src/core/crypto/pbkdf2_cmac.cpp

/*
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 *     derived from this software without specific prior written permission.
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/**
 * @file
 *   This file implements PBKDF2 using AES-CMAC-PRF-128
 */

#include <openthread/config.h>

#include "pbkdf2_cmac.h"

#include "utils/wrap_string.h"

#include <mbedtls/cmac.h>

#if OPENTHREAD_ENABLE_COMMISSIONER && OPENTHREAD_FTD

void otPbkdf2Cmac(
    const uint8_t *aPassword, uint16_t aPasswordLen,
    const uint8_t *aSalt, uint16_t aSaltLen,
    uint32_t aIterationCounter, uint16_t aKeyLen,
    uint8_t *aKey)
{
    uint32_t blockCounter = 0;
    uint16_t useLen = 0;
    uint16_t prfBlockLen = MBEDTLS_CIPHER_BLKSIZE_MAX;
    uint8_t prfInput[OT_PBKDF2_SALT_MAX_LEN + 4]; // Salt || INT(), for U1 calculation
    uint8_t prfOutput[MBEDTLS_CIPHER_BLKSIZE_MAX];
    uint8_t keyBlock[MBEDTLS_CIPHER_BLKSIZE_MAX];
    uint8_t *key = aKey;
    uint16_t keyLen = aKeyLen;

    while (keyLen)
    {
        memcpy(prfInput, aSalt, aSaltLen);

        blockCounter++;
        prfInput[aSaltLen + 0] = (uint8_t)(blockCounter >> 24);
        prfInput[aSaltLen + 1] = (uint8_t)(blockCounter >> 16);
        prfInput[aSaltLen + 2] = (uint8_t)(blockCounter >> 8);
        prfInput[aSaltLen + 3] = (uint8_t)(blockCounter);

        // Calculate U_1
        mbedtls_aes_cmac_prf_128(aPassword, aPasswordLen, prfInput, aSaltLen + 4, prfOutput);
        memcpy(keyBlock, prfOutput, prfBlockLen);

        for (uint32_t i = 1; i < aIterationCounter; i++)
        {
            memcpy(prfInput, prfOutput, prfBlockLen);

            // Calculate U_i
            mbedtls_aes_cmac_prf_128(aPassword, aPasswordLen, prfInput, prfBlockLen, prfOutput);

            // xor
            for (uint32_t j = 0; j < prfBlockLen; j++)
            {
                keyBlock[j] ^= prfOutput[j];
            }
        }

        useLen = (keyLen < prfBlockLen) ? keyLen : prfBlockLen;
        memcpy(key, keyBlock, useLen);
        key += useLen;
        keyLen -= useLen;
    }
}

#endif // OPENTHREAD_ENABLE_COMMISSIONER && OPENTHREAD_FTD