[proxmark3-svn] / armsrc / hitag2.c

/*
 * Hitag2 emulation
 * 
 * Contains state and functions for an emulated Hitag2 tag. Offers an entry
 * point to handle commands, needs a callback to send response.
 * 
 * (c) 2009 Henryk Plötz <henryk@ploetzli.ch>
 */

#include <proxmark3.h>
#include <stdint.h>

#include "apps.h"
#include "hitag2.h"

struct hitag2_cipher_state {
	uint64_t state;
};

struct hitag2_tag {
	uint32_t uid;
	enum { 
		TAG_STATE_RESET,          // Just powered up, awaiting GetSnr
		TAG_STATE_ACTIVATING,     // In activation phase (password mode), sent UID, awaiting reader password
		TAG_STATE_AUTHENTICATING, // In activation phase (crypto mode), awaiting reader authentication
		TAG_STATE_ACTIVATED,      // Activation complete, awaiting read/write commands
		TAG_STATE_WRITING,        // In write command, awaiting sector contents to be written
	} state;
	unsigned int active_sector;
	char crypto_active;
	struct hitag2_cipher_state cs;
	char sectors[8][4];
};

static void hitag2_cipher_reset(struct hitag2_tag *tag, const char *challenge);
static int hitag2_cipher_authenticate(struct hitag2_cipher_state *cs, const char *authenticator);
static int hitag2_cipher_transcrypt(struct hitag2_cipher_state *cs, char *data, unsigned int bytes, unsigned int bits);

static struct hitag2_tag tag;
static const struct hitag2_tag resetdata = {
		.state = TAG_STATE_RESET,
		.sectors = {                                     // Password mode:               | Crypto mode:
				[0] = { 0x35, 0x33, 0x70, 0x11}, // UID                          | UID
				[1] = { 0x4d, 0x49, 0x4b, 0x52}, // Password RWD                 | 32 bit LSB key
				[2] = { 0x20, 0xf0, 0x4f, 0x4e}, // Reserved                     | 16 bit MSB key, 16 bit reserved
				[3] = { 0x0e, 0xaa, 'H', 'T'},   // Configuration, password TAG  | Configuration, password TAG
		},
};

int hitag2_reset(void)
{
	tag.state = TAG_STATE_RESET;
	tag.crypto_active = 0;
	return 0;
}

int hitag2_init(void)
{
	memcpy(&tag, &resetdata, sizeof(tag));
	hitag2_reset();
	return 0;
}

int hitag2_handle_command(const char* data, const int length, hitag2_response_callback_t cb, void *cb_cookie)
{
	(void)data; (void)length; (void)cb; (void)cb_cookie;
	int retry = 0, done = 0, result=0;
	char temp[10];

	if(tag.crypto_active && length < sizeof(temp)*8) {
		/* Decrypt command */
		memcpy(temp, data, (length+7)/8);
		hitag2_cipher_transcrypt(&(tag.cs), temp, length/8, length%8);
		data = temp;
	}

