src/ciphers/skipjack.c - third_party/dropbear - Git at Google

 /* LibTomCrypt, modular cryptographic library -- Tom St Denis
  *
  * LibTomCrypt is a library that provides various cryptographic
  * algorithms in a highly modular and flexible manner.
  *
  * The library is free for all purposes without any express
  * guarantee it works.
  *
  * Tom St Denis, tomstdenis@gmail.com, http://libtomcrypt.org
  */

 /**
   @file skipjack.c
   Skipjack Implementation by Tom St Denis
 */
 #include "tomcrypt.h"

 #ifdef SKIPJACK

 const struct ltc_cipher_descriptor skipjack_desc =
 {
     "skipjack",
     17,
     10, 10, 8, 32,
     &skipjack_setup,
     &skipjack_ecb_encrypt,
     &skipjack_ecb_decrypt,
     &skipjack_test,
     &skipjack_done,
     &skipjack_keysize,
     NULL, NULL, NULL, NULL, NULL, NULL, NULL
 };

 static const unsigned char sbox[256] = {
    0xa3,0xd7,0x09,0x83,0xf8,0x48,0xf6,0xf4,0xb3,0x21,0x15,0x78,0x99,0xb1,0xaf,0xf9,
    0xe7,0x2d,0x4d,0x8a,0xce,0x4c,0xca,0x2e,0x52,0x95,0xd9,0x1e,0x4e,0x38,0x44,0x28,
    0x0a,0xdf,0x02,0xa0,0x17,0xf1,0x60,0x68,0x12,0xb7,0x7a,0xc3,0xe9,0xfa,0x3d,0x53,
    0x96,0x84,0x6b,0xba,0xf2,0x63,0x9a,0x19,0x7c,0xae,0xe5,0xf5,0xf7,0x16,0x6a,0xa2,
    0x39,0xb6,0x7b,0x0f,0xc1,0x93,0x81,0x1b,0xee,0xb4,0x1a,0xea,0xd0,0x91,0x2f,0xb8,
    0x55,0xb9,0xda,0x85,0x3f,0x41,0xbf,0xe0,0x5a,0x58,0x80,0x5f,0x66,0x0b,0xd8,0x90,
    0x35,0xd5,0xc0,0xa7,0x33,0x06,0x65,0x69,0x45,0x00,0x94,0x56,0x6d,0x98,0x9b,0x76,
    0x97,0xfc,0xb2,0xc2,0xb0,0xfe,0xdb,0x20,0xe1,0xeb,0xd6,0xe4,0xdd,0x47,0x4a,0x1d,
    0x42,0xed,0x9e,0x6e,0x49,0x3c,0xcd,0x43,0x27,0xd2,0x07,0xd4,0xde,0xc7,0x67,0x18,
    0x89,0xcb,0x30,0x1f,0x8d,0xc6,0x8f,0xaa,0xc8,0x74,0xdc,0xc9,0x5d,0x5c,0x31,0xa4,
    0x70,0x88,0x61,0x2c,0x9f,0x0d,0x2b,0x87,0x50,0x82,0x54,0x64,0x26,0x7d,0x03,0x40,
    0x34,0x4b,0x1c,0x73,0xd1,0xc4,0xfd,0x3b,0xcc,0xfb,0x7f,0xab,0xe6,0x3e,0x5b,0xa5,
    0xad,0x04,0x23,0x9c,0x14,0x51,0x22,0xf0,0x29,0x79,0x71,0x7e,0xff,0x8c,0x0e,0xe2,
    0x0c,0xef,0xbc,0x72,0x75,0x6f,0x37,0xa1,0xec,0xd3,0x8e,0x62,0x8b,0x86,0x10,0xe8,
    0x08,0x77,0x11,0xbe,0x92,0x4f,0x24,0xc5,0x32,0x36,0x9d,0xcf,0xf3,0xa6,0xbb,0xac,
    0x5e,0x6c,0xa9,0x13,0x57,0x25,0xb5,0xe3,0xbd,0xa8,0x3a,0x01,0x05,0x59,0x2a,0x46
 };

 /* simple x + 1 (mod 10) in one step. */
 static const int keystep[] =  { 1, 2, 3, 4, 5, 6, 7, 8, 9, 0 };

