samv71_crypto_cipher.c

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/**
 * @file samv71_crypto_cipher.c
 * @brief SAMV71 cipher hardware accelerator
 *
 * @section License
 *
 * SPDX-License-Identifier: GPL-2.0-or-later
 *
 * Copyright (C) 2010-2024 Oryx Embedded SARL. All rights reserved.
 *
 * This file is part of CycloneCRYPTO Open.
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License
 * as published by the Free Software Foundation; either version 2
 * of the License, or (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
 *
 * @author Oryx Embedded SARL (www.oryx-embedded.com)
 * @version 2.4.4
 **/
 
//Switch to the appropriate trace level
#define TRACE_LEVEL CRYPTO_TRACE_LEVEL
 
//Dependencies
#include "sam.h"
#include "core/crypto.h"
#include "hardware/samv71/samv71_crypto.h"
#include "hardware/samv71/samv71_crypto_cipher.h"
#include "cipher/cipher_algorithms.h"
#include "cipher_modes/cipher_modes.h"
#include "aead/aead_algorithms.h"
#include "debug.h"
 
//Check crypto library configuration
#if (SAMV71_CRYPTO_CIPHER_SUPPORT == ENABLED && AES_SUPPORT == ENABLED)
 
 
/**
 * @brief Load AES key
 * @param[in] context AES algorithm context
 **/
 
void aesLoadKey(AesContext *context)
{
   uint32_t temp;
 
   //Read mode register
   temp = AES_REGS->AES_MR & ~AES_MR_KEYSIZE_Msk;
 
   //Check the length of the key
   if(context->nr == 10)
   {
      //10 rounds are required for 128-bit key
      AES_REGS->AES_MR = temp | AES_MR_KEYSIZE_AES128;
 
      //Set the 128-bit encryption key
      AES_REGS->AES_KEYWR[0] = context->ek[0];
      AES_REGS->AES_KEYWR[1] = context->ek[1];
      AES_REGS->AES_KEYWR[2] = context->ek[2];
      AES_REGS->AES_KEYWR[3] = context->ek[3];
   }
   else if(context->nr == 12)
   {
      //12 rounds are required for 192-bit key
      AES_REGS->AES_MR = temp | AES_MR_KEYSIZE_AES192;
 
      //Set the 192-bit encryption key
      AES_REGS->AES_KEYWR[0] = context->ek[0];
      AES_REGS->AES_KEYWR[1] = context->ek[1];
      AES_REGS->AES_KEYWR[2] = context->ek[2];
      AES_REGS->AES_KEYWR[3] = context->ek[3];
      AES_REGS->AES_KEYWR[4] = context->ek[4];
      AES_REGS->AES_KEYWR[5] = context->ek[5];
   }
   else
   {
      //14 rounds are required for 256-bit key
      AES_REGS->AES_MR = temp | AES_MR_KEYSIZE_AES256;
 
      //Set the 256-bit encryption key
      AES_REGS->AES_KEYWR[0] = context->ek[0];
      AES_REGS->AES_KEYWR[1] = context->ek[1];
      AES_REGS->AES_KEYWR[2] = context->ek[2];
      AES_REGS->AES_KEYWR[3] = context->ek[3];
      AES_REGS->AES_KEYWR[4] = context->ek[4];
      AES_REGS->AES_KEYWR[5] = context->ek[5];
      AES_REGS->AES_KEYWR[6] = context->ek[6];
      AES_REGS->AES_KEYWR[7] = context->ek[7];
   }
}
 
 
/**
 * @brief Encrypt/decrypt a 16-byte block using AES algorithm
 * @param[in] input Input block to be encrypted/decrypted
 * @param[out] output Resulting block
 **/
 
void aesProcessDataBlock(const uint8_t *input, uint8_t *output)
{
   uint32_t *p;
 
   //Write input block
   p = (uint32_t *) input;
   AES_REGS->AES_IDATAR[0] = p[0];
   AES_REGS->AES_IDATAR[1] = p[1];
   AES_REGS->AES_IDATAR[2] = p[2];
   AES_REGS->AES_IDATAR[3] = p[3];
 
   //Start encryption/decryption
   AES_REGS->AES_CR = AES_CR_START_Msk;
 
   //When processing completes, the DATRDY flag is raised
   while((AES_REGS->AES_ISR & AES_ISR_DATRDY_Msk) == 0)
   {
   }
 
   //Read output block
   p = (uint32_t *) output;
   p[0] = AES_REGS->AES_ODATAR[0];
   p[1] = AES_REGS->AES_ODATAR[1];
   p[2] = AES_REGS->AES_ODATAR[2];
   p[3] = AES_REGS->AES_ODATAR[3];
}
 
