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linux/drivers/usb/wusbcore/crypto.c

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// SPDX-License-Identifier: GPL-2.0
/*
* Ultra Wide Band
* AES-128 CCM Encryption
*
* Copyright (C) 2007 Intel Corporation
* Inaky Perez-Gonzalez <inaky.perez-gonzalez@intel.com>
*
* We don't do any encryption here; we use the Linux Kernel's AES-128
* crypto modules to construct keys and payload blocks in a way
* defined by WUSB1.0[6]. Check the erratas, as typos are are patched
* there.
*
* Thanks a zillion to John Keys for his help and clarifications over
* the designed-by-a-committee text.
*
* So the idea is that there is this basic Pseudo-Random-Function
* defined in WUSB1.0[6.5] which is the core of everything. It works
* by tweaking some blocks, AES crypting them and then xoring
* something else with them (this seems to be called CBC(AES) -- can
* you tell I know jack about crypto?). So we just funnel it into the
* Linux Crypto API.
*
* We leave a crypto test module so we can verify that vectors match,
* every now and then.
*
* Block size: 16 bytes -- AES seems to do things in 'block sizes'. I
* am learning a lot...
*
* Conveniently, some data structures that need to be
* funneled through AES are...16 bytes in size!
*/
#include <crypto/skcipher.h>
#include <linux/crypto.h>
#include <linux/module.h>
#include <linux/err.h>
#include <linux/uwb.h>
#include <linux/slab.h>
#include <linux/usb/wusb.h>
#include <linux/scatterlist.h>
static int debug_crypto_verify;
module_param(debug_crypto_verify, int, 0);
MODULE_PARM_DESC(debug_crypto_verify, "verify the key generation algorithms");
static void wusb_key_dump(const void *buf, size_t len)
{
print_hex_dump(KERN_ERR, " ", DUMP_PREFIX_OFFSET, 16, 1,
buf, len, 0);
}
/*
* Block of data, as understood by AES-CCM
*
* The code assumes this structure is nothing but a 16 byte array
* (packed in a struct to avoid common mess ups that I usually do with
* arrays and enforcing type checking).
*/
struct aes_ccm_block {
u8 data[16];
} __attribute__((packed));
/*
* Counter-mode Blocks (WUSB1.0[6.4])
*
* According to CCM (or so it seems), for the purpose of calculating
* the MIC, the message is broken in N counter-mode blocks, B0, B1,
* ... BN.
*
* B0 contains flags, the CCM nonce and l(m).
*
* B1 contains l(a), the MAC header, the encryption offset and padding.
*
* If EO is nonzero, additional blocks are built from payload bytes
* until EO is exhausted (FIXME: padding to 16 bytes, I guess). The
* padding is not xmitted.
*/
/* WUSB1.0[T6.4] */
struct aes_ccm_b0 {
u8 flags; /* 0x59, per CCM spec */
struct aes_ccm_nonce ccm_nonce;
__be16 lm;
} __attribute__((packed));
/* WUSB1.0[T6.5] */
struct aes_ccm_b1 {
__be16 la;
u8 mac_header[10];
__le16 eo;
u8 security_reserved; /* This is always zero */
u8 padding; /* 0 */
} __attribute__((packed));
/*
* Encryption Blocks (WUSB1.0[6.4.4])
*
* CCM uses Ax blocks to generate a keystream with which the MIC and
* the message's payload are encoded. A0 always encrypts/decrypts the
* MIC. Ax (x>0) are used for the successive payload blocks.
*
* The x is the counter, and is increased for each block.
*/
struct aes_ccm_a {
u8 flags; /* 0x01, per CCM spec */
struct aes_ccm_nonce ccm_nonce;
__be16 counter; /* Value of x */
} __attribute__((packed));
static void bytewise_xor(void *_bo, const void *_bi1, const void *_bi2,
size_t size)
{
u8 *bo = _bo;
const u8 *bi1 = _bi1, *bi2 = _bi2;
size_t itr;
for (itr = 0; itr < size; itr++)
bo[itr] = bi1[itr] ^ bi2[itr];
}
/* Scratch space for MAC calculations. */
struct wusb_mac_scratch {
struct aes_ccm_b0 b0;
struct aes_ccm_b1 b1;
struct aes_ccm_a ax;
};
/*
* CC-MAC function WUSB1.0[6.5]
*
* Take a data string and produce the encrypted CBC Counter-mode MIC
*
* Note the names for most function arguments are made to (more or
* less) match those used in the pseudo-function definition given in
* WUSB1.0[6.5].
