/* 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/. */
// 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.DERDecoder(bytes);
// let contents = new DER.DERDecoder(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).
//
// NB: While DERDecoder must be given an array, it does not validate that each
// element in the array is an integer in the range [0, 255]. If the input to be
// decoded could conceivably violate this property, callers should perform this
// check before using DERDecoder.
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
*
* @returns {number} the number of unused bits
*/
get unusedBits() {
return this._unusedBits;
}
/**
* Get the contents of the BIT STRING
*
* @returns {number[]} an array of bytes representing the contents
*/
get contents() {
return this._contents;
}
}
/** Class representing DER-encoded data. Provides methods for decoding it. */
class DERDecoder {
/**
* @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);
}
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.
*
* @returns {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.
*
* @returns {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.
*
* @returns {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.
* @returns {number[]} the next <length> bytes of data
*/
readBytes(length) {
if (length < 0) {
throw new Error(ERROR_INVALID_LENGTH);
}
if (this._cursor + length > this._bytes.length) {
throw new Error(ERROR_DATA_TRUNCATED);
}
let bytes = this._bytes.slice(this._cursor, this._cursor + length);
this._cursor += length;
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
* @returns {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.
*
* @returns {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
* @returns {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.
*
* @returns {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.
*
* @returns {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
* @returns {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
* @returns {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);
}
}
export const DER = {
UNIVERSAL,
CONSTRUCTED,
CONTEXT_SPECIFIC,
INTEGER,
BIT_STRING,
NULL,
OBJECT_IDENTIFIER,
PrintableString,
TeletexString,
IA5String,
UTCTime,
GeneralizedTime,
UTF8String,
SEQUENCE,
SET,
DERDecoder,
};