 
/**
 * @brief Perform AES encryption or decryption
 * @param[in] context AES algorithm context
 * @param[in] iv Initialization vector
 * @param[in] input Data to be encrypted/decrypted
 * @param[out] output Data resulting from the encryption/decryption process
 * @param[in] length Total number of data bytes to be processed
 * @param[in] mode Operation mode
 **/
 
void aesProcessData(AesContext *context, uint8_t *iv, const uint8_t *input,
   uint8_t *output, size_t length, uint32_t mode)
{
   uint32_t *p;
 
   //Acquire exclusive access to the AES module
   osAcquireMutex(&samv71CryptoMutex);
 
   //Perform software reset
   AES_REGS->AES_CR = AES_CR_SWRST_Msk;
 
   //Set operation mode
   AES_REGS->AES_MR = AES_MR_SMOD_MANUAL_START | mode;
   //Set encryption key
   aesLoadKey(context);
 
   //Valid initialization vector?
   if(iv != NULL)
   {
      //Set initialization vector
      p = (uint32_t *) iv;
      AES_REGS->AES_IVR[0] = p[0];
      AES_REGS->AES_IVR[1] = p[1];
      AES_REGS->AES_IVR[2] = p[2];
      AES_REGS->AES_IVR[3] = p[3];
   }
 
   //Process data
   while(length >= AES_BLOCK_SIZE)
   {
      //The data is encrypted block by block
      aesProcessDataBlock(input, output);
 
      //Next block
      input += AES_BLOCK_SIZE;
      output += AES_BLOCK_SIZE;
      length -= AES_BLOCK_SIZE;
   }
 
   //Process final block of data
   if(length > 0)
   {
      uint8_t buffer[AES_BLOCK_SIZE];
 
      //Copy input data
      osMemset(buffer, 0, AES_BLOCK_SIZE);
      osMemcpy(buffer, input, length);
 
      //Encrypt the final block of data
      aesProcessDataBlock(buffer, buffer);
 
      //Copy output data
      osMemcpy(output, buffer, length);
   }
 
   //Release exclusive access to the AES module
   osReleaseMutex(&samv71CryptoMutex);
}
 
 
/**
 * @brief Key expansion
 * @param[in] context Pointer to the AES context to initialize
 * @param[in] key Pointer to the key
 * @param[in] keyLen Length of the key
 * @return Error code
 **/
 
error_t aesInit(AesContext *context, const uint8_t *key, size_t keyLen)
{
   //Check parameters
   if(context == NULL || key == NULL)
      return ERROR_INVALID_PARAMETER;
 
   //Check the length of the key
   if(keyLen == 16)
   {
      //10 rounds are required for 128-bit key
      context->nr = 10;
   }
   else if(keyLen == 24)
   {
      //12 rounds are required for 192-bit key
      context->nr = 12;
   }
   else if(keyLen == 32)
   {
      //14 rounds are required for 256-bit key
      context->nr = 14;
   }
   else
   {
      //Report an error
      return ERROR_INVALID_KEY_LENGTH;
   }
 
   //Copy the original key
   osMemcpy(context->ek, key, keyLen);
 
   //No error to report
   return NO_ERROR;
}
 
 
/**
 * @brief Encrypt a 16-byte block using AES algorithm
 * @param[in] context Pointer to the AES context
 * @param[in] input Plaintext block to encrypt
 * @param[out] output Ciphertext block resulting from encryption
 **/
 
void aesEncryptBlock(AesContext *context, const uint8_t *input, uint8_t *output)
{
   //Perform AES encryption
   aesProcessData(context, NULL, input, output, AES_BLOCK_SIZE,
      AES_MR_CIPHER_Msk | AES_MR_OPMOD_ECB);
}
 
 
/**
 * @brief Decrypt a 16-byte block using AES algorithm
 * @param[in] context Pointer to the AES context
 * @param[in] input Ciphertext block to decrypt
 * @param[out] output Plaintext block resulting from decryption
 **/
 
void aesDecryptBlock(AesContext *context, const uint8_t *input, uint8_t *output)
{
   //Perform AES decryption
   aesProcessData(context, NULL, input, output, AES_BLOCK_SIZE,
      AES_MR_OPMOD_ECB);
}
 
 
#if (ECB_SUPPORT == ENABLED)
 
/**
 * @brief ECB encryption
 * @param[in] cipher Cipher algorithm
 * @param[in] context Cipher algorithm context
 * @param[in] p Plaintext to be encrypted
 * @param[out] c Ciphertext resulting from the encryption
 * @param[in] length Total number of data bytes to be encrypted
 * @return Error code
 **/
 
error_t ecbEncrypt(const CipherAlgo *cipher, void *context,
   const uint8_t *p, uint8_t *c, size_t length)
{
   error_t error;
 
