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mumble-voip_mumble/src/crypto/CryptStateOCB2.cpp

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// Copyright 2020-2023 The Mumble Developers. All rights reserved.
// Use of this source code is governed by a BSD-style license
// that can be found in the LICENSE file at the root of the
// Mumble source tree or at <https://www.mumble.info/LICENSE>.
/*
* This code implements OCB-AES128.
* The algorithm design was dedicated to the public domain.
* https://www.cs.ucdavis.edu/~rogaway/ocb/license.htm
* https://www.cs.ucdavis.edu/~rogaway/ocb/ocb-faq.htm
*/
#include <QtCore/QtGlobal>
#ifndef __LP64__
# ifdef Q_OS_WIN
# include "win.h"
# include <winsock2.h>
# else
# include <arpa/inet.h>
# endif
#endif
#include "ByteSwap.h"
#include "CryptStateOCB2.h"
#include "CryptographicRandom.h"
#include <cstring>
#include <openssl/rand.h>
CryptStateOCB2::CryptStateOCB2()
: CryptState(), enc_ctx_ocb_enc(EVP_CIPHER_CTX_new()), dec_ctx_ocb_enc(EVP_CIPHER_CTX_new()),
enc_ctx_ocb_dec(EVP_CIPHER_CTX_new()), dec_ctx_ocb_dec(EVP_CIPHER_CTX_new()) {
for (int i = 0; i < 0x100; i++)
decrypt_history[i] = 0;
memset(raw_key, 0, AES_KEY_SIZE_BYTES);
memset(encrypt_iv, 0, AES_BLOCK_SIZE);
memset(decrypt_iv, 0, AES_BLOCK_SIZE);
}
CryptStateOCB2::~CryptStateOCB2() noexcept {
EVP_CIPHER_CTX_free(enc_ctx_ocb_enc);
EVP_CIPHER_CTX_free(dec_ctx_ocb_enc);
EVP_CIPHER_CTX_free(enc_ctx_ocb_dec);
EVP_CIPHER_CTX_free(dec_ctx_ocb_dec);
}
bool CryptStateOCB2::isValid() const {
return bInit;
}
void CryptStateOCB2::genKey() {
CryptographicRandom::fillBuffer(raw_key, AES_KEY_SIZE_BYTES);
CryptographicRandom::fillBuffer(encrypt_iv, AES_BLOCK_SIZE);
CryptographicRandom::fillBuffer(decrypt_iv, AES_BLOCK_SIZE);
bInit = true;
}
bool CryptStateOCB2::setKey(const std::string &rkey, const std::string &eiv, const std::string &div) {
if (rkey.length() == AES_KEY_SIZE_BYTES && eiv.length() == AES_BLOCK_SIZE && div.length() == AES_BLOCK_SIZE) {
memcpy(raw_key, rkey.data(), AES_KEY_SIZE_BYTES);
memcpy(encrypt_iv, eiv.data(), AES_BLOCK_SIZE);
memcpy(decrypt_iv, div.data(), AES_BLOCK_SIZE);
bInit = true;
return true;
}
return false;
}
bool CryptStateOCB2::setRawKey(const std::string &rkey) {
if (rkey.length() == AES_KEY_SIZE_BYTES) {
memcpy(raw_key, rkey.data(), AES_KEY_SIZE_BYTES);
return true;
}
return false;
}
bool CryptStateOCB2::setEncryptIV(const std::string &iv) {
if (iv.length() == AES_BLOCK_SIZE) {
memcpy(encrypt_iv, iv.data(), AES_BLOCK_SIZE);
return true;
}
return false;
}
bool CryptStateOCB2::setDecryptIV(const std::string &iv) {
if (iv.length() == AES_BLOCK_SIZE) {
memcpy(decrypt_iv, iv.data(), AES_BLOCK_SIZE);
return true;
}
return false;
}
std::string CryptStateOCB2::getRawKey() {
return std::string(reinterpret_cast< const char * >(raw_key), AES_KEY_SIZE_BYTES);
}
std::string CryptStateOCB2::getEncryptIV() {
return std::string(reinterpret_cast< const char * >(encrypt_iv), AES_BLOCK_SIZE);
}
std::string CryptStateOCB2::getDecryptIV() {
return std::string(reinterpret_cast< const char * >(decrypt_iv), AES_BLOCK_SIZE);
}
bool CryptStateOCB2::encrypt(const unsigned char *source, unsigned char *dst, unsigned int plain_length) {
unsigned char tag[AES_BLOCK_SIZE];
// First, increase our IV.