	
handle_command_retry:
	switch(tag.state) {
	case TAG_STATE_RESET:
		if(length == 5 && data[0] == 0xC0) {
			/* Received 11000 from the reader, request for UID, send UID */
			result=cb(tag.sectors[0], sizeof(tag.sectors[0])*8, 208, cb_cookie);
			done=1;
			if(tag.sectors[3][0] & 0x08) {
				tag.state=TAG_STATE_AUTHENTICATING;
			} else {
				tag.state=TAG_STATE_ACTIVATING;
			}
		}
		break;
	case TAG_STATE_ACTIVATING:
		if(length == 0x20) {
			/* Received RWD password, respond with configuration and our password */
			result=cb(tag.sectors[3], sizeof(tag.sectors[3])*8, 208, cb_cookie);
			done=1;
			tag.state=TAG_STATE_ACTIVATED;
		}
		break;
	case TAG_STATE_AUTHENTICATING:
		if(length == 0x40) {
			/* Received initialisation vector || authentication token, fire up cipher, send our password */
			hitag2_cipher_reset(&tag, data);
			if(hitag2_cipher_authenticate(&(tag.cs), data+4)) {
				char response_enc[4];
				memcpy(response_enc, tag.sectors[3], 4);
				hitag2_cipher_transcrypt(&(tag.cs), response_enc, 4, 0);
				result=cb(response_enc, 4*8, 208, cb_cookie);
				done=1;
				tag.crypto_active = 1;
				tag.state = TAG_STATE_ACTIVATED;
			} else {
				/* The reader failed to authenticate, do nothing */
				DbpString("Reader authentication failed");
			}
		}
		break;
	case TAG_STATE_ACTIVATED:
		if(length == 10) {
			if( ((data[0] & 0xC0) == 0xC0) && ((data[0] & 0x06) == 0) ) {
				/* Read command: 11xx x00y  yy with yyy == ~xxx, xxx is sector number */
				unsigned int sector = (~( ((data[0]<<2)&0x04) | ((data[1]>>6)&0x03) ) & 0x07);
				if(sector == ( (data[0]>>3)&0x07 ) ) {
					memcpy(temp, tag.sectors[sector], 4);
					if(tag.crypto_active) {
						hitag2_cipher_transcrypt(&(tag.cs), temp, 4, 0);
					}
					/* Respond with contents of sector sector */
					result = cb(temp, 4*8, 208, cb_cookie);
					done=1;
				} else {
					/* transmission error */
					DbpString("Transmission error (read) in activated state");
				}
			} else if( ((data[0] & 0xC0) == 0x80) && ((data[0] & 0x06) == 2) ) {
				/* Write command: 10xx x01y  yy with yyy == ~xxx, xxx is sector number */
				unsigned int sector = (~( ((data[0]<<2)&0x04) | ((data[1]>>6)&0x03) ) & 0x07);
				if(sector == ( (data[0]>>3)&0x07 ) ) {
					/* Prepare write, acknowledge by repeating command */
					if(tag.crypto_active) {
						hitag2_cipher_transcrypt(&(tag.cs), temp, length/8, length%8);
					}
					result = cb(data, length, 208, cb_cookie);
					done=1;
					tag.active_sector = sector;
					tag.state=TAG_STATE_WRITING;
				} else {
					/* transmission error */
					DbpString("Transmission error (write) in activated state");
				}
			} 
				
		}
	case TAG_STATE_WRITING:
		if(length == 32) {
			/* These are the sector contents to be written. We don't have to do anything else. */
			memcpy(tag.sectors[tag.active_sector], data, length/8);
			tag.state=TAG_STATE_ACTIVATED;
			done=1;
		}
	}
	
	if(!done && !retry) {
		/* We didn't respond, maybe our state is faulty. Reset and try again. */
		retry=1;
		if(tag.crypto_active) {
			/* Restore undeciphered data */
			memcpy(temp, data, (length+7)/8);
		}
		hitag2_reset();
		goto handle_command_retry;
	}

	return result;
}

/* Following is a modified version of cryptolib.com/ciphers/hitag2/ */
// Software optimized 48-bit Philips/NXP Mifare Hitag2 PCF7936/46/47/52 stream cipher algorithm by I.C. Wiener 2006-2007.
// For educational purposes only.
// No warranties or guarantees of any kind.
// This code is released into the public domain by its author.

// Basic macros:

#define u8				uint8_t
#define u32				uint32_t
#define u64				uint64_t
#define rev8(x)			((((x)>>7)&1)+((((x)>>6)&1)<<1)+((((x)>>5)&1)<<2)+((((x)>>4)&1)<<3)+((((x)>>3)&1)<<4)+((((x)>>2)&1)<<5)+((((x)>>1)&1)<<6)+(((x)&1)<<7))
#define rev16(x)		(rev8 (x)+(rev8 (x>> 8)<< 8))
#define rev32(x)		(rev16(x)+(rev16(x>>16)<<16))
#define rev64(x)		(rev32(x)+(rev32(x>>32)<<32))
#define bit(x,n)		(((x)>>(n))&1)
#define bit32(x,n)		((((x)[(n)>>5])>>((n)))&1)
#define inv32(x,i,n)	((x)[(i)>>5]^=((u32)(n))<<((i)&31))
#define rotl64(x, n)	((((u64)(x))<<((n)&63))+(((u64)(x))>>((0-(n))&63)))

// Single bit Hitag2 functions:

