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/* eax.c
* Encryption and decryption routines implementing the EAX' encryption mode
* Copyright 2010, Edward J. Beroset, edward.j.beroset@us.elster.com
*
* Wireshark - Network traffic analyzer
* By Gerald Combs <gerald@wireshark.org>
* Copyright 1998 Gerald Combs
*
* SPDX-License-Identifier: GPL-2.0-or-later
*/
#include "config.h"
#include "eax.h"
#include <stdlib.h>
#include <string.h>
/* Use libgcrypt for cipher libraries. */
#include <gcrypt.h>
typedef struct {
uint8_t L[EAX_SIZEOF_KEY];
uint8_t D[EAX_SIZEOF_KEY];
uint8_t Q[EAX_SIZEOF_KEY];
} eax_s;
static eax_s instance;
/* these are defined as macros so they'll be easy to redo in assembly if desired */
#define BLK_CPY(dst, src) { memcpy(dst, src, EAX_SIZEOF_KEY); }
#define BLK_XOR(dst, src) { int z; for (z=0; z < EAX_SIZEOF_KEY; z++) dst[z] ^= src[z]; }
static void Dbl(uint8_t *out, const uint8_t *in);
static void CTR(const uint8_t *ws, uint8_t *pK, uint8_t *pN, uint16_t SizeN);
static void CMAC(uint8_t *pK, uint8_t *ws, const uint8_t *pN, uint16_t SizeN);
static void dCMAC(uint8_t *pK, uint8_t *ws, const uint8_t *pN, uint16_t SizeN, const uint8_t *pC, uint16_t SizeC);
void AesEncrypt(unsigned char msg[EAX_SIZEOF_KEY], unsigned char key[EAX_SIZEOF_KEY]);
/*!
Decrypts cleartext data using EAX' mode (see ANSI Standard C12.22-2008).
@param[in] pN pointer to cleartext (canonified form)
@param[in] pK pointer to secret key
@param[in,out] pC pointer to ciphertext
@param[in] SizeN byte length of cleartext (pN) buffer
@param[in] SizeK byte length of secret key (pK)
@param[in] SizeC byte length of ciphertext (pC) buffer
@param[in] pMac four-byte Message Authentication Code
@param[in] Mode EAX_MODE_CLEARTEXT_AUTH or EAX_MODE_CIPHERTEXT_AUTH
@return true if message has been authenticated; false if not
authenticated, invalid Mode or error
*/
bool Eax_Decrypt(uint8_t *pN, uint8_t *pK, uint8_t *pC,
uint32_t SizeN, uint32_t SizeK, uint32_t SizeC, MAC_T *pMac,
uint8_t Mode)
{
uint8_t wsn[EAX_SIZEOF_KEY];
uint8_t wsc[EAX_SIZEOF_KEY];
int i;
/* key size must match this implementation */
if (SizeK != EAX_SIZEOF_KEY)
return false;
/* the key is new */
for (i = 0; i < EAX_SIZEOF_KEY; i++)
instance.L[i] = 0;
AesEncrypt(instance.L, pK);
Dbl(instance.D, instance.L);
Dbl(instance.Q, instance.D);
/* the key is set up */
/* first copy the nonce into our working space */
BLK_CPY(wsn, instance.D);
if (Mode == EAX_MODE_CLEARTEXT_AUTH) {
dCMAC(pK, wsn, pN, SizeN, pC, SizeC);
} else {
CMAC(pK, wsn, pN, SizeN);
}
/*
* In authentication mode the inputs are: pN, pK (and associated sizes),
* the result is the 4 byte MAC.
*/
if (Mode == EAX_MODE_CLEARTEXT_AUTH)
{
return (memcmp(pMac, &wsn[EAX_SIZEOF_KEY-sizeof(*pMac)], sizeof(*pMac)) ? false : true);
}
/*
* In cipher mode the inputs are: pN, pK, pP (and associated sizes),
* the results are pC (and its size) along with the 4 byte MAC.
