1// Copyright (c) 2013 The Chromium Authors. All rights reserved.
2// Use of this source code is governed by a BSD-style license that can be
3// found in the LICENSE file.
4
5#include "net/quic/crypto/aes_128_gcm_12_decrypter.h"
6
7#include <pk11pub.h>
8#include <secerr.h>
9
10#include "base/lazy_instance.h"
11#include "crypto/ghash.h"
12#include "crypto/scoped_nss_types.h"
13
14#if defined(USE_NSS)
15#include <dlfcn.h>
16#endif
17
18using base::StringPiece;
19
20namespace net {
21
22namespace {
23
24const size_t kKeySize = 16;
25const size_t kNoncePrefixSize = 4;
26
27// On Linux, dynamically link against the system version of libnss3.so. In
28// order to continue working on systems without up-to-date versions of NSS,
29// lookup PK11_Decrypt with dlsym.
30
31// GcmSupportChecker is a singleton which caches the results of runtime symbol
32// resolution of PK11_Decrypt.
33class GcmSupportChecker {
34 public:
35  static PK11_DecryptFunction pk11_decrypt_func() {
36    return pk11_decrypt_func_;
37  }
38
39 private:
40  friend struct base::DefaultLazyInstanceTraits<GcmSupportChecker>;
41
42  GcmSupportChecker() {
43#if !defined(USE_NSS)
44    // Using a bundled version of NSS that is guaranteed to have this symbol.
45    pk11_decrypt_func_ = PK11_Decrypt;
46#else
47    // Using system NSS libraries and PCKS #11 modules, which may not have the
48    // necessary function (PK11_Decrypt) or mechanism support (CKM_AES_GCM).
49
50    // If PK11_Decrypt() was successfully resolved, then NSS will support
51    // AES-GCM directly. This was introduced in NSS 3.15.
52    pk11_decrypt_func_ = (PK11_DecryptFunction)dlsym(RTLD_DEFAULT,
53                                                     "PK11_Decrypt");
54#endif
55  }
56
57  // |pk11_decrypt_func_| stores the runtime symbol resolution of PK11_Decrypt.
58  static PK11_DecryptFunction pk11_decrypt_func_;
59};
60
61// static
62PK11_DecryptFunction GcmSupportChecker::pk11_decrypt_func_ = NULL;
63
64base::LazyInstance<GcmSupportChecker>::Leaky g_gcm_support_checker =
65    LAZY_INSTANCE_INITIALIZER;
66
67// Calls PK11_Decrypt if it's available.  Otherwise, emulates CKM_AES_GCM using
68// CKM_AES_CTR and the GaloisHash class.
69SECStatus My_Decrypt(PK11SymKey* key,
70                     CK_MECHANISM_TYPE mechanism,
71                     SECItem* param,
72                     unsigned char* out,
73                     unsigned int* out_len,
74                     unsigned int max_len,
75                     const unsigned char* enc,
76                     unsigned int enc_len) {
77  // If PK11_Decrypt() was successfully resolved or if bundled version of NSS is
78  // being used, then NSS will support AES-GCM directly.
79  PK11_DecryptFunction pk11_decrypt_func =
80      GcmSupportChecker::pk11_decrypt_func();
81  if (pk11_decrypt_func != NULL) {
82    return pk11_decrypt_func(key, mechanism, param, out, out_len, max_len, enc,
83                             enc_len);
84  }
85
86  // Otherwise, the user has an older version of NSS. Regrettably, NSS 3.14.x
87  // has a bug in the AES GCM code
88  // (https://bugzilla.mozilla.org/show_bug.cgi?id=853285), as well as missing
89  // the PK11_Decrypt function
90  // (https://bugzilla.mozilla.org/show_bug.cgi?id=854063), both of which are
91  // resolved in NSS 3.15.
92
93  DCHECK_EQ(mechanism, static_cast<CK_MECHANISM_TYPE>(CKM_AES_GCM));
94  DCHECK_EQ(param->len, sizeof(CK_GCM_PARAMS));
95
96  const CK_GCM_PARAMS* gcm_params =
97      reinterpret_cast<CK_GCM_PARAMS*>(param->data);
98
99  DCHECK_EQ(gcm_params->ulTagBits,
100            static_cast<CK_ULONG>(Aes128Gcm12Decrypter::kAuthTagSize * 8));
101  if (gcm_params->ulIvLen != 12u) {
102    DVLOG(1) << "ulIvLen is not equal to 12";
103    PORT_SetError(SEC_ERROR_INPUT_LEN);
104    return SECFailure;
105  }
106
107  SECItem my_param = { siBuffer, NULL, 0 };
108
109  // Step 2. Let H = CIPH_K(128 '0' bits).
110  unsigned char ghash_key[16] = {0};
111  crypto::ScopedPK11Context ctx(PK11_CreateContextBySymKey(
112      CKM_AES_ECB, CKA_ENCRYPT, key, &my_param));
113  if (!ctx) {
114    DVLOG(1) << "PK11_CreateContextBySymKey failed";
115    return SECFailure;
116  }
117  int output_len;
118  if (PK11_CipherOp(ctx.get(), ghash_key, &output_len, sizeof(ghash_key),
119                    ghash_key, sizeof(ghash_key)) != SECSuccess) {
120    DVLOG(1) << "PK11_CipherOp failed";
121    return SECFailure;
122  }
123
124  PK11_Finalize(ctx.get());
125
126  if (output_len != sizeof(ghash_key)) {
127    DVLOG(1) << "Wrong output length";
128    PORT_SetError(SEC_ERROR_LIBRARY_FAILURE);
129    return SECFailure;
130  }
131
132  // Step 3. If len(IV)=96, then let J0 = IV || 31 '0' bits || 1.
