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- aes encryption with 128 successfully tested

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This commit is contained in:
Jan Hutter
2005-11-28 10:16:54 +00:00
parent 6906d8fe84
commit 7f0e85216e
2 changed files with 237 additions and 187 deletions
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Source/charon/testcases/aes_cbc_crypter_test.c
+68 -2
View File
@@ -75,7 +75,7 @@ void test_aes_cbc_crypter(tester_t *tester)
logger->log_chunk(logger,RAW,"expected decrypted :", &data1);
logger->log_chunk(logger,RAW,"decrypted :", &decrypted1);
allocator_free_chunk(&encrypted1);
allocator_free_chunk(&decrypted1);
tester->assert_true(tester, (crypter->destroy(crypter) == SUCCESS), "destroy call test");
@@ -130,11 +130,77 @@ void test_aes_cbc_crypter(tester_t *tester)
logger->log_chunk(logger,RAW,"expected decrypted :", &data2);
logger->log_chunk(logger,RAW,"decrypted :", &decrypted2);
allocator_free_chunk(&encrypted2);
allocator_free_chunk(&decrypted2);
/*
* Test 3 of RFC3603
* Key : 0x56e47a38c5598974bc46903dba290349
* IV : 0x8ce82eefbea0da3c44699ed7db51b7d9
* Plaintext : 0xa0a1a2a3a4a5a6a7a8a9aaabacadaeaf
* b0b1b2b3b4b5b6b7b8b9babbbcbdbebf
* c0c1c2c3c4c5c6c7c8c9cacbcccdcecf
* d0d1d2d3d4d5d6d7d8d9dadbdcdddedf
* Ciphertext: 0xc30e32ffedc0774e6aff6af0869f71aa
* 0f3af07a9a31a9c684db207eb0ef8e4e
* 35907aa632c3ffdf868bb7b29d3d46ad
* 83ce9f9a102ee99d49a53e87f4c3da55
*/
u_int8_t key3[] = {0x56,0xe4,0x7a,0x38,0xc5,0x59,0x89,0x74,
0xbc,0x46,0x90,0x3d,0xba,0x29,0x03,0x49};
chunk_t key3_chunk = {ptr: key3, len : 16};
u_int8_t iv3[] = {0x8c,0xe8,0x2e,0xef,0xbe,0xa0,0xda,0x3c,
0x44,0x69,0x9e,0xd7,0xdb,0x51,0xb7,0xd9};
chunk_t iv3_chunk = {ptr: iv3, len : 16};
u_int8_t ciphertext3[] = { 0xc3,0x0e,0x32,0xff,0xed,0xc0,0x77,0x4e,
0x6a,0xff,0x6a,0xf0,0x86,0x9f,0x71,0xaa,
0x0f,0x3a,0xf0,0x7a,0x9a,0x31,0xa9,0xc6,
0x84,0xdb,0x20,0x7e,0xb0,0xef,0x8e,0x4e,
0x35,0x90,0x7a,0xa6,0x32,0xc3,0xff,0xdf,
0x86,0x8b,0xb7,0xb2,0x9d,0x3d,0x46,0xad,
0x83,0xce,0x9f,0x9a,0x10,0x2e,0xe9,0x9d,
0x49,0xa5,0x3e,0x87,0xf4,0xc3,0xda,0x55};
chunk_t expected_encrypted3 = {ptr: ciphertext3, len : 64};
u_int8_t plaintext3[] = {0xa0,0xa1,0xa2,0xa3,0xa4,0xa5,0xa6,0xa7,
0xa8,0xa9,0xaa,0xab,0xac,0xad,0xae,0xaf,
0xb0,0xb1,0xb2,0xb3,0xb4,0xb5,0xb6,0xb7,
0xb8,0xb9,0xba,0xbb,0xbc,0xbd,0xbe,0xbf,
0xc0,0xc1,0xc2,0xc3,0xc4,0xc5,0xc6,0xc7,
0xc8,0xc9,0xca,0xcb,0xcc,0xcd,0xce,0xcf,
0xd0,0xd1,0xd2,0xd3,0xd4,0xd5,0xd6,0xd7,
0xd8,0xd9,0xda,0xdb,0xdc,0xdd,0xde,0xdf};
chunk_t data3 = {ptr: plaintext3, len : 64};
chunk_t encrypted3;
chunk_t decrypted3;
crypter = (crypter_t *) aes_cbc_crypter_create(16);
tester->assert_true(tester, (crypter != NULL), "create call test");
tester->assert_true(tester, (crypter->set_key(crypter,key3_chunk) == SUCCESS), "set_key call test");
tester->assert_true(tester, (crypter->encrypt(crypter,data3,iv3_chunk,&encrypted3) == SUCCESS), "encrypt call test");
tester->assert_true(tester, (memcmp(encrypted3.ptr, expected_encrypted3.ptr, 64) == 0), "Encrypted value");
logger->log_chunk(logger,RAW,"exptected encrypted :", &expected_encrypted3);
logger->log_chunk(logger,RAW,"encrypted :", &encrypted3);