for (int i = 0; i < AES_BLOCK_SIZE; i++)
if (++encrypt_iv[i])
break;
if (!ocb_encrypt(source, dst + 4, plain_length, encrypt_iv, tag)) {
return false;
}
dst[0] = encrypt_iv[0];
dst[1] = tag[0];
dst[2] = tag[1];
dst[3] = tag[2];
return true;
}
bool CryptStateOCB2::decrypt(const unsigned char *source, unsigned char *dst, unsigned int crypted_length) {
if (crypted_length < 4)
return false;
unsigned int plain_length = crypted_length - 4;
unsigned char saveiv[AES_BLOCK_SIZE];
unsigned char ivbyte = source[0];
bool restore = false;
unsigned char tag[AES_BLOCK_SIZE];
int lost = 0;
int late = 0;
memcpy(saveiv, decrypt_iv, AES_BLOCK_SIZE);
if (((decrypt_iv[0] + 1) & 0xFF) == ivbyte) {
// In order as expected.
if (ivbyte > decrypt_iv[0]) {
decrypt_iv[0] = ivbyte;
} else if (ivbyte < decrypt_iv[0]) {
decrypt_iv[0] = ivbyte;
for (int i = 1; i < AES_BLOCK_SIZE; i++)
if (++decrypt_iv[i])
break;
} else {
return false;
}
} else {
// This is either out of order or a repeat.
int diff = ivbyte - decrypt_iv[0];
if (diff > 128)
diff = diff - 256;
else if (diff < -128)
diff = diff + 256;
if ((ivbyte < decrypt_iv[0]) && (diff > -30) && (diff < 0)) {
// Late packet, but no wraparound.
late = 1;
lost = -1;
decrypt_iv[0] = ivbyte;
restore = true;
} else if ((ivbyte > decrypt_iv[0]) && (diff > -30) && (diff < 0)) {
// Last was 0x02, here comes 0xff from last round
late = 1;
lost = -1;
decrypt_iv[0] = ivbyte;
for (int i = 1; i < AES_BLOCK_SIZE; i++)
if (decrypt_iv[i]--)
break;
restore = true;
} else if ((ivbyte > decrypt_iv[0]) && (diff > 0)) {
// Lost a few packets, but beyond that we're good.
lost = ivbyte - decrypt_iv[0] - 1;
decrypt_iv[0] = ivbyte;
} else if ((ivbyte < decrypt_iv[0]) && (diff > 0)) {
// Lost a few packets, and wrapped around
lost = 256 - decrypt_iv[0] + ivbyte - 1;
decrypt_iv[0] = ivbyte;
for (int i = 1; i < AES_BLOCK_SIZE; i++)
if (++decrypt_iv[i])
break;
} else {
return false;
}
if (decrypt_history[decrypt_iv[0]] == decrypt_iv[1]) {
memcpy(decrypt_iv, saveiv, AES_BLOCK_SIZE);
return false;
}
}
bool ocb_success = ocb_decrypt(source + 4, dst, plain_length, decrypt_iv, tag);
if (!ocb_success || memcmp(tag, source + 1, 3) != 0) {
memcpy(decrypt_iv, saveiv, AES_BLOCK_SIZE);
return false;
}
decrypt_history[decrypt_iv[0]] = decrypt_iv[1];
if (restore)
memcpy(decrypt_iv, saveiv, AES_BLOCK_SIZE);
uiGood++;
// uiLate += late, but we have to make sure we don't cause wrap-arounds on the unsigned lhs
if (late > 0) {
uiLate += static_cast< unsigned int >(late);
} else if (static_cast< int >(uiLate) > std::abs(late)) {
uiLate -= static_cast< unsigned int >(std::abs(late));
}
// uiLost += lost, but we have to make sure we don't cause wrap-arounds on the unsigned lhs
if (lost > 0) {
uiLost += static_cast< unsigned int >(lost);
} else if (static_cast< int >(uiLost) > std::abs(lost)) {
uiLost -= static_cast< unsigned int >(std::abs(lost));
}
tLastGood.restart();
return true;
}
#if defined(__LP64__)
# define BLOCKSIZE 2
# define SHIFTBITS 63
typedef quint64 subblock;
# define SWAPPED(x) SWAP64(x)
#else
