nuclei-sdk/application/baremetal/demo_profiling/aes.c

/*

This is an implementation of the AES algorithm, specifically ECB, CTR and CBC
mode. Block size can be chosen in aes.h - available choices are AES128, AES192,
AES256.

The implementation is verified against the test vectors in:
  National Institute of Standards and Technology Special Publication 800-38A
2001 ED

ECB-AES128
----------

  plain-text:
    6bc1bee22e409f96e93d7e117393172a
    ae2d8a571e03ac9c9eb76fac45af8e51
    30c81c46a35ce411e5fbc1191a0a52ef
    f69f2445df4f9b17ad2b417be66c3710

  key:
    2b7e151628aed2a6abf7158809cf4f3c

  resulting cipher
    3ad77bb40d7a3660a89ecaf32466ef97
    f5d3d58503b9699de785895a96fdbaaf
    43b1cd7f598ece23881b00e3ed030688
    7b0c785e27e8ad3f8223207104725dd4


NOTE:   String length must be evenly divisible by 16byte (str_len % 16 == 0)
        You should pad the end of the string with zeros if this is not the case.
        For AES192/256 the key size is proportionally larger.

*/

/*****************************************************************************/
/* Includes:                                                                 */
/*****************************************************************************/
#include "aes.h"
#include <string.h> // CBC mode, for memset

/*****************************************************************************/
/* Defines:                                                                  */
/*****************************************************************************/
// The number of columns comprising a state in AES. This is a constant in AES.
// Value=4
#define Nb 4

#if defined(AES256) && (AES256 == 1)
#define Nk 8
#define Nr 14
#elif defined(AES192) && (AES192 == 1)
#define Nk 6
#define Nr 12
#else
#define Nk 4  // The number of 32 bit words in a key.
#define Nr 10 // The number of rounds in AES Cipher.
#endif

// jcallan@github points out that declaring Multiply as a function
// reduces code size considerably with the Keil ARM compiler.
// See this link for more information:
// https://github.com/kokke/tiny-AES-C/pull/3
#ifndef MULTIPLY_AS_A_FUNCTION
#define MULTIPLY_AS_A_FUNCTION 0
#endif

/*****************************************************************************/
/* Private variables:                                                        */
/*****************************************************************************/
// state - array holding the intermediate results during decryption.
typedef uint8_t state_t[4][4];

// The lookup-tables are marked const so they can be placed in read-only storage
// instead of RAM The numbers below can be computed dynamically trading ROM for
// RAM - This can be useful in (embedded) bootloader applications, where ROM is
// often limited.
static const uint8_t sbox[256] = {
    // 0     1    2      3     4    5     6     7      8    9     A      B    C
    // D     E     F
    0x63, 0x7c, 0x77, 0x7b, 0xf2, 0x6b, 0x6f, 0xc5, 0x30, 0x01, 0x67, 0x2b,
    0xfe, 0xd7, 0xab, 0x76, 0xca, 0x82, 0xc9, 0x7d, 0xfa, 0x59, 0x47, 0xf0,
    0xad, 0xd4, 0xa2, 0xaf, 0x9c, 0xa4, 0x72, 0xc0, 0xb7, 0xfd, 0x93, 0x26,
    0x36, 0x3f, 0xf7, 0xcc, 0x34, 0xa5, 0xe5, 0xf1, 0x71, 0xd8, 0x31, 0x15,
    0x04, 0xc7, 0x23, 0xc3, 0x18, 0x96, 0x05, 0x9a, 0x07, 0x12, 0x80, 0xe2,
    0xeb, 0x27, 0xb2, 0x75, 0x09, 0x83, 0x2c, 0x1a, 0x1b, 0x6e, 0x5a, 0xa0,
    0x52, 0x3b, 0xd6, 0xb3, 0x29, 0xe3, 0x2f, 0x84, 0x53, 0xd1, 0x00, 0xed,
    0x20, 0xfc, 0xb1, 0x5b, 0x6a, 0xcb, 0xbe, 0x39, 0x4a, 0x4c, 0x58, 0xcf,
    0xd0, 0xef, 0xaa, 0xfb, 0x43, 0x4d, 0x33, 0x85, 0x45, 0xf9, 0x02, 0x7f,
    0x50, 0x3c, 0x9f, 0xa8, 0x51, 0xa3, 0x40, 0x8f, 0x92, 0x9d, 0x38, 0xf5,
    0xbc, 0xb6, 0xda, 0x21, 0x10, 0xff, 0xf3, 0xd2, 0xcd, 0x0c, 0x13, 0xec,
    0x5f, 0x97, 0x44, 0x17, 0xc4, 0xa7, 0x7e, 0x3d, 0x64, 0x5d, 0x19, 0x73,
    0x60, 0x81, 0x4f, 0xdc, 0x22, 0x2a, 0x90, 0x88, 0x46, 0xee, 0xb8, 0x14,
    0xde, 0x5e, 0x0b, 0xdb, 0xe0, 0x32, 0x3a, 0x0a, 0x49, 0x06, 0x24, 0x5c,
    0xc2, 0xd3, 0xac, 0x62, 0x91, 0x95, 0xe4, 0x79, 0xe7, 0xc8, 0x37, 0x6d,
    0x8d, 0xd5, 0x4e, 0xa9, 0x6c, 0x56, 0xf4, 0xea, 0x65, 0x7a, 0xae, 0x08,
    0xba, 0x78, 0x25, 0x2e, 0x1c, 0xa6, 0xb4, 0xc6, 0xe8, 0xdd, 0x74, 0x1f,
    0x4b, 0xbd, 0x8b, 0x8a, 0x70, 0x3e, 0xb5, 0x66, 0x48, 0x03, 0xf6, 0x0e,
    0x61, 0x35, 0x57, 0xb9, 0x86, 0xc1, 0x1d, 0x9e, 0xe1, 0xf8, 0x98, 0x11,
    0x69, 0xd9, 0x8e, 0x94, 0x9b, 0x1e, 0x87, 0xe9, 0xce, 0x55, 0x28, 0xdf,
    0x8c, 0xa1, 0x89, 0x0d, 0xbf, 0xe6, 0x42, 0x68, 0x41, 0x99, 0x2d, 0x0f,
    0xb0, 0x54, 0xbb, 0x16};