#define i4(x,a,b,c,d)	((u32)((((x)>>(a))&1)+(((x)>>(b))&1)*2+(((x)>>(c))&1)*4+(((x)>>(d))&1)*8))

static const u32 ht2_f4a = 0x2C79;		// 0010 1100 0111 1001
static const u32 ht2_f4b = 0x6671;		// 0110 0110 0111 0001
static const u32 ht2_f5c = 0x7907287B;	// 0111 1001 0000 0111 0010 1000 0111 1011

static u32 _f20 (const u64 x)
{
	u32					i5;
	
	i5 = ((ht2_f4a >> i4 (x, 1, 2, 4, 5)) & 1)* 1
	   + ((ht2_f4b >> i4 (x, 7,11,13,14)) & 1)* 2
	   + ((ht2_f4b >> i4 (x,16,20,22,25)) & 1)* 4
	   + ((ht2_f4b >> i4 (x,27,28,30,32)) & 1)* 8
	   + ((ht2_f4a >> i4 (x,33,42,43,45)) & 1)*16;
	
	return (ht2_f5c >> i5) & 1;
}

static u64 _hitag2_init (const u64 key, const u32 serial, const u32 IV)
{
	u32					i;
	u64					x = ((key & 0xFFFF) << 32) + serial;
	
	for (i = 0; i < 32; i++)
	{
		x >>= 1;
		x += (u64) (_f20 (x) ^ (((IV >> i) ^ (key >> (i+16))) & 1)) << 47;
	}
	return x;
}

static u64 _hitag2_round (u64 *state)
{
	u64					x = *state;
	
	x = (x >>  1) +
	 ((((x >>  0) ^ (x >>  2) ^ (x >>  3) ^ (x >>  6)
	  ^ (x >>  7) ^ (x >>  8) ^ (x >> 16) ^ (x >> 22)
	  ^ (x >> 23) ^ (x >> 26) ^ (x >> 30) ^ (x >> 41)
	  ^ (x >> 42) ^ (x >> 43) ^ (x >> 46) ^ (x >> 47)) & 1) << 47);
	
	*state = x;
	return _f20 (x);
}

static u32 _hitag2_byte (u64 * x)
{
	u32					i, c;
	
	for (i = 0, c = 0; i < 8; i++) c += (u32) _hitag2_round (x) << (i^7);
	return c;
}


/* Cipher/tag glue code: */

static void hitag2_cipher_reset(struct hitag2_tag *tag, const char *iv)
{
	uint64_t key = ((uint64_t)tag->sectors[2][2]) |
			((uint64_t)tag->sectors[2][3] << 8) |
			((uint64_t)tag->sectors[1][0] << 16) |
			((uint64_t)tag->sectors[1][1] << 24) |
			((uint64_t)tag->sectors[1][2] << 32) |
			((uint64_t)tag->sectors[1][3] << 40);
	uint32_t uid = ((uint32_t)tag->sectors[0][0]) |
			((uint32_t)tag->sectors[0][1] << 8) |
			((uint32_t)tag->sectors[0][2] << 16) |
			((uint32_t)tag->sectors[0][3] << 24);
	uint32_t iv_ = (((uint32_t)(iv[0]))) |
			(((uint32_t)(iv[1])) << 8) |
			(((uint32_t)(iv[2])) << 16) |
			(((uint32_t)(iv[3])) << 24);
	tag->cs.state = _hitag2_init(rev64(key), rev32(uid), rev32(iv_));
}

static int hitag2_cipher_authenticate(struct hitag2_cipher_state *cs, const char *authenticator_is)
{
	char authenticator_should[4];
	authenticator_should[0] = ~_hitag2_byte(&(cs->state));
	authenticator_should[1] = ~_hitag2_byte(&(cs->state));
	authenticator_should[2] = ~_hitag2_byte(&(cs->state));
	authenticator_should[3] = ~_hitag2_byte(&(cs->state));
	return memcmp(authenticator_should, authenticator_is, 4) == 0;
}