 /* simple x - 1 (mod 10) in one step */
 static const int ikeystep[] = { 9, 0, 1, 2, 3, 4, 5, 6, 7, 8 };

  /**
     Initialize the Skipjack block cipher
     @param key The symmetric key you wish to pass
     @param keylen The key length in bytes
     @param num_rounds The number of rounds desired (0 for default)
     @param skey The key in as scheduled by this function.
     @return CRYPT_OK if successful
  */
 int skipjack_setup(const unsigned char *key, int keylen, int num_rounds, symmetric_key *skey)
 {
    int x;

    LTC_ARGCHK(key  != NULL);
    LTC_ARGCHK(skey != NULL);

    if (keylen != 10) {
       return CRYPT_INVALID_KEYSIZE;
    }

    if (num_rounds != 32 && num_rounds != 0) {
       return CRYPT_INVALID_ROUNDS;
    }

    /* make sure the key is in range for platforms where CHAR_BIT != 8 */
    for (x = 0; x < 10; x++) {
        skey->skipjack.key[x] = key[x] & 255;
    }

    return CRYPT_OK;
 }

 #define RULE_A \
    tmp = g_func(w1, &kp, skey->skipjack.key);      \
    w1  = tmp ^ w4 ^ x;                            \
    w4  = w3; w3 = w2;                             \
    w2  = tmp;

 #define RULE_B \
    tmp  = g_func(w1, &kp, skey->skipjack.key);     \
    tmp1 = w4; w4  = w3;                           \
    w3   = w1 ^ w2 ^ x;                            \
    w1   = tmp1; w2 = tmp;

 #define RULE_A1 \
    tmp = w1 ^ w2 ^ x;                             \
    w1  = ig_func(w2, &kp, skey->skipjack.key);     \
    w2  = w3; w3 = w4; w4 = tmp;

 #define RULE_B1 \
    tmp = ig_func(w2, &kp, skey->skipjack.key);     \
    w2  = tmp ^ w3 ^ x;                            \
    w3  = w4; w4 = w1; w1 = tmp;

 static unsigned g_func(unsigned w, int *kp, unsigned char *key)
 {
    unsigned char g1,g2;

    g1 = (w >> 8) & 255; g2 = w & 255;
    g1 ^= sbox[g2^key[*kp]]; *kp = keystep[*kp];
    g2 ^= sbox[g1^key[*kp]]; *kp = keystep[*kp];
    g1 ^= sbox[g2^key[*kp]]; *kp = keystep[*kp];
    g2 ^= sbox[g1^key[*kp]]; *kp = keystep[*kp];
    return ((unsigned)g1<<8)|(unsigned)g2;
 }

 static unsigned ig_func(unsigned w, int *kp, unsigned char *key)
 {
    unsigned char g1,g2;

    g1 = (w >> 8) & 255; g2 = w & 255;
    *kp = ikeystep[*kp]; g2 ^= sbox[g1^key[*kp]];
    *kp = ikeystep[*kp]; g1 ^= sbox[g2^key[*kp]];
    *kp = ikeystep[*kp]; g2 ^= sbox[g1^key[*kp]];
    *kp = ikeystep[*kp]; g1 ^= sbox[g2^key[*kp]];
    return ((unsigned)g1<<8)|(unsigned)g2;
 }

 /**
   Encrypts a block of text with Skipjack
   @param pt The input plaintext (8 bytes)
   @param ct The output ciphertext (8 bytes)
   @param skey The key as scheduled
 */
 #ifdef LTC_CLEAN_STACK
 static void _skipjack_ecb_encrypt(const unsigned char *pt, unsigned char *ct, symmetric_key *skey)
 #else
 void skipjack_ecb_encrypt(const unsigned char *pt, unsigned char *ct, symmetric_key *skey)
 #endif
 {
    unsigned w1,w2,w3,w4,tmp,tmp1;
    int x, kp;

    LTC_ARGCHK(pt   != NULL);
    LTC_ARGCHK(ct   != NULL);
    LTC_ARGCHK(skey != NULL);

    /* load block */
    w1 = ((unsigned)pt[0]<<8)|pt[1];
    w2 = ((unsigned)pt[2]<<8)|pt[3];
    w3 = ((unsigned)pt[4]<<8)|pt[5];
    w4 = ((unsigned)pt[6]<<8)|pt[7];