#if (defined(CBC) && CBC == 1) || (defined(ECB) && ECB == 1)
static const uint8_t rsbox[256] = {
    0x52, 0x09, 0x6a, 0xd5, 0x30, 0x36, 0xa5, 0x38, 0xbf, 0x40, 0xa3, 0x9e,
    0x81, 0xf3, 0xd7, 0xfb, 0x7c, 0xe3, 0x39, 0x82, 0x9b, 0x2f, 0xff, 0x87,
    0x34, 0x8e, 0x43, 0x44, 0xc4, 0xde, 0xe9, 0xcb, 0x54, 0x7b, 0x94, 0x32,
    0xa6, 0xc2, 0x23, 0x3d, 0xee, 0x4c, 0x95, 0x0b, 0x42, 0xfa, 0xc3, 0x4e,
    0x08, 0x2e, 0xa1, 0x66, 0x28, 0xd9, 0x24, 0xb2, 0x76, 0x5b, 0xa2, 0x49,
    0x6d, 0x8b, 0xd1, 0x25, 0x72, 0xf8, 0xf6, 0x64, 0x86, 0x68, 0x98, 0x16,
    0xd4, 0xa4, 0x5c, 0xcc, 0x5d, 0x65, 0xb6, 0x92, 0x6c, 0x70, 0x48, 0x50,
    0xfd, 0xed, 0xb9, 0xda, 0x5e, 0x15, 0x46, 0x57, 0xa7, 0x8d, 0x9d, 0x84,
    0x90, 0xd8, 0xab, 0x00, 0x8c, 0xbc, 0xd3, 0x0a, 0xf7, 0xe4, 0x58, 0x05,
    0xb8, 0xb3, 0x45, 0x06, 0xd0, 0x2c, 0x1e, 0x8f, 0xca, 0x3f, 0x0f, 0x02,
    0xc1, 0xaf, 0xbd, 0x03, 0x01, 0x13, 0x8a, 0x6b, 0x3a, 0x91, 0x11, 0x41,
    0x4f, 0x67, 0xdc, 0xea, 0x97, 0xf2, 0xcf, 0xce, 0xf0, 0xb4, 0xe6, 0x73,
    0x96, 0xac, 0x74, 0x22, 0xe7, 0xad, 0x35, 0x85, 0xe2, 0xf9, 0x37, 0xe8,
    0x1c, 0x75, 0xdf, 0x6e, 0x47, 0xf1, 0x1a, 0x71, 0x1d, 0x29, 0xc5, 0x89,
    0x6f, 0xb7, 0x62, 0x0e, 0xaa, 0x18, 0xbe, 0x1b, 0xfc, 0x56, 0x3e, 0x4b,
    0xc6, 0xd2, 0x79, 0x20, 0x9a, 0xdb, 0xc0, 0xfe, 0x78, 0xcd, 0x5a, 0xf4,
    0x1f, 0xdd, 0xa8, 0x33, 0x88, 0x07, 0xc7, 0x31, 0xb1, 0x12, 0x10, 0x59,
    0x27, 0x80, 0xec, 0x5f, 0x60, 0x51, 0x7f, 0xa9, 0x19, 0xb5, 0x4a, 0x0d,
    0x2d, 0xe5, 0x7a, 0x9f, 0x93, 0xc9, 0x9c, 0xef, 0xa0, 0xe0, 0x3b, 0x4d,
    0xae, 0x2a, 0xf5, 0xb0, 0xc8, 0xeb, 0xbb, 0x3c, 0x83, 0x53, 0x99, 0x61,
    0x17, 0x2b, 0x04, 0x7e, 0xba, 0x77, 0xd6, 0x26, 0xe1, 0x69, 0x14, 0x63,
    0x55, 0x21, 0x0c, 0x7d};
#endif