# define BLOCKSIZE 4
# define SHIFTBITS 31
typedef quint32 subblock;
# define SWAPPED(x) htonl(x)
#endif
typedef subblock keyblock[BLOCKSIZE];
#define HIGHBIT (1 << SHIFTBITS);
static void inline XOR(subblock *dst, const subblock *a, const subblock *b) {
for (int i = 0; i < BLOCKSIZE; i++) {
dst[i] = a[i] ^ b[i];
}
}
static void inline S2(subblock *block) {
subblock carry = SWAPPED(block[0]) >> SHIFTBITS;
for (int i = 0; i < BLOCKSIZE - 1; i++)
block[i] = SWAPPED((SWAPPED(block[i]) << 1) | (SWAPPED(block[i + 1]) >> SHIFTBITS));
block[BLOCKSIZE - 1] = SWAPPED((SWAPPED(block[BLOCKSIZE - 1]) << 1) ^ (carry * 0x87));
}
static void inline S3(subblock *block) {
subblock carry = SWAPPED(block[0]) >> SHIFTBITS;
for (int i = 0; i < BLOCKSIZE - 1; i++)
block[i] ^= SWAPPED((SWAPPED(block[i]) << 1) | (SWAPPED(block[i + 1]) >> SHIFTBITS));
block[BLOCKSIZE - 1] ^= SWAPPED((SWAPPED(block[BLOCKSIZE - 1]) << 1) ^ (carry * 0x87));
}
static void inline ZERO(keyblock &block) {
for (int i = 0; i < BLOCKSIZE; i++)
block[i] = 0;
}
#define AESencrypt_ctx(src, dst, key, enc_ctx) \
{ \
int outlen = 0; \
EVP_EncryptInit_ex(enc_ctx, EVP_aes_128_ecb(), NULL, key, NULL); \
EVP_CIPHER_CTX_set_padding(enc_ctx, 0); \
EVP_EncryptUpdate(enc_ctx, reinterpret_cast< unsigned char * >(dst), &outlen, \
reinterpret_cast< const unsigned char * >(src), AES_BLOCK_SIZE); \
EVP_EncryptFinal_ex(enc_ctx, reinterpret_cast< unsigned char * >((dst) + outlen), &outlen); \
}
#define AESdecrypt_ctx(src, dst, key, dec_ctx) \
{ \
int outlen = 0; \
EVP_DecryptInit_ex(dec_ctx, EVP_aes_128_ecb(), NULL, key, NULL); \
EVP_CIPHER_CTX_set_padding(dec_ctx, 0); \
EVP_DecryptUpdate(dec_ctx, reinterpret_cast< unsigned char * >(dst), &outlen, \
reinterpret_cast< const unsigned char * >(src), AES_BLOCK_SIZE); \
EVP_DecryptFinal_ex(dec_ctx, reinterpret_cast< unsigned char * >((dst) + outlen), &outlen); \
}
#define AESencrypt(src, dst, key) AESencrypt_ctx(src, dst, key, enc_ctx_ocb_enc)
#define AESdecrypt(src, dst, key) AESdecrypt_ctx(src, dst, key, dec_ctx_ocb_enc)
bool CryptStateOCB2::ocb_encrypt(const unsigned char *plain, unsigned char *encrypted, unsigned int len,
const unsigned char *nonce, unsigned char *tag, bool modifyPlainOnXEXStarAttack) {
keyblock checksum, delta, tmp, pad;
bool success = true;
// Initialize
AESencrypt(nonce, delta, raw_key);
ZERO(checksum);
while (len > AES_BLOCK_SIZE) {
// Counter-cryptanalysis described in section 9 of https://eprint.iacr.org/2019/311
// For an attack, the second to last block (i.e. the last iteration of this loop)
// must be all 0 except for the last byte (which may be 0 - 128).
bool flipABit = false; // *plain is const, so we can't directly modify it
if (len - AES_BLOCK_SIZE <= AES_BLOCK_SIZE) {
unsigned char sum = 0;
for (int i = 0; i < AES_BLOCK_SIZE - 1; ++i) {
sum |= plain[i];
}
if (sum == 0) {
if (modifyPlainOnXEXStarAttack) {
// The assumption that critical packets do not turn up by pure chance turned out to be incorrect
// since digital silence appears to produce them in mass.
