59 @@ static void rand_bytes(u8 *buf, size_t count)
while (count--)
*buf++ = rand();
}
-#endif
+
+#include <linux/if_alg.h>
+#include <sys/socket.h>
+#define SOL_ALG 279
+static void af_alg_crypt(int algfd, int op, const u8 *key, size_t keylen,
+ const u8 *iv, size_t ivlen,
+ const u8 *src, u8 *dst, size_t datalen)
+{
+ size_t controllen = CMSG_SPACE(sizeof(int)) +
+ CMSG_SPACE(sizeof(struct af_alg_iv) + ivlen);
+ u8 *control = xmalloc(controllen);
+ struct iovec iov = { .iov_base = (u8 *)src, .iov_len = datalen };
+ struct msghdr msg = {
+ .msg_iov = &iov,
+ .msg_iovlen = 1,
+ .msg_control = control,
+ .msg_controllen = controllen,
+ };
+ struct cmsghdr *cmsg;
+ struct af_alg_iv *algiv;
+ int reqfd;
+
+ memset(control, 0, controllen);
+
+ cmsg = CMSG_FIRSTHDR(&msg);
+ cmsg->cmsg_len = CMSG_LEN(sizeof(int));
+ cmsg->cmsg_level = SOL_ALG;
+ cmsg->cmsg_type = ALG_SET_OP;
+ *(int *)CMSG_DATA(cmsg) = op;
+
+ cmsg = CMSG_NXTHDR(&msg, cmsg);
+ cmsg->cmsg_len = CMSG_LEN(sizeof(struct af_alg_iv) + ivlen);
+ cmsg->cmsg_level = SOL_ALG;
+ cmsg->cmsg_type = ALG_SET_IV;
+ algiv = (struct af_alg_iv *)CMSG_DATA(cmsg);
+ algiv->ivlen = ivlen;
+ memcpy(algiv->iv, iv, ivlen);
+
+ if (setsockopt(algfd, SOL_ALG, ALG_SET_KEY, key, keylen) != 0)
+ die_errno("can't set key on AF_ALG socket");
+
+ reqfd = accept(algfd, NULL, NULL);
+ if (reqfd < 0)
+ die_errno("can't accept() AF_ALG socket");
+ if (sendmsg(reqfd, &msg, 0) != datalen)
+ die_errno("can't sendmsg() AF_ALG request socket");
+ if (xread(reqfd, dst, datalen) != datalen)
+ die("short read from AF_ALG request socket");
+ close(reqfd);
+
+ free(control);
+}
+#endif /* ENABLE_ALG_TESTS */

/*----------------------------------------------------------------------------*
* Finite field arithmetic *
@@ -293,7 +347,7 @@ typedef struct {
} ble128;

/* Multiply a GF(2^128) element by the polynomial 'x' */
-static inline void gf2_128_mul_x(ble128 *t)
+static inline void gf2_128_mul_x_xts(ble128 *t)
{
u64 lo = le64_to_cpu(t->lo);
u64 hi = le64_to_cpu(t->hi);
@@ -302,6 +356,38 @@ static inline void gf2_128_mul_x(ble128 *t)
t->lo = cpu_to_le64((lo << 1) ^ ((hi & (1ULL << 63)) ? 0x87 : 0));
}

+static inline void gf2_128_mul_x_polyval(ble128 *t)
+{
+ u64 lo = le64_to_cpu(t->lo);
+ u64 hi = le64_to_cpu(t->hi);
+ u64 lo_reducer = (hi & (1ULL << 63)) ? 1 : 0;
+ u64 hi_reducer = (hi & (1ULL << 63)) ? 0xc2ULL << 56 : 0;
+
+ t->hi = cpu_to_le64(((hi << 1) | (lo >> 63)) ^ hi_reducer);
+ t->lo = cpu_to_le64((lo << 1) ^ lo_reducer);
+}
+
+static void gf2_128_mul_polyval(ble128 *r, const ble128 *b)
+{
+ int i;
+ ble128 p;
+ u64 lo = le64_to_cpu(b->lo);
+ u64 hi = le64_to_cpu(b->hi);
+
+ memset(&p, 0, sizeof(p));
+ for (i = 0; i < 64; i++) {
+ if (lo & (1ULL << i))
+ xor((u8 *)&p, (u8 *)&p, (u8 *)r, sizeof(p));
+ gf2_128_mul_x_polyval(r);
+ }
+ for (i = 0; i < 64; i++) {
+ if (hi & (1ULL << i))
+ xor((u8 *)&p, (u8 *)&p, (u8 *)r, sizeof(p));
+ gf2_128_mul_x_polyval(r);
+ }
+ *r = p;
+}
+
/*----------------------------------------------------------------------------*
* Group arithmetic *
*----------------------------------------------------------------------------*/
@@ -901,6 +987,48 @@ static void test_hkdf_sha512(void)
}
#endif /* ENABLE_ALG_TESTS */

