libsecurity_apple_csp/lib/DH_exchange.cpp

   1 /*
   2  * Copyright (c) 2000-2002 Apple Computer, Inc. All Rights Reserved.
   3  *
   4  * The contents of this file constitute Original Code as defined in and are
   5  * subject to the Apple Public Source License Version 1.2 (the 'License').
   6  * You may not use this file except in compliance with the License. Please obtain
   7  * a copy of the License at http://www.apple.com/publicsource and read it before
   8  * using this file.
   9  *
  10  * This Original Code and all software distributed under the License are
  11  * distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER EXPRESS
  12  * OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES, INCLUDING WITHOUT
  13  * LIMITATION, ANY WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR
  14  * PURPOSE, QUIET ENJOYMENT OR NON-INFRINGEMENT. Please see the License for the
  15  * specific language governing rights and limitations under the License.
  16  */
  17
  18
  19 /*
  20  * DH_exchange.cp - Diffie-Hellman key exchange
  21  */
  22
  23 #include "DH_exchange.h"
  24 #include <Security/cssmerr.h>
  25 #include "DH_utils.h"
  26 #include "DH_keys.h"
  27 #include <strings.h>
  28 #include <opensslUtils/opensslUtils.h>
  29
  30 void DeriveKey_DH (
  31         const Context &context,
  32         const CssmData &Param,                  // other's public key. may be empty
  33         CSSM_DATA *keyData,                             // mallocd by caller
  34                                                                         // we fill in keyData->Length bytes
  35         AppleCSPSession &session)
  36 {
  37         bool mallocdPrivKey;
  38         size_t privSize;
  39
  40         /* private DH key from context - required */
  41         DH *privKey = contextToDhKey(context, session, CSSM_ATTRIBUTE_KEY,
  42                 CSSM_KEYCLASS_PRIVATE_KEY, CSSM_KEYUSE_DERIVE, mallocdPrivKey);
  43         if(privKey == NULL) {
  44                 CssmError::throwMe(CSSMERR_CSP_MISSING_ATTR_KEY);
  45         }
  46         cspDhDebug("DeriveKey_DH, privKey %p", privKey);
  47         privSize = DH_size(privKey);
  48         if(privSize < keyData->Length) {
  49                 /* we've been asked for more bits than this key can generate */
  50                 CssmError::throwMe(CSSMERR_CSP_UNSUPPORTED_KEY_SIZE);
  51         }
  52
  53         /*
  54          * Public key ("their" key) can come from two places:
  55          * -- in the context as a CSSM_ATTRIBUTE_PUBLIC_KEY. This is how
  56          *    public keys in X509 format must be used in this function
  57          * -- in the incoming Param, the raw unformatted (PKCS3) form
  58          */
  59         bool mallocdPubKey = false;
  60         BIGNUM *pubKeyBn = NULL;
  61         bool allocdPubKeyBn = false;
  62         DH *pubKey = contextToDhKey(context, session, CSSM_ATTRIBUTE_PUBLIC_KEY,
  63                 CSSM_KEYCLASS_PUBLIC_KEY, CSSM_KEYUSE_DERIVE, mallocdPubKey);
  64         if(pubKey != NULL) {
  65                 if(pubKey->pub_key == NULL) {
  66                         errorLog0("DeriveKey_DH: public key in context with no pub_key\n");
  67                         CssmError::throwMe(CSSMERR_CSP_INVALID_KEY);
  68                 }
  69                 pubKeyBn = pubKey->pub_key;
  70                 cspDhDebug("DeriveKey_DH, pubKey from context %p", pubKey);
  71         }
  72         else {
  73                 if((Param.Data == NULL) || (Param.Length == 0)) {
  74                         errorLog0("DeriveKey_DH: no pub_key, no Param\n");
  75                         CssmError::throwMe(CSSMERR_CSP_INVALID_KEY);
  76                 }
  77                 pubKeyBn = BN_bin2bn(Param.Data, (int)Param.Length, NULL);
  78                 if(pubKeyBn == NULL) {
  79                         CssmError::throwMe(CSSMERR_CSP_MEMORY_ERROR);
  80                 }
  81                 allocdPubKeyBn = true;
  82                 cspDhDebug("DeriveKey_DH, no pubKey in context");
  83         }
  84         unsigned char *buf = (unsigned char *)session.malloc(privSize);
  85         int rtn = DH_compute_key(buf, pubKeyBn, privKey);
  86         if(rtn > 0) {
  87                 /*
  88                  * FIXME : I have not found a specification describing *which*
  89                  * bytes of the value we just computed we are supposed to
  90                  * use as the actual key bytes. We use the M.S. bytes.
  91                  *
  92                  * Note that due to modulo arithmetic, we may have gotten fewer
  93                  * bytes than we asked for. If so, the caller will have
  94                  * to deal with that if they really need privSize bytes.
  95                  */
  96                 assert((uint32)rtn <= privSize);
  97                 CSSM_SIZE toMove = keyData->Length;
  98                 if((uint32)rtn < toMove) {
  99                         toMove = (uint32)rtn;
 100                 }
 101                 memmove(keyData->Data, buf, toMove);
 102                 keyData->Length = toMove;
 103         }
 104         if(mallocdPrivKey) {
 105                 DH_free(privKey);
 106         }
 107         if(mallocdPubKey) {
 108                 DH_free(pubKey);
 109         }
 110         if(allocdPubKeyBn) {
 111                 BN_free(pubKeyBn);
 112         }
 113         session.free(buf);
 114         if(rtn <= 0) {
 115                 throwRsaDsa("DH_compute_key");
 116         }
 117 }
 118