Crypto AES

Table of Contents

• Features Supported
• SysConfig Features
• Features NOT Supported
• Usage Overview
  • AES Cipher Block Chaining (CBC) API Sequence
  • AES Cipher-based Message Authentication Code (CMAC) API Sequence
  • Initializing the AES Driver context buffer
  • AES_CBC Encryption and Decryption
  • Generating AES_CMAC
  • Clearing the AES Driver context buffer
• Important Usage Guidelines
• Example Usage
• API

Advanced Encryption Standard (AES) is widely adopted symmetric Encrypt/Decrypt algorithm provides information security such as confidentiality ..

Features Supported

• Supports Aes_cbc_256, Aes_cbc_128 and Aes_cbc_192 operations
• Supports Aes_cmac_256, Aes_cmac_128 and Aes_cmac_192 operations
• Encryption and Decryption
• Symmetric key symmetric block cipher

SysConfig Features

Features NOT Supported

Usage Overview

AES Cipher Block Chaining (CBC) API Sequence

To use the AES driver to do Encryption and decryption. Use the following APIs:

• Crypto_AesParams_init() : Call this API to set defaults and then override the fields as needed before calling Crypto_aesOpen.
• Crypto_aesOpen() : Initializes a AES context and gives the configuration based on instance.
• Crypto_aesSetKeyEnc() : This function sets the Advance Encryption Standard (AES) encryption key
• Crypto_aesSetKeyDec() : This function sets the Advance Encryption Standard (AES) decryption key
• Crypto_aesCbc() : This function finishes the Advance Encryption Standard (AES) operation, and writes the result to the output buffer.
• Crypto_aesClose() : De-initialize the AES instance and Clears AES context.

AES Cipher-based Message Authentication Code (CMAC) API Sequence

To use the AES driver to do CMAC. Use the following APIs:

• Crypto_AesParams_init() : Call this API to set defaults and then override the fields as needed before calling Crypto_aesOpen.
• Crypto_aesOpen() : Initializes a AES context and gives the configuration based on instance.
• Crypto_cmacSingleShot() : This function calculates the Advance Encryption Standard Cipher-based Message Authentication Code (AES-CMAC) of a buffer.
• Crypto_cmacSetup() : This function prepares a cipher context for use with the given cipher primitive.
• Crypto_cmacStarts() : This function sets the CMAC key, and prepares to authenticate the input data.
• Crypto_cmacUpdate() : This function feeds an input buffer into an ongoing CMAC computation.
• Crypto_cmacFinish() : This function finishes the CMAC operation, and writes the result to the output buffer.
• Crypto_aesClose() : De-initialize the AES instance and Clears AES context.

Initializing the AES Driver context buffer

• Crypto_aesOpen() must be called before any other AES APIs. This function Initializes a AES context and iterates through the elements of the gCryptoAesConfig[] array. Please note that initializing AES driver is taken care by the SysConfig generated code.

AES_CBC Encryption and Decryption

• AES_CBC Encryption: Set the input parameters using Crypto_AesParams structure, all necessary parametets set to Crypto_AesParams variables and call Crypto_aesOpen() for Initialize the AES ctx, For encryption operation to set the key call Crypto_aesSetKeyEnc(), finally call Crypto_aesCbc() for encryption operation, Aes output will store in output buffer, reset the Aes ctx buffer using Crypto_aesClose().
• AES_CBC Decryption: Set the input parameters using Crypto_AesParams structure, all necessary parametets set to Crypto_AesParams variables and call Crypto_aesOpen() for Initialize the AES ctx, For encryption operation to set the key call Crypto_aesSetKeyDec(), finally call Crypto_aesCbc() for encryption operation, Aes output will store in output buffer, reset the Aes ctx buffer using Crypto_aesClose().