+/*----------------------------------------------------------------------------*
+ * POLYVAL *
+ *----------------------------------------------------------------------------*/
+
+/*
+ * Reference: "AES-GCM-SIV: Nonce Misuse-Resistant Authenticated Encryption"
+ * https://datatracker.ietf.org/doc/html/rfc8452
+ */
+
+#define POLYVAL_KEY_SIZE 16
+#define POLYVAL_BLOCK_SIZE 16
+
+static void polyval_update(const u8 key[POLYVAL_KEY_SIZE],
+ const u8 *msg, size_t msglen,
+ u8 accumulator[POLYVAL_BLOCK_SIZE])
+{
+ ble128 h;
+ ble128 aligned_accumulator;
+ size_t chunk_size;
+ // x^{-128} = x^127 + x^124 + x^121 + x^114 + 1
+ static const ble128 inv128 = {
+ cpu_to_le64(1),
+ cpu_to_le64(0x9204ULL << 48)
+ };
+
+ /* Partial block support is not necessary for HCTR2 */
+ ASSERT(msglen % POLYVAL_BLOCK_SIZE == 0);
+
+ memcpy(&h, key, POLYVAL_BLOCK_SIZE);
+ memcpy(&aligned_accumulator, accumulator, POLYVAL_BLOCK_SIZE);
+ gf2_128_mul_polyval(&h, &inv128);
+
+ while (msglen > 0) {
+ xor((u8 *)&aligned_accumulator, (u8 *)&aligned_accumulator, msg,
+ POLYVAL_BLOCK_SIZE);
+ gf2_128_mul_polyval(&aligned_accumulator, &h);
+ msg += POLYVAL_BLOCK_SIZE;
+ msglen -= POLYVAL_BLOCK_SIZE;
+ }
+ memcpy(accumulator, &aligned_accumulator, POLYVAL_BLOCK_SIZE);
+}
+
/*----------------------------------------------------------------------------*
* AES encryption modes *
*----------------------------------------------------------------------------*/
@@ -924,7 +1052,7 @@ static void aes_256_xts_crypt(const u8 key[2 * AES_256_KEY_SIZE],
else
aes_encrypt(&cipher_key, &dst[i], &dst[i]);
xor(&dst[i], &dst[i], (const u8 *)&t, AES_BLOCK_SIZE);
- gf2_128_mul_x(&t);
+ gf2_128_mul_x_xts(&t);
}
}

@@ -1173,6 +1301,167 @@ static void aes_128_cts_cbc_decrypt(const u8 key[AES_128_KEY_SIZE],
aes_cts_cbc_decrypt(key, AES_128_KEY_SIZE, iv, src, dst, nbytes);
}