tester->assert_true(tester, (crypter->decrypt(crypter,encrypted3,iv3_chunk,&decrypted3) == SUCCESS), "decrypt call test");
allocator_free_chunk(&encrypted3);
tester->assert_true(tester, (memcmp(decrypted3.ptr, plaintext3, 64) == 0), "decrypted value");
logger->log_chunk(logger,RAW,"expected decrypted :", &data3);
logger->log_chunk(logger,RAW,"decrypted :", &decrypted3);
allocator_free_chunk(&decrypted3);
tester->assert_true(tester, (crypter->destroy(crypter) == SUCCESS), "destroy call test");
global_logger_manager->destroy_logger(global_logger_manager,logger);
}
Source/charon/transforms/crypters/aes_cbc_crypter.c
+169 -185
View File
@@ -84,34 +84,52 @@ struct private_aes_cbc_crypter_t {
*/
u_int32_t blocksize;
/**
* Decrypts a block.
*
* No memory gets allocated.
*
* @param this calling object
* @param[in] in_blk block to decrypt
* @param[out] out_blk decrypted data are written to this location
*/
void (*decrypt_block) (const private_aes_cbc_crypter_t *this, const unsigned char in_blk[], unsigned char out_blk[]);
/**
* Encrypts a block.
*
* No memory gets allocated.
*
* @param this calling object
* @param[in] in_blk block to encrypt
* @param[out] out_blk encrypted data are written to this location
*/
void (*encrypt_block) (const private_aes_cbc_crypter_t *this, const unsigned char in_blk[], unsigned char out_blk[]);
};
/* ugly macro stuff */
/*******************************/
// CONFIGURATION OPTIONS (see also aes.h)
//
// 1. Define UNROLL for full loop unrolling in encryption and decryption.
// 2. Define PARTIAL_UNROLL to unroll two loops in encryption and decryption.
// 3. Define FIXED_TABLES for compiled rather than dynamic tables.
// 4. Define FF_TABLES to use tables for field multiplies and inverses.
// Do not enable this without understanding stack space requirements.
// 5. Define ARRAYS to use arrays to hold the local state block. If this
// is not defined, individually declared 32-bit words are used.
// 6. Define FAST_VARIABLE if a high speed variable block implementation
// is needed (essentially three separate fixed block size code sequences)
// 7. Define either ONE_TABLE or FOUR_TABLES for a fast table driven
// version using 1 table (2 kbytes of table space) or 4 tables (8
// kbytes of table space) for higher speed.
// 8. Define either ONE_LR_TABLE or FOUR_LR_TABLES for a further speed
// increase by using tables for the last rounds but with more table
// space (2 or 8 kbytes extra).
// 9. If neither ONE_TABLE nor FOUR_TABLES is defined, a compact but
// slower version is provided.
// 10. If fast decryption key scheduling is needed define ONE_IM_TABLE
// or FOUR_IM_TABLES for higher speed (2 or 8 kbytes extra).
/* 1. Define UNROLL for full loop unrolling in encryption and decryption.
* 2. Define PARTIAL_UNROLL to unroll two loops in encryption and decryption.
* 3. Define FIXED_TABLES for compiled rather than dynamic tables.
* 4. Define FF_TABLES to use tables for field multiplies and inverses.
* Do not enable this without understanding stack space requirements.
* 5. Define ARRAYS to use arrays to hold the local state block. If this
* is not defined, individually declared 32-bit words are used.
