Modo de encapsulación de clave: confidencialidad y a prueba de manipulaciones, adecuado para cifrar una pequeña cantidad de datos, como claves; dividido en modo de llenado y modo de no llenado;
| RFC 3217 | Envoltura de teclas Triple-DES y RC2 |
| RFC 3394 | Algoritmo de ajuste de clave del estándar de cifrado avanzado (AES) |
| RFC 5649 | Ajuste de clave de estándar de cifrado avanzado (AES) con algoritmo de relleno |
implementación de referencia de openssl
warp128.c:
size_t CRYPTO_128_wrap(void *key, const unsigned char *iv,
unsigned char *out,
const unsigned char *in, size_t inlen,
block128_f block)
{
unsigned char *A, B[16], *R;
size_t i, j, t;
if ((inlen & 0x7) || (inlen < 16) || (inlen > CRYPTO128_WRAP_MAX))
return 0;
A = B;
t = 1;
memmove(out + 8, in, inlen);
if (!iv)
iv = default_iv;
memcpy(A, iv, 8);
for (j = 0; j < 6; j++) {
R = out + 8;
for (i = 0; i < inlen; i += 8, t++, R += 8) {
memcpy(B + 8, R, 8);
block(B, B, key);
A[7] ^= (unsigned char)(t & 0xff);
if (t > 0xff) {
A[6] ^= (unsigned char)((t >> 8) & 0xff);
A[5] ^= (unsigned char)((t >> 16) & 0xff);
A[4] ^= (unsigned char)((t >> 24) & 0xff);
}
memcpy(R, B + 8, 8);
}
}
memcpy(out, A, 8);
return inlen + 8;
}
static size_t crypto_128_unwrap_raw(void *key, unsigned char *iv,
unsigned char *out,
const unsigned char *in, size_t inlen,
block128_f block)
{
unsigned char *A, B[16], *R;
size_t i, j, t;
inlen -= 8;
if ((inlen & 0x7) || (inlen < 16) || (inlen > CRYPTO128_WRAP_MAX))
return 0;
A = B;
t = 6 * (inlen >> 3);
memcpy(A, in, 8);
memmove(out, in + 8, inlen);
for (j = 0; j < 6; j++) {
R = out + inlen - 8;
for (i = 0; i < inlen; i += 8, t--, R -= 8) {
A[7] ^= (unsigned char)(t & 0xff);
if (t > 0xff) {
A[6] ^= (unsigned char)((t >> 8) & 0xff);
A[5] ^= (unsigned char)((t >> 16) & 0xff);
A[4] ^= (unsigned char)((t >> 24) & 0xff);
}
memcpy(B + 8, R, 8);
block(B, B, key);
memcpy(R, B + 8, 8);
}
}
memcpy(iv, A, 8);
return inlen;
}
size_t CRYPTO_128_unwrap(void *key, const unsigned char *iv,
unsigned char *out, const unsigned char *in,
size_t inlen, block128_f block)
{
size_t ret;
unsigned char got_iv[8];
ret = crypto_128_unwrap_raw(key, got_iv, out, in, inlen, block);
if (ret == 0)
return 0;
if (!iv)
iv = default_iv;
if (CRYPTO_memcmp(got_iv, iv, 8)) {
OPENSSL_cleanse(out, ret);
return 0;
}
return ret;
}
size_t CRYPTO_128_wrap_pad(void *key, const unsigned char *icv,
unsigned char *out,
const unsigned char *in, size_t inlen,
block128_f block)
{
/* n: number of 64-bit blocks in the padded key data
*
* If length of plain text is not a multiple of 8, pad the plain text octet
* string on the right with octets of zeros, where final length is the
* smallest multiple of 8 that is greater than length of plain text.
