1 | /*
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2 | * Copyright 2015-2016 The OpenSSL Project Authors. All Rights Reserved.
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3 | *
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4 | * Licensed under the OpenSSL license (the "License"). You may not use
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5 | * this file except in compliance with the License. You can obtain a copy
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6 | * in the file LICENSE in the source distribution or at
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7 | * https://www.openssl.org/source/license.html
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8 | */
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9 |
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10 | #include <string.h>
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11 | #include <openssl/ec.h>
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12 | #include <openssl/evp.h>
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13 |
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14 | /* Key derivation function from X9.62/SECG */
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15 | /* Way more than we will ever need */
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16 | #define ECDH_KDF_MAX (1 << 30)
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17 |
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18 | int ECDH_KDF_X9_62(unsigned char *out, size_t outlen,
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19 | const unsigned char *Z, size_t Zlen,
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20 | const unsigned char *sinfo, size_t sinfolen,
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21 | const EVP_MD *md)
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22 | {
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23 | EVP_MD_CTX *mctx = NULL;
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24 | int rv = 0;
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25 | unsigned int i;
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26 | size_t mdlen;
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27 | unsigned char ctr[4];
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28 | if (sinfolen > ECDH_KDF_MAX || outlen > ECDH_KDF_MAX
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29 | || Zlen > ECDH_KDF_MAX)
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30 | return 0;
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31 | mctx = EVP_MD_CTX_new();
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32 | if (mctx == NULL)
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33 | return 0;
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34 | mdlen = EVP_MD_size(md);
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35 | for (i = 1;; i++) {
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36 | unsigned char mtmp[EVP_MAX_MD_SIZE];
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37 | if (!EVP_DigestInit_ex(mctx, md, NULL))
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38 | goto err;
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39 | ctr[3] = i & 0xFF;
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40 | ctr[2] = (i >> 8) & 0xFF;
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41 | ctr[1] = (i >> 16) & 0xFF;
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42 | ctr[0] = (i >> 24) & 0xFF;
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43 | if (!EVP_DigestUpdate(mctx, Z, Zlen))
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44 | goto err;
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45 | if (!EVP_DigestUpdate(mctx, ctr, sizeof(ctr)))
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46 | goto err;
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47 | if (!EVP_DigestUpdate(mctx, sinfo, sinfolen))
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48 | goto err;
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49 | if (outlen >= mdlen) {
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50 | if (!EVP_DigestFinal(mctx, out, NULL))
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51 | goto err;
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52 | outlen -= mdlen;
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53 | if (outlen == 0)
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54 | break;
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55 | out += mdlen;
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56 | } else {
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57 | if (!EVP_DigestFinal(mctx, mtmp, NULL))
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58 | goto err;
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59 | memcpy(out, mtmp, outlen);
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60 | OPENSSL_cleanse(mtmp, mdlen);
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61 | break;
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62 | }
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63 | }
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64 | rv = 1;
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65 | err:
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66 | EVP_MD_CTX_free(mctx);
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67 | return rv;
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68 | }
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