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+/* 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"];