   //Initialize status code
   error = NO_ERROR;
 
   //AES cipher algorithm?
   if(cipher == AES_CIPHER_ALGO)
   {
      //Check the length of the payload
      if(length == 0)
      {
         //No data to process
      }
      else if((length % AES_BLOCK_SIZE) == 0)
      {
         //Encrypt payload data
         aesProcessData(context, NULL, p, c, length, AES_MR_CIPHER_Msk |
            AES_MR_OPMOD_ECB);
      }
      else
      {
         //The length of the payload must be a multiple of the block size
         error = ERROR_INVALID_LENGTH;
      }
   }
   else
   {
      //ECB mode operates in a block-by-block fashion
      while(length >= cipher->blockSize)
      {
         //Encrypt current block
         cipher->encryptBlock(context, p, c);
 
         //Next block
         p += cipher->blockSize;
         c += cipher->blockSize;
         length -= cipher->blockSize;
      }
 
      //The length of the payload must be a multiple of the block size
      if(length != 0)
      {
         error = ERROR_INVALID_LENGTH;
      }
   }
 
   //Return status code
   return error;
}
 
 
/**
 * @brief ECB decryption
 * @param[in] cipher Cipher algorithm
 * @param[in] context Cipher algorithm context
 * @param[in] c Ciphertext to be decrypted
 * @param[out] p Plaintext resulting from the decryption
 * @param[in] length Total number of data bytes to be decrypted
 * @return Error code
 **/
 
error_t ecbDecrypt(const CipherAlgo *cipher, void *context,
   const uint8_t *c, uint8_t *p, size_t length)
{
   error_t error;
 
   //Initialize status code
   error = NO_ERROR;
 
   //AES cipher algorithm?
   if(cipher == AES_CIPHER_ALGO)
   {
      //Check the length of the payload
      if(length == 0)
      {
         //No data to process
      }
      else if((length % AES_BLOCK_SIZE) == 0)
      {
         //Decrypt payload data
         aesProcessData(context, NULL, c, p, length, AES_MR_OPMOD_ECB);
      }
      else
      {
         //The length of the payload must be a multiple of the block size
         error = ERROR_INVALID_LENGTH;
      }
   }
   else
   {
      //ECB mode operates in a block-by-block fashion
      while(length >= cipher->blockSize)
      {
         //Decrypt current block
         cipher->decryptBlock(context, c, p);
 
         //Next block
         c += cipher->blockSize;
         p += cipher->blockSize;
         length -= cipher->blockSize;
      }
 
      //The length of the payload must be a multiple of the block size
      if(length != 0)
      {
         error = ERROR_INVALID_LENGTH;
      }
   }
 
   //Return status code
   return error;
}
 
#endif
#if (CBC_SUPPORT == ENABLED)
 
/**
 * @brief CBC encryption
 * @param[in] cipher Cipher algorithm
 * @param[in] context Cipher algorithm context
 * @param[in,out] iv Initialization vector
 * @param[in] p Plaintext to be encrypted
 * @param[out] c Ciphertext resulting from the encryption
 * @param[in] length Total number of data bytes to be encrypted
 * @return Error code
 **/
 
error_t cbcEncrypt(const CipherAlgo *cipher, void *context,
   uint8_t *iv, const uint8_t *p, uint8_t *c, size_t length)
{
   error_t error;
 
   //Initialize status code
   error = NO_ERROR;
 
   //AES cipher algorithm?
   if(cipher == AES_CIPHER_ALGO)
   {
      //Check the length of the payload
      if(length == 0)
      {
         //No data to process
      }
      else if((length % AES_BLOCK_SIZE) == 0)
      {
         //Encrypt payload data
         aesProcessData(context, iv, p, c, length, AES_MR_CIPHER_Msk |
            AES_MR_OPMOD_CBC);
 
         //Update the value of the initialization vector
         osMemcpy(iv, c + length - AES_BLOCK_SIZE, AES_BLOCK_SIZE);
      }
      else
      {
         //The length of the payload must be a multiple of the block size
         error = ERROR_INVALID_LENGTH;
      }
   }
   else
   {
      size_t i;
 
      //CBC mode operates in a block-by-block fashion
      while(length >= cipher->blockSize)
      {
         //XOR input block with IV contents
         for(i = 0; i < cipher->blockSize; i++)
         {
            c[i] = p[i] ^ iv[i];
         }
 
         //Encrypt the current block based upon the output of the previous
         //encryption
         cipher->encryptBlock(context, c, c);
 