*
* @tfm_cbc: CBC(AES) blkcipher handle (initialized)
*
* @tfm_aes: AES cipher handle (initialized)
*
* @mic: buffer for placing the computed MIC (Message Integrity
* Code). This is exactly 8 bytes, and we expect the buffer to
* be at least eight bytes in length.
*
* @key: 128 bit symmetric key
*
* @n: CCM nonce
*
* @a: ASCII string, 14 bytes long (I guess zero padded if needed;
* we use exactly 14 bytes).
*
* @b: data stream to be processed; cannot be a global or const local
* (will confuse the scatterlists)
*
* @blen: size of b...
*
* Still not very clear how this is done, but looks like this: we
* create block B0 (as WUSB1.0[6.5] says), then we AES-crypt it with
* @key. We bytewise xor B0 with B1 (1) and AES-crypt that. Then we
* take the payload and divide it in blocks (16 bytes), xor them with
* the previous crypto result (16 bytes) and crypt it, repeat the next
* block with the output of the previous one, rinse wash (I guess this
* is what AES CBC mode means...but I truly have no idea). So we use
* the CBC(AES) blkcipher, that does precisely that. The IV (Initial
* Vector) is 16 bytes and is set to zero, so
*
* See rfc3610. Linux crypto has a CBC implementation, but the
* documentation is scarce, to say the least, and the example code is
* so intricated that is difficult to understand how things work. Most
* of this is guess work -- bite me.
*
* (1) Created as 6.5 says, again, using as l(a) 'Blen + 14', and
* using the 14 bytes of @a to fill up
* b1.{mac_header,e0,security_reserved,padding}.
*
* NOTE: The definition of l(a) in WUSB1.0[6.5] vs the definition of
* l(m) is orthogonal, they bear no relationship, so it is not
* in conflict with the parameter's relation that
* WUSB1.0[6.4.2]) defines.
*
* NOTE: WUSB1.0[A.1]: Host Nonce is missing a nibble? (1e); fixed in
* first errata released on 2005/07.
*
* NOTE: we need to clean IV to zero at each invocation to make sure
* we start with a fresh empty Initial Vector, so that the CBC
* works ok.
*
* NOTE: blen is not aligned to a block size, we'll pad zeros, that's
* what sg[4] is for. Maybe there is a smarter way to do this.
*/
static int wusb_ccm_mac(struct crypto_sync_skcipher *tfm_cbc,
struct crypto_cipher *tfm_aes,
struct wusb_mac_scratch *scratch,
void *mic,
const struct aes_ccm_nonce *n,
const struct aes_ccm_label *a, const void *b,
size_t blen)
{
int result = 0;
SYNC_SKCIPHER_REQUEST_ON_STACK(req, tfm_cbc);
struct scatterlist sg[4], sg_dst;
void *dst_buf;
size_t dst_size;
u8 *iv;
size_t zero_padding;
/*
* These checks should be compile time optimized out
* ensure @a fills b1's mac_header and following fields
*/
WARN_ON(sizeof(*a) != sizeof(scratch->b1) - sizeof(scratch->b1.la));
WARN_ON(sizeof(scratch->b0) != sizeof(struct aes_ccm_block));
WARN_ON(sizeof(scratch->b1) != sizeof(struct aes_ccm_block));
WARN_ON(sizeof(scratch->ax) != sizeof(struct aes_ccm_block));
result = -ENOMEM;
zero_padding = blen % sizeof(struct aes_ccm_block);
if (zero_padding)
zero_padding = sizeof(struct aes_ccm_block) - zero_padding;
dst_size = blen + sizeof(scratch->b0) + sizeof(scratch->b1) +
zero_padding;
dst_buf = kzalloc(dst_size, GFP_KERNEL);
if (!dst_buf)
goto error_dst_buf;
iv = kzalloc(crypto_sync_skcipher_ivsize(tfm_cbc), GFP_KERNEL);
if (!iv)
goto error_iv;
/* Setup B0 */
scratch->b0.flags = 0x59; /* Format B0 */
scratch->b0.ccm_nonce = *n;
scratch->b0.lm = cpu_to_be16(0); /* WUSB1.0[6.5] sez l(m) is 0 */
/* Setup B1
*
* The WUSB spec is anything but clear! WUSB1.0[6.5]
* says that to initialize B1 from A with 'l(a) = blen +
* 14'--after clarification, it means to use A's contents
* for MAC Header, EO, sec reserved and padding.
