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annotate libtomcrypt/src/pk/dh/dh_shared_secret.c @ 1930:299f4f19ba19

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Add /usr/sbin and /sbin to default root PATH When dropbear is used in a very restricted environment (such as in a initrd), the default user shell is often also very restricted and doesn't take care of setting the PATH so the user ends up with the PATH set by dropbear. Unfortunately, dropbear always sets "/usr/bin:/bin" as default PATH even for the root user which should have /usr/sbin and /sbin too. For a concrete instance of this problem, see the "Remote Unlocking" section in this tutorial: https://paxswill.com/blog/2013/11/04/encrypted-raspberry-pi/ It speaks of a bug in the initramfs script because it's written "blkid" instead of "/sbin/blkid"... this is just because the scripts from the initramfs do not expect to have a PATH without the sbin directories and because dropbear is not setting the PATH appropriately for the root user. I'm thus suggesting to use the attached patch to fix this misbehaviour (I did not test it, but it's easy enough). It might seem anecdotic but multiple Kali users have been bitten by this. From https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=903403
author Raphael Hertzog <hertzog@debian.org>
date Mon, 09 Jul 2018 16:27:53 +0200
parents 6dba84798cd5
children
Ignore whitespace changes - Everywhere: Within whitespace: At end of lines:
rev   line source
1471
6dba84798cd5 Update to libtomcrypt 1.18.1, merged with Dropbear changes
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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
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10 #include "tomcrypt.h"
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11
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12 #ifdef LTC_MDH
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13
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14 /**
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15 Create a DH shared secret.
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16 @param private_key The private DH key in the pair
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17 @param public_key The public DH key in the pair
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18 @param out [out] The destination of the shared data
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19 @param outlen [in/out] The max size and resulting size of the shared data.
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20 @return CRYPT_OK if successful
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21 */
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22 int dh_shared_secret(dh_key *private_key, dh_key *public_key,
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23 unsigned char *out, unsigned long *outlen)
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24 {
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25 void *tmp;
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26 unsigned long x;
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27 int err;
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28
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29 LTC_ARGCHK(private_key != NULL);
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30 LTC_ARGCHK(public_key != NULL);
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31 LTC_ARGCHK(out != NULL);
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32 LTC_ARGCHK(outlen != NULL);
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33
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34 /* types valid? */
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35 if (private_key->type != PK_PRIVATE) {
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36 return CRYPT_PK_NOT_PRIVATE;
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37 }
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38
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39 /* same DH group? */
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40 if (mp_cmp(private_key->prime, public_key->prime) != LTC_MP_EQ) { return CRYPT_PK_TYPE_MISMATCH; }
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41 if (mp_cmp(private_key->base, public_key->base) != LTC_MP_EQ) { return CRYPT_PK_TYPE_MISMATCH; }
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42
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43 /* init big numbers */
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44 if ((err = mp_init(&tmp)) != CRYPT_OK) {
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45 return err;
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46 }
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47
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48 /* check public key */
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49 if ((err = dh_check_pubkey(public_key)) != CRYPT_OK) {
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50 goto error;
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51 }
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52
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53 /* compute tmp = y^x mod p */
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54 if ((err = mp_exptmod(public_key->y, private_key->x, private_key->prime, tmp)) != CRYPT_OK) {
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55 goto error;
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56 }
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57
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58 /* enough space for output? */
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59 x = (unsigned long)mp_unsigned_bin_size(tmp);
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60 if (*outlen < x) {
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61 *outlen = x;
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62 err = CRYPT_BUFFER_OVERFLOW;
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63 goto error;
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64 }
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65 if ((err = mp_to_unsigned_bin(tmp, out)) != CRYPT_OK) {
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66 goto error;
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67 }
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68 *outlen = x;
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69 err = CRYPT_OK;
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70
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71 error:
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72 mp_clear(tmp);
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73 return err;
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74 }
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75
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76 #endif /* LTC_MDH */
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77
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78 /* ref: $Format:%D$ */
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79 /* git commit: $Format:%H$ */
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80 /* commit time: $Format:%ai$ */