         //Update IV with output block contents
         osMemcpy(iv, c, cipher->blockSize);
 
         //Next block
         p += cipher->blockSize;
         c += cipher->blockSize;
         length -= cipher->blockSize;
      }
 
      //The length of the payload must be a multiple of the block size
      if(length != 0)
      {
         error = ERROR_INVALID_LENGTH;
      }
   }
 
   //Return status code
   return error;
}
 
 
/**
 * @brief CBC decryption
 * @param[in] cipher Cipher algorithm
 * @param[in] context Cipher algorithm context
 * @param[in,out] iv Initialization vector
 * @param[in] c Ciphertext to be decrypted
 * @param[out] p Plaintext resulting from the decryption
 * @param[in] length Total number of data bytes to be decrypted
 * @return Error code
 **/
 
error_t cbcDecrypt(const CipherAlgo *cipher, void *context,
   uint8_t *iv, const uint8_t *c, uint8_t *p, size_t length)
{
   error_t error;
 
   //Initialize status code
   error = NO_ERROR;
 
   //AES cipher algorithm?
   if(cipher == AES_CIPHER_ALGO)
   {
      //Check the length of the payload
      if(length == 0)
      {
         //No data to process
      }
      else if((length % AES_BLOCK_SIZE) == 0)
      {
         uint8_t block[AES_BLOCK_SIZE];
 
         //Save the last input block
         osMemcpy(block, c + length - AES_BLOCK_SIZE, AES_BLOCK_SIZE);
 
         //Decrypt payload data
         aesProcessData(context, iv, c, p, length, AES_MR_OPMOD_CBC);
 
         //Update the value of the initialization vector
         osMemcpy(iv, block, AES_BLOCK_SIZE);
      }
      else
      {
         //The length of the payload must be a multiple of the block size
         error = ERROR_INVALID_LENGTH;
      }
   }
   else
   {
      size_t i;
      uint8_t t[16];
 
      //CBC mode operates in a block-by-block fashion
      while(length >= cipher->blockSize)
      {
         //Save input block
         osMemcpy(t, c, cipher->blockSize);
 
         //Decrypt the current block
         cipher->decryptBlock(context, c, p);
 
         //XOR output block with IV contents
         for(i = 0; i < cipher->blockSize; i++)
         {
            p[i] ^= iv[i];
         }
 
         //Update IV with input block contents
         osMemcpy(iv, t, cipher->blockSize);
 
         //Next block
         c += cipher->blockSize;
         p += cipher->blockSize;
         length -= cipher->blockSize;
      }
 
      //The length of the payload must be a multiple of the block size
      if(length != 0)
      {
         error = ERROR_INVALID_LENGTH;
      }
   }
 
   //Return status code
   return error;
}
 
#endif
#if (CFB_SUPPORT == ENABLED)
 
/**
 * @brief CFB encryption
 * @param[in] cipher Cipher algorithm
 * @param[in] context Cipher algorithm context
 * @param[in] s Size of the plaintext and ciphertext segments
 * @param[in,out] iv Initialization vector
 * @param[in] p Plaintext to be encrypted
 * @param[out] c Ciphertext resulting from the encryption
 * @param[in] length Total number of data bytes to be encrypted
 * @return Error code
 **/
 
error_t cfbEncrypt(const CipherAlgo *cipher, void *context, uint_t s,
   uint8_t *iv, const uint8_t *p, uint8_t *c, size_t length)
{
   error_t error;
 
   //Initialize status code
   error = NO_ERROR;
 
   //AES cipher algorithm?
   if(cipher == AES_CIPHER_ALGO)
   {
      //Check the value of the parameter
      if(s == (AES_BLOCK_SIZE * 8))
      {
         //Check the length of the payload
         if(length > 0)
         {
            //Encrypt payload data
            aesProcessData(context, iv, p, c, length, AES_MR_CIPHER_Msk |
               AES_MR_OPMOD_CFB | AES_MR_CFBS_SIZE_128BIT);
         }
         else
         {
            //No data to process
         }
      }
      else
      {
         //The value of the parameter is not valid
         error = ERROR_INVALID_PARAMETER;
      }
   }
   else
   {
      //Check the value of the parameter
      if((s % 8) == 0 && s >= 1 && s <= (cipher->blockSize * 8))
      {
         size_t i;
         size_t n;
         uint8_t o[16];
 
         //Determine the size, in bytes, of the plaintext and ciphertext segments
         s = s / 8;
 
         //Process each plaintext segment
         while(length > 0)
         {
            //Compute the number of bytes to process at a time
            n = MIN(length, s);
 