*/
scratch->b1.la = cpu_to_be16(blen + 14);
memcpy(&scratch->b1.mac_header, a, sizeof(*a));
sg_init_table(sg, ARRAY_SIZE(sg));
sg_set_buf(&sg[0], &scratch->b0, sizeof(scratch->b0));
sg_set_buf(&sg[1], &scratch->b1, sizeof(scratch->b1));
sg_set_buf(&sg[2], b, blen);
/* 0 if well behaved :) */
sg_set_page(&sg[3], ZERO_PAGE(0), zero_padding, 0);
sg_init_one(&sg_dst, dst_buf, dst_size);
skcipher_request_set_sync_tfm(req, tfm_cbc);
skcipher_request_set_callback(req, 0, NULL, NULL);
skcipher_request_set_crypt(req, sg, &sg_dst, dst_size, iv);
result = crypto_skcipher_encrypt(req);
skcipher_request_zero(req);
if (result < 0) {
printk(KERN_ERR "E: can't compute CBC-MAC tag (MIC): %d\n",
result);
goto error_cbc_crypt;
}
/* Now we crypt the MIC Tag (*iv) with Ax -- values per WUSB1.0[6.5]
* The procedure is to AES crypt the A0 block and XOR the MIC
* Tag against it; we only do the first 8 bytes and place it
* directly in the destination buffer.
*
* POS Crypto API: size is assumed to be AES's block size.
* Thanks for documenting it -- tip taken from airo.c
*/
scratch->ax.flags = 0x01; /* as per WUSB 1.0 spec */
scratch->ax.ccm_nonce = *n;
scratch->ax.counter = 0;
crypto_cipher_encrypt_one(tfm_aes, (void *)&scratch->ax,
(void *)&scratch->ax);
bytewise_xor(mic, &scratch->ax, iv, 8);
result = 8;
error_cbc_crypt:
kfree(iv);
error_iv:
kfree(dst_buf);
error_dst_buf:
return result;
}
/*
* WUSB Pseudo Random Function (WUSB1.0[6.5])
*
* @b: buffer to the source data; cannot be a global or const local
* (will confuse the scatterlists)
*/
ssize_t wusb_prf(void *out, size_t out_size,
const u8 key[16], const struct aes_ccm_nonce *_n,
const struct aes_ccm_label *a,
const void *b, size_t blen, size_t len)
{
ssize_t result, bytes = 0, bitr;
struct aes_ccm_nonce n = *_n;
struct crypto_sync_skcipher *tfm_cbc;
struct crypto_cipher *tfm_aes;
struct wusb_mac_scratch *scratch;
u64 sfn = 0;
__le64 sfn_le;
tfm_cbc = crypto_alloc_sync_skcipher("cbc(aes)", 0, 0);
if (IS_ERR(tfm_cbc)) {
result = PTR_ERR(tfm_cbc);
printk(KERN_ERR "E: can't load CBC(AES): %d\n", (int)result);
goto error_alloc_cbc;
}
result = crypto_sync_skcipher_setkey(tfm_cbc, key, 16);
if (result < 0) {
printk(KERN_ERR "E: can't set CBC key: %d\n", (int)result);
goto error_setkey_cbc;
}
tfm_aes = crypto_alloc_cipher("aes", 0, CRYPTO_ALG_ASYNC);
if (IS_ERR(tfm_aes)) {
result = PTR_ERR(tfm_aes);
printk(KERN_ERR "E: can't load AES: %d\n", (int)result);
goto error_alloc_aes;
}
result = crypto_cipher_setkey(tfm_aes, key, 16);
if (result < 0) {
printk(KERN_ERR "E: can't set AES key: %d\n", (int)result);