    /* 8 rounds of RULE A */
    for (x = 1, kp = 0; x < 9; x++) {
        RULE_A;
    }

    /* 8 rounds of RULE B */
    for (; x < 17; x++) {
        RULE_B;
    }

    /* 8 rounds of RULE A */
    for (; x < 25; x++) {
        RULE_A;
    }

    /* 8 rounds of RULE B */
    for (; x < 33; x++) {
        RULE_B;
    }

    /* store block */
    ct[0] = (w1>>8)&255; ct[1] = w1&255;
    ct[2] = (w2>>8)&255; ct[3] = w2&255;
    ct[4] = (w3>>8)&255; ct[5] = w3&255;
    ct[6] = (w4>>8)&255; ct[7] = w4&255;
 }

 #ifdef LTC_CLEAN_STACK
 void skipjack_ecb_encrypt(const unsigned char *pt, unsigned char *ct, symmetric_key *skey)
 {
    _skipjack_ecb_encrypt(pt, ct, skey);
    burn_stack(sizeof(unsigned) * 8 + sizeof(int) * 2);
 }
 #endif

 /**
   Decrypts a block of text with Skipjack
   @param ct The input ciphertext (8 bytes)
   @param pt The output plaintext (8 bytes)
   @param skey The key as scheduled
 */
 #ifdef LTC_CLEAN_STACK
 static void _skipjack_ecb_decrypt(const unsigned char *ct, unsigned char *pt, symmetric_key *skey)
 #else
 void skipjack_ecb_decrypt(const unsigned char *ct, unsigned char *pt, symmetric_key *skey)
 #endif
 {
    unsigned w1,w2,w3,w4,tmp;
    int x, kp;

    LTC_ARGCHK(pt   != NULL);
    LTC_ARGCHK(ct   != NULL);
    LTC_ARGCHK(skey != NULL);

    /* load block */
    w1 = ((unsigned)ct[0]<<8)|ct[1];
    w2 = ((unsigned)ct[2]<<8)|ct[3];
    w3 = ((unsigned)ct[4]<<8)|ct[5];
    w4 = ((unsigned)ct[6]<<8)|ct[7];

    /* 8 rounds of RULE B^-1

       Note the value "kp = 8" comes from "kp = (32 * 4) mod 10" where 32*4 is 128 which mod 10 is 8
     */
    for (x = 32, kp = 8; x > 24; x--) {
        RULE_B1;
    }

    /* 8 rounds of RULE A^-1 */
    for (; x > 16; x--) {
        RULE_A1;
    }


    /* 8 rounds of RULE B^-1 */
    for (; x > 8; x--) {
        RULE_B1;
    }

    /* 8 rounds of RULE A^-1 */
    for (; x > 0; x--) {
        RULE_A1;
    }

    /* store block */
    pt[0] = (w1>>8)&255; pt[1] = w1&255;
    pt[2] = (w2>>8)&255; pt[3] = w2&255;
    pt[4] = (w3>>8)&255; pt[5] = w3&255;
    pt[6] = (w4>>8)&255; pt[7] = w4&255;
 }

 #ifdef LTC_CLEAN_STACK
 void skipjack_ecb_decrypt(const unsigned char *ct, unsigned char *pt, symmetric_key *skey)
 {
    _skipjack_ecb_decrypt(ct, pt, skey);
    burn_stack(sizeof(unsigned) * 7 + sizeof(int) * 2);
 }
 #endif

 /**
   Performs a self-test of the Skipjack block cipher
   @return CRYPT_OK if functional, CRYPT_NOP if self-test has been disabled
 */
 int skipjack_test(void)
 {
  #ifndef LTC_TEST
     return CRYPT_NOP;
  #else
    static const struct {
        unsigned char key[10], pt[8], ct[8];
    } tests[] = {
    {
        { 0x00, 0x99, 0x88, 0x77, 0x66, 0x55, 0x44, 0x33, 0x22, 0x11 },
        { 0x33, 0x22, 0x11, 0x00, 0xdd, 0xcc, 0xbb, 0xaa },
        { 0x25, 0x87, 0xca, 0xe2, 0x7a, 0x12, 0xd3, 0x00 }
    }
    };
    unsigned char buf[2][8];
    int x, y, err;
    symmetric_key key;

    for (x = 0; x < (int)(sizeof(tests) / sizeof(tests[0])); x++) {
       /* setup key */
       if ((err = skipjack_setup(tests[x].key, 10, 0, &key)) != CRYPT_OK) {
          return err;
       }