* 6. Define FAST_VARIABLE if a high speed variable block implementation
* is needed (essentially three separate fixed block size code sequences)
* 7. Define either ONE_TABLE or FOUR_TABLES for a fast table driven
* version using 1 table (2 kbytes of table space) or 4 tables (8
* kbytes of table space) for higher speed.
* 8. Define either ONE_LR_TABLE or FOUR_LR_TABLES for a further speed
* increase by using tables for the last rounds but with more table
* space (2 or 8 kbytes extra).
* 9. If neither ONE_TABLE nor FOUR_TABLES is defined, a compact but
* slower version is provided.
* 10. If fast decryption key scheduling is needed define ONE_IM_TABLE
* or FOUR_IM_TABLES for higher speed (2 or 8 kbytes extra).
*/
#define UNROLL
//#define PARTIAL_UNROLL
@@ -150,14 +168,20 @@ struct private_aes_cbc_crypter_t {
#error an illegal block size has been specified
#endif
// upr(x,n): rotates bytes within words by n positions, moving bytes
// to higher index positions with wrap around into low positions
// ups(x,n): moves bytes by n positions to higher index positions in
// words but without wrap around
// bval(x,n): extracts a byte from a word
/**
* Rotates bytes within words by n positions, moving bytes
* to higher index positions with wrap around into low positions.
*/
#define upr(x,n) (((x) << 8 * (n)) | ((x) >> (32 - 8 * (n))))
/**
* Moves bytes by n positions to higher index positions in
* words but without wrap around.
*/
#define ups(x,n) ((x) << 8 * (n))
/**
* Extracts a byte from a word.
*/
#define bval(x,n) ((unsigned char)((x) >> 8 * (n)))
#define bytes2word(b0, b1, b2, b3) \
((u_int32_t)(b3) << 24 | (u_int32_t)(b2) << 16 | (u_int32_t)(b1) << 8 | (b0))
@@ -941,38 +965,7 @@ static void gen_tabs(void)
f2 ^= f4 ^ f8 ^ upr(f2 ^ f9,3) ^ upr(f4 ^ f9,2) ^ upr(f9,1))
#endif
// Subroutine to set the block size (if variable) in bytes, legal
// values being 16, 24 and 32.
#if defined(AES_BLOCK_SIZE)
#define nc (AES_BLOCK_SIZE / 4)
#else
#define nc (cx->aes_Ncol)
void aes_set_blk(private_aes_cbc_crypter_t *cx, int n_bytes)
{
#if !defined(FIXED_TABLES)
if(!tab_gen) { gen_tabs(); tab_gen = 1; }
#endif
switch(n_bytes) {
case 32: /* bytes */
case 256: /* bits */
nc = 8;
break;
case 24: /* bytes */
case 192: /* bits */
nc = 6;
break;
case 16: /* bytes */
case 128: /* bits */
default:
nc = 4;
break;
}
}
#endif
#define nc (this->aes_Ncol)
// Initialise the key schedule from the user supplied key. The key
// length is now specified in bytes - 16, 24 or 32 as appropriate.
@@ -1015,110 +1008,6 @@ switch(nc) \
#endif
void aes_set_key(private_aes_cbc_crypter_t *cx, const unsigned char in_key[], int n_bytes, const int f)
{ u_int32_t *kf, *kt, rci;
#if !defined(FIXED_TABLES)
if(!tab_gen) { gen_tabs(); tab_gen = 1; }
#endif
switch(n_bytes) {
case 32: /* bytes */
case 256: /* bits */
cx->aes_Nkey = 8;
break;
case 24: /* bytes */
case 192: /* bits */
cx->aes_Nkey = 6;
break;
case 16: /* bytes */
case 128: /* bits */
default:
cx->aes_Nkey = 4;
break;
}
cx->aes_Nrnd = (cx->aes_Nkey > nc ? cx->aes_Nkey : nc) + 6;
cx->aes_e_key[0] = const_word_in(in_key );
cx->aes_e_key[1] = const_word_in(in_key + 4);
cx->aes_e_key[2] = const_word_in(in_key + 8);
cx->aes_e_key[3] = const_word_in(in_key + 12);