            //Compute O(j) = CIPH(I(j))
            cipher->encryptBlock(context, iv, o);
 
            //Compute C(j) = P(j) XOR MSB(O(j))
            for(i = 0; i < n; i++)
            {
               c[i] = p[i] ^ o[i];
            }
 
            //Compute I(j+1) = LSB(I(j)) | C(j)
            osMemmove(iv, iv + s, cipher->blockSize - s);
            osMemcpy(iv + cipher->blockSize - s, c, s);
 
            //Next block
            p += n;
            c += n;
            length -= n;
         }
      }
      else
      {
         //The value of the parameter is not valid
         error = ERROR_INVALID_PARAMETER;
      }
   }
 
   //Return status code
   return error;
}
 
 
/**
 * @brief CFB decryption
 * @param[in] cipher Cipher algorithm
 * @param[in] context Cipher algorithm context
 * @param[in] s Size of the plaintext and ciphertext segments
 * @param[in,out] iv Initialization vector
 * @param[in] c Ciphertext to be decrypted
 * @param[out] p Plaintext resulting from the decryption
 * @param[in] length Total number of data bytes to be decrypted
 * @return Error code
 **/
 
error_t cfbDecrypt(const CipherAlgo *cipher, void *context, uint_t s,
   uint8_t *iv, const uint8_t *c, uint8_t *p, size_t length)
{
   error_t error;
 
   //Initialize status code
   error = NO_ERROR;
 
   //AES cipher algorithm?
   if(cipher == AES_CIPHER_ALGO)
   {
      //Check the value of the parameter
      if(s == (AES_BLOCK_SIZE * 8))
      {
         //Check the length of the payload
         if(length > 0)
         {
            //Decrypt payload data
            aesProcessData(context, iv, c, p, length, AES_MR_OPMOD_CFB |
               AES_MR_CFBS_SIZE_128BIT);
         }
         else
         {
            //No data to process
         }
      }
      else
      {
         //The value of the parameter is not valid
         error = ERROR_INVALID_PARAMETER;
      }
   }
   else
   {
      //Check the value of the parameter
      if((s % 8) == 0 && s >= 1 && s <= (cipher->blockSize * 8))
      {
         size_t i;
         size_t n;
         uint8_t o[16];
 
         //Determine the size, in bytes, of the plaintext and ciphertext segments
         s = s / 8;
 
         //Process each ciphertext segment
         while(length > 0)
         {
            //Compute the number of bytes to process at a time
            n = MIN(length, s);
 
            //Compute O(j) = CIPH(I(j))
            cipher->encryptBlock(context, iv, o);
 
            //Compute I(j+1) = LSB(I(j)) | C(j)
            osMemmove(iv, iv + s, cipher->blockSize - s);
            osMemcpy(iv + cipher->blockSize - s, c, s);
 
            //Compute P(j) = C(j) XOR MSB(O(j))
            for(i = 0; i < n; i++)
            {
               p[i] = c[i] ^ o[i];
            }
 
            //Next block
            c += n;
            p += n;
            length -= n;
         }
      }
      else
      {
         //The value of the parameter is not valid
         error = ERROR_INVALID_PARAMETER;
      }
   }
 
   //Return status code
   return error;
}
 
#endif
#if (OFB_SUPPORT == ENABLED)
 
/**
 * @brief OFB encryption
 * @param[in] cipher Cipher algorithm
 * @param[in] context Cipher algorithm context
 * @param[in] s Size of the plaintext and ciphertext segments
 * @param[in,out] iv Initialization vector
 * @param[in] p Plaintext to be encrypted
 * @param[out] c Ciphertext resulting from the encryption
 * @param[in] length Total number of data bytes to be encrypted
 * @return Error code
 **/
 
error_t ofbEncrypt(const CipherAlgo *cipher, void *context, uint_t s,
   uint8_t *iv, const uint8_t *p, uint8_t *c, size_t length)
{
   error_t error;
 
   //Initialize status code
   error = NO_ERROR;
 
   //AES cipher algorithm?
   if(cipher == AES_CIPHER_ALGO)
   {
      //Check the value of the parameter
      if(s == (AES_BLOCK_SIZE * 8))
      {
         //Check the length of the payload
         if(length > 0)
         {
            //Encrypt payload data
            aesProcessData(context, iv, p, c, length, AES_MR_CIPHER_Msk |
               AES_MR_OPMOD_OFB);
         }
         else
         {
            //No data to process
         }
      }
      else
      {
         //The value of the parameter is not valid
         error = ERROR_INVALID_PARAMETER;
      }
   }
   else
   {
      //Check the value of the parameter
      if((s % 8) == 0 && s >= 1 && s <= (cipher->blockSize * 8))
      {
         size_t i;
         size_t n;
         uint8_t o[16];
 