*/
else if (Mode == EAX_MODE_CIPHERTEXT_AUTH)
{
if (SizeC == 0)
return (memcmp(pMac, &wsn[EAX_SIZEOF_KEY-sizeof(*pMac)], sizeof(*pMac)) ? false : true);
{
/* first copy the nonce into our working space */
BLK_CPY(wsc, instance.Q);
CMAC(pK, wsc, pC, SizeC);
BLK_XOR(wsc, wsn);
}
if (memcmp(pMac, &wsc[EAX_SIZEOF_KEY-sizeof(*pMac)], sizeof(*pMac)) == 0)
{
CTR(wsn, pK, pC, SizeC);
return true;
}
}
return false;
}
/* set up D or Q from L */
static void Dbl(uint8_t *out, const uint8_t *in)
{
int i;
uint8_t carry = 0;
/* this might be a lot more efficient in assembly language */
for (i=0; i < EAX_SIZEOF_KEY; i++)
{
out[i] = ( in[i] << 1 ) | carry;
carry = (in[i] & 0x80) ? 1 : 0;
}
if (carry)
out[0] ^= 0x87;
}
static void CMAC(uint8_t *pK, uint8_t *ws, const uint8_t *pN, uint16_t SizeN)
{
dCMAC(pK, ws, pN, SizeN, NULL, 0);
}
static void dCMAC(uint8_t *pK, uint8_t *ws, const uint8_t *pN, uint16_t SizeN, const uint8_t *pC, uint16_t SizeC)
{
gcry_cipher_hd_t cipher_hd;
uint8_t *work;
uint8_t *ptr;
uint16_t SizeT = SizeN + SizeC;
uint16_t worksize = SizeT;
/* worksize must be an integral multiple of 16 */
if (SizeT & 0xf) {
worksize += 0x10 - (worksize & 0xf);
}
work = (uint8_t *)g_malloc(worksize);
if (work == NULL) {
return;
}
memcpy(work, pN, SizeN);
if (pC != NULL) {
memcpy(&work[SizeN], pC, SizeC);
}
/*
* pad the data if necessary, and XOR Q or D, depending on
* whether data was padded or not
*/
if (worksize != SizeT) {
work[SizeT] = 0x80;
for (ptr = &work[SizeT+1]; ptr < &work[worksize]; ptr++)
*ptr = 0;
ptr= &work[worksize-0x10];
BLK_XOR(ptr, instance.Q);
} else {
ptr = &work[worksize-0x10];
BLK_XOR(ptr, instance.D);
}
/* open the cipher */
if (gcry_cipher_open(&cipher_hd, GCRY_CIPHER_AES128, GCRY_CIPHER_MODE_CBC,0)){/* GCRY_CIPHER_CBC_MAC)) { */
g_free(work);
return;
}
if (gcry_cipher_setkey(cipher_hd, pK, EAX_SIZEOF_KEY)) {
g_free(work);
gcry_cipher_close(cipher_hd);
return;
}
if (gcry_cipher_setiv(cipher_hd, ws, EAX_SIZEOF_KEY)) {
g_free(work);
gcry_cipher_close(cipher_hd);
return;
}
if (gcry_cipher_encrypt(cipher_hd, work, worksize, work, worksize)) {
g_free(work);
gcry_cipher_close(cipher_hd);
return;
}
memcpy(ws, ptr, EAX_SIZEOF_KEY);
g_free(work);
gcry_cipher_close(cipher_hd);
return;
}
static void CTR(const uint8_t *ws, uint8_t *pK, uint8_t *pN, uint16_t SizeN)
{
gcry_cipher_hd_t cipher_hd;
uint8_t ctr[EAX_SIZEOF_KEY];
BLK_CPY(ctr, ws);
ctr[12] &= 0x7f;
ctr[14] &= 0x7f;
/* open the cipher */
if (gcry_cipher_open(&cipher_hd, GCRY_CIPHER_AES128, GCRY_CIPHER_MODE_CTR, 0)) {
return;
}
if (gcry_cipher_setkey(cipher_hd, pK, EAX_SIZEOF_KEY)) {
gcry_cipher_close(cipher_hd);
return;
}
if (gcry_cipher_setctr(cipher_hd, ctr, EAX_SIZEOF_KEY)) {
gcry_cipher_close(cipher_hd);
return;
}
if (gcry_cipher_encrypt(cipher_hd, pN, SizeN, pN, SizeN)) {
gcry_cipher_close(cipher_hd);
return;
}
gcry_cipher_close(cipher_hd);
return;
}
void AesEncrypt(unsigned char msg[EAX_SIZEOF_KEY], unsigned char key[EAX_SIZEOF_KEY])
{
gcry_cipher_hd_t cipher_hd;
/* open the cipher */
if (gcry_cipher_open(&cipher_hd, GCRY_CIPHER_AES128, GCRY_CIPHER_MODE_ECB, 0)) {
return;
}
if (gcry_cipher_setkey(cipher_hd, key, EAX_SIZEOF_KEY)) {
gcry_cipher_close(cipher_hd);
return;
}
if (gcry_cipher_encrypt(cipher_hd, msg, EAX_SIZEOF_KEY, msg, EAX_SIZEOF_KEY)) {
gcry_cipher_close(cipher_hd);
return;
}
gcry_cipher_close(cipher_hd);
return;
}
/*
* Editor modelines - https://www.wireshark.org/tools/modelines.html
*
* Local variables:
* c-basic-offset: 4
* tab-width: 8
* indent-tabs-mode: nil
* End:
*
* vi: set shiftwidth=4 tabstop=8 expandtab:
* :indentSize=4:tabSize=8:noTabs=true:
*/
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