/*
* Implementation of RFC 5649 variant of AES Key Wrap, using Cryptlib
* to supply the AES ECB encryption and decryption functions.
*
* Note that there are two different block sizes involved here: the
* key wrap algorithm deals entirely with 64-bit blocks, while AES
* itself deals with 128-bit blocks. In practice, this is not as
* confusing as it sounds, because we combine two 64-bit blocks to
* create one 128-bit block just prior to performing an AES operation,
* then split the result back to 64-bit blocks immediately afterwards.
*/
#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>
#include <string.h>
#include <assert.h>
#include "cryptech.h"
/*
* How long the ciphertext will be for a given plaintext length.
*/
size_t hal_aes_keywrap_ciphertext_length(const size_t plaintext_length)
{
return (plaintext_length + 15) & ~7;
}
/*
* Check the KEK, then load it into the AES core.
* Note that our AES core only supports 128 and 256 bit keys.
*/
typedef enum { KEK_encrypting, KEK_decrypting } kek_action_t;
static hal_error_t load_kek(const uint8_t *K, const size_t K_len, const kek_action_t action)
{
uint8_t config[4];
hal_error_t err;
if (K == NULL)
return HAL_ERROR_BAD_ARGUMENTS;
memset(config, 0, sizeof(config));
switch (K_len) {
case bitsToBytes(128):
config[3] &= ~AES_CONFIG_KEYLEN;
break;
case bitsToBytes(256):
config[3] |= AES_CONFIG_KEYLEN;
break;
case bitsToBytes(192):
return HAL_ERROR_UNSUPPORTED_KEY;
default:
return HAL_ERROR_BAD_ARGUMENTS;
}
switch (action) {
case KEK_encrypting:
config[3] |= AES_CONFIG_ENCDEC;
break;
case KEK_decrypting:
config[3] &= !AES_CONFIG_ENCDEC;
break;
default:
return HAL_ERROR_BAD_ARGUMENTS;
}
/*
* Load the KEK and tell the core to expand it.
*/
if ((err = hal_io_write(AES_ADDR_KEY0, K, K_len)) != HAL_OK ||
(err = hal_io_write(AES_ADDR_CONFIG, config, sizeof(config))) != HAL_OK ||
(err = hal_io_init(AES_ADDR_CTRL)) != HAL_OK)
return err;
return HAL_OK;
}
/*
* Process one block. Since AES Key Wrap always deals with 64-bit
* half blocks and since the bus is going to break this up into 32-bit
* words no matter what we do, we can eliminate a few gratuitous
* memcpy() operations by receiving our arguments as two half blocks.
*
* Since the length of these half blocks is constant, there's no real
* point in passing the length as an argument, we'd just be checking a
* constant against a constant and a smart compiler will optimize
* the whole check out.
*
* Just be VERY careful if you change anything here.
*/
static hal_error_t do_block(uint8_t *b1, uint8_t *b2)
{
hal_error_t err;
assert(b1 != NULL && b2 != NULL);
if ((err = hal_io_write(AES_ADDR_BLOCK0, b1, 8)) != HAL_OK ||
(err = hal_io_write(AES_ADDR_BLOCK2, b2, 8)) != HAL_OK ||
(err = hal_io_next(AES_ADDR_CTRL)) != HAL_OK ||
(err = hal_io_wait_ready(AES_ADDR_STATUS)) != HAL_OK ||
(err = hal_io_read(AES_ADDR_RESULT0, b1, 8)) != HAL_OK ||
(err = hal_io_read(AES_ADDR_RESULT2, b2, 8)) != HAL_OK)
return err;
return HAL_OK;
}
/*
* Wrap plaintext Q using KEK K, placing result in C.
*
* Q and C can overlap. For encrypt-in-place, use Q = C + 8 (that is,
* leave 8 empty bytes before the plaintext).
*
* Use hal_aes_keywrap_ciphertext_length() to calculate the correct
* buffer size.