goto error_setkey_aes;
}
scratch = kmalloc(sizeof(*scratch), GFP_KERNEL);
if (!scratch) {
result = -ENOMEM;
goto error_alloc_scratch;
}
for (bitr = 0; bitr < (len + 63) / 64; bitr++) {
sfn_le = cpu_to_le64(sfn++);
memcpy(&n.sfn, &sfn_le, sizeof(n.sfn)); /* n.sfn++... */
result = wusb_ccm_mac(tfm_cbc, tfm_aes, scratch, out + bytes,
&n, a, b, blen);
if (result < 0)
goto error_ccm_mac;
bytes += result;
}
result = bytes;
kfree(scratch);
error_alloc_scratch:
error_ccm_mac:
error_setkey_aes:
crypto_free_cipher(tfm_aes);
error_alloc_aes:
error_setkey_cbc:
crypto_free_sync_skcipher(tfm_cbc);
error_alloc_cbc:
return result;
}
/* WUSB1.0[A.2] test vectors */
static const u8 stv_hsmic_key[16] = {
0x4b, 0x79, 0xa3, 0xcf, 0xe5, 0x53, 0x23, 0x9d,
0xd7, 0xc1, 0x6d, 0x1c, 0x2d, 0xab, 0x6d, 0x3f
};
static const struct aes_ccm_nonce stv_hsmic_n = {
.sfn = { 0 },
.tkid = { 0x76, 0x98, 0x01, },
.dest_addr = { .data = { 0xbe, 0x00 } },
.src_addr = { .data = { 0x76, 0x98 } },
};
/*
* Out-of-band MIC Generation verification code
*
*/
static int wusb_oob_mic_verify(void)
{
int result;
u8 mic[8];
/* WUSB1.0[A.2] test vectors
*
* Need to keep it in the local stack as GCC 4.1.3something
* messes up and generates noise.
*/
struct usb_handshake stv_hsmic_hs = {
.bMessageNumber = 2,
.bStatus = 00,
.tTKID = { 0x76, 0x98, 0x01 },
.bReserved = 00,
.CDID = { 0x30, 0x31, 0x32, 0x33, 0x34, 0x35,
0x36, 0x37, 0x38, 0x39, 0x3a, 0x3b,
0x3c, 0x3d, 0x3e, 0x3f },
.nonce = { 0x20, 0x21, 0x22, 0x23, 0x24, 0x25,
0x26, 0x27, 0x28, 0x29, 0x2a, 0x2b,
0x2c, 0x2d, 0x2e, 0x2f },
.MIC = { 0x75, 0x6a, 0x97, 0x51, 0x0c, 0x8c,
0x14, 0x7b },
};
size_t hs_size;
result = wusb_oob_mic(mic, stv_hsmic_key, &stv_hsmic_n, &stv_hsmic_hs);
if (result < 0)
printk(KERN_ERR "E: WUSB OOB MIC test: failed: %d\n", result);
else if (memcmp(stv_hsmic_hs.MIC, mic, sizeof(mic))) {
printk(KERN_ERR "E: OOB MIC test: "
"mismatch between MIC result and WUSB1.0[A2]\n");
hs_size = sizeof(stv_hsmic_hs) - sizeof(stv_hsmic_hs.MIC);
printk(KERN_ERR "E: Handshake2 in: (%zu bytes)\n", hs_size);
wusb_key_dump(&stv_hsmic_hs, hs_size);
printk(KERN_ERR "E: CCM Nonce in: (%zu bytes)\n",
sizeof(stv_hsmic_n));
wusb_key_dump(&stv_hsmic_n, sizeof(stv_hsmic_n));
printk(KERN_ERR "E: MIC out:\n");
wusb_key_dump(mic, sizeof(mic));
printk(KERN_ERR "E: MIC out (from WUSB1.0[A.2]):\n");
wusb_key_dump(stv_hsmic_hs.MIC, sizeof(stv_hsmic_hs.MIC));
result = -EINVAL;
} else
result = 0;
return result;
}
/*
* Test vectors for Key derivation
*
* These come from WUSB1.0[6.5.1], the vectors in WUSB1.0[A.1]
* (errata corrected in 2005/07).