// The round constant word array, Rcon[i], contains the values given by
// x to the power (i-1) being powers of x (x is denoted as {02}) in the field
// GF(2^8)
static const uint8_t Rcon[11] = {0x8d, 0x01, 0x02, 0x04, 0x08, 0x10,
                                 0x20, 0x40, 0x80, 0x1b, 0x36};

/*
 * Jordan Goulder points out in PR #12
 * (https://github.com/kokke/tiny-AES-C/pull/12), that you can remove most of
 * the elements in the Rcon array, because they are unused.
 *
 * From Wikipedia's article on the Rijndael key schedule @
 * https://en.wikipedia.org/wiki/Rijndael_key_schedule#Rcon
 *
 * "Only the first some of these constants are actually used – up to rcon[10]
 * for AES-128 (as 11 round keys are needed), up to rcon[8] for AES-192, up to
 * rcon[7] for AES-256. rcon[0] is not used in AES algorithm."
 */

/*****************************************************************************/
/* Private functions:                                                        */
/*****************************************************************************/
/*
static uint8_t getSBoxValue(uint8_t num)
{
  return sbox[num];
}
*/
#define getSBoxValue(num) (sbox[(num)])

// This function produces Nb(Nr+1) round keys. The round keys are used in each
// round to decrypt the states.
static void KeyExpansion(uint8_t *RoundKey, const uint8_t *Key)
{
    unsigned i, j, k;
    uint8_t tempa[4]; // Used for the column/row operations

    // The first round key is the key itself.
    for (i = 0; i < Nk; ++i) {
        RoundKey[(i * 4) + 0] = Key[(i * 4) + 0];
        RoundKey[(i * 4) + 1] = Key[(i * 4) + 1];
        RoundKey[(i * 4) + 2] = Key[(i * 4) + 2];
        RoundKey[(i * 4) + 3] = Key[(i * 4) + 3];
    }

    // All other round keys are found from the previous round keys.
    for (i = Nk; i < Nb * (Nr + 1); ++i) {
        {
            k = (i - 1) * 4;
            tempa[0] = RoundKey[k + 0];
            tempa[1] = RoundKey[k + 1];
            tempa[2] = RoundKey[k + 2];
            tempa[3] = RoundKey[k + 3];
        }

        if (i % Nk == 0) {
            // This function shifts the 4 bytes in a word to the left once.
            // [a0,a1,a2,a3] becomes [a1,a2,a3,a0]

            // Function RotWord()
            {
                const uint8_t u8tmp = tempa[0];
                tempa[0] = tempa[1];
                tempa[1] = tempa[2];
                tempa[2] = tempa[3];
                tempa[3] = u8tmp;
            }

            // SubWord() is a function that takes a four-byte input word and
            // applies the S-box to each of the four bytes to produce an output
            // word.