       /* encrypt and decrypt */
       skipjack_ecb_encrypt(tests[x].pt, buf[0], &key);
       skipjack_ecb_decrypt(buf[0], buf[1], &key);

       /* compare */
       if (memcmp(buf[0], tests[x].ct, 8) != 0 || memcmp(buf[1], tests[x].pt, 8) != 0) {
          return CRYPT_FAIL_TESTVECTOR;
       }

       /* now see if we can encrypt all zero bytes 1000 times, decrypt and come back where we started */
       for (y = 0; y < 8; y++) buf[0][y] = 0;
       for (y = 0; y < 1000; y++) skipjack_ecb_encrypt(buf[0], buf[0], &key);
       for (y = 0; y < 1000; y++) skipjack_ecb_decrypt(buf[0], buf[0], &key);
       for (y = 0; y < 8; y++) if (buf[0][y] != 0) return CRYPT_FAIL_TESTVECTOR;
    }

    return CRYPT_OK;
   #endif
 }

 /** Terminate the context
    @param skey    The scheduled key
 */
 void skipjack_done(symmetric_key *skey)
 {
 }

 /**
   Gets suitable key size
   @param keysize [in/out] The length of the recommended key (in bytes).  This function will store the suitable size back in this variable.
   @return CRYPT_OK if the input key size is acceptable.
 */
 int skipjack_keysize(int *keysize)
 {
    LTC_ARGCHK(keysize != NULL);
    if (*keysize < 10) {
       return CRYPT_INVALID_KEYSIZE;
    } else if (*keysize > 10) {
       *keysize = 10;
    }
    return CRYPT_OK;
 }

 #endif

 /* $Source: /cvs/libtom/libtomcrypt/src/ciphers/skipjack.c,v $ */
 /* $Revision: 1.7 $ */
 /* $Date: 2005/05/05 14:35:58 $ */
	/* LibTomCrypt, modular cryptographic library -- Tom St Denis
	*
	* LibTomCrypt is a library that provides various cryptographic
	* algorithms in a highly modular and flexible manner.
	*
	* The library is free for all purposes without any express
	* guarantee it works.
	*
	* Tom St Denis, tomstdenis@gmail.com, http://libtomcrypt.org
	*/

	/**
	@file skipjack.c
	Skipjack Implementation by Tom St Denis
	*/
	#include "tomcrypt.h"

	#ifdef SKIPJACK

	const struct ltc_cipher_descriptor skipjack_desc =
	{
	"skipjack",
	17,
	10, 10, 8, 32,
	&skipjack_setup,
	&skipjack_ecb_encrypt,
	&skipjack_ecb_decrypt,
	&skipjack_test,
	&skipjack_done,
	&skipjack_keysize,
	NULL, NULL, NULL, NULL, NULL, NULL, NULL
	};

