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annotate src/pk/rsa/rsa_exptmod.c @ 191:1c15b283127b libtomcrypt-orig

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Import of libtomcrypt 1.02 with manual path rename rearrangement etc
author Matt Johnston <matt@ucc.asn.au>
date Fri, 06 May 2005 13:23:02 +0000
parents
children 39d5d58461d6
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191
1c15b283127b Import of libtomcrypt 1.02 with manual path rename rearrangement etc
Matt Johnston <matt@ucc.asn.au>
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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 "tomcrypt.h"
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12
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13 /**
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14 @file rsa_exptmod.c
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15 RSA PKCS exptmod, Tom St Denis
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16 */
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17
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18 #ifdef MRSA
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19
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20 /**
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21 Compute an RSA modular exponentiation
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22 @param in The input data to send into RSA
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23 @param inlen The length of the input (octets)
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24 @param out [out] The destination
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25 @param outlen [in/out] The max size and resulting size of the output
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26 @param which Which exponent to use, e.g. PK_PRIVATE or PK_PUBLIC
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27 @param key The RSA key to use
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28 @return CRYPT_OK if successful
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29 */
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30 int rsa_exptmod(const unsigned char *in, unsigned long inlen,
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31 unsigned char *out, unsigned long *outlen, int which,
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32 rsa_key *key)
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33 {
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34 mp_int tmp, tmpa, tmpb;
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35 unsigned long x;
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36 int err;
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37
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38 LTC_ARGCHK(in != NULL);
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39 LTC_ARGCHK(out != NULL);
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40 LTC_ARGCHK(outlen != NULL);
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41 LTC_ARGCHK(key != NULL);
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42
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43 /* is the key of the right type for the operation? */
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44 if (which == PK_PRIVATE && (key->type != PK_PRIVATE)) {
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45 return CRYPT_PK_NOT_PRIVATE;
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46 }
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47
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48 /* must be a private or public operation */
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49 if (which != PK_PRIVATE && which != PK_PUBLIC) {
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50 return CRYPT_PK_INVALID_TYPE;
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51 }
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52
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53 /* init and copy into tmp */
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54 if ((err = mp_init_multi(&tmp, &tmpa, &tmpb, NULL)) != MP_OKAY) { return mpi_to_ltc_error(err); }
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55 if ((err = mp_read_unsigned_bin(&tmp, (unsigned char *)in, (int)inlen)) != MP_OKAY) { goto error; }
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56
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57 /* sanity check on the input */
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58 if (mp_cmp(&key->N, &tmp) == MP_LT) {
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59 err = CRYPT_PK_INVALID_SIZE;
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60 goto done;
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61 }
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62
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63 /* are we using the private exponent and is the key optimized? */
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64 if (which == PK_PRIVATE) {
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65 /* tmpa = tmp^dP mod p */
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66 if ((err = mp_exptmod(&tmp, &key->dP, &key->p, &tmpa)) != MP_OKAY) { goto error; }
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67
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68 /* tmpb = tmp^dQ mod q */
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69 if ((err = mp_exptmod(&tmp, &key->dQ, &key->q, &tmpb)) != MP_OKAY) { goto error; }
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70
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71 /* tmp = (tmpa - tmpb) * qInv (mod p) */
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72 if ((err = mp_sub(&tmpa, &tmpb, &tmp)) != MP_OKAY) { goto error; }
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73 if ((err = mp_mulmod(&tmp, &key->qP, &key->p, &tmp)) != MP_OKAY) { goto error; }
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74
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75 /* tmp = tmpb + q * tmp */
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76 if ((err = mp_mul(&tmp, &key->q, &tmp)) != MP_OKAY) { goto error; }
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77 if ((err = mp_add(&tmp, &tmpb, &tmp)) != MP_OKAY) { goto error; }
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78 } else {
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79 /* exptmod it */
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80 if ((err = mp_exptmod(&tmp, &key->e, &key->N, &tmp)) != MP_OKAY) { goto error; }
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81 }
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82
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83 /* read it back */
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84 x = (unsigned long)mp_unsigned_bin_size(&key->N);
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85 if (x > *outlen) {
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86 err = CRYPT_BUFFER_OVERFLOW;
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87 goto done;
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88 }
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89 *outlen = x;
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90
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91 /* convert it */
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92 zeromem(out, x);
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93 if ((err = mp_to_unsigned_bin(&tmp, out+(x-mp_unsigned_bin_size(&tmp)))) != MP_OKAY) { goto error; }
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94
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95 /* clean up and return */
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96 err = CRYPT_OK;
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97 goto done;
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98 error:
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99 err = mpi_to_ltc_error(err);
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100 done:
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101 mp_clear_multi(&tmp, &tmpa, &tmpb, NULL);
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102 return err;
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103 }
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104
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105 #endif