static int hitag2_cipher_transcrypt(struct hitag2_cipher_state *cs, char *data, unsigned int bytes, unsigned int bits)
{
	int i;
	for(i=0; i<bytes; i++) data[i] ^= _hitag2_byte(&(cs->state));
	for(i=0; i<bits; i++) data[bytes] ^= _hitag2_round(&(cs->state)) << (7-i);
	return 0;
}
Commit	Line	Data
3742d905	1	/*
	2	* Hitag2 emulation
	3	*
	4	* Contains state and functions for an emulated Hitag2 tag. Offers an entry
	5	* point to handle commands, needs a callback to send response.
	6	*
	7	* (c) 2009 Henryk Plötz <henryk@ploetzli.ch>
	8	*/
	9
	10	#include <proxmark3.h>
	11	#include <stdint.h>
	12
	13	#include "apps.h"
	14	#include "hitag2.h"
	15
	16	struct hitag2_cipher_state {
	17	uint64_t state;
	18	};
	19
	20	struct hitag2_tag {
	21	uint32_t uid;
	22	enum {
	23	TAG_STATE_RESET, // Just powered up, awaiting GetSnr
	24	TAG_STATE_ACTIVATING, // In activation phase (password mode), sent UID, awaiting reader password
	25	TAG_STATE_AUTHENTICATING, // In activation phase (crypto mode), awaiting reader authentication
	26	TAG_STATE_ACTIVATED, // Activation complete, awaiting read/write commands
	27	TAG_STATE_WRITING, // In write command, awaiting sector contents to be written
	28	} state;
	29	unsigned int active_sector;
	30	char crypto_active;
	31	struct hitag2_cipher_state cs;
	32	char sectors[8][4];
	33	};
	34
	35	static void hitag2_cipher_reset(struct hitag2_tag tag, const char challenge);
	36	static int hitag2_cipher_authenticate(struct hitag2_cipher_state cs, const char authenticator);
	37	static int hitag2_cipher_transcrypt(struct hitag2_cipher_state cs, char data, unsigned int bytes, unsigned int bits);
	38
	39	static struct hitag2_tag tag;
	40	static const struct hitag2_tag resetdata = {
	41	.state = TAG_STATE_RESET,
	42	.sectors = { // Password mode: \| Crypto mode:
	43	[0] = { 0x35, 0x33, 0x70, 0x11}, // UID \| UID
	44	[1] = { 0x4d, 0x49, 0x4b, 0x52}, // Password RWD \| 32 bit LSB key
	45	[2] = { 0x20, 0xf0, 0x4f, 0x4e}, // Reserved \| 16 bit MSB key, 16 bit reserved
	46	[3] = { 0x0e, 0xaa, 'H', 'T'}, // Configuration, password TAG \| Configuration, password TAG
	47	},
	48	};
	49
	50	int hitag2_reset(void)
	51	{
	52	tag.state = TAG_STATE_RESET;
	53	tag.crypto_active = 0;
	54	return 0;
	55	}
	56
	57	int hitag2_init(void)
	58	{
	59	memcpy(&tag, &resetdata, sizeof(tag));
	60	hitag2_reset();
	61	return 0;
	62	}
	63
	64	int hitag2_handle_command(const char* data, const int length, hitag2_response_callback_t cb, void *cb_cookie)
65	{
66	(void)data; (void)length; (void)cb; (void)cb_cookie;
67	int retry = 0, done = 0, result=0;
68	char temp[10];
69
70	if(tag.crypto_active && length < sizeof(temp)*8) {
71	/* Decrypt command */
72	memcpy(temp, data, (length+7)/8);
73	hitag2_cipher_transcrypt(&(tag.cs), temp, length/8, length%8);
74	data = temp;
75	}
76
77
78	handle_command_retry:
79	switch(tag.state) {
80	case TAG_STATE_RESET:
81	if(length == 5 && data[0] == 0xC0) {
82	/* Received 11000 from the reader, request for UID, send UID */
83	result=cb(tag.sectors[0], sizeof(tag.sectors[0])*8, 208, cb_cookie);
84	done=1;
85	if(tag.sectors[3][0] & 0x08) {
86	tag.state=TAG_STATE_AUTHENTICATING;
87	} else {
88	tag.state=TAG_STATE_ACTIVATING;
89	}
90	}
91	break;
92	case TAG_STATE_ACTIVATING:
93	if(length == 0x20) {
94	/* Received RWD password, respond with configuration and our password */
95	result=cb(tag.sectors[3], sizeof(tag.sectors[3])*8, 208, cb_cookie);