Generating AES_CMAC

• Single Block AES_CMAC Computation: Set the input parameters using Crypto_AesParams structure, all necessary parametets set to Crypto_AesParams variables and call Crypto_aesOpen() for Initialize the Aes ctx. To compute fixed block CMAC i.e call Crypto_cmacSingleShot() by updating references to input buffer, length and Output buffer. result will be available at output buffer on successful computation. Once CMAC computation is done for the required data length, reset the AES CMAC ctx buffer using Crypto_aesClose().
• Multi Block AES_CMAC Computation: Set the input parameters using Crypto_AesParams structure, all necessary parametets set to Crypto_AesParams variables and call Crypto_aesOpen() for Initialize the AES CMAC ctx. For prepare the cipher context by using Crypto_cmacSetup(), Crypto_cmacStarts() Sets the CMAC key, and prepares to authenticate the input data. Buffer processing is handled by Crypto_cmacUpdate(), use this API for multi buffer processing and extract final hash using Crypto_cmacFinish(). Once AES CMAC computation is done for the required data length , reset the AES CMAC ctx buffer using Crypto_aesClose().

Clearing the AES Driver context buffer

• Crypto_aesClose() clears context buffer data.

Important Usage Guidelines

Example Usage

Include the below file to access the APIs

 
#include <stdio.h>
#include <string.h>
#include <security/crypto/include/crypto_aes.h>
 
#define APP_AES_OUTPUT_LENGTH           (16)
uint8_t gCryptoAesTestBuf[16]={0x81,0xEA,0x5B,0xA4,0x69,0x45,0xC1,0x70,0x5F,0x6F,0x89,0x77,0x88,0x68,0xCC,0x67};
uint8_t gCryptoAesTestKey[32]={0x33,0xA3,0x66,0x46,0xFE,0x56,0xF7,0x0D,0xC0,0xC5,0x1A,0x31,0x17,0xE6,0x39,0xF1,0x82,0xDE,0xF8,0xCA,0xB5,0xC0,0x66,0x71,0xEE,0xA0,0x40,0x7C,0x48,0xA9,0xC7,0x57};
uint8_t gCryptoAesTestIv[16]={0x7C,0xE2,0xAB,0xAF,0x8B,0xEF,0x23,0xC4,0x81,0x6D,0xC8,0xCE,0x84,0x20,0x48,0xA7};

Aes cbc Example

 
Crypto_AesParams            params;
Crypto_AesHandle            aesHandle;
uint8_t                     aesResultBuf[APP_AES_OUTPUT_LENGTH];
int32_t                     status;
/* Context memory */
static Crypto_AesContext    gCryptoAesContext;
 
/* Aes encryption */
memcpy(&params.iv, gCryptoAesTestIv, CRYPTO_AES_IV_LENGTH);
memcpy(&params.key, gCryptoAesTestKey, CRYPTO_AES_KEY_LENGTH);
params.keySizeInBits = 256;
params.type          = CRYPTO_TYPE_SW;
params.algoType      = CRYPTO_AES_ENCRYPT;
                                    
aesHandle = Crypto_aesOpen(&gCryptoAesContext, &params);
status = Crypto_aesSetKeyEnc(aesHandle);
status = Crypto_aesCbc(aesHandle, gCryptoAesTestBuf, sizeof(gCryptoAesTestBuf), aesResultBuf );
status = Crypto_aesClose(aesHandle);
 
/* Aes Decryption */
memcpy(&params.iv, gCryptoAesTestIv, CRYPTO_AES_IV_LENGTH);
memcpy(&params.key, gCryptoAesTestKey, CRYPTO_AES_KEY_LENGTH);
params.keySizeInBits = 256;
params.type          = CRYPTO_TYPE_SW;
params.algoType      = CRYPTO_AES_DECRYPT;
 
aesHandle = Crypto_aesOpen(&gCryptoAesContext, &params);
status = Crypto_aesSetKeyDec(aesHandle);
status = Crypto_aesCbc(aesHandle, gCryptoAesTestBuf, sizeof(gCryptoAesTestBuf), aesResultBuf );
status = Crypto_aesClose(aesHandle);
 
 

API

APIs for CRYPTO AES