         //Determine the size, in bytes, of the plaintext and ciphertext segments
         s = s / 8;
 
         //Process each plaintext segment
         while(length > 0)
         {
            //Compute the number of bytes to process at a time
            n = MIN(length, s);
 
            //Compute O(j) = CIPH(I(j))
            cipher->encryptBlock(context, iv, o);
 
            //Compute C(j) = P(j) XOR MSB(O(j))
            for(i = 0; i < n; i++)
            {
               c[i] = p[i] ^ o[i];
            }
 
            //Compute I(j+1) = LSB(I(j)) | O(j)
            osMemmove(iv, iv + s, cipher->blockSize - s);
            osMemcpy(iv + cipher->blockSize - s, o, s);
 
            //Next block
            p += n;
            c += n;
            length -= n;
         }
      }
      else
      {
         //The value of the parameter is not valid
         error = ERROR_INVALID_PARAMETER;
      }
   }
 
   //Return status code
   return error;
}
 
#endif
#if (CTR_SUPPORT == ENABLED)
 
/**
 * @brief CTR encryption
 * @param[in] cipher Cipher algorithm
 * @param[in] context Cipher algorithm context
 * @param[in] m Size in bits of the specific part of the block to be incremented
 * @param[in,out] t Initial counter block
 * @param[in] p Plaintext to be encrypted
 * @param[out] c Ciphertext resulting from the encryption
 * @param[in] length Total number of data bytes to be encrypted
 * @return Error code
 **/
 
error_t ctrEncrypt(const CipherAlgo *cipher, void *context, uint_t m,
   uint8_t *t, const uint8_t *p, uint8_t *c, size_t length)
{
   error_t error;
 
   //Initialize status code
   error = NO_ERROR;
 
   //Check the value of the parameter
   if((m % 8) == 0 && m <= (cipher->blockSize * 8))
   {
      //Determine the size, in bytes, of the specific part of the block to be
      //incremented
      m = m / 8;
 
      //AES cipher algorithm?
      if(cipher == AES_CIPHER_ALGO)
      {
         size_t k;
         size_t n;
 
         //Process plaintext
         while(length > 0)
         {
            //Limit the number of blocks to process at a time
            k = 256 - t[AES_BLOCK_SIZE - 1];
            n = MIN(length, k * AES_BLOCK_SIZE);
            k = (n + AES_BLOCK_SIZE - 1) / AES_BLOCK_SIZE;
 
            //Encrypt payload data
            aesProcessData(context, t, p, c, n, AES_MR_CIPHER_Msk |
               AES_MR_OPMOD_CTR);
 
            //Standard incrementing function
            ctrIncBlock(t, k, AES_BLOCK_SIZE, m);
 
            //Next block
            p += n;
            c += n;
            length -= n;
         }
      }
      else
      {
         size_t i;
         size_t n;
         uint8_t o[16];
 
         //Process plaintext
         while(length > 0)
         {
            //CTR mode operates in a block-by-block fashion
            n = MIN(length, cipher->blockSize);
 
            //Compute O(j) = CIPH(T(j))
            cipher->encryptBlock(context, t, o);
 
            //Compute C(j) = P(j) XOR T(j)
            for(i = 0; i < n; i++)
            {
               c[i] = p[i] ^ o[i];
            }
 
            //Standard incrementing function
            ctrIncBlock(t, 1, cipher->blockSize, m);
 
            //Next block
            p += n;
            c += n;
            length -= n;
         }
      }
   }
   else
   {
      //The value of the parameter is not valid
      error = ERROR_INVALID_PARAMETER;
   }
 
   //Return status code
   return error;
}
 
#endif
#if (GCM_SUPPORT == ENABLED)
 
/**
 * @brief Update GHASH value
 * @param[in] data Input block of data
 **/
 
void gcmUpdateGhash(const uint8_t *data)
{
   uint32_t *p;
 
   //Write data block
   p = (uint32_t *) data;
   AES_REGS->AES_IDATAR[0] = p[0];
   AES_REGS->AES_IDATAR[1] = p[1];
   AES_REGS->AES_IDATAR[2] = p[2];
   AES_REGS->AES_IDATAR[3] = p[3];
 
   //Process data
   AES_REGS->AES_CR = AES_CR_START_Msk;
 
   //The DATRDY bit indicates when the data have been processed. However, no
   //output data are generated when processing AAD
   while((AES_REGS->AES_ISR & AES_ISR_DATRDY_Msk) == 0)
   {
   }
}
 
