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1 /* LibTomCrypt, modular cryptographic library -- Tom St Denis |
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2 * |
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3 * LibTomCrypt is a library that provides various cryptographic |
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4 * algorithms in a highly modular and flexible manner. |
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5 * |
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6 * The library is free for all purposes without any express |
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7 * guarantee it works. |
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8 * |
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9 * Tom St Denis, [email protected], http://libtomcrypt.org |
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10 */ |
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11 #include "mycrypt.h" |
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12 |
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13 #ifdef CFB |
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14 |
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15 int cfb_decrypt(const unsigned char *ct, unsigned char *pt, unsigned long len, symmetric_CFB *cfb) |
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16 { |
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17 int err; |
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18 |
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19 _ARGCHK(pt != NULL); |
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20 _ARGCHK(ct != NULL); |
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21 _ARGCHK(cfb != NULL); |
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22 |
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23 if ((err = cipher_is_valid(cfb->cipher)) != CRYPT_OK) { |
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24 return err; |
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25 } |
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26 |
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27 /* is blocklen/padlen valid? */ |
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28 if (cfb->blocklen < 0 || cfb->blocklen > (int)sizeof(cfb->IV) || |
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29 cfb->padlen < 0 || cfb->padlen > (int)sizeof(cfb->pad)) { |
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30 return CRYPT_INVALID_ARG; |
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31 } |
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32 |
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33 while (len-- > 0) { |
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34 if (cfb->padlen == cfb->blocklen) { |
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35 cipher_descriptor[cfb->cipher].ecb_encrypt(cfb->pad, cfb->IV, &cfb->key); |
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36 cfb->padlen = 0; |
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37 } |
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38 cfb->pad[cfb->padlen] = *ct; |
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39 *pt = *ct ^ cfb->IV[cfb->padlen]; |
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40 ++pt; |
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41 ++ct; |
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42 ++cfb->padlen; |
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43 } |
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44 return CRYPT_OK; |
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45 } |
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46 |
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47 #endif |
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48 |