96	done=1;
97	tag.state=TAG_STATE_ACTIVATED;
98	}
99	break;
100	case TAG_STATE_AUTHENTICATING:
101	if(length == 0x40) {
102	/* Received initialisation vector \|\| authentication token, fire up cipher, send our password */
103	hitag2_cipher_reset(&tag, data);
104	if(hitag2_cipher_authenticate(&(tag.cs), data+4)) {
105	char response_enc[4];
106	memcpy(response_enc, tag.sectors[3], 4);
107	hitag2_cipher_transcrypt(&(tag.cs), response_enc, 4, 0);
108	result=cb(response_enc, 4*8, 208, cb_cookie);
109	done=1;
110	tag.crypto_active = 1;
111	tag.state = TAG_STATE_ACTIVATED;
112	} else {
113	/* The reader failed to authenticate, do nothing */
114	DbpString("Reader authentication failed");
115	}
116	}
117	break;
118	case TAG_STATE_ACTIVATED:
119	if(length == 10) {
120	if( ((data[0] & 0xC0) == 0xC0) && ((data[0] & 0x06) == 0) ) {
121	/* Read command: 11xx x00y yy with yyy == ~xxx, xxx is sector number */
122	unsigned int sector = (~( ((data[0]<<2)&0x04) \| ((data[1]>>6)&0x03) ) & 0x07);
123	if(sector == ( (data[0]>>3)&0x07 ) ) {
124	memcpy(temp, tag.sectors[sector], 4);
125	if(tag.crypto_active) {
126	hitag2_cipher_transcrypt(&(tag.cs), temp, 4, 0);
127	}
128	/* Respond with contents of sector sector */
129	result = cb(temp, 4*8, 208, cb_cookie);
130	done=1;
131	} else {
132	/* transmission error */
133	DbpString("Transmission error (read) in activated state");
134	}
135	} else if( ((data[0] & 0xC0) == 0x80) && ((data[0] & 0x06) == 2) ) {
136	/* Write command: 10xx x01y yy with yyy == ~xxx, xxx is sector number */
137	unsigned int sector = (~( ((data[0]<<2)&0x04) \| ((data[1]>>6)&0x03) ) & 0x07);
138	if(sector == ( (data[0]>>3)&0x07 ) ) {
139	/* Prepare write, acknowledge by repeating command */
140	if(tag.crypto_active) {
141	hitag2_cipher_transcrypt(&(tag.cs), temp, length/8, length%8);
142	}
143	result = cb(data, length, 208, cb_cookie);
144	done=1;
145	tag.active_sector = sector;
146	tag.state=TAG_STATE_WRITING;
147	} else {
148	/* transmission error */
149	DbpString("Transmission error (write) in activated state");
150	}
151	}
152
153	}
154	case TAG_STATE_WRITING:
155	if(length == 32) {
156	/* These are the sector contents to be written. We don't have to do anything else. */
157	memcpy(tag.sectors[tag.active_sector], data, length/8);
158	tag.state=TAG_STATE_ACTIVATED;
159	done=1;
160	}
161	}
162
163	if(!done && !retry) {
164	/* We didn't respond, maybe our state is faulty. Reset and try again. */
165	retry=1;
166	if(tag.crypto_active) {
167	/* Restore undeciphered data */
168	memcpy(temp, data, (length+7)/8);
169	}
170	hitag2_reset();
171	goto handle_command_retry;
172	}
173
174	return result;
175	}
176
177	/* Following is a modified version of cryptolib.com/ciphers/hitag2/ */
178	// Software optimized 48-bit Philips/NXP Mifare Hitag2 PCF7936/46/47/52 stream cipher algorithm by I.C. Wiener 2006-2007.
179	// For educational purposes only.
180	// No warranties or guarantees of any kind.
181	// This code is released into the public domain by its author.
182
183	// Basic macros:
184
185	#define u8 uint8_t
186	#define u32 uint32_t
187	#define u64 uint64_t
188	#define rev8(x) ((((x)>>7)&1)+((((x)>>6)&1)<<1)+((((x)>>5)&1)<<2)+((((x)>>4)&1)<<3)+((((x)>>3)&1)<<4)+((((x)>>2)&1)<<5)+((((x)>>1)&1)<<6)+(((x)&1)<<7))
189	#define rev16(x) (rev8 (x)+(rev8 (x>> 8)<< 8))
190	#define rev32(x) (rev16(x)+(rev16(x>>16)<<16))