            // Function Subword()
            {
                tempa[0] = getSBoxValue(tempa[0]);
                tempa[1] = getSBoxValue(tempa[1]);
                tempa[2] = getSBoxValue(tempa[2]);
                tempa[3] = getSBoxValue(tempa[3]);
            }

            tempa[0] = tempa[0] ^ Rcon[i / Nk];
        }
#if defined(AES256) && (AES256 == 1)
        if (i % Nk == 4) {
            // Function Subword()
            {
                tempa[0] = getSBoxValue(tempa[0]);
                tempa[1] = getSBoxValue(tempa[1]);
                tempa[2] = getSBoxValue(tempa[2]);
                tempa[3] = getSBoxValue(tempa[3]);
            }
        }
#endif
        j = i * 4;
        k = (i - Nk) * 4;
        RoundKey[j + 0] = RoundKey[k + 0] ^ tempa[0];
        RoundKey[j + 1] = RoundKey[k + 1] ^ tempa[1];
        RoundKey[j + 2] = RoundKey[k + 2] ^ tempa[2];
        RoundKey[j + 3] = RoundKey[k + 3] ^ tempa[3];
    }
}

void AES_init_ctx(struct AES_ctx *ctx, const uint8_t *key)
{
    KeyExpansion(ctx->RoundKey, key);
}
#if (defined(CBC) && (CBC == 1)) || (defined(CTR) && (CTR == 1))
void AES_init_ctx_iv(struct AES_ctx *ctx, const uint8_t *key, const uint8_t *iv)
{
    KeyExpansion(ctx->RoundKey, key);
    memcpy(ctx->Iv, iv, AES_BLOCKLEN);
}
void AES_ctx_set_iv(struct AES_ctx *ctx, const uint8_t *iv)
{
    memcpy(ctx->Iv, iv, AES_BLOCKLEN);
}
#endif

// This function adds the round key to state.
// The round key is added to the state by an XOR function.
static void AddRoundKey(uint8_t round, state_t *state, const uint8_t *RoundKey)
{
    uint8_t i, j;
    for (i = 0; i < 4; ++i) {
        for (j = 0; j < 4; ++j) {
            (*state)[i][j] ^= RoundKey[(round * Nb * 4) + (i * Nb) + j];
        }
    }
}

// The SubBytes Function Substitutes the values in the
// state matrix with values in an S-box.
static void SubBytes(state_t *state)
{
    uint8_t i, j;
    for (i = 0; i < 4; ++i) {
        for (j = 0; j < 4; ++j) {
            (*state)[j][i] = getSBoxValue((*state)[j][i]);
        }
    }
}

// The ShiftRows() function shifts the rows in the state to the left.
// Each row is shifted with different offset.
// Offset = Row number. So the first row is not shifted.
static void ShiftRows(state_t *state)
{
    uint8_t temp;

    // Rotate first row 1 columns to left
    temp = (*state)[0][1];
    (*state)[0][1] = (*state)[1][1];
    (*state)[1][1] = (*state)[2][1];
    (*state)[2][1] = (*state)[3][1];
    (*state)[3][1] = temp;

    // Rotate second row 2 columns to left
    temp = (*state)[0][2];
    (*state)[0][2] = (*state)[2][2];
    (*state)[2][2] = temp;

    temp = (*state)[1][2];
    (*state)[1][2] = (*state)[3][2];
    (*state)[3][2] = temp;

    // Rotate third row 3 columns to left
    temp = (*state)[0][3];
    (*state)[0][3] = (*state)[3][3];
    (*state)[3][3] = (*state)[2][3];
    (*state)[2][3] = (*state)[1][3];
    (*state)[1][3] = temp;
}

static uint8_t xtime(uint8_t x) { return ((x << 1) ^ (((x >> 7) & 1) * 0x1b)); }

// MixColumns function mixes the columns of the state matrix
static void MixColumns(state_t *state)
{
    uint8_t i;
    uint8_t Tmp, Tm, t;
    for (i = 0; i < 4; ++i) {
        t = (*state)[i][0];
        Tmp = (*state)[i][0] ^ (*state)[i][1] ^ (*state)[i][2] ^ (*state)[i][3];
        Tm = (*state)[i][0] ^ (*state)[i][1];
        Tm = xtime(Tm);
        (*state)[i][0] ^= Tm ^ Tmp;
        Tm = (*state)[i][1] ^ (*state)[i][2];
        Tm = xtime(Tm);
        (*state)[i][1] ^= Tm ^ Tmp;
        Tm = (*state)[i][2] ^ (*state)[i][3];
        Tm = xtime(Tm);
        (*state)[i][2] ^= Tm ^ Tmp;
        Tm = (*state)[i][3] ^ t;
        Tm = xtime(Tm);
        (*state)[i][3] ^= Tm ^ Tmp;
    }
}

