crypto: allow to restrict valid GCM tag length

This change allows users to restrict accepted GCM authentication tag lengths to a single value. PR-URL: #20039 Fixes: #17523 Reviewed-By: James M Snell <jasnell@gmail.com> Reviewed-By: Yihong Wang <yh.wang@ibm.com> Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
nodejs · Apr 13, 2018 · 358d8ffad650b6fb966082e7bd1460b0d6a4eacc · 358d8ff
1 parent 854f840
commit 358d8ffad650b6fb966082e7bd1460b0d6a4eacc
Unified Split

Showing with 74 additions and 7 deletions.

+7 −1 doc/api/crypto.md

+28 −5 src/node_crypto.cc

+2 −1 src/node_crypto.h

+37 −0 test/parallel/test-crypto-authenticated.js
diff --git a/doc/api/crypto.md b/doc/api/crypto.md
@@ -1457,6 +1457,10 @@ to create the `Decipher` object.
 <!-- YAML
 added: v0.1.94
 changes:
+  - version: REPLACEME
+    pr-url: https://github.com/nodejs/node/pull/20039
+    description: The `authTagLength` option can now be used to restrict accepted
+                 GCM authentication tag lengths.
  - version: v9.9.0
    pr-url: https://github.com/nodejs/node/pull/18644
    description: The `iv` parameter may now be `null` for ciphers which do not
@@ -1474,7 +1478,9 @@ and initialization vector (`iv`).
 The `options` argument controls stream behavior and is optional except when a
 cipher in CCM mode is used (e.g. `'aes-128-ccm'`). In that case, the
 `authTagLength` option is required and specifies the length of the
-authentication tag in bytes, see [CCM mode][].
+authentication tag in bytes, see [CCM mode][]. In GCM mode, the `authTagLength`
+option is not required but can be used to restrict accepted authentication tags
+to those with the specified length.

 The `algorithm` is dependent on OpenSSL, examples are `'aes192'`, etc. On
 recent OpenSSL releases, `openssl list-cipher-algorithms` will display the
diff --git a/src/node_crypto.cc b/src/node_crypto.cc
@@ -2797,6 +2797,10 @@ void CipherBase::InitIv(const FunctionCallbackInfo<Value>& args) {
 }


+static bool IsValidGCMTagLength(unsigned int tag_len) {
+  return tag_len == 4 || tag_len == 8 || tag_len >= 12 && tag_len <= 16;
+}
+
 bool CipherBase::InitAuthenticated(const char *cipher_type, int iv_len,
                                   int auth_tag_len) {
  CHECK(IsAuthenticatedMode());
@@ -2809,7 +2813,8 @@ bool CipherBase::InitAuthenticated(const char *cipher_type, int iv_len,
    return false;
  }

-  if (EVP_CIPHER_CTX_mode(ctx_) == EVP_CIPH_CCM_MODE) {
+  const int mode = EVP_CIPHER_CTX_mode(ctx_);
+  if (mode == EVP_CIPH_CCM_MODE) {
    if (auth_tag_len < 0) {
      char msg[128];
      snprintf(msg, sizeof(msg), "authTagLength required for %s", cipher_type);
@@ -2842,6 +2847,21 @@ bool CipherBase::InitAuthenticated(const char *cipher_type, int iv_len,
    } else {
      max_message_size_ = INT_MAX;
    }
+  } else {
+    CHECK_EQ(mode, EVP_CIPH_GCM_MODE);
+
+    if (auth_tag_len >= 0) {
+      if (!IsValidGCMTagLength(auth_tag_len)) {
+        char msg[50];
+        snprintf(msg, sizeof(msg),
+            "Invalid GCM authentication tag length: %u", auth_tag_len);
+        env()->ThrowError(msg);
+        return false;
+      }
+
+      // Remember the given authentication tag length for later.
+      auth_tag_len_ = auth_tag_len;
+    }
  }

  return true;
@@ -2877,7 +2897,7 @@ void CipherBase::GetAuthTag(const FunctionCallbackInfo<Value>& args) {
  // Only callable after Final and if encrypting.
  if (cipher->ctx_ != nullptr ||
      cipher->kind_ != kCipher ||
-      cipher->auth_tag_len_ == 0) {
+      cipher->auth_tag_len_ == kNoAuthTagLength) {
    return args.GetReturnValue().SetUndefined();
  }

