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// Copyright (c) 2013 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#include "net/quic/crypto/aes_128_gcm_12_decrypter.h"
#include <pk11pub.h>
#include <secerr.h>
#include "base/lazy_instance.h"
#include "crypto/ghash.h"
#include "crypto/scoped_nss_types.h"
#if defined(USE_NSS)
#include <dlfcn.h>
#endif
using base::StringPiece;
namespace net {
namespace {
const size_t kKeySize = 16;
const size_t kNoncePrefixSize = 4;
// On Linux, dynamically link against the system version of libnss3.so. In
// order to continue working on systems without up-to-date versions of NSS,
// lookup PK11_Decrypt with dlsym.
// GcmSupportChecker is a singleton which caches the results of runtime symbol
// resolution of PK11_Decrypt.
class GcmSupportChecker {
public:
static PK11_DecryptFunction pk11_decrypt_func() {
return pk11_decrypt_func_;
}
private:
friend struct base::DefaultLazyInstanceTraits<GcmSupportChecker>;
GcmSupportChecker() {
#if !defined(USE_NSS)
// Using a bundled version of NSS that is guaranteed to have this symbol.
pk11_decrypt_func_ = PK11_Decrypt;
#else
// Using system NSS libraries and PCKS #11 modules, which may not have the
// necessary function (PK11_Decrypt) or mechanism support (CKM_AES_GCM).
// If PK11_Decrypt() was successfully resolved, then NSS will support
// AES-GCM directly. This was introduced in NSS 3.15.
pk11_decrypt_func_ = (PK11_DecryptFunction)dlsym(RTLD_DEFAULT,
"PK11_Decrypt");
#endif
}
// |pk11_decrypt_func_| stores the runtime symbol resolution of PK11_Decrypt.
static PK11_DecryptFunction pk11_decrypt_func_;
};
// static
PK11_DecryptFunction GcmSupportChecker::pk11_decrypt_func_ = NULL;
base::LazyInstance<GcmSupportChecker>::Leaky g_gcm_support_checker =
LAZY_INSTANCE_INITIALIZER;
// Calls PK11_Decrypt if it's available. Otherwise, emulates CKM_AES_GCM using
// CKM_AES_CTR and the GaloisHash class.
SECStatus My_Decrypt(PK11SymKey* key,
CK_MECHANISM_TYPE mechanism,
SECItem* param,
unsigned char* out,
unsigned int* out_len,
unsigned int max_len,
const unsigned char* enc,
unsigned int enc_len) {
// If PK11_Decrypt() was successfully resolved or if bundled version of NSS is
// being used, then NSS will support AES-GCM directly.
PK11_DecryptFunction pk11_decrypt_func =
GcmSupportChecker::pk11_decrypt_func();
if (pk11_decrypt_func != NULL) {
return pk11_decrypt_func(key, mechanism, param, out, out_len, max_len, enc,
enc_len);
}
// Otherwise, the user has an older version of NSS. Regrettably, NSS 3.14.x
// has a bug in the AES GCM code
// (https://bugzilla.mozilla.org/show_bug.cgi?id=853285), as well as missing
// the PK11_Decrypt function
// (https://bugzilla.mozilla.org/show_bug.cgi?id=854063), both of which are
// resolved in NSS 3.15.
DCHECK_EQ(mechanism, static_cast<CK_MECHANISM_TYPE>(CKM_AES_GCM));
DCHECK_EQ(param->len, sizeof(CK_GCM_PARAMS));
const CK_GCM_PARAMS* gcm_params =
reinterpret_cast<CK_GCM_PARAMS*>(param->data);
DCHECK_EQ(gcm_params->ulTagBits,
static_cast<CK_ULONG>(Aes128Gcm12Decrypter::kAuthTagSize * 8));
if (gcm_params->ulIvLen != 12u) {
DVLOG(1) << "ulIvLen is not equal to 12";
PORT_SetError(SEC_ERROR_INPUT_LEN);
return SECFailure;
}
SECItem my_param = { siBuffer, NULL, 0 };
// Step 2. Let H = CIPH_K(128 '0' bits).
unsigned char ghash_key[16] = {0};
crypto::ScopedPK11Context ctx(PK11_CreateContextBySymKey(
CKM_AES_ECB, CKA_ENCRYPT, key, &my_param));
if (!ctx) {
DVLOG(1) << "PK11_CreateContextBySymKey failed";
return SECFailure;
}
int output_len;
if (PK11_CipherOp(ctx.get(), ghash_key, &output_len, sizeof(ghash_key),
ghash_key, sizeof(ghash_key)) != SECSuccess) {
DVLOG(1) << "PK11_CipherOp failed";
return SECFailure;
}
PK11_Finalize(ctx.get());
if (output_len != sizeof(ghash_key)) {
DVLOG(1) << "Wrong output length";
PORT_SetError(SEC_ERROR_LIBRARY_FAILURE);
return SECFailure;
}
// Step 3. If len(IV)=96, then let J0 = IV || 31 '0' bits || 1.