// So instead we now modify the packet in a way which should not affect the audio but will
// prevent the attack.
flipABit = true;
} else {
// This option still exists but only to allow us to test ocb_decrypt's detection.
success = false;
}
}
}
S2(delta);
XOR(tmp, delta, reinterpret_cast< const subblock * >(plain));
if (flipABit) {
*reinterpret_cast< unsigned char * >(tmp) ^= 1;
}
AESencrypt(tmp, tmp, raw_key);
XOR(reinterpret_cast< subblock * >(encrypted), delta, tmp);
XOR(checksum, checksum, reinterpret_cast< const subblock * >(plain));
if (flipABit) {
*reinterpret_cast< unsigned char * >(checksum) ^= 1;
}
len -= AES_BLOCK_SIZE;
plain += AES_BLOCK_SIZE;
encrypted += AES_BLOCK_SIZE;
}
S2(delta);
ZERO(tmp);
tmp[BLOCKSIZE - 1] = SWAPPED(len * 8);
XOR(tmp, tmp, delta);
AESencrypt(tmp, pad, raw_key);
memcpy(tmp, plain, len);
memcpy(reinterpret_cast< unsigned char * >(tmp) + len, reinterpret_cast< const unsigned char * >(pad) + len,
AES_BLOCK_SIZE - len);
XOR(checksum, checksum, tmp);
XOR(tmp, pad, tmp);
memcpy(encrypted, tmp, len);
S3(delta);
XOR(tmp, delta, checksum);
AESencrypt(tmp, tag, raw_key);
return success;
}
#undef AESencrypt
#undef AESdecrypt
#define AESencrypt(src, dst, key) AESencrypt_ctx(src, dst, key, enc_ctx_ocb_dec)
#define AESdecrypt(src, dst, key) AESdecrypt_ctx(src, dst, key, dec_ctx_ocb_dec)
bool CryptStateOCB2::ocb_decrypt(const unsigned char *encrypted, unsigned char *plain, unsigned int len,
const unsigned char *nonce, unsigned char *tag) {
keyblock checksum, delta, tmp, pad;
bool success = true;
// Initialize
AESencrypt(nonce, delta, raw_key);
ZERO(checksum);
while (len > AES_BLOCK_SIZE) {
S2(delta);
XOR(tmp, delta, reinterpret_cast< const subblock * >(encrypted));
AESdecrypt(tmp, tmp, raw_key);
XOR(reinterpret_cast< subblock * >(plain), delta, tmp);
XOR(checksum, checksum, reinterpret_cast< const subblock * >(plain));
len -= AES_BLOCK_SIZE;
plain += AES_BLOCK_SIZE;
encrypted += AES_BLOCK_SIZE;
}
S2(delta);
ZERO(tmp);
tmp[BLOCKSIZE - 1] = SWAPPED(len * 8);
XOR(tmp, tmp, delta);
AESencrypt(tmp, pad, raw_key);
memset(tmp, 0, AES_BLOCK_SIZE);
memcpy(tmp, encrypted, len);
XOR(tmp, tmp, pad);
XOR(checksum, checksum, tmp);
memcpy(plain, tmp, len);
// Counter-cryptanalysis described in section 9 of https://eprint.iacr.org/2019/311
// In an attack, the decrypted last block would need to equal `delta ^ len(128)`.
// With a bit of luck (or many packets), smaller values than 128 (i.e. non-full blocks) are also
// feasible, so we check `tmp` instead of `plain`.
// Since our `len` only ever modifies the last byte, we simply check all remaining ones.
if (memcmp(tmp, delta, AES_BLOCK_SIZE - 1) == 0) {
success = false;
}
S3(delta);
XOR(tmp, delta, checksum);
AESencrypt(tmp, tag, raw_key);
return success;
}
#undef AESencrypt
#undef AESdecrypt
#undef BLOCKSIZE
#undef SHIFTBITS
#undef SWAPPED
#undef HIGHBIT
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