@@ -2902,7 +2922,9 @@ void CipherBase::SetAuthTag(const FunctionCallbackInfo<Value>& args) {
  unsigned int tag_len = Buffer::Length(args[0]);
  const int mode = EVP_CIPHER_CTX_mode(cipher->ctx_);
  if (mode == EVP_CIPH_GCM_MODE) {
-    if (tag_len > 16 || (tag_len < 12 && tag_len != 8 && tag_len != 4)) {
+    if (cipher->auth_tag_len_ != kNoAuthTagLength &&
+        cipher->auth_tag_len_ != tag_len ||
+        !IsValidGCMTagLength(tag_len)) {
      char msg[50];
      snprintf(msg, sizeof(msg),
          "Invalid GCM authentication tag length: %u", tag_len);
@@ -2938,7 +2960,8 @@ bool CipherBase::SetAAD(const char* data, unsigned int len, int plaintext_len) {
    if (!CheckCCMMessageLength(plaintext_len))
      return false;

-    if (kind_ == kDecipher && !auth_tag_set_ && auth_tag_len_ > 0) {
+    if (kind_ == kDecipher && !auth_tag_set_ && auth_tag_len_ > 0 &&
+        auth_tag_len_ != kNoAuthTagLength) {
      if (!EVP_CIPHER_CTX_ctrl(ctx_,
                               EVP_CTRL_CCM_SET_TAG,
                               auth_tag_len_,
@@ -2991,7 +3014,7 @@ CipherBase::UpdateResult CipherBase::Update(const char* data,

  // on first update:
  if (kind_ == kDecipher && IsAuthenticatedMode() && auth_tag_len_ > 0 &&
-      !auth_tag_set_) {
+      auth_tag_len_ != kNoAuthTagLength && !auth_tag_set_) {
    EVP_CIPHER_CTX_ctrl(ctx_,
                        EVP_CTRL_GCM_SET_TAG,
                        auth_tag_len_,
diff --git a/src/node_crypto.h b/src/node_crypto.h
@@ -359,6 +359,7 @@ class CipherBase : public BaseObject {
    kErrorMessageSize,
    kErrorState
  };
+  static const unsigned kNoAuthTagLength = static_cast<unsigned>(-1);

  void Init(const char* cipher_type,
            const char* key_buf,
@@ -398,7 +399,7 @@ class CipherBase : public BaseObject {
        ctx_(nullptr),
        kind_(kind),
        auth_tag_set_(false),
-        auth_tag_len_(0),
+        auth_tag_len_(kNoAuthTagLength),
        pending_auth_failed_(false) {
    MakeWeak<CipherBase>(this);
  }
diff --git a/test/parallel/test-crypto-authenticated.js b/test/parallel/test-crypto-authenticated.js
@@ -726,9 +726,46 @@ for (const test of TEST_CASES) {
      type: Error,
      message: `Invalid GCM authentication tag length: ${length}`
    });
+
+    common.expectsError(() => {
+      crypto.createDecipheriv('aes-256-gcm',
+                              'FxLKsqdmv0E9xrQhp0b1ZgI0K7JFZJM8',
+                              'qkuZpJWCewa6Szih',
+                              {
+                                authTagLength: length
+                              });
+    }, {
+      type: Error,
+      message: `Invalid GCM authentication tag length: ${length}`
+    });
  }
 }

+// Test that users can manually restrict the GCM tag length to a single value.
+{
+  const decipher = crypto.createDecipheriv('aes-256-gcm',
+                                           'FxLKsqdmv0E9xrQhp0b1ZgI0K7JFZJM8',
+                                           'qkuZpJWCewa6Szih', {
+                                             authTagLength: 8
+                                           });
+
+  common.expectsError(() => {
+    // This tag would normally be allowed.
+    decipher.setAuthTag(Buffer.from('1'.repeat(12)));
+  }, {
+    type: Error,
+    message: 'Invalid GCM authentication tag length: 12'
+  });
+
+  // The Decipher object should be left intact.
+  decipher.setAuthTag(Buffer.from('445352d3ff85cf94', 'hex'));
+  const text = Buffer.concat([
+    decipher.update('3a2a3647', 'hex'),
+    decipher.final()
+  ]);
+  assert.strictEqual(text.toString('utf8'), 'node');
+}
+
 // Test that create(De|C)ipher(iv)? throws if the mode is CCM and an invalid
 // authentication tag length has been specified.
 {