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Implemented the correct way to calculate MAC from a tag, feeding it an extra 32 zeroes. Also divided it up into two parts, one of which can be precalculated by the device before the simulation begins

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Martin Holst Swende 2015-03-02 00:38:36 +01:00
commit 61fe90736b
3 changed files with 131 additions and 42 deletions
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45
armsrc/optimized_cipher.h
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@ -1,5 +1,48 @@
#ifndef OPTIMIZED_CIPHER_H
#define OPTIMIZED_CIPHER_H
#include <stdint.h>
void opt_doMAC(uint8_t *cc_nr_p, uint8_t *div_key_p, uint8_t mac[4]);
/**
* Definition 1 (Cipher state). A cipher state of iClass s is an element of F 40/2
* consisting of the following four components:
* 1. the left register l = (l 0 . . . l 7 ) ∈ F 8/2 ;
* 2. the right register r = (r 0 . . . r 7 ) ∈ F 8/2 ;
* 3. the top register t = (t 0 . . . t 15 ) ∈ F 16/2 .
* 4. the bottom register b = (b 0 . . . b 7 ) ∈ F 8/2 .
**/
typedef struct {
uint8_t l;
uint8_t r;
uint8_t b;
uint16_t t;
} State;
/** The reader MAC is MAC(key, CC * NR )
**/
void opt_doReaderMAC(uint8_t *cc_nr_p, uint8_t *div_key_p, uint8_t mac[4]);
/**
* The tag MAC is MAC(key, CC * NR * 32x0))
*/
void opt_doTagMAC(uint8_t *cc_p, const uint8_t *div_key_p, uint8_t mac[4]);
/**
* The tag MAC can be divided (both can, but no point in dividing the reader mac) into
* two functions, since the first 8 bytes are known, we can pre-calculate the state
* reached after feeding CC to the cipher.
* @param cc_p
* @param div_key_p
* @return the cipher state
*/
State opt_doTagMAC_1(uint8_t *cc_p, const uint8_t *div_key_p);
/**
* The second part of the tag MAC calculation, since the CC is already calculated into the state,
* this function is fed only the NR, and internally feeds the remaining 32 0-bits to generate the tag
* MAC response.
* @param _init - precalculated cipher state
* @param nr - the reader challenge
* @param mac - where to store the MAC
* @param div_key_p - the key to use
*/
void opt_doTagMAC_2(State _init, uint8_t* nr, uint8_t mac[4], const uint8_t* div_key_p);
#endif // OPTIMIZED_CIPHER_H