Add DER parser to //net

The DER parsing code is split into 2 main sections - the Parser class for parsing constructed values, and the ParseType free functions for parsing primitive values. The Parser class should be complete at this point (with the exception of adding more convenience methods to match free functions). This CL has only a very limited number of free functions for parsing primitive values; more will be added in later CLs based on the demand needed for other types.

Review URL: https://codereview.chromium.org/878813002

Cr-Commit-Position: refs/heads/master@{#326389}

1 files changed, 192 insertions, 0 deletions

diff --git a/net/der/parser.cc b/net/der/parser.cc
new file mode 100644
index 0000000..7263fba
--- /dev/null
+++ b/net/der/parser.cc
@@ -0,0 +1,192 @@
+// Copyright 2015 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 "base/logging.h"
+#include "base/numerics/safe_math.h"
+#include "net/der/parse_values.h"
+#include "net/der/parser.h"
+
+namespace net {
+
+namespace der {
+
+Parser::Parser() : input_(Input()), advance_mark_(Mark::NullMark()) {
+}
+Parser::Parser(const Input& input)
+    : input_(input), advance_mark_(Mark::NullMark()) {
+}
+
+// Reads the next TLV from the input and writes the tag and value to the
+// output parameters |tag| and |out|.
+bool Parser::PeekTagAndValue(Tag* tag, Input* out) {
+  ByteReader reader = input_;
+
+  // Don't support tags > 30.
+  uint8_t tag_byte;
+  if (!reader.ReadByte(&tag_byte))
+    return false;
+
+  // ITU-T X.690 section 8.1.2.3 specifies the format for identifiers with a
+  // tag number no greater than 30. This parser only supports tag numbers up
+  // to 30.
+  // If the tag number is 31 (0x1F, the largest value that fits in the allotted
+  // bytes), then the tag is more than one byte long and the continuation bytes
+  // contain the real tag number. We only support tag numbers < 31 (and thus
+  // single-byte tags).
+  if ((tag_byte & kTagNumberMask) == 31)
+    return false;
+
+  // Parse length. The format for the length encoding is specified in
+  // ITU-T X.690 section 8.1.3.
+  size_t value_len = 0;  // Number of bytes used to encode just the value.
+
+  uint8_t length_first_byte;
+  if (!reader.ReadByte(&length_first_byte))
+    return false;
+  if ((length_first_byte & 0x80) == 0) {
+    // Short form for length - it's only one byte long.
+    value_len = length_first_byte & 0x7f;
+  } else {
+    // Long form for length - it's encoded across multiple bytes.
+    if (length_first_byte == 0xff) {
+      // ITU-T X.690 clause 8.1.3.5.c specifies the value 0xff shall not be
+      // used.
+      return false;
+    }
+    // The high bit indicated that this is the long form, while the next 7 bits
+    // encode the number of subsequent octets used to encode the length
+    // (ITU-T X.690 clause 8.1.3.5.b).
+    size_t length_len = length_first_byte & 0x7f;
+    if (length_len == 0) {
+      // ITU-T X.690 section 10.1 (DER length forms) requires encoding the
+      // length with the minimum number of octets. Besides, it makes no sense
+      // for the length to be encoded in 0 octets.
+      return false;
+    }
+    if (length_len > sizeof(value_len)) {
+      // The length is encoded in multiple octets, with the first octet
+      // indicating how many octets follow. Those octets need to be combined
+      // to form a size_t, so the number of octets to follow (length_len)
+      // must be small enough so that they fit in a size_t.
+      return false;
+    }
+    uint8_t length_byte;
+    for (size_t i = 0; i < length_len; i++) {
+      if (!reader.ReadByte(&length_byte))
+        return false;
+      // A first length byte of all zeroes means the length was not encoded in
+      // minimum length.
+      if (i == 0 && length_byte == 0)
+        return false;
+      value_len <<= 8;
+      value_len += length_byte;
+    }
+    if (value_len < 0x80) {
+      // If value_len is < 0x80, then it could have been encoded in a single
+      // byte, meaning it was not encoded in minimum length.
+      return false;
+    }
+  }
+
+  if (!reader.ReadBytes(value_len, out))
+    return false;
+  advance_mark_ = reader.NewMark();
+  *tag = tag_byte;
+  return true;
+}
+
+bool Parser::Advance() {
+  if (advance_mark_.IsEmpty())
+    return false;
+  if (!input_.AdvanceToMark(advance_mark_))
+    return false;
+  advance_mark_ = Mark::NullMark();
+  return true;
+}
+
+bool Parser::HasMore() {
+  return input_.HasMore();
+}
+
+bool Parser::ReadRawTLV(Input* out) {
+  Tag tag;
+  Input value;
+  if (!PeekTagAndValue(&tag, &value))
+    return false;
+  if (!input_.ReadToMark(advance_mark_, out))
+    return false;
+  advance_mark_ = Mark::NullMark();
+
+  return true;
+}
+
+bool Parser::ReadTagAndValue(Tag* tag, Input* out) {
+  if (!PeekTagAndValue(tag, out))
+    return false;
+  CHECK(Advance());
+  return true;
+}
+
+bool Parser::ReadOptionalTag(Tag tag, Input* out, bool* present) {
+  if (!HasMore()) {
+    *present = false;
+    return true;
+  }
+
+  Tag read_tag;
+  Input value;
+  if (!PeekTagAndValue(&read_tag, &value))
+    return false;
+  *present = false;
+  if (read_tag == tag) {
+    *present = true;
+    *out = value;
+    CHECK(Advance());
+  } else {
+    advance_mark_ = Mark::NullMark();
+  }
+  return true;
+}
+
+bool Parser::SkipOptionalTag(Tag tag, bool* present) {
+  Input out;
+  return ReadOptionalTag(tag, &out, present);
+}
+
+bool Parser::ReadTag(Tag tag, Input* out) {
+  bool present;
+  return ReadOptionalTag(tag, out, &present) && present;
+}
+
+bool Parser::SkipTag(Tag tag) {
+  Input out;
+  return ReadTag(tag, &out);
+}
+
+// Type-specific variants of ReadTag
+
+bool Parser::ReadConstructed(Tag tag, Parser* out) {
+  if (!IsConstructed(tag))
+    return false;
+  Input data;
+  if (!ReadTag(tag, &data))
+    return false;
+  *out = Parser(data);
+  return true;
+}
+
+bool Parser::ReadSequence(Parser* out) {
+  return ReadConstructed(kSequence, out);
+}
+
+bool Parser::ReadUint64(uint64_t* out) {
+  Input encodedInt;
+  if (!ReadTag(kInteger, &encodedInt))
+    return false;
+  return ParseUint64(encodedInt, out);
+}
+
+}  // namespace der
+
+}  // namespace net