kf = cx->aes_e_key;
kt = kf + nc * (cx->aes_Nrnd + 1) - cx->aes_Nkey;
rci = 0;
switch(cx->aes_Nkey)
{
case 4: do
{ kf[4] = kf[0] ^ ls_box(kf[3],3) ^ rcon_tab[rci++];
kf[5] = kf[1] ^ kf[4];
kf[6] = kf[2] ^ kf[5];
kf[7] = kf[3] ^ kf[6];
kf += 4;
}
while(kf < kt);
break;
case 6: cx->aes_e_key[4] = const_word_in(in_key + 16);
cx->aes_e_key[5] = const_word_in(in_key + 20);
do
{ kf[ 6] = kf[0] ^ ls_box(kf[5],3) ^ rcon_tab[rci++];
kf[ 7] = kf[1] ^ kf[ 6];
kf[ 8] = kf[2] ^ kf[ 7];
kf[ 9] = kf[3] ^ kf[ 8];
kf[10] = kf[4] ^ kf[ 9];
kf[11] = kf[5] ^ kf[10];
kf += 6;
}
while(kf < kt);
break;
case 8: cx->aes_e_key[4] = const_word_in(in_key + 16);
cx->aes_e_key[5] = const_word_in(in_key + 20);
cx->aes_e_key[6] = const_word_in(in_key + 24);
cx->aes_e_key[7] = const_word_in(in_key + 28);
do
{ kf[ 8] = kf[0] ^ ls_box(kf[7],3) ^ rcon_tab[rci++];
kf[ 9] = kf[1] ^ kf[ 8];
kf[10] = kf[2] ^ kf[ 9];
kf[11] = kf[3] ^ kf[10];
kf[12] = kf[4] ^ ls_box(kf[11],0);
kf[13] = kf[5] ^ kf[12];
kf[14] = kf[6] ^ kf[13];
kf[15] = kf[7] ^ kf[14];
kf += 8;
}
while (kf < kt);
break;
}
if(!f)
{ u_int32_t i;
kt = cx->aes_d_key + nc * cx->aes_Nrnd;
kf = cx->aes_e_key;
cpy(kt, kf); kt -= 2 * nc;
for(i = 1; i < cx->aes_Nrnd; ++i)
{
#if defined(ONE_TABLE) || defined(FOUR_TABLES)
#if !defined(ONE_IM_TABLE) && !defined(FOUR_IM_TABLES)
u_int32_t f2, f4, f8, f9;
#endif
mix(kt, kf);
#else
cpy(kt, kf);
#endif
kt -= 2 * nc;
}
cpy(kt, kf);
}
}
// y = output word, x = input word, r = row, c = column
// for r = 0, 1, 2 and 3 = column accessed for row r
@@ -1355,9 +1244,12 @@ switch(nc) \
#endif
#endif
void aes_encrypt(const private_aes_cbc_crypter_t *cx, const unsigned char in_blk[], unsigned char out_blk[])
/**
* Implementation of private_aes_cbc_crypter_t.encrypt_block.
*/
static void encrypt_block(const private_aes_cbc_crypter_t *this, const unsigned char in_blk[], unsigned char out_blk[])
{ u_int32_t locals(b0, b1);
const u_int32_t *kp = cx->aes_e_key;
const u_int32_t *kp = this->aes_e_key;
#if !defined(ONE_TABLE) && !defined(FOUR_TABLES)
u_int32_t f2;
@@ -1367,7 +1259,7 @@ void aes_encrypt(const private_aes_cbc_crypter_t *cx, const unsigned char in_blk
#if defined(UNROLL)
switch(cx->aes_Nrnd)
switch(this->aes_Nrnd)
{
case 14: round(fwd_rnd, b1, b0, kp );
round(fwd_rnd, b0, b1, kp + nc ); kp += 2 * nc;
@@ -1388,7 +1280,7 @@ void aes_encrypt(const private_aes_cbc_crypter_t *cx, const unsigned char in_blk
#elif defined(PARTIAL_UNROLL)
{ u_int32_t rnd;
for(rnd = 0; rnd < (cx->aes_Nrnd >> 1) - 1; ++rnd)
for(rnd = 0; rnd < (this->aes_Nrnd >> 1) - 1; ++rnd)
{
round(fwd_rnd, b1, b0, kp);
round(fwd_rnd, b0, b1, kp + nc); kp += 2 * nc;
@@ -1400,7 +1292,7 @@ void aes_encrypt(const private_aes_cbc_crypter_t *cx, const unsigned char in_blk
#else
{ u_int32_t rnd;
for(rnd = 0; rnd < cx->aes_Nrnd - 1; ++rnd)
for(rnd = 0; rnd < this->aes_Nrnd - 1; ++rnd)
{
round(fwd_rnd, b1, b0, kp);
l_copy(b0, b1); kp += nc;
@@ -1413,9 +1305,12 @@ void aes_encrypt(const private_aes_cbc_crypter_t *cx, const unsigned char in_blk
state_out(out_blk, b0);
}
void aes_decrypt(const private_aes_cbc_crypter_t *cx, const unsigned char in_blk[], unsigned char out_blk[])
/**
* Implementation of private_aes_cbc_crypter_t.decrypt_block.
