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/*
* Copyright 2015-2016 The OpenSSL Project Authors. All Rights Reserved.
*
* Licensed under the OpenSSL license (the "License"). You may not use
* this file except in compliance with the License. You can obtain a copy
* in the file LICENSE in the source distribution or at
* https://www.openssl.org/source/license.html
*/
#include <string.h>
#include <openssl/ec.h>
#include <openssl/evp.h>
/* Key derivation function from X9.62/SECG */
/* Way more than we will ever need */
#define ECDH_KDF_MAX (1 << 30)
int ECDH_KDF_X9_62(unsigned char *out, size_t outlen,
const unsigned char *Z, size_t Zlen,
const unsigned char *sinfo, size_t sinfolen,
const EVP_MD *md)
{
EVP_MD_CTX *mctx = NULL;
int rv = 0;
unsigned int i;
size_t mdlen;
unsigned char ctr[4];
if (sinfolen > ECDH_KDF_MAX || outlen > ECDH_KDF_MAX
|| Zlen > ECDH_KDF_MAX)
return 0;
mctx = EVP_MD_CTX_new();
if (mctx == NULL)
return 0;
mdlen = EVP_MD_size(md);
for (i = 1;; i++) {
unsigned char mtmp[EVP_MAX_MD_SIZE];
if (!EVP_DigestInit_ex(mctx, md, NULL))
goto err;
ctr[3] = i & 0xFF;
ctr[2] = (i >> 8) & 0xFF;
ctr[1] = (i >> 16) & 0xFF;
ctr[0] = (i >> 24) & 0xFF;
if (!EVP_DigestUpdate(mctx, Z, Zlen))
goto err;
if (!EVP_DigestUpdate(mctx, ctr, sizeof(ctr)))
goto err;
if (!EVP_DigestUpdate(mctx, sinfo, sinfolen))
goto err;
if (outlen >= mdlen) {
if (!EVP_DigestFinal(mctx, out, NULL))
goto err;
outlen -= mdlen;
if (outlen == 0)
break;
out += mdlen;
} else {
if (!EVP_DigestFinal(mctx, mtmp, NULL))
goto err;
memcpy(out, mtmp, outlen);
OPENSSL_cleanse(mtmp, mdlen);
break;
}
}
rv = 1;
err:
EVP_MD_CTX_free(mctx);
return rv;
}
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