 
/**
 * @brief Perform AES-GCM encryption or decryption
 * @param[in] context AES algorithm context
 * @param[in] iv Initialization vector
 * @param[in] a Additional authenticated data
 * @param[in] aLen Length of the additional data
 * @param[in] input Data to be encrypted/decrypted
 * @param[out] output Data resulting from the encryption/decryption process
 * @param[in] length Total number of data bytes to be processed
 * @param[out] t Authentication tag
 * @param[in] mode Operation mode
 **/
 
void gcmProcessData(AesContext *context, const uint8_t *iv,
   const uint8_t *a, size_t aLen, const uint8_t *input, uint8_t *output,
   size_t length, uint8_t *t, uint32_t mode)
{
   uint32_t temp;
   uint8_t buffer[16];
 
   //Acquire exclusive access to the AES module
   osAcquireMutex(&samv71CryptoMutex);
 
   //Perform software reset
   AES_REGS->AES_CR = AES_CR_SWRST_Msk;
 
   //Check parameters
   if(aLen > 0 || length > 0)
   {
      //Select GCM operation mode
      AES_REGS->AES_MR |= AES_MR_SMOD_MANUAL_START | AES_MR_OPMOD_GCM |
         AES_MR_GTAGEN_Msk | mode;
 
      //Whenever a new key is written to the hardware, the hash subkey is
      //automatically generated. The hash subkey generation must be complete
      //before doing any other action
      aesLoadKey(context);
 
      //The DATRDY bit of the AES_ISR indicates when the subkey generation is
      //complete
      while((AES_REGS->AES_ISR & AES_ISR_DATRDY_Msk) == 0)
      {
      }
 
      //When the length of the IV is 96 bits, the padding string is appended to
      //the IV to form the pre-counter block
      AES_REGS->AES_IVR[0] = LOAD32LE(iv);
      AES_REGS->AES_IVR[1] = LOAD32LE(iv + 4);
      AES_REGS->AES_IVR[2] = LOAD32LE(iv + 8);
      AES_REGS->AES_IVR[3] = BETOH32(2);
 
      //Set AADLEN field in AES_AADLENR and CLEN field in AES_CLENR
      AES_REGS->AES_AADLENR = aLen;
      AES_REGS->AES_CLENR = length;
 
      //Process additional authenticated data
      while(aLen > 16)
      {
         //Additional authenticated data is written block by block
         gcmUpdateGhash(a);
 
         //Next block
         a += 16;
         aLen -= 16;
      }
 
      //Process final block of additional authenticated data
      if(aLen > 0)
      {
         //Copy partial block
         osMemset(buffer, 0, 16);
         osMemcpy(buffer, a, aLen);
 
         //Write the resulting block
         gcmUpdateGhash(buffer);
      }
 
      //Process data
      while(length >= AES_BLOCK_SIZE)
      {
         //The data is encrypted block by block
         aesProcessDataBlock(input, output);
 
         //Next block
         input += AES_BLOCK_SIZE;
         output += AES_BLOCK_SIZE;
         length -= AES_BLOCK_SIZE;
      }
 
      //Process final block of data
      if(length > 0)
      {
         //Copy input data
         osMemset(buffer, 0, AES_BLOCK_SIZE);
         osMemcpy(buffer, input, length);
 
         //Encrypt the final block of data
         aesProcessDataBlock(buffer, buffer);
 
         //Copy output data
         osMemcpy(output, buffer, length);
      }
 
      //Wait for TAGRDY to be set
      while((AES_REGS->AES_ISR & AES_ISR_TAGRDY_Msk) == 0)
      {
      }
 
      //Read the value from AES_TAGR registers to obtain the authentication tag
      //of the message
      temp = AES_REGS->AES_TAGR[0];
      STORE32LE(temp, t);
      temp = AES_REGS->AES_TAGR[1];
      STORE32LE(temp, t + 4);
      temp = AES_REGS->AES_TAGR[2];
      STORE32LE(temp, t + 8);
      temp = AES_REGS->AES_TAGR[3];
      STORE32LE(temp, t + 12);
   }
   else
   {
      //Select CTR operation mode
      AES_REGS->AES_MR |= AES_MR_SMOD_MANUAL_START | AES_MR_OPMOD_CTR |
         AES_MR_CIPHER_Msk;
 
      //Set encryption key
      aesLoadKey(context);
 
      //When the length of the IV is 96 bits, the padding string is appended to
      //the IV to form the pre-counter block
      AES_REGS->AES_IVR[0] = LOAD32LE(iv);
      AES_REGS->AES_IVR[1] = LOAD32LE(iv + 4);
      AES_REGS->AES_IVR[2] = LOAD32LE(iv + 8);
      AES_REGS->AES_IVR[3] = BETOH32(1);
 