*/
static void decrypt_block(const private_aes_cbc_crypter_t *this, const unsigned char in_blk[], unsigned char out_blk[])
{ u_int32_t locals(b0, b1);
const u_int32_t *kp = cx->aes_d_key;
const u_int32_t *kp = this->aes_d_key;
#if !defined(ONE_TABLE) && !defined(FOUR_TABLES)
u_int32_t f2, f4, f8, f9;
@@ -1425,7 +1320,7 @@ void aes_decrypt(const private_aes_cbc_crypter_t *cx, const unsigned char in_blk
#if defined(UNROLL)
switch(cx->aes_Nrnd)
switch(this->aes_Nrnd)
{
case 14: round(inv_rnd, b1, b0, kp );
round(inv_rnd, b0, b1, kp + nc ); kp += 2 * nc;
@@ -1446,7 +1341,7 @@ void aes_decrypt(const private_aes_cbc_crypter_t *cx, const unsigned char in_blk
#elif defined(PARTIAL_UNROLL)
{ u_int32_t rnd;
for(rnd = 0; rnd < (cx->aes_Nrnd >> 1) - 1; ++rnd)
for(rnd = 0; rnd < (this->aes_Nrnd >> 1) - 1; ++rnd)
{
round(inv_rnd, b1, b0, kp);
round(inv_rnd, b0, b1, kp + nc); kp += 2 * nc;
@@ -1458,7 +1353,7 @@ void aes_decrypt(const private_aes_cbc_crypter_t *cx, const unsigned char in_blk
#else
{ u_int32_t rnd;
for(rnd = 0; rnd < cx->aes_Nrnd - 1; ++rnd)
for(rnd = 0; rnd < this->aes_Nrnd - 1; ++rnd)
{
round(inv_rnd, b1, b0, kp);
l_copy(b0, b1); kp += nc;
@@ -1471,11 +1366,6 @@ void aes_decrypt(const private_aes_cbc_crypter_t *cx, const unsigned char in_blk
state_out(out_blk, b0);
}
/* *************************/
/**
* Implementation of crypter_t.decrypt.
*/
@@ -1506,7 +1396,7 @@ static status_t decrypt (private_aes_cbc_crypter_t *this, chunk_t data, chunk_t
in+=pos;
out+=pos;
while(pos>=0) {
aes_decrypt(this,in,out);
this->decrypt_block(this,in,out);
if (pos==0)
iv_i=(const u_int32_t*) (iv.ptr);
else
@@ -1561,7 +1451,7 @@ static status_t encrypt (private_aes_cbc_crypter_t *this, chunk_t data, chunk_t
*((u_int32_t *)(&out[ 4])) = iv_i[1]^*((const u_int32_t *)(&in[ 4]));
*((u_int32_t *)(&out[ 8])) = iv_i[2]^*((const u_int32_t *)(&in[ 8]));
*((u_int32_t *)(&out[12])) = iv_i[3]^*((const u_int32_t *)(&in[12]));
aes_encrypt(this,out,out);
this->encrypt_block(this,out,out);
in+=16;
out+=16;
pos+=16;
@@ -1582,7 +1472,94 @@ static size_t get_block_size (private_aes_cbc_crypter_t *this)
*/
static status_t set_key (private_aes_cbc_crypter_t *this, chunk_t key)
{
aes_set_key(this, key.ptr, key.len,0);
u_int32_t *kf, *kt, rci, f = 0;
u_int8_t *in_key = key.ptr;
if (key.len != this->blocksize)
{
return INVALID_ARG;
}
this->aes_Nrnd = (this->aes_Nkey > (this->aes_Ncol) ? this->aes_Nkey : (this->aes_Ncol)) + 6;
this->aes_e_key[0] = const_word_in(in_key );
this->aes_e_key[1] = const_word_in(in_key + 4);
this->aes_e_key[2] = const_word_in(in_key + 8);
this->aes_e_key[3] = const_word_in(in_key + 12);
