DXR is a code search and navigation tool aimed at making sense of large projects. It supports full-text and regex searches as well as structural queries.

Mercurial (27bbc1fba015)

VCS Links

Line Code
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320
/* This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

"use strict";

// A minimal ASN.1 DER decoder. Supports input lengths up to 65539 (one byte for
// the outer tag, one byte for the 0x82 length-length indicator, two bytes
// indicating a contents length of 65535, and then the 65535 bytes of contents).
// Intended to be used like so:
//
// let bytes = <an array of bytes describing a SEQUENCE OF INTEGER>;
// let der = new DER.DER(bytes);
// let contents = new DER.DER(der.readTagAndGetContents(DER.SEQUENCE));
// while (!contents.atEnd()) {
//   let integerBytes = contents.readTagAndGetContents(DER.INTEGER);
//   <... do something with integerBytes ...>
// }
// der.assertAtEnd();
//
// For CHOICE, use readTLVChoice and pass an array of acceptable tags.
// The convenience function readBIT_STRING is provided to handle the unused bits
// aspect of BIT STRING. It returns an object that has the properties contents
// (an array of bytes consisting of the bytes making up the BIT STRING) and
// unusedBits (indicating the number of unused bits at the end).
// All other functions generally return an array of bytes or a single byte as
// appropriate.
// peekTag can be used to see if the next tag is an expected given tag.
// readTLV reads and returns an entire (tag, length, value) tuple (again
// returned as an array of bytes).

const UNIVERSAL = 0 << 6;
const CONSTRUCTED = 1 << 5;
const CONTEXT_SPECIFIC = 2 << 6;

const INTEGER = UNIVERSAL | 0x02; // 0x02
const BIT_STRING = UNIVERSAL | 0x03; // 0x03
const NULL = UNIVERSAL | 0x05; // 0x05
const OBJECT_IDENTIFIER = UNIVERSAL | 0x06; // 0x06
const PrintableString = UNIVERSAL | 0x13; // 0x13
const TeletexString = UNIVERSAL | 0x14; // 0x14
const IA5String = UNIVERSAL | 0x16; // 0x16
const UTCTime = UNIVERSAL | 0x17; // 0x17
const GeneralizedTime = UNIVERSAL | 0x18; // 0x18
const UTF8String = UNIVERSAL | 0x0c; // 0x0c
const SEQUENCE = UNIVERSAL | CONSTRUCTED | 0x10; // 0x30
const SET = UNIVERSAL | CONSTRUCTED | 0x11; // 0x31

const ERROR_INVALID_INPUT = "invalid input";
const ERROR_DATA_TRUNCATED = "data truncated";
const ERROR_EXTRA_DATA = "extra data";
const ERROR_INVALID_LENGTH = "invalid length";
const ERROR_UNSUPPORTED_ASN1 = "unsupported asn.1";
const ERROR_UNSUPPORTED_LENGTH = "unsupported length";
const ERROR_INVALID_BIT_STRING = "invalid BIT STRING encoding";

/** Class representing a decoded BIT STRING. */
class BitString {
  /**
   * @param {Number} unusedBits the number of unused bits
   * @param {Number[]} contents an array of bytes comprising the BIT STRING
   */
  constructor(unusedBits, contents) {
    this._unusedBits = unusedBits;
    this._contents = contents;
  }

  /**
   * Get the number of unused bits in the BIT STRING
   * @return {Number} the number of unused bits
   */
  get unusedBits() {
    return this._unusedBits;
  }

  /**
   * Get the contents of the BIT STRING
   * @return {Number[]} an array of bytes representing the contents
   */
  get contents() {
    return this._contents;
  }
}

/** Class representing DER-encoded data. Provides methods for decoding it. */
class DER {
  /**
   * @param {Number[]} bytes an array of bytes representing the encoded data
   */
  constructor(bytes) {
    // Reject non-array inputs.
    if (!Array.isArray(bytes)) {
      throw new Error(ERROR_INVALID_INPUT);
    }
    if (bytes.length > 65539) {
      throw new Error(ERROR_UNSUPPORTED_LENGTH);
    }
    // Reject inputs containing non-integer values or values too small or large.
    if (bytes.some(b => !Number.isInteger(b) || b < 0 || b > 255)) {
      throw new Error(ERROR_INVALID_INPUT);
    }
    this._bytes = bytes;
    this._cursor = 0;
  }

  /**
   * Asserts that the decoder is at the end of the given data. Throws an error
   * if this is not the case.
   */
  assertAtEnd() {
    if (!this.atEnd()) {
      throw new Error(ERROR_EXTRA_DATA);
    }
  }

  /**
   * Determines whether or not the decoder is at the end of the given data.
   * @return {Boolean} true if the decoder is at the end and false otherwise
   */
  atEnd() {
    return this._cursor == this._bytes.length;
  }

  /**
   * Reads the next byte of data. Throws if no more data is available.
   * @return {Number} the next byte of data
   */
  readByte() {
    if (this._cursor >= this._bytes.length) {
      throw new Error(ERROR_DATA_TRUNCATED);
    }
    let val = this._bytes[this._cursor];
    this._cursor++;
    return val;
  }

  /**
   * Given the next expected tag, reads and asserts that the next tag is in fact
   * the given tag.
   * @param {Number} expectedTag the expected next tag
   */
  _readExpectedTag(expectedTag) {
    let tag = this.readByte();
    if (tag != expectedTag) {
      throw new Error(`unexpected tag: found ${tag} instead of ${expectedTag}`);
    }
  }