*/
hal_error_t hal_aes_keywrap(const uint8_t *K, const size_t K_len,
const uint8_t * const Q,
const size_t m,
uint8_t *C,
size_t *C_len)
{
const size_t calculated_C_len = hal_aes_keywrap_ciphertext_length(m);
hal_error_t err;
uint32_t n;
long i, j;
assert(calculated_C_len % 8 == 0);
if (Q == NULL || C == NULL || C_len == NULL || *C_len < calculated_C_len)
return HAL_ERROR_BAD_ARGUMENTS;
if ((err = load_kek(K, K_len, KEK_encrypting)) != HAL_OK)
return err;
*C_len = calculated_C_len;
if (C + 8 != Q)
memmove(C + 8, Q, m);
if (m % 8 != 0)
memset(C + 8 + m, 0, 8 - (m % 8));
C[0] = 0xA6;
C[1] = 0x59;
C[2] = 0x59;
C[3] = 0xA6;
C[4] = (m >> 24) & 0xFF;
C[5] = (m >> 16) & 0xFF;
C[6] = (m >> 8) & 0xFF;
C[7] = (m >> 0) & 0xFF;
n = calculated_C_len/8 - 1;
if (n == 1) {
if ((err = do_block(C, C + 8)) != HAL_OK)
return err;
}
else {
for (j = 0; j <= 5; j++) {
for (i = 1; i <= n; i++) {
uint32_t t = n * j + i;
if ((err = do_block(C, C + i * 8)) != HAL_OK)
return err;
C[7] ^= t & 0xFF; t >>= 8;
C[6] ^= t & 0xFF; t >>= 8;
C[5] ^= t & 0xFF; t >>= 8;
C[4] ^= t & 0xFF;
}
}
}
return HAL_OK;
}
/*
* Unwrap ciphertext C using KEK K, placing result in Q.
*
* Q should be the same size as C. Q and C can overlap.
*/
hal_error_t hal_aes_keyunwrap(const uint8_t *K, const size_t K_len,
const uint8_t * const C,
const size_t C_len,
uint8_t *Q,
size_t *Q_len)
{
hal_error_t err;
uint32_t n;
long i, j;
size_t m;
if (C == NULL || Q == NULL || C_len % 8 != 0 || C_len < 16 || Q_len == NULL || *Q_len < C_len)
return HAL_ERROR_BAD_ARGUMENTS;
if ((err = load_kek(K, K_len, KEK_decrypting)) != HAL_OK)
return err;
n = (C_len / 8) - 1;
if (Q != C)
memmove(Q, C, C_len);
if (n == 1) {
if ((err = do_block(Q, Q + 8)) != HAL_OK)
return err;
}
else {
for (j = 5; j >= 0; j--) {
for (i = n; i >= 1; i--) {
uint32_t t = n * j + i;
Q[7] ^= t & 0xFF; t >>= 8;
Q[6] ^= t & 0xFF; t >>= 8;
Q[5] ^= t & 0xFF; t >>= 8;
Q[4] ^= t & 0xFF;
if ((err = do_block(Q, Q + i * 8)) != HAL_OK)
return err;
}
}
}
if (Q[0] != 0xA6 || Q[1] != 0x59 || Q[2] != 0x59 || Q[3] != 0xA6)
return HAL_ERROR_KEYWRAP_BAD_MAGIC;
m = (((((Q[4] << 8) + Q[5]) << 8) + Q[6]) << 8) + Q[7];
if (m <= 8 * (n - 1) || m > 8 * n)
return HAL_ERROR_KEYWRAP_BAD_LENGTH;
if (m % 8 != 0)
for (i = m + 8; i < 8 * (n + 1); i++)
if (Q[i] != 0x00)
return HAL_ERROR_KEYWRAP_BAD_PADDING;
*Q_len = m;
memmove(Q, Q + 8, m);
return HAL_OK;
}
/*
* "Any programmer who fails to comply with the standard naming, formatting,
* or commenting conventions should be shot. If it so happens that it is
* inconvenient to shoot him, then he is to be politely requested to recode
* his program in adherence to the above standard."
* -- Michael Spier, Digital Equipment Corporation
*
* Local variables:
* indent-tabs-mode: nil
* End:
*/