// Multiply is used to multiply numbers in the field GF(2^8)
// Note: The last call to xtime() is unneeded, but often ends up generating a
// smaller binary
//       The compiler seems to be able to vectorize the operation better this
//       way. See https://github.com/kokke/tiny-AES-c/pull/34
#if MULTIPLY_AS_A_FUNCTION
static uint8_t Multiply(uint8_t x, uint8_t y)
{
    return (((y & 1) * x) ^ ((y >> 1 & 1) * xtime(x)) ^
            ((y >> 2 & 1) * xtime(xtime(x))) ^
            ((y >> 3 & 1) * xtime(xtime(xtime(x)))) ^
            ((y >> 4 & 1) *
             xtime(xtime(xtime(
                 xtime(x)))))); /* this last call to xtime() can be omitted */
}
#else
#define Multiply(x, y)                                                         \
    (((y & 1) * x) ^ ((y >> 1 & 1) * xtime(x)) ^                               \
     ((y >> 2 & 1) * xtime(xtime(x))) ^                                        \
     ((y >> 3 & 1) * xtime(xtime(xtime(x)))) ^                                 \
     ((y >> 4 & 1) * xtime(xtime(xtime(xtime(x))))))

#endif

#if (defined(CBC) && CBC == 1) || (defined(ECB) && ECB == 1)
/*
static uint8_t getSBoxInvert(uint8_t num)
{
  return rsbox[num];
}
*/
#define getSBoxInvert(num) (rsbox[(num)])

// MixColumns function mixes the columns of the state matrix.
// The method used to multiply may be difficult to understand for the
// inexperienced. Please use the references to gain more information.
static void InvMixColumns(state_t *state)
{
    int i;
    uint8_t a, b, c, d;
    for (i = 0; i < 4; ++i) {
        a = (*state)[i][0];
        b = (*state)[i][1];
        c = (*state)[i][2];
        d = (*state)[i][3];

        (*state)[i][0] = Multiply(a, 0x0e) ^ Multiply(b, 0x0b) ^
                         Multiply(c, 0x0d) ^ Multiply(d, 0x09);
        (*state)[i][1] = Multiply(a, 0x09) ^ Multiply(b, 0x0e) ^
                         Multiply(c, 0x0b) ^ Multiply(d, 0x0d);
        (*state)[i][2] = Multiply(a, 0x0d) ^ Multiply(b, 0x09) ^
                         Multiply(c, 0x0e) ^ Multiply(d, 0x0b);
        (*state)[i][3] = Multiply(a, 0x0b) ^ Multiply(b, 0x0d) ^
                         Multiply(c, 0x09) ^ Multiply(d, 0x0e);
    }
}

// The SubBytes Function Substitutes the values in the
// state matrix with values in an S-box.
static void InvSubBytes(state_t *state)
{
    uint8_t i, j;
    for (i = 0; i < 4; ++i) {
        for (j = 0; j < 4; ++j) {
            (*state)[j][i] = getSBoxInvert((*state)[j][i]);
        }
    }
}

static void InvShiftRows(state_t *state)
{
    uint8_t temp;

    // Rotate first row 1 columns to right
    temp = (*state)[3][1];
    (*state)[3][1] = (*state)[2][1];
    (*state)[2][1] = (*state)[1][1];
    (*state)[1][1] = (*state)[0][1];
    (*state)[0][1] = temp;

    // Rotate second row 2 columns to right
    temp = (*state)[0][2];
    (*state)[0][2] = (*state)[2][2];
    (*state)[2][2] = temp;

    temp = (*state)[1][2];
    (*state)[1][2] = (*state)[3][2];
    (*state)[3][2] = temp;

    // Rotate third row 3 columns to right
    temp = (*state)[0][3];
    (*state)[0][3] = (*state)[1][3];
    (*state)[1][3] = (*state)[2][3];
    (*state)[2][3] = (*state)[3][3];
    (*state)[3][3] = temp;
}
#endif // #if (defined(CBC) && CBC == 1) || (defined(ECB) && ECB == 1)

// Cipher is the main function that encrypts the PlainText.
static void Cipher(state_t *state, const uint8_t *RoundKey)
{
    uint8_t round = 0;

    // Add the First round key to the state before starting the rounds.
    AddRoundKey(0, state, RoundKey);

    // There will be Nr rounds.
    // The first Nr-1 rounds are identical.
    // These Nr rounds are executed in the loop below.
    // Last one without MixColumns()
    for (round = 1;; ++round) {
        SubBytes(state);
        ShiftRows(state);
        if (round == Nr) {
            break;
        }
        MixColumns(state);
        AddRoundKey(round, state, RoundKey);
    }
    // Add round key to last round
    AddRoundKey(Nr, state, RoundKey);
}