  /**
   * Decodes and returns the length portion of an ASN.1 TLV tuple. Throws if the
   * length is incorrectly encoded or if it describes a length greater than
   * 65535 bytes. Indefinite-length encoding is not supported.
   * @return {Number} the length of the value of the TLV tuple
   */
  _readLength() {
    let nextByte = this.readByte();
    if (nextByte < 0x80) {
      return nextByte;
    }
    if (nextByte == 0x80) {
      throw new Error(ERROR_UNSUPPORTED_ASN1);
    }
    if (nextByte == 0x81) {
      let length = this.readByte();
      if (length < 0x80) {
        throw new Error(ERROR_INVALID_LENGTH);
      }
      return length;
    }
    if (nextByte == 0x82) {
      let length1 = this.readByte();
      let length2 = this.readByte();
      let length = (length1 << 8) | length2;
      if (length < 256) {
        throw new Error(ERROR_INVALID_LENGTH);
      }
      return length;
    }
    throw new Error(ERROR_UNSUPPORTED_LENGTH);
  }

  /**
   * Reads <length> bytes of data if available. Throws if less than <length>
   * bytes are available.
   * @param {Number} length the number of bytes to read. Must be non-negative.
   * @return {Number[]} the next <length> bytes of data
   */
  readBytes(length) {
    if (length < 0) {
      throw new Error(ERROR_INVALID_LENGTH);
    }
    let bytes = [];
    for (let i = 0; i < length; i++) {
      bytes.push(this.readByte());
    }
    return bytes;
  }

  /**
   * Given an expected next ASN.1 tag, ensures that that tag is next and returns
   * the contents of that tag. Throws if a different tag is encountered or if
   * the data is otherwise incorrectly encoded.
   * @param {Number} tag the next expected ASN.1 tag
   * @return {Number[]} the contents of the tag
   */
  readTagAndGetContents(tag) {
    this._readExpectedTag(tag);
    let length = this._readLength();
    return this.readBytes(length);
  }

  /**
   * Returns the next byte without advancing the decoder. Throws if no more data
   * is available.
   * @return {Number} the next available byte
   */
  _peekByte() {
    if (this._cursor >= this._bytes.length) {
      throw new Error(ERROR_DATA_TRUNCATED);
    }
    return this._bytes[this._cursor];
  }

  /**
   * Given an expected tag, reads the next entire ASN.1 TLV tuple, asserting
   * that the tag matches.
   * @param {Number} tag the expected tag
   * @return {Number[]} an array of bytes representing the TLV tuple
   */
  _readExpectedTLV(tag) {
    let mark = this._cursor;
    this._readExpectedTag(tag);
    let length = this._readLength();
    // read the bytes so we know they're there (also to advance the cursor)
    this.readBytes(length);
    return this._bytes.slice(mark, this._cursor);
  }

  /**
   * Reads the next ASN.1 tag, length, and value and returns them as an array of
   * bytes.
   * @return {Number[]} an array of bytes representing the next ASN.1 TLV
   */
  readTLV() {
    let nextTag = this._peekByte();
    return this._readExpectedTLV(nextTag);
  }

  /**
   * Convenience function for decoding a BIT STRING. Reads and returns the
   * contents of the expected next BIT STRING. Throws if the next TLV isn't a
   * BIT STRING or if the BIT STRING is incorrectly encoded.
   * @return {BitString} the next BIT STRING
   */
  readBIT_STRING() {
    let contents = this.readTagAndGetContents(BIT_STRING);
    if (contents.length < 1) {
      throw new Error(ERROR_INVALID_BIT_STRING);
    }
    let unusedBits = contents[0];
    if (unusedBits > 7) {
      throw new Error(ERROR_INVALID_BIT_STRING);
    }
    // Zero bytes of content but some amount of padding is invalid.
    if (contents.length == 1 && unusedBits != 0) {
      throw new Error(ERROR_INVALID_BIT_STRING);
    }
    return new BitString(unusedBits, contents.slice(1, contents.length));
  }

  /**
   * Looks to see if the next ASN.1 tag is the expected given tag.
   * @param {Number} tag the expected next ASN.1 tag
   * @return {Boolean} true if the next tag is the given one and false otherwise
   */
  peekTag(tag) {
    if (this._cursor >= this._bytes.length) {
      return false;
    }
    return this._bytes[this._cursor] == tag;
  }

  /**
   * Given a list of possible next ASN.1 tags, returns the next TLV if the next
   * tag is in the list. Throws if the next tag is not in the list or if the
   * data is incorrectly encoded.
   * @param {Number[]} tagList the list of potential next tags
   * @return {Number[]} the contents of the next TLV if the next tag is in
   *                    <tagList>
   */
  readTLVChoice(tagList) {
    let tag = this._peekByte();
    if (!tagList.includes(tag)) {
      throw new Error(
        `unexpected tag: found ${tag} instead of one of ${tagList}`
      );
    }
    return this._readExpectedTLV(tag);
  }
}

this.DER = {
  UNIVERSAL,
  CONSTRUCTED,
  CONTEXT_SPECIFIC,
  INTEGER,
  BIT_STRING,
  NULL,
  OBJECT_IDENTIFIER,
  PrintableString,
  TeletexString,
  IA5String,
  UTCTime,
  GeneralizedTime,
  UTF8String,
  SEQUENCE,
  SET,
  DER,
};
this.EXPORTED_SYMBOLS = ["DER"];