* If length of plain text is a multiple of 8, then there is no padding. */
const size_t blocks_padded = (inlen + 7) / 8; /* CEILING(m/8) */
const size_t padded_len = blocks_padded * 8;
const size_t padding_len = padded_len - inlen;
/* RFC 5649 section 3: Alternative Initial Value */
unsigned char aiv[8];
int ret;
/* Section 1: use 32-bit fixed field for plaintext octet length */
if (inlen == 0 || inlen >= CRYPTO128_WRAP_MAX)
return 0;
/* Section 3: Alternative Initial Value */
if (!icv)
memcpy(aiv, default_aiv, 4);
else
memcpy(aiv, icv, 4); /* Standard doesn't mention this. */
aiv[4] = (inlen >> 24) & 0xFF;
aiv[5] = (inlen >> 16) & 0xFF;
aiv[6] = (inlen >> 8) & 0xFF;
aiv[7] = inlen & 0xFF;
if (padded_len == 8) {
/*
* Section 4.1 - special case in step 2: If the padded plaintext
* contains exactly eight octets, then prepend the AIV and encrypt
* the resulting 128-bit block using AES in ECB mode.
*/
memmove(out + 8, in, inlen);
memcpy(out, aiv, 8);
memset(out + 8 + inlen, 0, padding_len);
block(out, out, key);
ret = 16; /* AIV + padded input */
} else {
memmove(out, in, inlen);
memset(out + inlen, 0, padding_len); /* Section 4.1 step 1 */
ret = CRYPTO_128_wrap(key, aiv, out, out, padded_len, block);
}
return ret;
}
size_t CRYPTO_128_unwrap_pad(void *key, const unsigned char *icv,
unsigned char *out,
const unsigned char *in, size_t inlen,
block128_f block)
{
/* n: number of 64-bit blocks in the padded key data */
size_t n = inlen / 8 - 1;
size_t padded_len;
size_t padding_len;
size_t ptext_len;
/* RFC 5649 section 3: Alternative Initial Value */
unsigned char aiv[8];
static unsigned char zeros[8] = { 0x0 };
size_t ret;
/* Section 4.2: Ciphertext length has to be (n+1) 64-bit blocks. */
if ((inlen & 0x7) != 0 || inlen < 16 || inlen >= CRYPTO128_WRAP_MAX)
return 0;
if (inlen == 16) {
/*
* Section 4.2 - special case in step 1: When n=1, the ciphertext
* contains exactly two 64-bit blocks and they are decrypted as a
* single AES block using AES in ECB mode: AIV | P[1] = DEC(K, C[0] |
* C[1])
*/
unsigned char buff[16];
block(in, buff, key);
memcpy(aiv, buff, 8);
/* Remove AIV */
memcpy(out, buff + 8, 8);
padded_len = 8;
OPENSSL_cleanse(buff, inlen);
} else {
padded_len = inlen - 8;
ret = crypto_128_unwrap_raw(key, aiv, out, in, inlen, block);
if (padded_len != ret) {
OPENSSL_cleanse(out, inlen);
return 0;
}
}
/*
* Section 3: AIV checks: Check that MSB(32,A) = A65959A6. Optionally a
* user-supplied value can be used (even if standard doesn't mention
* this).
*/
if ((!icv && CRYPTO_memcmp(aiv, default_aiv, 4))
|| (icv && CRYPTO_memcmp(aiv, icv, 4))) {
OPENSSL_cleanse(out, inlen);
return 0;
}
/*
* Check that 8*(n-1) < LSB(32,AIV) <= 8*n. If so, let ptext_len =
* LSB(32,AIV).
*/
ptext_len = ((unsigned int)aiv[4] << 24)
| ((unsigned int)aiv[5] << 16)
| ((unsigned int)aiv[6] << 8)
| (unsigned int)aiv[7];
if (8 * (n - 1) >= ptext_len || ptext_len > 8 * n) {
OPENSSL_cleanse(out, inlen);
return 0;
}
/*
* Check that the rightmost padding_len octets of the output data are
* zero.
*/
padding_len = padded_len - ptext_len;
if (CRYPTO_memcmp(out + ptext_len, zeros, padding_len) != 0) {
OPENSSL_cleanse(out, inlen);
return 0;
}
/* Section 4.2 step 3: Remove padding */
return ptext_len;
}