kf = this->aes_e_key;
kt = kf + nc * (this->aes_Nrnd + 1) - this->aes_Nkey;
rci = 0;
switch(this->aes_Nkey)
{
case 4: do
{ kf[4] = kf[0] ^ ls_box(kf[3],3) ^ rcon_tab[rci++];
kf[5] = kf[1] ^ kf[4];
kf[6] = kf[2] ^ kf[5];
kf[7] = kf[3] ^ kf[6];
kf += 4;
}
while(kf < kt);
break;
case 6: this->aes_e_key[4] = const_word_in(in_key + 16);
this->aes_e_key[5] = const_word_in(in_key + 20);
do
{ kf[ 6] = kf[0] ^ ls_box(kf[5],3) ^ rcon_tab[rci++];
kf[ 7] = kf[1] ^ kf[ 6];
kf[ 8] = kf[2] ^ kf[ 7];
kf[ 9] = kf[3] ^ kf[ 8];
kf[10] = kf[4] ^ kf[ 9];
kf[11] = kf[5] ^ kf[10];
kf += 6;
}
while(kf < kt);
break;
case 8: this->aes_e_key[4] = const_word_in(in_key + 16);
this->aes_e_key[5] = const_word_in(in_key + 20);
this->aes_e_key[6] = const_word_in(in_key + 24);
this->aes_e_key[7] = const_word_in(in_key + 28);
do
{ kf[ 8] = kf[0] ^ ls_box(kf[7],3) ^ rcon_tab[rci++];
kf[ 9] = kf[1] ^ kf[ 8];
kf[10] = kf[2] ^ kf[ 9];
kf[11] = kf[3] ^ kf[10];
kf[12] = kf[4] ^ ls_box(kf[11],0);
kf[13] = kf[5] ^ kf[12];
kf[14] = kf[6] ^ kf[13];
kf[15] = kf[7] ^ kf[14];
kf += 8;
}
while (kf < kt);
break;
}
if(!f)
{ u_int32_t i;
kt = this->aes_d_key + nc * this->aes_Nrnd;
kf = this->aes_e_key;
cpy(kt, kf); kt -= 2 * nc;
for(i = 1; i < this->aes_Nrnd; ++i)
{
#if defined(ONE_TABLE) || defined(FOUR_TABLES)
#if !defined(ONE_IM_TABLE) && !defined(FOUR_IM_TABLES)
u_int32_t f2, f4, f8, f9;
#endif
mix(kt, kf);
#else
cpy(kt, kf);
#endif
kt -= 2 * nc;
}
cpy(kt, kf);
}
return SUCCESS;
}
@@ -1595,7 +1572,9 @@ static status_t destroy (private_aes_cbc_crypter_t *this)
return SUCCESS;
}
/*
* Described in header
*/
aes_cbc_crypter_t *aes_cbc_crypter_create(size_t blocksize)
{
private_aes_cbc_crypter_t *this = allocator_alloc_thing(private_aes_cbc_crypter_t);
@@ -1610,19 +1589,21 @@ aes_cbc_crypter_t *aes_cbc_crypter_create(size_t blocksize)
switch(blocksize) {
case 32: /* bytes */
this->aes_Ncol = 8;
this->aes_Nkey = 8;
this->blocksize = blocksize;
break;
case 24: /* bytes */
this->aes_Ncol = 6;
this->aes_Nkey = 6;
this->blocksize = blocksize;
break;
case 16: /* bytes */
default:
this->aes_Ncol = 4;
this->aes_Nkey = 4;
this->blocksize = 16;
break;
}
/* functions of crypter_t interface */
this->public.crypter_interface.encrypt = (status_t (*) (crypter_t *, chunk_t,chunk_t, chunk_t *)) encrypt;
@@ -1634,6 +1615,9 @@ aes_cbc_crypter_t *aes_cbc_crypter_create(size_t blocksize)
/* public functions */
this->public.destroy = (status_t (*) (aes_cbc_crypter_t *)) destroy;
/* private functions */
this->decrypt_block = decrypt_block;
this->encrypt_block = encrypt_block;
return &(this->public);
}