133  CK_AES_CTR_PARAMS ctr_params = {0};
134  ctr_params.ulCounterBits = 32;
135  memcpy(ctr_params.cb, gcm_params->pIv, gcm_params->ulIvLen);
136  ctr_params.cb[12] = 0;
137  ctr_params.cb[13] = 0;
138  ctr_params.cb[14] = 0;
139  ctr_params.cb[15] = 1;
140
141  my_param.type = siBuffer;
142  my_param.data = reinterpret_cast<unsigned char*>(&ctr_params);
143  my_param.len = sizeof(ctr_params);
144
145  ctx.reset(PK11_CreateContextBySymKey(CKM_AES_CTR, CKA_ENCRYPT, key,
146                                       &my_param));
147  if (!ctx) {
148    DVLOG(1) << "PK11_CreateContextBySymKey failed";
149    return SECFailure;
150  }
151
152  // Step 6. Calculate the encryption mask of GCTR_K(J0, ...).
153  unsigned char tag_mask[16] = {0};
154  if (PK11_CipherOp(ctx.get(), tag_mask, &output_len, sizeof(tag_mask),
155                    tag_mask, sizeof(tag_mask)) != SECSuccess) {
156    DVLOG(1) << "PK11_CipherOp failed";
157    return SECFailure;
158  }
159  if (output_len != sizeof(tag_mask)) {
160    DVLOG(1) << "Wrong output length";
161    PORT_SetError(SEC_ERROR_LIBRARY_FAILURE);
162    return SECFailure;
163  }
164
165  if (enc_len < Aes128Gcm12Decrypter::kAuthTagSize) {
166    PORT_SetError(SEC_ERROR_INPUT_LEN);
167    return SECFailure;
168  }
169
170  // The const_cast for |enc| can be removed if system NSS libraries are
171  // NSS 3.14.1 or later (NSS bug
172  // https://bugzilla.mozilla.org/show_bug.cgi?id=808218).
173  if (PK11_CipherOp(ctx.get(), out, &output_len, max_len,
174          const_cast<unsigned char*>(enc),
175          enc_len - Aes128Gcm12Decrypter::kAuthTagSize) != SECSuccess) {
176    DVLOG(1) << "PK11_CipherOp failed";
177    return SECFailure;
178  }
179
180  PK11_Finalize(ctx.get());
181
182  if (static_cast<unsigned int>(output_len) !=
183      enc_len - Aes128Gcm12Decrypter::kAuthTagSize) {
184    DVLOG(1) << "Wrong output length";
185    PORT_SetError(SEC_ERROR_LIBRARY_FAILURE);
186    return SECFailure;
187  }
188
189  crypto::GaloisHash ghash(ghash_key);
190  ghash.UpdateAdditional(gcm_params->pAAD, gcm_params->ulAADLen);
191  ghash.UpdateCiphertext(enc, output_len);
192  unsigned char auth_tag[Aes128Gcm12Decrypter::kAuthTagSize];
193  ghash.Finish(auth_tag, Aes128Gcm12Decrypter::kAuthTagSize);
194  for (unsigned int i = 0; i < Aes128Gcm12Decrypter::kAuthTagSize; i++) {
195    auth_tag[i] ^= tag_mask[i];
196  }
197
198  if (NSS_SecureMemcmp(auth_tag, enc + output_len,
199                       Aes128Gcm12Decrypter::kAuthTagSize) != 0) {
200    PORT_SetError(SEC_ERROR_BAD_DATA);
201    return SECFailure;
202  }
203
204  *out_len = output_len;
205  return SECSuccess;
206}
207
208}  // namespace
209
210Aes128Gcm12Decrypter::Aes128Gcm12Decrypter()
211    : AeadBaseDecrypter(CKM_AES_GCM, My_Decrypt, kKeySize, kAuthTagSize,
212                        kNoncePrefixSize) {
213  COMPILE_ASSERT(kKeySize <= kMaxKeySize, key_size_too_big);
214  COMPILE_ASSERT(kNoncePrefixSize <= kMaxNoncePrefixSize,
215                 nonce_prefix_size_too_big);
216  ignore_result(g_gcm_support_checker.Get());
217}
218
219Aes128Gcm12Decrypter::~Aes128Gcm12Decrypter() {}
220
221void Aes128Gcm12Decrypter::FillAeadParams(StringPiece nonce,
222                                          StringPiece associated_data,
223                                          size_t auth_tag_size,
224                                          AeadParams* aead_params) const {
225  aead_params->len = sizeof(aead_params->data.gcm_params);
226  CK_GCM_PARAMS* gcm_params = &aead_params->data.gcm_params;
227  gcm_params->pIv =
228      reinterpret_cast<CK_BYTE*>(const_cast<char*>(nonce.data()));
229  gcm_params->ulIvLen = nonce.size();
230  gcm_params->pAAD =
231      reinterpret_cast<CK_BYTE*>(const_cast<char*>(associated_data.data()));
232  gcm_params->ulAADLen = associated_data.size();
233  gcm_params->ulTagBits = auth_tag_size * 8;
234}
235
236}  // namespace net
237