CK_AES_CTR_PARAMS ctr_params = {0};
ctr_params.ulCounterBits = 32;
memcpy(ctr_params.cb, gcm_params->pIv, gcm_params->ulIvLen);
ctr_params.cb[12] = 0;
ctr_params.cb[13] = 0;
ctr_params.cb[14] = 0;
ctr_params.cb[15] = 1;
my_param.type = siBuffer;
my_param.data = reinterpret_cast<unsigned char*>(&ctr_params);
my_param.len = sizeof(ctr_params);
ctx.reset(PK11_CreateContextBySymKey(CKM_AES_CTR, CKA_ENCRYPT, key,
&my_param));
if (!ctx) {
DVLOG(1) << "PK11_CreateContextBySymKey failed";
return SECFailure;
}
// Step 6. Calculate the encryption mask of GCTR_K(J0, ...).
unsigned char tag_mask[16] = {0};
if (PK11_CipherOp(ctx.get(), tag_mask, &output_len, sizeof(tag_mask),
tag_mask, sizeof(tag_mask)) != SECSuccess) {
DVLOG(1) << "PK11_CipherOp failed";
return SECFailure;
}
if (output_len != sizeof(tag_mask)) {
DVLOG(1) << "Wrong output length";
PORT_SetError(SEC_ERROR_LIBRARY_FAILURE);
return SECFailure;
}
if (enc_len < Aes128Gcm12Decrypter::kAuthTagSize) {
PORT_SetError(SEC_ERROR_INPUT_LEN);
return SECFailure;
}
// The const_cast for |enc| can be removed if system NSS libraries are
// NSS 3.14.1 or later (NSS bug
// https://bugzilla.mozilla.org/show_bug.cgi?id=808218).
if (PK11_CipherOp(ctx.get(), out, &output_len, max_len,
const_cast<unsigned char*>(enc),
enc_len - Aes128Gcm12Decrypter::kAuthTagSize) != SECSuccess) {
DVLOG(1) << "PK11_CipherOp failed";
return SECFailure;
}
PK11_Finalize(ctx.get());
if (static_cast<unsigned int>(output_len) !=
enc_len - Aes128Gcm12Decrypter::kAuthTagSize) {
DVLOG(1) << "Wrong output length";
PORT_SetError(SEC_ERROR_LIBRARY_FAILURE);
return SECFailure;
}
crypto::GaloisHash ghash(ghash_key);
ghash.UpdateAdditional(gcm_params->pAAD, gcm_params->ulAADLen);
ghash.UpdateCiphertext(enc, output_len);
unsigned char auth_tag[Aes128Gcm12Decrypter::kAuthTagSize];
ghash.Finish(auth_tag, Aes128Gcm12Decrypter::kAuthTagSize);
for (unsigned int i = 0; i < Aes128Gcm12Decrypter::kAuthTagSize; i++) {
auth_tag[i] ^= tag_mask[i];
}
if (NSS_SecureMemcmp(auth_tag, enc + output_len,
Aes128Gcm12Decrypter::kAuthTagSize) != 0) {
PORT_SetError(SEC_ERROR_BAD_DATA);
return SECFailure;
}
*out_len = output_len;
return SECSuccess;
}
} // namespace
Aes128Gcm12Decrypter::Aes128Gcm12Decrypter()
: AeadBaseDecrypter(CKM_AES_GCM, My_Decrypt, kKeySize, kAuthTagSize,
kNoncePrefixSize) {
COMPILE_ASSERT(kKeySize <= kMaxKeySize, key_size_too_big);
COMPILE_ASSERT(kNoncePrefixSize <= kMaxNoncePrefixSize,
nonce_prefix_size_too_big);
ignore_result(g_gcm_support_checker.Get());
}
Aes128Gcm12Decrypter::~Aes128Gcm12Decrypter() {}
void Aes128Gcm12Decrypter::FillAeadParams(StringPiece nonce,
StringPiece associated_data,
size_t auth_tag_size,
AeadParams* aead_params) const {
aead_params->len = sizeof(aead_params->data.gcm_params);
CK_GCM_PARAMS* gcm_params = &aead_params->data.gcm_params;
gcm_params->pIv =
reinterpret_cast<CK_BYTE*>(const_cast<char*>(nonce.data()));
gcm_params->ulIvLen = nonce.size();
gcm_params->pAAD =
reinterpret_cast<CK_BYTE*>(const_cast<char*>(associated_data.data()));
gcm_params->ulAADLen = associated_data.size();
gcm_params->ulTagBits = auth_tag_size * 8;
}
} // namespace net
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