#if (defined(CBC) && CBC == 1) || (defined(ECB) && ECB == 1)
static void InvCipher(state_t *state, const uint8_t *RoundKey)
{
    uint8_t round = 0;

    // Add the First round key to the state before starting the rounds.
    AddRoundKey(Nr, state, RoundKey);

    // There will be Nr rounds.
    // The first Nr-1 rounds are identical.
    // These Nr rounds are executed in the loop below.
    // Last one without InvMixColumn()
    for (round = (Nr - 1);; --round) {
        InvShiftRows(state);
        InvSubBytes(state);
        AddRoundKey(round, state, RoundKey);
        if (round == 0) {
            break;
        }
        InvMixColumns(state);
    }
}
#endif // #if (defined(CBC) && CBC == 1) || (defined(ECB) && ECB == 1)

/*****************************************************************************/
/* Public functions:                                                         */
/*****************************************************************************/
#if defined(ECB) && (ECB == 1)

void AES_ECB_encrypt(const struct AES_ctx *ctx, uint8_t *buf)
{
    // The next function call encrypts the PlainText with the Key using AES
    // algorithm.
    Cipher((state_t *)buf, ctx->RoundKey);
}

void AES_ECB_decrypt(const struct AES_ctx *ctx, uint8_t *buf)
{
    // The next function call decrypts the PlainText with the Key using AES
    // algorithm.
    InvCipher((state_t *)buf, ctx->RoundKey);
}

#endif // #if defined(ECB) && (ECB == 1)

#if defined(CBC) && (CBC == 1)

static void XorWithIv(uint8_t *buf, const uint8_t *Iv)
{
    uint8_t i;
    for (i = 0; i < AES_BLOCKLEN;
         ++i) // The block in AES is always 128bit no matter the key size
    {
        buf[i] ^= Iv[i];
    }
}

void AES_CBC_encrypt_buffer(struct AES_ctx *ctx, uint8_t *buf, size_t length)
{
    size_t i;
    uint8_t *Iv = ctx->Iv;
    for (i = 0; i < length; i += AES_BLOCKLEN) {
        XorWithIv(buf, Iv);
        Cipher((state_t *)buf, ctx->RoundKey);
        Iv = buf;
        buf += AES_BLOCKLEN;
    }
    /* store Iv in ctx for next call */
    memcpy(ctx->Iv, Iv, AES_BLOCKLEN);
}

void AES_CBC_decrypt_buffer(struct AES_ctx *ctx, uint8_t *buf, size_t length)
{
    size_t i;
    uint8_t storeNextIv[AES_BLOCKLEN];
    for (i = 0; i < length; i += AES_BLOCKLEN) {
        memcpy(storeNextIv, buf, AES_BLOCKLEN);
        InvCipher((state_t *)buf, ctx->RoundKey);
        XorWithIv(buf, ctx->Iv);
        memcpy(ctx->Iv, storeNextIv, AES_BLOCKLEN);
        buf += AES_BLOCKLEN;
    }
}

#endif // #if defined(CBC) && (CBC == 1)

#if defined(CTR) && (CTR == 1)

/* Symmetrical operation: same function for encrypting as for decrypting. Note
 * any IV/nonce should never be reused with the same key */
void AES_CTR_xcrypt_buffer(struct AES_ctx *ctx, uint8_t *buf, size_t length)
{
    uint8_t buffer[AES_BLOCKLEN];

    size_t i;
    int bi;
    for (i = 0, bi = AES_BLOCKLEN; i < length; ++i, ++bi) {
        if (bi == AES_BLOCKLEN) /* we need to regen xor compliment in buffer */
        {

            memcpy(buffer, ctx->Iv, AES_BLOCKLEN);
            Cipher((state_t *)buffer, ctx->RoundKey);

            /* Increment Iv and handle overflow */
            for (bi = (AES_BLOCKLEN - 1); bi >= 0; --bi) {
                /* inc will overflow */
                if (ctx->Iv[bi] == 255) {
                    ctx->Iv[bi] = 0;
                    continue;
                }
                ctx->Iv[bi] += 1;
                break;
            }
            bi = 0;
        }

        buf[i] = (buf[i] ^ buffer[bi]);
    }
}

#endif // #if defined(CTR) && (CTR == 1)