+/*
+ * Reference: "Length-preserving encryption with HCTR2"
+ * https://ia.cr/2021/1441
+ */
+
+static void aes_256_xctr_crypt(const u8 key[AES_256_KEY_SIZE],
+ const u8 iv[AES_BLOCK_SIZE], const u8 *src,
+ u8 *dst, size_t nbytes)
+{
+ struct aes_key k;
+ union {
+ u8 bytes[AES_BLOCK_SIZE];
+ __le64 ctr;
+ } blk;
+ size_t i;
+
+ aes_setkey(&k, key, AES_256_KEY_SIZE);
+
+ for (i = 0; i < nbytes; i += AES_BLOCK_SIZE) {
+ memcpy(blk.bytes, iv, AES_BLOCK_SIZE);
+ blk.ctr ^= cpu_to_le64((i / AES_BLOCK_SIZE) + 1);
+ aes_encrypt(&k, blk.bytes, blk.bytes);
+ xor(&dst[i], blk.bytes, &src[i], MIN(AES_BLOCK_SIZE, nbytes - i));
+ }
+}
+
+/*
+ * Reference: "Length-preserving encryption with HCTR2"
+ * https://ia.cr/2021/1441
+ */
+
+#define HCTR2_IV_SIZE 32
+static void hctr2_hash_iv(const u8 hbar[POLYVAL_KEY_SIZE],
+ const u8 iv[HCTR2_IV_SIZE], size_t msglen,
+ u8 digest[POLYVAL_BLOCK_SIZE])
+{
+ le128 tweaklen_blk = {
+ .lo = cpu_to_le64(HCTR2_IV_SIZE * 8 * 2 + 2 +
+ (msglen % AES_BLOCK_SIZE != 0))
+ };
+
+ memset(digest, 0, POLYVAL_BLOCK_SIZE);
+ polyval_update(hbar, (u8 *)&tweaklen_blk, POLYVAL_BLOCK_SIZE, digest);
+ polyval_update(hbar, iv, HCTR2_IV_SIZE, digest);
+}
+
+static void hctr2_hash_message(const u8 hbar[POLYVAL_KEY_SIZE],
+ const u8 *msg, size_t msglen,
+ u8 digest[POLYVAL_BLOCK_SIZE])
+{
+ size_t remainder = msglen % AES_BLOCK_SIZE;
+ u8 padded_block[POLYVAL_BLOCK_SIZE] = {0};
+
+ polyval_update(hbar, msg, msglen - remainder, digest);
+ if (remainder) {
+ memcpy(padded_block, &msg[msglen - remainder], remainder);
+ padded_block[remainder] = 1;
+ polyval_update(hbar, padded_block, POLYVAL_BLOCK_SIZE, digest);
+ }
+}
+
+static void aes_256_hctr2_crypt(const u8 key[AES_256_KEY_SIZE],
+ const u8 iv[HCTR2_IV_SIZE], const u8 *src,
+ u8 *dst, size_t nbytes, bool decrypting)
+{
+ struct aes_key k;
+ u8 hbar[AES_BLOCK_SIZE] = {0};
+ u8 L[AES_BLOCK_SIZE] = {1};
+ size_t bulk_bytes = nbytes - AES_BLOCK_SIZE;
+ u8 digest[POLYVAL_BLOCK_SIZE];
+ const u8 *M = src;
+ const u8 *N = src + AES_BLOCK_SIZE;
+ u8 MM[AES_BLOCK_SIZE];
+ u8 UU[AES_BLOCK_SIZE];
+ u8 S[AES_BLOCK_SIZE];
+ u8 *U = dst;
+ u8 *V = dst + AES_BLOCK_SIZE;
+
+ ASSERT(nbytes >= AES_BLOCK_SIZE);
+ aes_setkey(&k, key, AES_256_KEY_SIZE);
+
+ aes_encrypt(&k, hbar, hbar);
+ aes_encrypt(&k, L, L);
+
+ hctr2_hash_iv(hbar, iv, bulk_bytes, digest);
+ hctr2_hash_message(hbar, N, bulk_bytes, digest);
+
+ xor(MM, M, digest, AES_BLOCK_SIZE);
+
+ if (decrypting)
+ aes_decrypt(&k, MM, UU);
+ else
+ aes_encrypt(&k, MM, UU);
+
+ xor(S, MM, UU, AES_BLOCK_SIZE);
+ xor(S, L, S, AES_BLOCK_SIZE);
+
+ aes_256_xctr_crypt(key, S, N, V, bulk_bytes);
+
+ hctr2_hash_iv(hbar, iv, bulk_bytes, digest);
+ hctr2_hash_message(hbar, V, bulk_bytes, digest);
+
+ xor(U, UU, digest, AES_BLOCK_SIZE);
+}
+
+static void aes_256_hctr2_encrypt(const u8 key[AES_256_KEY_SIZE],
+ const u8 iv[HCTR2_IV_SIZE], const u8 *src,
+ u8 *dst, size_t nbytes)
+{
+ aes_256_hctr2_crypt(key, iv, src, dst, nbytes, false);
+}
+
+static void aes_256_hctr2_decrypt(const u8 key[AES_256_KEY_SIZE],
+ const u8 iv[HCTR2_IV_SIZE], const u8 *src,
+ u8 *dst, size_t nbytes)
+{
+ aes_256_hctr2_crypt(key, iv, src, dst, nbytes, true);
+}
+
+#ifdef ENABLE_ALG_TESTS
+#include <linux/if_alg.h>
+#include <sys/socket.h>
+static void test_aes_256_hctr2(void)
+{
+ int algfd = socket(AF_ALG, SOCK_SEQPACKET, 0);
+ struct sockaddr_alg addr = {
+ .salg_type = "skcipher",
+ .salg_name = "hctr2(aes)",
+ };
+ unsigned long num_tests = NUM_ALG_TEST_ITERATIONS;
+
+ if (algfd < 0)
+ die_errno("can't create AF_ALG socket");
+ if (bind(algfd, (struct sockaddr *)&addr, sizeof(addr)) != 0)
+ die_errno("can't bind AF_ALG socket to HCTR2 algorithm");
+
+ while (num_tests--) {
+ u8 key[AES_256_KEY_SIZE];
+ u8 iv[HCTR2_IV_SIZE];
+ u8 ptext[4096];
+ u8 ctext[sizeof(ptext)];
+ u8 ref_ctext[sizeof(ptext)];
+ u8 decrypted[sizeof(ptext)];
+ const size_t datalen = 16 + (rand() % (sizeof(ptext) - 15));
+
+ rand_bytes(key, sizeof(key));
+ rand_bytes(iv, sizeof(iv));
+ rand_bytes(ptext, datalen);
+
+ aes_256_hctr2_encrypt(key, iv, ptext, ctext, datalen);
+ af_alg_crypt(algfd, ALG_OP_ENCRYPT, key, sizeof(key),
+ iv, sizeof(iv), ptext, ref_ctext, datalen);
+ ASSERT(memcmp(ctext, ref_ctext, datalen) == 0);
+
+ aes_256_hctr2_decrypt(key, iv, ctext, decrypted, datalen);
+ ASSERT(memcmp(ptext, decrypted, datalen) == 0);
+ }
+ close(algfd);
+}
+#endif /* ENABLE_ALG_TESTS */
+
/*----------------------------------------------------------------------------*
* XChaCha12 stream cipher *
*----------------------------------------------------------------------------*/
@@ -1500,58 +1789,6 @@ static void adiantum_decrypt(const u8 key[ADIANTUM_KEY_SIZE],
}