*/
static const u8 stv_key_a1[16] __attribute__ ((__aligned__(4))) = {
0xf0, 0xe1, 0xd2, 0xc3, 0xb4, 0xa5, 0x96, 0x87,
0x78, 0x69, 0x5a, 0x4b, 0x3c, 0x2d, 0x1e, 0x0f
};
static const struct aes_ccm_nonce stv_keydvt_n_a1 = {
.sfn = { 0 },
.tkid = { 0x76, 0x98, 0x01, },
.dest_addr = { .data = { 0xbe, 0x00 } },
.src_addr = { .data = { 0x76, 0x98 } },
};
static const struct wusb_keydvt_out stv_keydvt_out_a1 = {
.kck = {
0x4b, 0x79, 0xa3, 0xcf, 0xe5, 0x53, 0x23, 0x9d,
0xd7, 0xc1, 0x6d, 0x1c, 0x2d, 0xab, 0x6d, 0x3f
},
.ptk = {
0xc8, 0x70, 0x62, 0x82, 0xb6, 0x7c, 0xe9, 0x06,
0x7b, 0xc5, 0x25, 0x69, 0xf2, 0x36, 0x61, 0x2d
}
};
/*
* Performa a test to make sure we match the vectors defined in
* WUSB1.0[A.1](Errata2006/12)
*/
static int wusb_key_derive_verify(void)
{
int result = 0;
struct wusb_keydvt_out keydvt_out;
/* These come from WUSB1.0[A.1] + 2006/12 errata
* NOTE: can't make this const or global -- somehow it seems
* the scatterlists for crypto get confused and we get
* bad data. There is no doc on this... */
struct wusb_keydvt_in stv_keydvt_in_a1 = {
.hnonce = {
0x10, 0x11, 0x12, 0x13, 0x14, 0x15, 0x16, 0x17,
0x18, 0x19, 0x1a, 0x1b, 0x1c, 0x1d, 0x1e, 0x1f
},
.dnonce = {
0x20, 0x21, 0x22, 0x23, 0x24, 0x25, 0x26, 0x27,
0x28, 0x29, 0x2a, 0x2b, 0x2c, 0x2d, 0x2e, 0x2f
}
};
result = wusb_key_derive(&keydvt_out, stv_key_a1, &stv_keydvt_n_a1,
&stv_keydvt_in_a1);
if (result < 0)
printk(KERN_ERR "E: WUSB key derivation test: "
"derivation failed: %d\n", result);
if (memcmp(&stv_keydvt_out_a1, &keydvt_out, sizeof(keydvt_out))) {
printk(KERN_ERR "E: WUSB key derivation test: "
"mismatch between key derivation result "
"and WUSB1.0[A1] Errata 2006/12\n");
printk(KERN_ERR "E: keydvt in: key\n");
wusb_key_dump(stv_key_a1, sizeof(stv_key_a1));
printk(KERN_ERR "E: keydvt in: nonce\n");
wusb_key_dump(&stv_keydvt_n_a1, sizeof(stv_keydvt_n_a1));
printk(KERN_ERR "E: keydvt in: hnonce & dnonce\n");
wusb_key_dump(&stv_keydvt_in_a1, sizeof(stv_keydvt_in_a1));
printk(KERN_ERR "E: keydvt out: KCK\n");
wusb_key_dump(&keydvt_out.kck, sizeof(keydvt_out.kck));
printk(KERN_ERR "E: keydvt out: PTK\n");
wusb_key_dump(&keydvt_out.ptk, sizeof(keydvt_out.ptk));
result = -EINVAL;
} else
result = 0;
return result;
}
/*
* Initialize crypto system
*
* FIXME: we do nothing now, other than verifying. Later on we'll
* cache the encryption stuff, so that's why we have a separate init.
*/
int wusb_crypto_init(void)
{
int result;
if (debug_crypto_verify) {
result = wusb_key_derive_verify();
if (result < 0)
return result;
return wusb_oob_mic_verify();
}
return 0;
}
void wusb_crypto_exit(void)
{
/* FIXME: free cached crypto transforms */
}
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