	static const unsigned char sbox[256] = {
	0xa3,0xd7,0x09,0x83,0xf8,0x48,0xf6,0xf4,0xb3,0x21,0x15,0x78,0x99,0xb1,0xaf,0xf9,
	0xe7,0x2d,0x4d,0x8a,0xce,0x4c,0xca,0x2e,0x52,0x95,0xd9,0x1e,0x4e,0x38,0x44,0x28,
	0x0a,0xdf,0x02,0xa0,0x17,0xf1,0x60,0x68,0x12,0xb7,0x7a,0xc3,0xe9,0xfa,0x3d,0x53,
	0x96,0x84,0x6b,0xba,0xf2,0x63,0x9a,0x19,0x7c,0xae,0xe5,0xf5,0xf7,0x16,0x6a,0xa2,
	0x39,0xb6,0x7b,0x0f,0xc1,0x93,0x81,0x1b,0xee,0xb4,0x1a,0xea,0xd0,0x91,0x2f,0xb8,
	0x55,0xb9,0xda,0x85,0x3f,0x41,0xbf,0xe0,0x5a,0x58,0x80,0x5f,0x66,0x0b,0xd8,0x90,
	0x35,0xd5,0xc0,0xa7,0x33,0x06,0x65,0x69,0x45,0x00,0x94,0x56,0x6d,0x98,0x9b,0x76,
	0x97,0xfc,0xb2,0xc2,0xb0,0xfe,0xdb,0x20,0xe1,0xeb,0xd6,0xe4,0xdd,0x47,0x4a,0x1d,
	0x42,0xed,0x9e,0x6e,0x49,0x3c,0xcd,0x43,0x27,0xd2,0x07,0xd4,0xde,0xc7,0x67,0x18,
	0x89,0xcb,0x30,0x1f,0x8d,0xc6,0x8f,0xaa,0xc8,0x74,0xdc,0xc9,0x5d,0x5c,0x31,0xa4,
	0x70,0x88,0x61,0x2c,0x9f,0x0d,0x2b,0x87,0x50,0x82,0x54,0x64,0x26,0x7d,0x03,0x40,
	0x34,0x4b,0x1c,0x73,0xd1,0xc4,0xfd,0x3b,0xcc,0xfb,0x7f,0xab,0xe6,0x3e,0x5b,0xa5,
	0xad,0x04,0x23,0x9c,0x14,0x51,0x22,0xf0,0x29,0x79,0x71,0x7e,0xff,0x8c,0x0e,0xe2,
	0x0c,0xef,0xbc,0x72,0x75,0x6f,0x37,0xa1,0xec,0xd3,0x8e,0x62,0x8b,0x86,0x10,0xe8,
	0x08,0x77,0x11,0xbe,0x92,0x4f,0x24,0xc5,0x32,0x36,0x9d,0xcf,0xf3,0xa6,0xbb,0xac,
	0x5e,0x6c,0xa9,0x13,0x57,0x25,0xb5,0xe3,0xbd,0xa8,0x3a,0x01,0x05,0x59,0x2a,0x46
	};

	/* simple x + 1 (mod 10) in one step. */
	static const int keystep[] = { 1, 2, 3, 4, 5, 6, 7, 8, 9, 0 };

	/* simple x - 1 (mod 10) in one step */
	static const int ikeystep[] = { 9, 0, 1, 2, 3, 4, 5, 6, 7, 8 };

	/**
	Initialize the Skipjack block cipher
	@param key The symmetric key you wish to pass
	@param keylen The key length in bytes
	@param num_rounds The number of rounds desired (0 for default)
	@param skey The key in as scheduled by this function.
	@return CRYPT_OK if successful
	*/
	int skipjack_setup(const unsigned char key, int keylen, int num_rounds, symmetric_key skey)
	{
	int x;

	LTC_ARGCHK(key != NULL);
	LTC_ARGCHK(skey != NULL);

	if (keylen != 10) {
	return CRYPT_INVALID_KEYSIZE;
	}

	if (num_rounds != 32 && num_rounds != 0) {
	return CRYPT_INVALID_ROUNDS;
	}

	/* make sure the key is in range for platforms where CHAR_BIT != 8 */
	for (x = 0; x < 10; x++) {
	skey->skipjack.key[x] = key[x] & 255;
	}

	return CRYPT_OK;
	}

	#define RULE_A \
	tmp = g_func(w1, &kp, skey->skipjack.key); \
	w1 = tmp ^ w4 ^ x; \
	w4 = w3; w3 = w2; \
	w2 = tmp;

	#define RULE_B \
	tmp = g_func(w1, &kp, skey->skipjack.key); \
	tmp1 = w4; w4 = w3; \
	w3 = w1 ^ w2 ^ x; \
	w1 = tmp1; w2 = tmp;

	#define RULE_A1 \
	tmp = w1 ^ w2 ^ x; \
	w1 = ig_func(w2, &kp, skey->skipjack.key); \
	w2 = w3; w3 = w4; w4 = tmp;

