text: /*******************************************************************************
  * Copyright 2013-2021 Intel Corporation
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
  * You may obtain a copy of the License at
  *
  *     http://www.apache.org/licenses/LICENSE-2.0
  *
  * Unless required by applicable law or agreed to in writing, software
  * distributed under the License is distributed on an "AS IS" BASIS,
  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  * See the License for the specific language governing permissions and
  * limitations under the License.
  *******************************************************************************/
  
  /* 
  // 
  //  Purpose:
  //     Cryptography Primitive.
  //     AES encryption/decryption (CBC mode)
  //     AES encryption/decryption (CBC-CS mode)
  // 
  //  Contents:
  //        ippsAESDecryptCBC_CS3()
  //
  */
  
  #include "owndefs.h"
  #include "owncp.h"
  #include "pcpaesm.h"
  #include "pcptool.h"
  #include "pcpaes_cbc_decrypt.h"
  
  #if (_ALG_AES_SAFE_==_ALG_AES_SAFE_COMPACT_SBOX_)
  #  include "pcprijtables.h"
  #endif
  
  
  /*F*
  //    Name: ippsAESDecryptCBC_CS3
  //
  // Purpose: AES-CBC_CS3 decryption.
  //
  // Returns:                Reason:
  //    ippStsNullPtrErr        pCtx == NULL
  //                            pSrc == NULL
  //                            pDst == NULL
  //                            pIV  == NULL
  //    ippStsContextMatchErr   !VALID_AES_ID()
  //    ippStsLengthErr         len <=MBS_RIJ128 (different from CS1 and CS2)
  //    ippStsNoErr             no errors
  //
  // Parameters:
  //    pSrc        pointer to the source data buffer
  //    pDst        pointer to the target data buffer
  //    len         input/output buffer length (in bytes)
  //    pCtx        pointer to the AES context
  //    pIV         pointer to the initialization vector
  //
  *F*/
  IPPFUN(IppStatus, ippsAESDecryptCBC_CS3,(const Ipp8u* pSrc, Ipp8u* pDst, int len,
                                           const IppsAESSpec* pCtx,
                                           const Ipp8u* pIV))
  {
     /* test context */
     IPP_BAD_PTR1_RET(pCtx);
     /* test the context ID */
     IPP_BADARG_RET(!VALID_AES_ID(pCtx), ippStsContextMatchErr);
  
     /* test source, target buffers and initialization pointers */
     IPP_BAD_PTR3_RET(pSrc, pIV, pDst);
     /* test stream length */
     IPP_BADARG_RET((len<=MBS_RIJ128), ippStsLengthErr);
  
     {
        RijnCipher decoder = RIJ_DECODER(pCtx);
  
        Ipp8u lastIV[MBS_RIJ128];
        Ipp8u lastDecBlk[2*MBS_RIJ128];
  
        int n;
  
        int tail = len & (MBS_RIJ128-1); /* length of the last partial block */
        if(0==tail)
           tail = MBS_RIJ128;
  
        len -= MBS_RIJ128+tail;
  
        if(len) {
           CopyBlock16(pSrc+len-MBS_RIJ128, lastIV);
           cpDecryptAES_cbc(pIV, pSrc, pDst, len/MBS_RIJ128, pCtx);
           pSrc += len;
           pDst += len;
        }
        else
           CopyBlock16(pIV, lastIV);
  
        /* decrypt last  block */
        #if (_ALG_AES_SAFE_==_ALG_AES_SAFE_COMPACT_SBOX_)
        decoder(pSrc, lastDecBlk+MBS_RIJ128, RIJ_NR(pCtx), RIJ_EKEYS(pCtx), RijDecSbox/*NULL*/);
        #else
        decoder(pSrc, lastDecBlk+MBS_RIJ128, RIJ_NR(pCtx), RIJ_DKEYS(pCtx), NULL);
        #endif
        CopyBlock16(lastDecBlk+MBS_RIJ128, lastDecBlk);
  
        for(n=0; n<tail; n++) lastDecBlk[n] = pSrc[n+MBS_RIJ128];
        /* decrypt penultimate  block */
        #if (_ALG_AES_SAFE_==_ALG_AES_SAFE_COMPACT_SBOX_)
        decoder(lastDecBlk, lastDecBlk, RIJ_NR(pCtx), RIJ_EKEYS(pCtx), RijDecSbox/*NULL*/);
        #else
        decoder(lastDecBlk, lastDecBlk, RIJ_NR(pCtx), RIJ_DKEYS(pCtx), NULL);
        #endif
  
        for(n=0; n<MBS_RIJ128; n++) {
           Ipp8u c = pSrc[n];
           pDst[n] = lastDecBlk[n] ^ lastIV[n];
           lastIV[n] = c;
        }
        for(tail+=MBS_RIJ128; n<tail; n++)
           pDst[n] = lastDecBlk[n] ^ pSrc[n];
  
        /* clear secret data */
        PurgeBlock(lastDecBlk, sizeof(lastDecBlk));
  
        return ippStsNoErr;
     }
  }
  