191	#define rev64(x) (rev32(x)+(rev32(x>>32)<<32))
192	#define bit(x,n) (((x)>>(n))&1)
193	#define bit32(x,n) ((((x)[(n)>>5])>>((n)))&1)
194	#define inv32(x,i,n) ((x)[(i)>>5]^=((u32)(n))<<((i)&31))
195	#define rotl64(x, n) ((((u64)(x))<<((n)&63))+(((u64)(x))>>((0-(n))&63)))
196
197	// Single bit Hitag2 functions:
198
199	#define i4(x,a,b,c,d) ((u32)((((x)>>(a))&1)+(((x)>>(b))&1)2+(((x)>>(c))&1)4+(((x)>>(d))&1)*8))
200
201	static const u32 ht2_f4a = 0x2C79; // 0010 1100 0111 1001
202	static const u32 ht2_f4b = 0x6671; // 0110 0110 0111 0001
203	static const u32 ht2_f5c = 0x7907287B; // 0111 1001 0000 0111 0010 1000 0111 1011
204
205	static u32 _f20 (const u64 x)
206	{
207	u32 i5;
208
209	i5 = ((ht2_f4a >> i4 (x, 1, 2, 4, 5)) & 1)* 1
210	+ ((ht2_f4b >> i4 (x, 7,11,13,14)) & 1)* 2
211	+ ((ht2_f4b >> i4 (x,16,20,22,25)) & 1)* 4
212	+ ((ht2_f4b >> i4 (x,27,28,30,32)) & 1)* 8
213	+ ((ht2_f4a >> i4 (x,33,42,43,45)) & 1)*16;
214
215	return (ht2_f5c >> i5) & 1;
216	}
217
218	static u64 _hitag2_init (const u64 key, const u32 serial, const u32 IV)
219	{
220	u32 i;
221	u64 x = ((key & 0xFFFF) << 32) + serial;
222
223	for (i = 0; i < 32; i++)
224	{
225	x >>= 1;
226	x += (u64) (_f20 (x) ^ (((IV >> i) ^ (key >> (i+16))) & 1)) << 47;
227	}
228	return x;
229	}
230
231	static u64 _hitag2_round (u64 *state)
232	{
233	u64 x = *state;
234
235	x = (x >> 1) +
236	((((x >> 0) ^ (x >> 2) ^ (x >> 3) ^ (x >> 6)
237	^ (x >> 7) ^ (x >> 8) ^ (x >> 16) ^ (x >> 22)
238	^ (x >> 23) ^ (x >> 26) ^ (x >> 30) ^ (x >> 41)
239	^ (x >> 42) ^ (x >> 43) ^ (x >> 46) ^ (x >> 47)) & 1) << 47);
240
241	*state = x;
242	return _f20 (x);
243	}
244
3742d905	245	static u32 _hitag2_byte (u64 * x)
	246	{
	247	u32 i, c;
	248
	249	for (i = 0, c = 0; i < 8; i++) c += (u32) _hitag2_round (x) << (i^7);
	250	return c;
	251	}
	252
	253
	254	/* Cipher/tag glue code: */
	255
	256	static void hitag2_cipher_reset(struct hitag2_tag tag, const char iv)
	257	{
	258	uint64_t key = ((uint64_t)tag->sectors[2][2]) \|
	259	((uint64_t)tag->sectors[2][3] << 8) \|
	260	((uint64_t)tag->sectors[1][0] << 16) \|
	261	((uint64_t)tag->sectors[1][1] << 24) \|
	262	((uint64_t)tag->sectors[1][2] << 32) \|
	263	((uint64_t)tag->sectors[1][3] << 40);
	264	uint32_t uid = ((uint32_t)tag->sectors[0][0]) \|
	265	((uint32_t)tag->sectors[0][1] << 8) \|
	266	((uint32_t)tag->sectors[0][2] << 16) \|
	267	((uint32_t)tag->sectors[0][3] << 24);
	268	uint32_t iv_ = (((uint32_t)(iv[0]))) \|
	269	(((uint32_t)(iv[1])) << 8) \|
	270	(((uint32_t)(iv[2])) << 16) \|
	271	(((uint32_t)(iv[3])) << 24);
	272	tag->cs.state = _hitag2_init(rev64(key), rev32(uid), rev32(iv_));
	273	}
	274
	275	static int hitag2_cipher_authenticate(struct hitag2_cipher_state cs, const char authenticator_is)
	276	{
	277	char authenticator_should[4];
	278	authenticator_should[0] = ~_hitag2_byte(&(cs->state));
	279	authenticator_should[1] = ~_hitag2_byte(&(cs->state));
	280	authenticator_should[2] = ~_hitag2_byte(&(cs->state));
	281	authenticator_should[3] = ~_hitag2_byte(&(cs->state));
	282	return memcmp(authenticator_should, authenticator_is, 4) == 0;
	283	}
	284
	285	static int hitag2_cipher_transcrypt(struct hitag2_cipher_state cs, char data, unsigned int bytes, unsigned int bits)
	286	{
	287	int i;
	288	for(i=0; i<bytes; i++) data[i] ^= _hitag2_byte(&(cs->state));
	289	for(i=0; i<bits; i++) data[bytes] ^= _hitag2_round(&(cs->state)) << (7-i);
	290	return 0;
	291	}