	#define RULE_B1 \
	tmp = ig_func(w2, &kp, skey->skipjack.key); \
	w2 = tmp ^ w3 ^ x; \
	w3 = w4; w4 = w1; w1 = tmp;

	static unsigned g_func(unsigned w, int kp, unsigned char key)
	{
	unsigned char g1,g2;

	g1 = (w >> 8) & 255; g2 = w & 255;
	g1 ^= sbox[g2^key[kp]]; kp = keystep[*kp];
	g2 ^= sbox[g1^key[kp]]; kp = keystep[*kp];
	g1 ^= sbox[g2^key[kp]]; kp = keystep[*kp];
	g2 ^= sbox[g1^key[kp]]; kp = keystep[*kp];
	return ((unsigned)g1<<8)\|(unsigned)g2;
	}

	static unsigned ig_func(unsigned w, int kp, unsigned char key)
	{
	unsigned char g1,g2;

	g1 = (w >> 8) & 255; g2 = w & 255;
	kp = ikeystep[kp]; g2 ^= sbox[g1^key[*kp]];
	kp = ikeystep[kp]; g1 ^= sbox[g2^key[*kp]];
	kp = ikeystep[kp]; g2 ^= sbox[g1^key[*kp]];
	kp = ikeystep[kp]; g1 ^= sbox[g2^key[*kp]];
	return ((unsigned)g1<<8)\|(unsigned)g2;
	}

	/**
	Encrypts a block of text with Skipjack
	@param pt The input plaintext (8 bytes)
	@param ct The output ciphertext (8 bytes)
	@param skey The key as scheduled
	*/
	#ifdef LTC_CLEAN_STACK
	static void _skipjack_ecb_encrypt(const unsigned char pt, unsigned char ct, symmetric_key *skey)
	#else
	void skipjack_ecb_encrypt(const unsigned char pt, unsigned char ct, symmetric_key *skey)
	#endif
	{
	unsigned w1,w2,w3,w4,tmp,tmp1;
	int x, kp;

	LTC_ARGCHK(pt != NULL);
	LTC_ARGCHK(ct != NULL);
	LTC_ARGCHK(skey != NULL);

	/* load block */
	w1 = ((unsigned)pt[0]<<8)\|pt[1];
	w2 = ((unsigned)pt[2]<<8)\|pt[3];
	w3 = ((unsigned)pt[4]<<8)\|pt[5];
	w4 = ((unsigned)pt[6]<<8)\|pt[7];

	/* 8 rounds of RULE A */
	for (x = 1, kp = 0; x < 9; x++) {
	RULE_A;
	}

	/* 8 rounds of RULE B */
	for (; x < 17; x++) {
	RULE_B;
	}

	/* 8 rounds of RULE A */
	for (; x < 25; x++) {
	RULE_A;
	}

	/* 8 rounds of RULE B */
	for (; x < 33; x++) {
	RULE_B;
	}

	/* store block */
	ct[0] = (w1>>8)&255; ct[1] = w1&255;
	ct[2] = (w2>>8)&255; ct[3] = w2&255;
	ct[4] = (w3>>8)&255; ct[5] = w3&255;
	ct[6] = (w4>>8)&255; ct[7] = w4&255;
	}

	#ifdef LTC_CLEAN_STACK
	void skipjack_ecb_encrypt(const unsigned char pt, unsigned char ct, symmetric_key *skey)
	{
	_skipjack_ecb_encrypt(pt, ct, skey);
	burn_stack(sizeof(unsigned) * 8 + sizeof(int) * 2);
	}
	#endif

	/**
	Decrypts a block of text with Skipjack
	@param ct The input ciphertext (8 bytes)
	@param pt The output plaintext (8 bytes)
	@param skey The key as scheduled
	*/
	#ifdef LTC_CLEAN_STACK
	static void _skipjack_ecb_decrypt(const unsigned char ct, unsigned char pt, symmetric_key *skey)
	#else
	void skipjack_ecb_decrypt(const unsigned char ct, unsigned char pt, symmetric_key *skey)
	#endif
	{
	unsigned w1,w2,w3,w4,tmp;
	int x, kp;

	LTC_ARGCHK(pt != NULL);
	LTC_ARGCHK(ct != NULL);
	LTC_ARGCHK(skey != NULL);

	/* load block */
	w1 = ((unsigned)ct[0]<<8)\|ct[1];
	w2 = ((unsigned)ct[2]<<8)\|ct[3];
	w3 = ((unsigned)ct[4]<<8)\|ct[5];
	w4 = ((unsigned)ct[6]<<8)\|ct[7];