#ifdef ENABLE_ALG_TESTS
-#include <linux/if_alg.h>
-#include <sys/socket.h>
-#define SOL_ALG 279
-static void af_alg_crypt(int algfd, int op, const u8 *key, size_t keylen,
- const u8 *iv, size_t ivlen,
- const u8 *src, u8 *dst, size_t datalen)
-{
- size_t controllen = CMSG_SPACE(sizeof(int)) +
- CMSG_SPACE(sizeof(struct af_alg_iv) + ivlen);
- u8 *control = xmalloc(controllen);
- struct iovec iov = { .iov_base = (u8 *)src, .iov_len = datalen };
- struct msghdr msg = {
- .msg_iov = &iov,
- .msg_iovlen = 1,
- .msg_control = control,
- .msg_controllen = controllen,
- };
- struct cmsghdr *cmsg;
- struct af_alg_iv *algiv;
- int reqfd;
-
- memset(control, 0, controllen);
-
- cmsg = CMSG_FIRSTHDR(&msg);
- cmsg->cmsg_len = CMSG_LEN(sizeof(int));
- cmsg->cmsg_level = SOL_ALG;
- cmsg->cmsg_type = ALG_SET_OP;
- *(int *)CMSG_DATA(cmsg) = op;
-
- cmsg = CMSG_NXTHDR(&msg, cmsg);
- cmsg->cmsg_len = CMSG_LEN(sizeof(struct af_alg_iv) + ivlen);
- cmsg->cmsg_level = SOL_ALG;
- cmsg->cmsg_type = ALG_SET_IV;
- algiv = (struct af_alg_iv *)CMSG_DATA(cmsg);
- algiv->ivlen = ivlen;
- memcpy(algiv->iv, iv, ivlen);
-
- if (setsockopt(algfd, SOL_ALG, ALG_SET_KEY, key, keylen) != 0)
- die_errno("can't set key on AF_ALG socket");
-
- reqfd = accept(algfd, NULL, NULL);
- if (reqfd < 0)
- die_errno("can't accept() AF_ALG socket");
- if (sendmsg(reqfd, &msg, 0) != datalen)
- die_errno("can't sendmsg() AF_ALG request socket");
- if (xread(reqfd, dst, datalen) != datalen)
- die("short read from AF_ALG request socket");
- close(reqfd);
-
- free(control);
-}
-
static void test_adiantum(void)
{
int algfd = socket(AF_ALG, SOCK_SEQPACKET, 0);
@@ -1675,6 +1912,12 @@ static const struct fscrypt_cipher {
.decrypt = aes_128_cts_cbc_decrypt,
.keysize = AES_128_KEY_SIZE,
.min_input_size = AES_BLOCK_SIZE,
+ }, {
+ .name = "AES-256-HCTR2",
+ .encrypt = aes_256_hctr2_encrypt,
+ .decrypt = aes_256_hctr2_decrypt,
+ .keysize = AES_256_KEY_SIZE,
+ .min_input_size = AES_BLOCK_SIZE,
}, {
.name = "Adiantum",
.encrypt = adiantum_encrypt,
@@ -1980,6 +2223,7 @@ int main(int argc, char *argv[])
test_aes_256_xts();
test_aes_256_cts_cbc();
test_adiantum();
+ test_aes_256_hctr2();
#endif

while ((c = getopt_long(argc, argv, "", longopts, NULL)) != -1) {
--
2.37.1.455.g008518b4e5-goog