      //Clear data block
      osMemset(buffer, 0, AES_BLOCK_SIZE);
 
      //Generate authentication tag
      aesProcessDataBlock(buffer, t);
   }
 
   //Release exclusive access to the AES module
   osReleaseMutex(&samv71CryptoMutex);
}
 
 
/**
 * @brief Initialize GCM context
 * @param[in] context Pointer to the GCM context
 * @param[in] cipherAlgo Cipher algorithm
 * @param[in] cipherContext Pointer to the cipher algorithm context
 * @return Error code
 **/
 
error_t gcmInit(GcmContext *context, const CipherAlgo *cipherAlgo,
   void *cipherContext)
{
   //Check parameters
   if(context == NULL || cipherContext == NULL)
      return ERROR_INVALID_PARAMETER;
 
   //The CRYP module only supports AES cipher algorithm
   if(cipherAlgo != AES_CIPHER_ALGO)
      return ERROR_INVALID_PARAMETER;
 
   //Save cipher algorithm context
   context->cipherAlgo = cipherAlgo;
   context->cipherContext = cipherContext;
 
   //Successful initialization
   return NO_ERROR;
}
 
 
/**
 * @brief Authenticated encryption using GCM
 * @param[in] context Pointer to the GCM context
 * @param[in] iv Initialization vector
 * @param[in] ivLen Length of the initialization vector
 * @param[in] a Additional authenticated data
 * @param[in] aLen Length of the additional data
 * @param[in] p Plaintext to be encrypted
 * @param[out] c Ciphertext resulting from the encryption
 * @param[in] length Total number of data bytes to be encrypted
 * @param[out] t Authentication tag
 * @param[in] tLen Length of the authentication tag
 * @return Error code
 **/
 
error_t gcmEncrypt(GcmContext *context, const uint8_t *iv,
   size_t ivLen, const uint8_t *a, size_t aLen, const uint8_t *p,
   uint8_t *c, size_t length, uint8_t *t, size_t tLen)
{
   uint8_t authTag[16];
 
   //Make sure the GCM context is valid
   if(context == NULL)
      return ERROR_INVALID_PARAMETER;
 
   //Check whether the length of the IV is 96 bits
   if(ivLen != 12)
      return ERROR_INVALID_LENGTH;
 
   //Check the length of the authentication tag
   if(tLen < 4 || tLen > 16)
      return ERROR_INVALID_LENGTH;
 
   //Perform AES-GCM encryption
   gcmProcessData(context->cipherContext, iv, a, aLen, p, c, length,
      authTag, AES_MR_CIPHER_Msk);
 
   //Copy the resulting authentication tag
   osMemcpy(t, authTag, tLen);
 
   //Successful processing
   return NO_ERROR;
}
 
 
/**
 * @brief Authenticated decryption using GCM
 * @param[in] context Pointer to the GCM context
 * @param[in] iv Initialization vector
 * @param[in] ivLen Length of the initialization vector
 * @param[in] a Additional authenticated data
 * @param[in] aLen Length of the additional data
 * @param[in] c Ciphertext to be decrypted
 * @param[out] p Plaintext resulting from the decryption
 * @param[in] length Total number of data bytes to be decrypted
 * @param[in] t Authentication tag
 * @param[in] tLen Length of the authentication tag
 * @return Error code
 **/
 
error_t gcmDecrypt(GcmContext *context, const uint8_t *iv,
   size_t ivLen, const uint8_t *a, size_t aLen, const uint8_t *c,
   uint8_t *p, size_t length, const uint8_t *t, size_t tLen)
{
   size_t i;
   uint8_t mask;
   uint8_t authTag[16];
 
   //Make sure the GCM context is valid
   if(context == NULL)
      return ERROR_INVALID_PARAMETER;
 
   //Check whether the length of the IV is 96 bits
   if(ivLen != 12)
      return ERROR_INVALID_LENGTH;
 
   //Check the length of the authentication tag
   if(tLen < 4 || tLen > 16)
      return ERROR_INVALID_LENGTH;
 
   //Perform AES-GCM decryption
   gcmProcessData(context->cipherContext, iv, a, aLen, c, p, length,
      authTag, 0);
 
   //The calculated tag is bitwise compared to the received tag
   for(mask = 0, i = 0; i < tLen; i++)
   {
      mask |= authTag[i] ^ t[i];
   }
 
   //The message is authenticated if and only if the tags match
   return (mask == 0) ? NO_ERROR : ERROR_FAILURE;
}
 
#endif
#endif