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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 /* PKCS #1 v1.5 Encryption Padding -- Tom St Denis */ |
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14 |
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15 #ifdef PKCS_1 |
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16 |
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17 int pkcs_1_v15_es_decode(const unsigned char *msg, unsigned long msglen, |
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18 unsigned long modulus_bitlen, |
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19 unsigned char *out, unsigned long outlen, |
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20 int *res) |
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21 { |
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22 unsigned long x, modulus_bytelen; |
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23 |
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24 _ARGCHK(msg != NULL); |
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25 _ARGCHK(out != NULL); |
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26 _ARGCHK(res != NULL); |
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27 |
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28 /* default to failed */ |
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29 *res = 0; |
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30 |
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31 /* must be at least 12 bytes long */ |
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32 if (msglen < 12) { |
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33 return CRYPT_INVALID_ARG; |
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34 } |
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35 |
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36 modulus_bytelen = (modulus_bitlen>>3) + (modulus_bitlen & 7 ? 1 : 0); |
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37 |
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38 /* should start with 0x00 0x02 */ |
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39 if (msg[0] != 0x00 || msg[1] != 0x02) { |
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40 return CRYPT_OK; |
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41 } |
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42 |
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43 /* skip over PS */ |
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44 x = 2 + (modulus_bytelen - outlen - 3); |
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45 |
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46 /* should be 0x00 */ |
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47 if (msg[x++] != 0x00) { |
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48 return CRYPT_OK; |
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49 } |
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50 |
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51 /* the message is left */ |
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52 if (x + outlen > modulus_bytelen) { |
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53 return CRYPT_PK_INVALID_SIZE; |
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54 } |
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55 memcpy(out, msg + x, outlen); |
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56 *res = 1; |
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57 return CRYPT_OK; |
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58 } |
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59 |
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60 #endif |
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61 |