	/* 8 rounds of RULE B^-1

	Note the value "kp = 8" comes from "kp = (32 * 4) mod 10" where 32*4 is 128 which mod 10 is 8
	*/
	for (x = 32, kp = 8; x > 24; x--) {
	RULE_B1;
	}

	/* 8 rounds of RULE A^-1 */
	for (; x > 16; x--) {
	RULE_A1;
	}


	/* 8 rounds of RULE B^-1 */
	for (; x > 8; x--) {
	RULE_B1;
	}

	/* 8 rounds of RULE A^-1 */
	for (; x > 0; x--) {
	RULE_A1;
	}

	/* store block */
	pt[0] = (w1>>8)&255; pt[1] = w1&255;
	pt[2] = (w2>>8)&255; pt[3] = w2&255;
	pt[4] = (w3>>8)&255; pt[5] = w3&255;
	pt[6] = (w4>>8)&255; pt[7] = w4&255;
	}

	#ifdef LTC_CLEAN_STACK
	void skipjack_ecb_decrypt(const unsigned char ct, unsigned char pt, symmetric_key *skey)
	{
	_skipjack_ecb_decrypt(ct, pt, skey);
	burn_stack(sizeof(unsigned) * 7 + sizeof(int) * 2);
	}
	#endif

	/**
	Performs a self-test of the Skipjack block cipher
	@return CRYPT_OK if functional, CRYPT_NOP if self-test has been disabled
	*/
	int skipjack_test(void)
	{
	#ifndef LTC_TEST
	return CRYPT_NOP;
	#else
	static const struct {
	unsigned char key[10], pt[8], ct[8];
	} tests[] = {
	{
	{ 0x00, 0x99, 0x88, 0x77, 0x66, 0x55, 0x44, 0x33, 0x22, 0x11 },
	{ 0x33, 0x22, 0x11, 0x00, 0xdd, 0xcc, 0xbb, 0xaa },
	{ 0x25, 0x87, 0xca, 0xe2, 0x7a, 0x12, 0xd3, 0x00 }
	}
	};
	unsigned char buf[2][8];
	int x, y, err;
	symmetric_key key;

	for (x = 0; x < (int)(sizeof(tests) / sizeof(tests[0])); x++) {
	/* setup key */
	if ((err = skipjack_setup(tests[x].key, 10, 0, &key)) != CRYPT_OK) {
	return err;
	}

	/* encrypt and decrypt */
	skipjack_ecb_encrypt(tests[x].pt, buf[0], &key);
	skipjack_ecb_decrypt(buf[0], buf[1], &key);

	/* compare */
	if (memcmp(buf[0], tests[x].ct, 8) != 0 \|\| memcmp(buf[1], tests[x].pt, 8) != 0) {
	return CRYPT_FAIL_TESTVECTOR;
	}

	/* now see if we can encrypt all zero bytes 1000 times, decrypt and come back where we started */
	for (y = 0; y < 8; y++) buf[0][y] = 0;
	for (y = 0; y < 1000; y++) skipjack_ecb_encrypt(buf[0], buf[0], &key);
	for (y = 0; y < 1000; y++) skipjack_ecb_decrypt(buf[0], buf[0], &key);
	for (y = 0; y < 8; y++) if (buf[0][y] != 0) return CRYPT_FAIL_TESTVECTOR;
	}

	return CRYPT_OK;
	#endif
	}

	/** Terminate the context
	@param skey The scheduled key
	*/
	void skipjack_done(symmetric_key *skey)
	{
	}

	/**
	Gets suitable key size
	@param keysize [in/out] The length of the recommended key (in bytes). This function will store the suitable size back in this variable.
	@return CRYPT_OK if the input key size is acceptable.
	*/
	int skipjack_keysize(int *keysize)
	{
	LTC_ARGCHK(keysize != NULL);
	if (*keysize < 10) {
	return CRYPT_INVALID_KEYSIZE;
	} else if (*keysize > 10) {
	*keysize = 10;
	}
	return CRYPT_OK;
	}

	#endif

	/* $Source: /cvs/libtom/libtomcrypt/src/ciphers/skipjack.c,v $ */
	/* $Revision: 1.7 $ */
	/* $Date: 2005/05/05 14:35:58 $ */